Abstract:[Background] Inositol is a member of the vitamin B group and has been widely used in the fields of food, medicine, and feed. Microbial fermentation is considered as the most promising method for inositol production, while the inositol produced by Escherichia coli is restricted for food and medicine uses. As a GRAS (generally recognized as safe) strain, Komagataella phaffii has been employed as a robust host for producing heterologous proteins. K. phaffii possesses a native synthetic pathway of inositol and thus has great potential to be modified as a cell factory for the efficient production of inositol.[Objective] To reduce the by-products and enhance the inositol production via metabolic engineering of K. phaffii. [Methods] With the inositol-producing K. phaffii strain which was previously constructed in our lab as the starting strain, we identified the genes involved in the synthesis of arabitol, ribitol, and mannose. Through deletion of the key genes for synthesis and control of the glucose concentration in the fermentation, we decreased the production of by-products. The co-utilization of glycerol and glucose was achieved in the inositol-producing K. phaffii strain by overexpression of glycerol transporter, glycerol kinase, and glycerol-3-phosphate dehydrogenase, and a recombinant strain Z10 was obtained. Furthermore, inositol production was improved by optimization of the fermentation conditions. [Results] The inositol production of the recombinant strain Z10 under the optimal conditions reached 36.7 g/L, the highest titer reported to date by a yeast cell factory. The by-products of Z10 was reduced by 63.1% compared with that of the starting strain. [Conclusion] An effective strategy was established in K. phaffii for decreasing the production of arabitol, ribitol, and mannose. Through the co-utilization of glycerol and glucose and the optimization of fermentation conditions, the inositol production was increased. The findings of this study provide a reference to the application of K. phaffii for the efficient production of inositol and other high-value bioactive substances.

Abstract:[Background] Microbulbifer species isolated from the marine environments have the ability to degrade polysaccharides. They participate in the marine carbon cycle as an important player of carbohydrate metabolism in the environment. [Objective] To analyze the polysaccharide-degrading activities and genomics information of two Microbulbifer strains. [Methods] The 3,5-dinitrosalicylic acid colorimetry (DNS method) was employed to determine the polysaccharide-degrading activity. High-throughput sequencing was performed to sequence and assemble the genome sequence of the strains. [Results] Two strains of Microbulbifer species, namely YPW1 and YPW16, were isolated in this work, both of which were potential new species. YPW1 degraded 7 polysaccharides (agar, alginate, pectin, chitin, xylan, starch, and pullulan), while YPW16 only degraded starch and pullulan, with the activity lower than YPW1 under the experimental conditions. The genome comparison with other Microbulbifer strains showed that YPW1 had a wider polysaccharide degradation range due to its abundant genes for polysaccharide degradation. However, the polysaccharide degradation range of YPW16 was narrower. Moreover, the genes involved in polysaccharide degradation presented uneven distribution in the genomes of Microbulbifer species. [Conclusion] This study provided two potential new strain resources of Microbulbifer and a biological tool for polysaccharide degradation, laying a foundation for studying the distribution of polysaccharide degradation genes and the ecological functions of Microbulbifer.

Abstract:[Background] Magnetic nanoparticle-mediated isolation (MMI) is a culture-independent approach for identifying active degraders from complex microbial communities. However, there are few studies about the MMI-based identification of active bacteria involved in the degradation of recalcitrant 3,3',4,4'-tetrachlorobiphenyl (PCB77). [Objective] To isolate active PCB77 degraders from soil and assess the pollutant degradation capacity. [Methods] Magnetic nanoparticles (MNPs) were used to enrich the active PCB77 degraders in soil. The change in bacterial community composition was determined by high-throughput sequencing. A PCB77 degrader was isolated from MNP-enriched culture, and its performance of degrading polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) was assessed. [Results] The MNP-enriched culture was capable of degrading PCB77 with high efficiency compared with the control, which increased from 6% to 79.3%. The treatment with MNPs decreased the bacterial diversity and changed the community composition. PCB-degrading Rhodococcus sp. CT2 and Paenibacillus sp. MT2 were isolated from the control and MMI culture, respectively. Rhodococcus was dominant in the control group, while the dominant degraders included both Rhodococcus and Paenibacillus in the MMI group. The strain MT2 degraded 65.2% of PCB77 serving as the sole carbon source, and this degradation rate was close to that in MNP-enriched culture and significantly higher than that (26.3%) of strain CT2 under the same condition. In addition, the performance of Paenibacillus sp. MT2 in degrading PCBs and PBDEs was better than that of Rhodococcus sp. CT2. [Conclusion] MMI is a powerful approach to enrich active PCB77 degraders from complex microbial communities, with which Paenibacillus sp. MT2 having high PCB degradation efficiency was isolated. The study lays a theoretical basis for developing efficient approaches to remediate the soil contaminated by PCBs.

Abstract:[Background] Functional mapping is a genome-wide mapping method that uses statistics to analyze the development of dynamic and complex traits in organisms, with the aim of locating quantitative trait loci (QTL) during the development of traits. The application of functional mapping to microbiological studies can unravel complex interactions.[Objective] To locate significant QTLs in the growth and development of two microorganisms by functional mapping, and to identify the key genes affecting the phenotypic growth of the microorganisms functional annotation. [Methods] One hundred strains of Escherichia coli and 100 strains of Staphylococcus aureus were cultured separately or paired together for co-culture. The phenotypic data and SNP data obtained from each strain were used for correlation analysis to locate the significant QTL of the same species under different culture conditions. [Results] The functional mapping identified 217 QTL in E. coli and 152 QTL in S. aureus. The functional clustering and gene annotation analysis showed that scdA, sdrC, sdrD, and ftsA in S. aureus and phr, nagC, eptA, ppsA, priA, and flim in E. coli might play a role in the microbial growth. [Conclusion] We identified the key genes involved in the competitive interactions between E. coli and S. aureus by employing functional mapping. Our results not only provide fundamental data for the application of functional mapping in microbial research but also offer a new idea for deciphering the complex mechanisms of microbial interactions.

Abstract:[Background] The water environment with wide distribution and high mobility is the main medium for the spread of drug resistant bacteria and genes. [Objective] To understand the drug resistance genes and mobile genetic elements carried by Escherichia coli from a sewage plant in northern China. [Methods] A multi-drug resistant strain of E. coli was isolated from the sewage plant. The antimicrobial susceptibility test was carried out. The 96-well plate method was employed to determine the minimum inhibitory concentrations of antibiotics against this strain. The effects of antibiotics at sub-inhibitory concentrations on the growth of the strain were explored by a microplate reader. The whole genome sequencing was carried out to predict the resistance genes and mobile genetic elements carried by the strain. [Results] E. coli WEC was resistant to tetracycline, ciprofloxacin, norfloxacin, and erythromycin. Sub-inhibitory concentrations of tetracycline, ciprofloxacin, and norfloxacin stagnated or inhibited the growth of strains. The genome of WEC was composed of a circular chromosome of 4 782 114 bp and two circular plasmids of 60 306 bp (pWEC-1) and 92 065 bp (pWEC-2), respectively. The strain carried 129 drug resistance genes, of which 128 were located on the chromosome. Prophages, gene islands, and insertion sequences was predicted to be present on the chromosome, and some mobile genetic elements carried drug resistance genes. There was no drug resistance gene in plasmid pWEC-1, and pWEC-2 carried one drug resistance gene. Prophages and insertion sequences were predicted to be present in the plasmid genome. [Conclusion] E. coli WEC from sewage is a multi-drug resistant strain. Carrying drug resistance genes and a variety of mobile genetic elements, the strain has the potential of drug resistance transfer.

Abstract:[Background] Cytochrome bd terminal oxidase, existing in a variety of bacterial pathogens, protects bacteria from environmental stress conditions and enhances the virulence. As bd oxidase is absent in eukaryotes, it is considered as a promising target for developing novel antimicrobials. The role of terminal oxidase in Klebsiella pneumoniae remains unclear. [Objective] This study aims to explore the biological role of the terminal oxidase CyxA in K. pneumoniae. [Methods] The cyxA traceless deletion mutant and complemented strain were constructed. The wild-type strain (WT) and the mutant ΔcyxA were compared by in vitro experiments in regard to the growth, biofilm formation, capsule synthesis, and resistance to different environmental factors (acidity, hyperosmosis, oxidation, and reduction) and antibiotics. Further, in vivo infection experiment was carried out to study the effect of CyxA on the pathogenicity of K. pneumoniae. [Results] The deletion of cyxA significantly inhibited the aerobic growth of K. pneumoniae in vitro, did not affect the biofilm formation or capsule synthesis, and weakened the resistance to pH 5.5, 1.9% NaCl, H₂O₂, β-mercaptoethanol, and some β-lactam and aminoglycoside antibiotics. Nasal drip experiments of mice showed that the pathogenicity of K. pneumoniae decreased after the deletion of cyxA. [Conclusion] This study demonstrated for the first time that the terminal oxidase CyxA promotes the aerobic growth and enhances the resistance to acidic, hyperosmotic, redox environment and some antibiotics, thus increasing the pathogenicity of K. pneumoniae. The findings lay a foundation for further deciphering the molecular mechanism of terminal oxidase affecting the pathogenicity of K. pneumoniae and provide a theoretical basis for the subsequent development of novel antibacterial agents targeting K. pneumoniae terminal oxidase.

Abstract:[Background] Some minor ginsenosides possess valuable pharmacological activities. Mining glycosidases with high activity and specificity can realize the directional preparation of minor ginsenosides.Flavobacterium saccharophilum carries abundant and uncharacterized glycosidase genes, which are potential sources for excavating new glycosidases.[Objective] To obtain highly active and specific glycosidases from F. saccharophilum for the preparation of minor ginsenosides. [Methods] Fifteen putative glucosidase genes were cloned from F. saccharophilum and expressed. To screen out the enzymes for the preparation of minor ginsenosides, we fully characterized the recombinants and identified the biotransformation products by employing thin layer chromatography and high performance liquid chromatography. [Results] Three β-glucosidases (SA2629, SA0236, and SA2851) with high activities were obtained from F. saccharophilum. SA2629 showed the highest specific activity (78.7 U/mg) and catalytic efficiency [k_cat=(27.38±1.40) s⁻¹]. Furthermore, it could simultaneously hydrolyze the β-1,6-glucosidic bond at the C−20 position and the glucosidic bond directly connected to the aglycone at the C-3 position. SA2851 and SA0236 only had hydrolysis activity on the β-1,6 glucosidic bond at the C-20 position, and SA0236 had higher activity. Furthermore, we completely transformed ginsenoside Rb1 to the minor ginsenosides CK and F2 by using SA2629 and SA0236, respectively, with a β-1,2-glucosidase obtained in our lab. [Conclusion] The glycosidases that can be employed to prepare minor ginsenosides were obtained, which filled the gap in the study of β-glucosidases from F. saccharophilum.

Abstract:[Background] Quinoa is an example of functional food that is popular all over the world, while little has been reported about the endophyte Trichoderma afroharzianum of quinoa seeds. [Objective] To determine the antimicrobial activity and growth-promoting effect of endophytic fungi isolated from quinoa seeds. [Methods] The isolated endophytic fungi were identified based on morphology and the ITS, tef1, and rpb2 gene sequences characteristics. The antimicrobial effects of endophytic fungi were determined by plate confrontation method and plate culture method. The growth-promoting effect of the strain on quinoa was determined by pot experiment. [Results] The strain LMNS-M9 was identified as T. afroharzianum. The mycelial growth and sporulation of strain LMNS-M9 were promoted at 30 ℃, pH 5.0, and the presence of magnesium ion. Glucose, lactose, peptone, and potassium dihydrogen phosphate were suitable for mycelial growth of strain LMNS-M9, and glucose, ammonium nitrate, and dipotassium hydrogen phosphate were suitable for sporulation. LMNS-M9 showed inhibitory activity against Botrytis cinerea, Ascochyta caulina, Fusarium citri,Alternaria alternata, and Trichothecium roseum, with the inhibition rates of 12.53%, 51.96%, 52.38%, 59.25%, and 62.04%, respectively. The volatiles showed the inhibition rates of 35.86%, 61.54%, 33.33%, 41.95%, and 59.09%, respectively. LMNS-M9 could contact or entangle the mycelia of pathogens (B. cinerea, A. caulina, F. citri, and A. alternata) to rupture or lyse the mycelia. The pot experiment showed that LMNS-M9 advanced the germination of quinoa seeds by 2 days. Furthermore, LMNS-M9 increased the root length, underground fresh weight, and underground dry weight of quinoa seedlings by 71.88%, 104.66%, and 68.89%, respectively. [Conclusion] The endophytic fungus isolated from quinoa seeds was identified as T. afroharzianum. It inhibited the growth of five pathogens and promoted the root growth of quinoa, demonstrating good biocontrol potential.

Abstract:[Background] Phage cocktails have been reported as biocontrol agent against the kiwifruit canker pathogen Pseudomonas syringae pv. actinidiae (Psa). However, little is known about the control effect of phage cocktail in the field and the effect of phage cocktail on the phyllospheric bacterial community of kiwifruit plants. [Objective] To explore the biocontrol effect of phage cocktail against kiwifruit canker in the field, and reveal the effect of the cocktail on the microecology of endophytic bacteria in the stem phyllosphere of kiwifruit. [Methods] The healthy kiwifruit plants were infected with Psa, and the incidence of bacterial canker after application of phage cocktail or copper preparation was recorded. The changes in the community structure of bacteria in kiwifruit phyllosphere were analyzed by high-throughput sequencing. [Results] Compared with the copper preparation, the phage cocktail significantly reduced the incidence of bacterial canker, changed the richness and diversity of bacteria in the phyllosphere, enhanced the stability of bacterial community, and improved the abundance of functional genes, thus restoring the bacterial community to the healthy state. [Conclusion] Phage cocktails exert the role of microecological regulation while killing pathogenic bacteria, demonstrating great application potential in the biocontrol of kiwifruit canker caused by Psa.

Abstract:[Background] Revealing the microbiome structure of plants is critical for enhancing plant tolerance to biotic and abiotic stresses and improving the quality of agricultural and forestry products. The nitrogen-fixing nodules of Hippophae rhamnoides is the key to the tolerance to drought, cold, and barren soil. [Objective] To provide a theoretical basis for revealing the roles of H. rhamnoides-Frankia symbiosis and plant-microbiome interaction in plant tolerance to stress, we studied the structure and influencing factors of bacterial community in the rhizosphere soil and root nodules of H. rhamnoides. [Methods] The rhizosphere soil and root nodules of H. rhamnoides were collected from 3 sampling sites in Liaoning, Shaanxi, and Shanxi, and high-throughput sequencing was performed for the V3-V4 variable regions of the 16S rRNA gene. The bioinformatics tools were employed to compare the community structure and abundance of bacteria between the soil and nodule samples. Furthermore, the effects of soil physical and chemical properties on the bacterial community structure in rhizosphere soil were explored. [Results] Actinobacteria and Proteobacteria were the dominant phyla in the rhizosphere soil and root nodule, and Frankia was the dominant genus in the root nodule of H. rhamnoides. The three provinces showed significant differences in the abundance of the top 10 dominant phyla and 27 of the top 35 dominant genera in the rhizosphere soil, and they shared only one common dominant genus Sphingomonas. Soil pH and soluble potassium were the main factors affecting the bacterial diversity in rhizosphere soil of H. rhamnoides. The dominant phyla and genera in the root nodules were highly conserved among the three provinces, and only Allorhizobium had significant differences in abundance among the three provinces. The diversity and abundance of bacteria in rhizosphere soil and root nodules were not completely consistent.[Conclusion] The bacterial diversity in the rhizosphere soil of H. rhamnoides is strongly affected by soil pH and available potassium. The root nodules of H. rhamnoides assemble a conserved and stable microbiome by self-host selection of bacteria from the rhizosphere soil.

Abstract:[Background] The extreme eco-environment of Qinghai Plateau harbors unique microbial resources. [Objective] To explore the growth-promoting and disease-controlling effects of Bacillus adaptive to the alpine environment on the herbage. [Methods] The growth-promoting and disease-controlling effects of Bacillus halotolerans DGL6 isolated from the rhizosphere of Nitraria tangutorum in Haixi prefecture of Qinghai province on the germination and seedling growth of Triticum aestivum ‘Qingmai 7’ were determined by seed soaking and root irrigation methods, respectively. The changes in physiological indexes of the seedlings within 12 days were measured. The inhibitory activity of strain DGL6 on fungal infection was measured with the detached leaves of ‘Qingmai 7’ seedlings. The inhibition rate and hydrolase activity of strain DGL6 against pathogenic fungi were determined by plate confrontation method and inhibition zone method, respectively. [Results] Strain DGL6 had significant effect on the seed germination and seedling growth of ‘Qingmai 7’. It increased the sprout length, root length, and fresh weight of ‘Qingmai 7’ by 27.26%, 23.03%, and 45.42%, respectively. Furthermore, it increased the plant height, root length, and fresh weight of seedlings within 12 days by 33.42%, 107.85%, and 95.24%, respectively. The strain significantly increased the content of chlorophyll, soluble sugar, and soluble protein and decreased the content of malondialdehyde. Spraying DGL6 suspension significantly inhibited the growth of Fusarium graminearum on the detached leaves of ‘Qingmai 7’. DGL6 showed significant antagonistic activity to F. graminearum, with the mean inhibition zone diameter of 18 mm. DGL6 formed distinct inhibition zones in the media for detection of four hydrolases, demonstrating the ability to secrete cellulase, pectinase, protease, and b-1,3-glucanase. [Conclusion] This study provided an elite strain and a theoretical basis for promoting the growth and improving the disease resistance of the plateau crop ‘Qingmai 7’.

Abstract:[Background] The endophytic fungus Piriformospora indica colonizes plants and significantly promotes plant growth and development. miRNAs have been demonstrated to play a regulatory role in plant growth and development. [Objective] To reveal the response of miRNA to P. indica colonization and its regulatory role in the growth and development of barley. [Methods] After extraction of total barley RNA, high-throughput sequencing was performed, followed by sequence alignment and data mining. Then, qPCR was conducted to determine the levels of miRNA and target gene expression. High performance liquid chromatography was employed to measure the levels of growth hormones in barley. [Results] P. indica significantly promoted the growth of barley. The whole transcriptome sequencing results showed that the barley infected by P. indica for three days had 11 miRNAs up-regulated and 7 miRNAs down-regulated compared with the blank control group; the barley infected by P. indica for seven days had 11 miRNAs up-regulated and 13 miRNAs down-regulated compared with the blank control group; the barley infected by P. indica for seven days had 3 miRNAs up-regulated and 6 miRNAs down-regulated compared with the barley infected by P. indica for three days. The GO functional annotation and KEGG pathway enrichment analysis showed that predicted target genes of these differentially expressed miRNAs were mainly involved in transcription, cell division, auxin signal perception and transduction, photosynthesis, and response to hormone stimulus. These pathways were associated with barley growth, which suggested that miRNAs responded positively to the colonization of P. indica. In addition, the metabolites of the regulatory pathways involving the differentially expressed miRNAs changed. [Conclusion] This study explored the regulatory role of miRNA in barley growth and development, providing a new research direction for deciphering the growth promotion mechanism of P. indica colonization.

Abstract:[Background] Endophytic microorganisms often produce the same, similar or novel secondary metabolites as host plants. Clove has excellent antimicrobial activities, from which the endophytic bacteria with strong antimicrobial effects could be isolated. [Objective] To screen out clove endophytic bacteria against Ralstonia solanacearum and isolate active components. [Methods] The antimicrobial endophytic bacteria were screened out by oxford-cup tests and identified by 16S rRNA sequence analysis. The active components were isolated by organic solvent extraction, silica-gel column chromatography, and preparative thin layer chromatography, and identified by NMR. The inhibitory effects of the active component on pathogens were determined by filtering paper method and mycelial growth rate method. [Results] A total of 112 strains of endophytic bacteria were isolated, and most strains were obtained from leaves, accounting for 37.4%. Seventeen strains showed inhibitory effect on R. solanacearum. Among these strains, DX78 demonstrated the strongest activity and was identified as Bacillus vallismortis. Dibutyl phthalate (DBP) was isolated from the fermentation broth of DX78. The minimum inhibitory concentrations of DBP against R. solanacearum and Pseudomonas syringae were 0.3 mg/disc and 0.25 mg/disc, respectively. Furthermore, DBP inhibited plant pathogenic fungi, with the EC₅₀ values of 3.751, 18.568, and 22.019 µg/mL against Glomerella cingulata, Botrytis cinerea, and Valsa mali, respectively. With G. cingulata as the target fungus, the inhibitory toxicity of tebuconazole was about 4.5 times that of DBP, and the inhibitory toxicity of DBP was about 12.5 times that of carbendazim. [Conclusion] Clove harbors rich antimicrobial endophytic bacteria, and DBP isolated from B. vallismortis DX78 has strong inhibitory effect on G. cingulata, which is worthy of further study.

Abstract:[Background] Species of Trichoderma are common cellulose and hemicellulose- degrading fungi in nature and play an important role in the degradation of agricultural wastes.[Objective] To screen out Trichoderma strains that can degrade maize straw under low temperature. [Methods] This study determined the growth rates and the diameter of hydrolytic transparent circle produced by cellulase and xylanase of 111 strains belonging to 31 Trichoderma species under low temperature, as well as the relative degradation rate (RDR) of the representative strains on maize straw. The cellulose filter paper enzyme (FPase), carboxymethyl cellulase (CMCase), and xylanase activities of the representative strains with different RDR values were determined by the DNS method, and the relationship between their enzyme activities and RDR in different fermentation stages were further analyzed. [Results] All the tested strains were able to grow at 15 ℃, whereas, 100 and 42 out of them could grow at 10 ℃ and 5 ℃, respectively. Among them, 19 strains produced hydrolytic both cellulose and xylan transparent circles with diameters more than 60 mm after 6 days, and their RDRs on maize straw after 10 days were 0.45%-8.09%. The activities of FPase, CMCase, and xylanase of the strains 9145, TC425, TC505, and 8987 showed a dynamic change with the cultivation time, of which the tendency of FPase and CMCase was basically identical and closely related to the RDR. [Conclusion] The strains of T. atrobrunneum, T. atroviride, T. hamatum, and T. simmonsii show high degradation rates of maize straw at low temperatures, which will provide germplasm resources for subsequent development of ripening agent, degradation mechanism research, and resource utilization of maize straw.

Abstract:[Background] Myxobacteria are a group of higher prokaryotes with social behavior. They are versatile predators that prey on phytopathogenic fungi and bacteria, serving as excellent candidates for biocontrol agents. [Objective] To explore the diversity and antimicrobial activities of culturable myxobacteria in the primitive forest of Tianshan Grand Canyon in Urumqi, and lay a foundation for the discovery of myxobacteria strains for biocontrol. [Methods] Culturable myxobacteria were isolated from the soil and rotting wood samples collected from the primitive forest of Tianshan Grand Canyon by the rabbit dung pellets-inducing method and prey-inducing method. The isolates were identified based morphological characteristics, physiological and biochemical properties, and the 16S rRNA gene sequences. The antimicrobial activities of the isolates were determined with 6 phytopathogenic fungal species (Verticillium dahliae, Fusarium oxysporum f. sp. vasinfectum, Fusarium verticillioides, Rhizoctonia solani, Fusarium culmorum, and Alternaria tenuissima) and 1 phytopathogenic bacterial species (Erwinia amylovora) by plate confrontation method and lawn predation method. [Results] Seventy potential strains were isolated from the collected samples, and 36 pure cultures of myxobacteria were obtained after purification. The 36 strains belonged to 4 genera: Myxococcus (30 strains), Cystobacter (3 strains), Corallococcus (2 strains), and Archangium (1 strain). The 36 strains of myxobacteria presented activities against at least two species of phytopathogenic fungi, exhibiting broad-spectrum antifungal activities. One strain NSE37-1 with both broad-spectrum efficient antifungal activity was screened out. Fifteen strains had predatory activity against E. amylovora, and one strain NSE25 with strong predatory activity was screened out. [Conclusion] The culturable myxobacteria are abundant in Tianshan Grand Canyon, among which Myxococcus is the dominant genus. The isolated and purified myxobacteria strains all exhibited broad-spectrum activities against phytopathogens, demonstrating the value for research in the future.

Abstract:[Background] Tobacco-specific nitrosamines (TSNAs) are produced by the nitrosation of tobacco alkaloids with nitrogen oxides during the processing of tobacco, especially during the modulation and fermentation stages. [Objective] To mine the microorganisms that can tolerate high-temperature fermentation of cigar tobacco leaves and reduce the accumulation of TSNAs. [Methods] We examined the high-temperature tolerance, nitrite degradation, and nitrite tolerance of the bacterial strains derived from cigar tobacco leaves that could efficiently degrade nitrite and tolerate high concentrations of nitrite at 50 ℃. A efficient strain was then selected and used for a 35-day high-temperature fermentation of cigar tobacco leaves. We determined the levels of nitrite, TSNAs, conventional chemical components, and neutral aromatic components before and after fermentation to analyze the effects of the strain on TSNAs and tobacco quality during the fermentation process. [Results] Three bacterial strains capable of degrading nitrite at 50 ℃ were isolated and identified, which were Bacillus mojavensis NY7, B. halotolerans NY8, and B. subtilis NY9. Among them, B. halotolerans NY8 exhibited the strongest nitrite-degrading capacity. The high-temperature fermentation of cigar tobacco leaves with NY8 reduced nitrite by 96.86% and TSNAs by 67.14%. Moreover, the nicotine reduction caused by the inoculation of NY8 was significantly higher than that of the control group, and the total neutral aromatic components (except neophytadiene) were slightly increased. [Conclusion] The isolated strains are suitable for high-temperature fermentation of cigar tobacco leaves and demonstrate high efficiency in degrading nitrite and reducing the accumulation of TSNAs. The findings provide inspiration for reducing the harm of cigar tobacco leaves.

Abstract:[Background] Atractylodes macrocephala Koidz is an important and widely used Chinese medicinal plant, while its cultivation suffers from poor soil fertility which is often dealt with the heavy application of pesticides and fertilizers. [Objective] To provide a material basis for the preparation of a biofertilizer for A. macrocephala with the plant growth-promoting microorganisms isolated from the plant. [Methods] Mo-Sb colorimetry and Salkowski’s method were employed to determine the abilities of the bacterial strain to solubilize inorganic phosphorus and synthesize indole-3-acetic acid (IAA). The effects of the tested strain on plant growth were assessed with the root irrigation method. The strain was identified based on the morphological and physiological characteristics and the 16S rRNA gene sequence. Response surface methodology was employed to optimize the culture conditions of the strain. [Results] The capabilities of the isolate BZ-8 to solubilize inorganic phosphorus and produce IAA reached 4.89 mol/L and 45.52 μg/mL, respectively. Its genome was 1 363 bp long, and phylogenetic analysis identified the strain as Serratia marcescens. The fermentation broth of the strain significantly promoted the growth of A. macrocephala seedlings. The optimized culture conditions of BZ-8 were 5.0 g/L maltose, 3.0 g/L beef extract, 5.0 g/L yeast extract, 10.0 g/L tryptone, 5.0 g/L sodium citrate, initial pH 7.01, and incubation at 30.4 ℃ and 180 r/min. [Conclusion] S. marcescens BZ-8, an endophytic bacterium of A. macrocephala, is capable of solubilizing phosphorus and producing IAA, demonstrating a significant promoting effect on the growth of A. macrocephala. The optimal culture conditions of strain BZ-8 were determined via response surface test.

Abstract:[Background] The endophytic fungi of medicinal plants have good biocontrol potential because the secondary metabolites they produced have a variety of antimicrobial activities. [Objective] To identify an endophytic fungus EF-WCH-51 with inhibitory activity against Colletotrichum orbiculare (a pathogen causing anthracnose of melons) from Yulania denudata ‘Hailuo’ and determine its main antifungal component. [Methods] Strain EF-WCH-51 was identified based on morphological characteristics and molecular sequences. The growth rate method was employed to determine the antifungal activity of EF-WCH-51, and semi-preparative HPLC and HPLC-MS/MS to identify the active component. [Results] Strain EF-WCH-51 was identified as Lecanicillium aphanocladii. The crude extract of its fermentation broth had a strong inhibitory effect on the mycelial growth of C.orbiculare, with EC₅₀ of 0.086 2 mg/mL. The inhibitory rate of the bioactive compound A (0.085 0 mg/mL) against C.orbiculare was 76.08%. The compound was identified as oosporein by data comparison with MS, MS/MS databases and related literature. [Conclusion] L. aphanocladii, with oosporein as the main antifungal active component, had good inhibitory activity against C. orbiculare, demonstrating the potential as a biocontrol strain against C. orbiculare.

Abstract:[Background] Strain degradation is a difficult problem in the production of Volvariella volvacea. Exploring a simple and efficient rejuvenation method is an urgent problem to be solved in the V. volvacea industry. [Objective] To investigate the effects of exogenous addition of five mineral elements on mycelial traits and active oxygen scavenging ability of degraded strains of V. volvacea. [Methods] The optimum concentrations of five mineral elements were selected and added to the potato dextrose agar (PDA) medium. The colony morphology, mycelial growth rate, mycelial biomass, active oxygen content, antioxidant enzyme activity, and antioxidant substance content of V. volvacea were determined. [Results] MnSO₄, Na₂SeO₃, CaSO₄, and FeSO₄ could effectively improve the mycelial growth rate and biomass of the degraded strains D1 and D2. The content of active oxygens such as O₂·^- and H₂O₂ was decreased, and the content of reduced glutathione (GSH) and oxidized glutathione (GSSG) and the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR) were increased. However, ZnSO₄ had no significant effect on mycelial traits and active oxygen scavenging ability of D1 and D2. [Conclusion] Exogenous addition of MnSO₄, Na₂SeO₃, CaSO₄, and FeSO₄ can effectively improve the mycelial growth and active oxygen scavenging ability of V. volvacea, and the effect of MnSO₄ was optimal.

Abstract:[Background] The application of commercial yeasts has caused a serious problem of wine homogenization. It is significant to explore excellent indigenous strains of Saccharomyces cerevisiae. [Objective] To screen out the S. cerevisiae strains with excellent wine fermentation performance from 168 yeast strains isolated from the eastern foothills of Helan Mountains. [Methods] Duchenne tube fermentation, tolerance tests, and H₂S production experiments and growth curve establishment were employed to screen out the indigenous S. cerevisiae strains with excellent fermentation ability, strong stress tolerance, and low H₂S production for Cabernet Sauvignon wine production. We determined the basic physicochemical indexes and the content of phenols and volatile compounds in wine samples to explore the fermentation characteristics of the candidate yeast strains. [Results] Four indigenous S. cerevisiae strains, YC-E8, QTX-D17, QTX-D7, and YQY-E18 with rapid fermentation, low H₂S production, and tolerance to 13% ethanol, 350 g/L glucose, 250 mg/L SO₂, and pH 1.0 were preliminarily screened out. The strain YC-E8 showed high glycerol production and produced the wine sample with similar aroma to those prepared with commercial yeasts XR and F33, being suitable for brewing Cabernet Sauvignon wine. The wine sample fermented with strain QTX-D17 had the highest content of alcohol, tannin, total phenols, and anthocyanins, which indicated the excellent fermentation characteristics of QTX-D17. In the wine sample fermented with strain QTX-D7, the content of ethyl acetate, ethyl caprylate, and 1-nonanol endowing the wine with pleasant floral and fruity aromas such as banana, apple, pineapple, and coconut aromas were higher. [Conclusion] Finally, three indigenous S. cerevisiae strains QTX-D17, YC-E8, and QTX-D7 were screened out. The three strains exhibit diverse fermentation characteristics in the winemaking process and provide novel yeast strains for exploiting the microorganism resources in the wine-producing region at the eastern foothills of Helan Mountains in Ningxia.

Abstract:[Background] The fruiting body formation and development of ectomycorrhizal fungi such as Lanmaoa asiatica still unknown. [Objective] To identify the active components regulating the fruiting body development. [Methods] We employed Three metabolomics techniques including nuclear magnetic resonance, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry were employed to analyze the small molecular components in L. asiatica primordia cultured for 8 days (Y8) and feral sterile fruiting bodies (Z0). [Results] We found that each of the three analytical methods identified 451 and 473 compounds in Y8 and Z0, respectively. A total of 362 significantly differential components were identified, including 206 up-regulated components and 156 down-regulated components, which were involved in 47 pathways. [Conclusion] We hypothesized that the deep transformation and regulation of components were accomplished via nine main pathways. The significantly up-regulated and down-regulated differential components such as bolegrevilol may play a regulatory role in the development of fruiting bodies. The three methods used in this study complemented each other, expanding the scope and improving the sensitivity of the detection. The results provided some theoretical reference for deciphering the mechanism of fruiting body development and exploring the artificial cultivation of L. asiatica.

Abstract:[Background] The giant pandas are rare, difficult to be bred, and susceptible to digestive system diseases during the growth process. [Objective] To reveal the community structure features and the roles of lactic acid bacteria (LAB) in the intestinal tract of the giant panda and screen out the LAB strains with probiotic characteristics for the prevention of digestive system diseases and the research on intestinal flora in the giant panda. [Methods] Three culture media were employed to isolate the LAB from the intestines of giant pandas in captivity. The isolates were preliminarily identified by Gram staining microscopy and hydrogen peroxide test. The representative strains were selected for 16S rRNA gene sequencing and Principal component analysis (PCA) based on the genetic diversity of BOXA1R-PCR spectrum, and the safety and probiotics of LAB were further analyzed. [Results] A total of 58 LAB strains were isolated, from which 20 representative strains were selected for 16S rRNA gene sequencing according to BOXA1R-PCR results. The 20 strains belonged to Streptococcus, Leuconostoc, Weissella, and Enterococcus, respectively. The principal component analysis showed that the community structure of LAB varied in the giant pandas at different ages. All the 20 strains showed negative results in hemolysis, and 17, 11, and 14 strains were susceptible to 11 antibiotics, tolerant to acidic conditions of pH 2.0, and tolerant to 0.3% bile salts, respectively. Strains SW-51, SW-48, MQ-41, SW-58, and MX-23 demonstrated strong inhibitory activities to 3 pathogenic bacterial species. Over 50% of the strains showed high auto-aggregation and co-aggregation capacities. Three strains showed consistent acid production and growth rate, among which Leuconostoc lactis MX-23 showed the best performance in growth and acid production. [Conclusion] The intestines of giant pandas harbor abundant LAB with valuable probiotic characteristics and application prospects, and the structure and composition of the LAB were influenced by age.

Abstract:[Background] The development and screening of elite probiotics is the research hotspot of animal husbandry, and the potential function of probiotics has been extensively explored. [Objective] To isolate and screen the strains with good tolerance and high yield of extracellular protease and study their biological and enzymatic properties, so as to provide strain resources for the preparation of microbial protease and the development of microecological preparations. [Methods] Fresh feces samples were collected from healthy minks, from which the target strains were preliminarily screened with casein-containing medium and re-screened with optimized Folin method. The biological characteristics of the strains screened out were studied. The strains with high protease yield and good tolerance were obtained and identified by routine and molecular methods. Finally, the enzymatic properties of the protease were studied. [Results] A Bacillus strain with high protease yield and good tolerance was obtained and identified as B. subtilis (number 3). In the initial fermentation medium, the protease showed that the optimal reaction performance at 70 ℃ and pH 9.0, with the activity improved by K⁺ and inhibited by Cu²⁺ and Fe²⁺. In addition, 20% organic solvent did not deactivate the protease. [Conclusion] A B. subtilis strain with good biological characteristics, enzymatic characterization, and alkaline protease activity was isolated from mink feces. The findings of this study provide a basis for the production and application of this strain.

Abstract:[Background] Bacterial diseases are major factors limiting the large-scale cultivation of forest musk deer. Bacillus cereus has been detected in abscesses of forest musk deer. However, there are few studies about the B. cereus from forest musk deer. [Objective] We isolated, identified, and sequenced the whole genome of a suspected B. cereus strain from the liver of a dead forest musk deer, aiming to provide a foundation for the prevention and treatment of diseases cause by B. cereus in forest musk deer. [Methods] After strain purification, we conducted biochemical tests, drug sensitivity tests, and mouse pathogenicity tests on the pathogen. We then employed the third-generation sequencing to reveal its whole genome and phylogenetic relationship. Furthermore, gene function annotation and genetic evolution analysis were conducted. [Results] The average nucleotide identity (ANI) and phylogenetic tree suggested that the pathogen belonged to the B. cereus group, and the biochemical test results of the strain conformed to the general characteristics of B. cereus. The isolate was thus named SCBCM001. The strain showed the median lethal dose of 8.3×10⁷ CFU for mice. It was resistant to most β-lactams, tetracycline, and sulfamethoxazole and sensitive to cephalexin, cefoperazone, imipenem, and aminoglycosides. The chromosome size of the strain was 5 292 570 bp, with the GC content of 35.37%. Multilocus sequence typing showed that SCBCM001 was a strain of ST427. The genome of SCBCM001 carried a variety of virulence genes such as hblA, hblC,hblD, nheA, nheB, clo, and cytK and the genes conferring the resistance to antibiotics such as β-lactams, vancomycin, and tetracycline, which were not completely consistent with the drug-resistant phenotype. In addition, the genome of strain SCBCM001 contained 6 plasmids, one of which had a relatively complete phage region. [Conclusion] The whole genome of a B. cereus strain isolated from forest musk deer was sequenced and analyzed, which provided a basis for the prevention and treatment of bacterial diseases in forest musk deer.

Abstract:[Background] Rodent-borne diseases are a class of zoonoses harmful to humans. The epidemic areas of rodent-borne diseases keep expanding with the progress in globalization, and a variety of new rodent-borne diseases emerge while the old infectious diseases reoccur. [Objective] To investigate the prevalence of common rodent-borne pathogens in rodents in Altay prefecture of Xinjiang, and to provide a scientific basis for the prevention and control of local natural focus diseases. [Methods] The spleen and kidney tissue samples were collected aseptically from the rodents captured by night trapping method, and the genome DNA was extracted. Six common rodent-borne pathogens including Bartonella spp., Leptospira interrogans, Orientia tsutsugamushi, Rickettsia mooseri, Anaplasma phagocytophilum, and Francisella tularensis were detected by fluorescence quantitative polymerase chain reaction (qPCR) with TaqMan probe. Illumina sequencing and Nanopore sequencing after routine PCR amplification with universal primers for the 16S rRNA gene were employed to further detect the pathogens. Meanwhile, the spleen tissue was used for the isolation and culture of Bartonella in vitro. The results of qPCR, 16S rRNA gene sequencing, and bacterial isolation and culture were compared. [Results] A total of 66 rodents of 8 species were captured, of which 31 (46.97%) rodents were Apodemus uralensis, and the rest were Rattus norvegicus, Mus musculus, etc. The infection rates of common rodent-borne pathogens detected by qPCR were as follows: Bartonella 31.80% (21/66), L. interrogans 1.50% (1/66), O. tsutsugamushi 1.50% (2/66), R. mooseri 3.00% (1/66), and F. tularensis 13.60% (9/66). A. phagocytophilum was not detected. The Illumina sequencing of 16S rRNA gene detected pathogens (mainly Bartonella) in the 23 samples passing the quality control. The Nanopore sequencing of 16S rRNA gene detected Bartonella in 11 samples passing the quality control, and did not detect the other 5 common rodent-borne pathogens. Bartonella was isolated from 11 spleen tissue samples, with the infection rate of 16.67% (11/66). [Conclusion] Rodents in the Altay prefecture of Xinjiang can carry a variety of rodent-borne pathogens such as Bartonella. We should pay attention to and strengthen the prevention and control of related infectious diseases in this region. Quantitative polymerase chain reaction, bacterial isolation and culture, and 16S rRNA gene sequencing can complement with each other to provide a comprehensive understanding of the local rodents carrying pathogens.

Abstract:[Background] The crested ibis (Nipponia nippon) is a national protected animal in China and one of the most endangered birds in the world. In this study, we analyzed the microbial diversity and extracellular enzyme activity in the gut of crested ibis, aiming to provide ideas for restoring the population of crested ibis. [Objective] To reveal the intestinal microbial diversity and extracellular enzyme activities of crested ibis.[Methods] The intestinal microorganisms of crested ibis were isolated by the pure culture method. The bacteria were identified by Gram-staining, physiological and biochemical tests, and 16S rRNA gene sequencing. The strains producing amylase, protease, cellulose, and lipase were screened out by the hydrolysis circle method. [Results] A total of 296 strains of bacteria were isolated from the fresh excreta of artificially breeding Crested Ibis, belonging to 11 genera of 2 phyla. The 236 isolates of Proteobacteria accounted for 79.73% of the total isolates, including 137 (46.28%) isolates of Escherichia, 39 (13.18%) isolates of Hafnia, 28 (9.46%) isolates of Proteus sp., 23 (7.77%) isolates of Citrobacter sp., 6 (2.03%) isolates of Aeromonas, 1 (0.34%) isolate of Enterobacter, 1 (0.34%) isolate of Shigella, and 1 (0.34%) isolate of Klebsiella. The rest isolates (60, 20.27%) belonged to Firmicutes, including 33 (11.15%) isolates of Enterococcus, 14 (4.73%) isolates of Kurthia, 13 (4.39%) isolates of Bacillus. The dominant genus was Escherichia of Proteobacteria, with the isolates accounting for 46.28% of the total. The physiological and biochemical properties of each strain were consistent with the result of identification based on 16S rRNA gene sequence. The enzyme production experiments showed that 238, 25, 24, and 15 strains produced protease, lipase, amylase, and cellulase, accounting for 80.41%, 8.45%, 8.11%, and 5.07%, respectively. [Conclusion] The bacteria isolated from the intestine of crested ibis belonged to 11 genera of 2 phyla, among which Escherichia of Proteobacteria was dominant with the isolates accounting for 46.28% of the total, and 80.41% of the strains had the ability of producing protease.

Abstract:[Background] Porcine edema disease caused by Escherichia coli is a major disease attacking pigs. The existing culture medium used for vaccine preparation has a low cell density.[Objective] To develop a vaccine culture medium with high antigenic activity for the prevention of porcine edema disease. [Methods] A commercially available vaccine culture medium against porcine edema disease was used as the control. The response surface methodology was employed to optimize the composition of the culture medium through single-factor experiments, Plackett-Burman (PB) design, and Box-Behnken (BB) design. The optimized culture medium was used to culture the E. coli eliciting porcine edema disease, and the antigenic activity of the culture at different time points was evaluated. In addition, the inactivated vaccine was prepared and used for animal immunization. [Results] The expanded culture of the pathogen in the developed culture medium showed that the viable cell count of the strain reached more than 5×10⁹ CFU/mL, approximately twice that of the control group. Meanwhile, the titer of the inactivated vaccine reached 1:140 000, and the antigen protein titer peaked at the time point of 9 h. [Conclusion] The developed vaccine culture medium significantly improved the cell density and antigenic activity of E. coli causing porcine edema disease, providing technical guidance for preparing inactivated vaccines against porcine edema disease.

Abstract:[Background] Lactiplantibacillus plantarum P-8 is a lactic acid bacterium with excellent prebiotic properties. Exploring its genetic stability during short-term continuous subculturing helps to evaluate the stability of the cells in production. [Objective] To study the genetic stability of L. plantarum P-8 subcultured in MRS medium at 37 ℃ for 100 generations. [Methods] We observed the cell morphology and measured the carbohydrate utilization ability of L. plantarum P-8 subcultured for 0, 25, 50, 75, and 100 generations in MRS medium at 37 ℃. The whole genomes of cells subcultured for different generations were sequenced by the second- and third-generation sequencing. Comparative genomics was employed to comprehensively analyze the genetic stability of the cells during the 100 generations. [Results] The cell morphology and carbohydrate utilization ability of L. plantarum P-8 showed no significant changes during continuous subculturing for 100 generations. With the genome of the original cells as a reference, the genomic stability of different generations was compared. The cells of all the generations had single nucleotide polymorphism (SNP) sites, while the number of SNP sites was <21. The genomes of the cells at different generations had good collinearity and high similarity. The results of carbohydrate activity enzyme annotation showed no significant differences among different generations (P>0.05). [Conclusion] L. plantarum P-8 has good genetic stability during continuous subculturing for 100 generations in MRS medium at 37 ℃. This study laid a genetic foundation for the industrial application of this strain.

Abstract:[Background] Human norovirus is regarded as the leading cause of the outbreak of acute gastroenteritis with GII.4 being the predominant genotype during the past decades. The GII.17 variant that emerged in 2014/2015 was the first non-GII.4 epidemic strain causing a large-scale epidemic in China. The full-length genome sequencing of the GII.17 strain from South China confirmed that it was different from the previously identified GII variants. [Objective] To prepare the virus-like particles and systematically characterize the immunogenicity and functions of GII.17-GZ-L343 in Guangzhou. [Methods] The baculovirus expression system was employed to produce GII.17-GZ-L343 in Sf9 insect cells. The virus-like particle was purified by cesium chloride gradient ultracentrifugation. Finally, the antiserum was prepared and its immune function was evaluated. [Results] The results of SDS-PAGE and Western blotting showed that the molecular weight of the obtained protein was about 58 kDa. The prepared virus-like particle had a diameter of about 30 nm, good immunogenicity, and binding activities to the saliva of type A/B/O/AB secretors and non-secretors. The serum titer after immunization was above 10⁴, and the antiserum had no inhibitory effects on other variants. In addition, the antiserum only blocked the binding of homotypic virus-like particle to the receptor, and did not block the binding of heterotypic virus-like particle. [Conclusion] GII.17-GZ-L343 has a broad binding pattern. Its antiserum is not broad-spectrum for heterotypic virus-like particle and only has blocking effect on homotypic virus-like particle. The results provide theoretical support for further revealing the host adaptation characteristics and evolution mechanism of the virus and developing multivalent vaccines.

Abstract:[Background] Filamentous fungi are a key group of host fungi in industrial fermentation. How to carry out high-throughput cultivation and screen out the efficient strains is an important direction of the research on industrial filamentous fungi. [Objective] To establish a high-throughput cultivation technology of filamentous fungi and evaluate its efficiency. [Methods] After studying the seed production, inoculation, cultivation, and detection of filamentous fungi, we established a microplate-based high-throughput cultivation technology and evaluated its performance with Myceliophthora thermophila. [Results] Compared with the traditional methods using either plate or shake flask for seed production, the microplate-based method increased the seed production by 24 folds, the spore production per unit area by 350%, and the transfer efficiency of liquid culture by 10-40 folds. Furthermore, a 96-well microplate-based high-throughput technique was developed for ethanol content determination. [Conclusion] The developed high-throughput technology increased the cultivation and detection efficiency of filamentous fungi by 1−2 orders of magnitude. This study lays a foundation for rapid screening of the target strains from a large number of variants with different traits and provides a reference for the research on filamentous fungi.

Abstract:Irritable bowel syndrome (IBS) is one of the common functional bowel diseases, which lacks clinical features that can be explained by organic diseases. Recent studies describe the pathogenesis of IBS as the disturbance of the brain-gut-microbiota axis, emphasizing the mediating role of gut microbiota in regulating brain-gut interactions. Traditional Chinese medicine (TCM) has been applied to the regulation of brain-gut homeostasis for a long time and demonstrated good efficacy. However, the correlation between TCM and brain-gut homeostasis remains to be studied. We reviewed the TCM and western medicine studies of IBS involving brain-gut-microbiota axis based on the interaction between brain-gut axis and TCM and our previous work, aiming to provide a reference for researchers in this field.

Abstract:Extracellular vesicles (EVs) are a type of lipid bilayer membrane vesicles, which can be secreted by a variety of cells. EVs as the key players of interkingdom crosstalk participate in the transmission of signals between prokaryotes and eukaryotes to regulate biological processes. In gut ecosystems, microbe-host communication usually does not involve direct cell contact. Microbiome-derived and host-derived EVs are key participants in such interkingdom crosstalk. The gut-liver axis plays a bridging role in the interaction between gut microbiota and the liver, that can modulate liver diseases including alcoholic fatty liver disease. Recent studies have demonstrated that gut microbiota-derived EVs play a key role in liver diseases. This article summarizes the research progress in gut microbiota-derived EVs, especially the mechanism of EVs production, the contents of EVs, bacteria-host interaction and its role in liver diseases.

Abstract:Friedelin and its derivatives are ubiquitous in plants, with a wide variety of physiological and pharmacological activities. The derivatives of friedelin are modified from friedelin by cytochrome P450 oxidase (CYP450) and UDP-glucuronosyltransferase (UGT). Because of the extremely low content of natural friedelin and its derivatives in plants, the traditional extraction and chemical synthesis methods are inefficient, energy-consuming, and pollute the environment. Therefore, using Saccharomyces cerevisiae as the host bacteria to produce friedelin and its derivatives is an efficient and environmentally friendly approach. In this paper, we introduced and looked forward to the efficient production of friedelin in S. cerevisiae from the aspects of increasing precursor content, improving enzyme activity, and subcellular localization of product synthesis. In addition, this paper reviewed the current research status of several common friedelin derivatives, and put forward new ways for the synthesis of friedelin derivatives from the aspects of mining CYP450 based on carbon skeleton similarity, modifying CYP450 by protein engineering, and mining the gene clusters involved in the synthesis.

Abstract:Myxobacteria are a group of medical microorganisms showing complex multicellular behaviors. On one hand, they produce a variety of natural bioactive compounds with novel structures through secondary metabolism. On the other hand, they can secrete diverse functional enzymes. Therefore, myxobacteria are valuable for basic research and applications. However, the research on them has been impeded by the difficulties in resource mining and the low yield of secondary metabolites. This review introduces myxobacteria in terms of the biological characteristics, bioactive products, regulation on biosynthesis and applications in medicine, agriculture and food industry. Based on available results, the problems in the research on myxobacteria and the possible countermeasures are presented. This review is expected to provide reference for the in-depth research and the resource development and utilization of myxobacteria.

Abstract:Mycotoxins are widely present in agricultural products, posing a severe threat to human and animal health. As a group of recognized safe microorganisms, lactic acid bacteria have great application potential in the biological detoxification of food, with low cost and no adverse impact on food quality and the environment. By reviewing the recent research progress in this field, we introduced the detoxification effects (inhibition of fungal growth and adsorption and degradation of toxins) of lactic acid bacteria on several common mycotoxins in food and feed, with focuses on the practical application of lactic acid bacteria in biological detoxification. This review aims to provide theoretical guidance for the application of lactic acid bacteria in food preservation.

Abstract:[Background] Actinobacteria are a class of microorganisms capable of producing rich metabolites, which are widely used in medicine, biotechnology, agriculture, and enzyme industry. [Objective] To review the research progress in the metabolites of actinobacteria and provide effective information for the high-quality development of this field. [Methods] Statistical analyses were conducted on the number, countries, institutions, journals, publishers, and authors of publications, cited articles, and research directions of the metabolites of actinobacteria. The relevant articles were retrieved from the Web of Science (WOS) and China National Knowledge Infrastructure (CNKI). The H-index was calculated to comprehensively evaluate the impact. The research hotspots and development trends were visualized in CiteSpace and VOSviewer. [Results] The analysis based on WOS showed that the United States, the University of California, Applied and Environmental Microbiology, and Elsevier were the country, institution, journal, and publisher, respectively, with the highest impact in this field. Professor Mervyn J Bibb in the microbiology department of the John Innes Centre in the UK was the author with highest impact. The main research direction in the metabolites of actinobacteria worldwide was Microbiology, and the research focused on the biosynthesis. The research trend evolved from the genes and antibiotics before 2000 to gut microbiota and natural products after 2000. The analysis based on CNKI showed that Northwest A&F University, Microbiology China, and Professor Lihua Xu at Yunnan University were the institution, journal, and author, respectively, with the highest impact in this field in China. The main research direction was Biology, and the research focused on actinomycetes. The research trend in this field in China shifted from antibiotics and biosynthesis before 2000 to diversity and identification after 2000. [Conclusion] The research on the metabolites of actinobacteria is flourishing worldwide. The United States was a global leader in this field, ranking first in the world in terms of the number of publications and the H-index, with strongly influential institutions, journals, and publishers. China ranked second in terms of the number of publications and fifth in terms of the H-index, and the publishing institutions and scholars had influences at home and abroad. In the future, China should strengthen the publishing of high-quality articles and the building of journals and publishers in the research on the metabolites of actinobacteria and double the efforts to study gut microbiota and discover natural products, so as to build up the strength in this research field.