Abstract:[Background] Antibiotic resistance in bacteria is one of the current challenges,and the study of antibiotic resistance is therefore a critical way to address this challenge.Vibrio sp.FA2,a new strain isolated from the environment,has fast growth,and its growth rate is even faster than that of the reported fast-growing strain Vibrio natriegens 14048.Vibrio sp.FA2 can use a variety of carbon sources,showing great potential to serve as the next-generation biotechnological workhorse and can be used to develop efficient strains for compound production.[Objective] We have found that FA2 has multiple antibiotic resistance,which is not conducive to genetic engineering operation and will bring ecological risks in industrial application.Therefore,it is essential to study the antibiotic resistance and knock out the resistance genes from this strain.[Methods]We profiled the antibiotic resistance of FA2 by susceptibility experiments with multiple antibiotics such as β-lactams (represented by ampicillin) and aminoglycosides,and then mined the genes related to the resistance by genome annotation.The mutants were constructed through knockout of the target genes related to ampicillin resistance.Finally,the resistance to ampicillin and the growth were compared between the knockout mutants and FA2.[Results] FA2 had strong resistance to several β-lactam antibiotics and carried three possible ampicillin resistance genes:carB6,ampC2,and ampC1.The resistance changes of the mutants indicated that the genes knockout increased the strain susceptibility to ampicillin.[Conclusion] This study clarifies the antibiotic resistance of FA2 and eliminates the resistance of FA2 to ampicillin,laying a foundation for the development and transformation of FA2 as a microbial workhorse.

Abstract:[Background] Flavanone-3-hydroxylase (F3H) is one of the key enzymes in the metabolic pathway of flavonoids.The catalytic properties of F3H from different plants may be different,which has an important impact on the biosynthesis of flavonoids.[Objective] In order to compare and analyze the enzymatic properties and catalytic abilities of F3H,providing reference for the selection of F3H in the metabolic engineering of flavonoids in the future.[Methods] Three genes,CsF3H(Camellia sinensis),GbF3H(Ginkgo biloba) and GmF3H(Glycine max),were identified by phylogenetic analysis.The three F3H were purified by affinity chromatography,and the enzymatic properties were characterized by naringenin as substrate in vitro.Single-factor culture method was used to analyze the activities of F3H in Escherichia coli and Saccharomyces cerevisiae.[Results] Enzymatic analysis showed that the optimal temperature of CsF3H,GbF3H and GmF3H was 40,40 and 35℃,and the optimal pH was 7.5,7.0 and 7.5,respectively.The k_cat/K_m of CsF3H was 0.36 L/(mmol·s),which was higher than that of GbF3H and GmF3H.When substrate naringenin concentration was 500 μmol/L,the conversion rate was more than 80% of the E.coli contained CsF3H,GmF3H,while the strain contained GbF3H was only 23.8%.As for the S.cerevisiae with different F3H,the conversion efficiency was 40%,with no significant difference.[Conclusion] There were different catalytic activities of F3H from different plants.Moreover,one F3H also showed great differences within prokaryotic and eukaryotic chassis cells.CsF3H has excellent catalytic capacity and showed better development and application potential in prokaryotic chassis cells.

Abstract:[Background] There are abundant undeveloped microbial germplasm resources in the ocean,and the enzymes produced by marine microorganisms have attracted attention because of their tolerance to low temperature,high pressure,and high salt,which are different from those produced by terrestrial microorganisms.[Objective] To isolate and screen out the strains producing glucose oxidase (GOD) from the mud samples of the Bohai Sea,and to study its enzymatic properties.[Methods] The GOD-producing strain was preliminarily screened with plate culture method and re-screened based on enzyme activity.The candidate was identified based on morphological,physiological,and phylogenetic characteristics.The enzymatic properties of the GOD produced by the strain screened out were further characterized in detail.[Results] strain No.31 that produced GOD was screened out and initially identified as Basidiomycete sp.based on morphological and phylogenetic characteristics.The GOD produced by strain No.31 had high activity reaching 20 U/mL at 25–35℃.This enzyme had the optimum reaction temperature at 30℃ and still had activity at 0℃.Its activity was stable between pH 5.0 and 7.0 and peaked at pH 7.0.Ni²⁺,Na⁺,Zn²⁺,Mg²⁺ can improve GOD activity,and high concentrations of Ni²⁺,Na⁺,and Zn²⁺ had significant effect.Different concentrations of β-mercaptoethanol,urea,EDTA,Triton-100,sodium hyposulfite,and DTT had significant inhibitory effect on GOD activity.[Conclusion]The experimental results prove that strain No.31 is a valuable strain producing GOD tolerant to low temperature,which provide a good strain resource for the production of GOD,accumulate relevant data for follow-up research,and fill the blank of using this fungus to produce GOD.

Abstract:[Background] Pseudoalteromonas is a group of Gram-negative bacteria ubiquitous in the marine environment.They exist in the seabed sediments and can secrete a large amount of extracellular products to form a biofilm,which induces the attachment of invertebrates.[Objective] To explore the effect of fliC-02330 deletion from Pseudoalteromonas marina on the biofilm formation and the activity of Mytilus coruscus.[Methods] We constructed the fliC-02330-deleted mutant of P. marina by gene knockout and then compared the phenotype,the biofilm-forming ability,and the effect on settlement and metamorphosis of M. coruscus between the mutant and the wild-type strain.Confocal laser scanning microscopy (CLSM) was conducted to detect changes in the content of extracellular products in the biofilm.[Results]Compared with the wild-type strain,the mutant showed wrinkled colony,weakened motility,thickened biofilm,and decreased activity of inducing the larval settlement and metamorphosis of M. coruscus.CLSM revealed that the fliC-02330-deleted mutant had decreased extracellular polysaccharide content and increased protein content.[Conclusion]The fliC-02330-deleted mutant has increased biofilm-forming ability and can inhibit the settlement and metamorphosis of M. coruscus larvae.This study provides a theoretical basis for exploring the mechanism of bacterial flagellin gene and the role of microorganisms in the settlement and metamorphosis of marine invertebrates.

Abstract:[Background] Land salinization is serious in inland and plain areas of north China,and the role of microorganisms in the vegetation succession of extreme saline-alkali land has been seldom reported.[Objective] To study the relationship between soil conditions and microbial community in the salt marshes with five types of vegetation (S1:bare;S2:succulent;S3:carex;S4:grass;S5:weeds) on the Ordos plateau,and screen out salt-tolerant bacteria and the soil factors affecting salt-tolerant bacteria.[Methods] Illumina MiSeq high-throughput sequencing was performed to analyze the microbial community composition.[Results] The soil bacterial abundance and diversity in the Ordos salt marshes with 5 different types of vegetation ranked in the order of S3>S5>S4>S2>S1 and S3>S5>S2>S4>S1,respectively.Proteobacteria was the most abundant phylum in the soil bacteria of the 5 vegetation types,and its relative abundance first increased and then decreased with the succession of the 4 salt marshes,which was contrary to the trend of Deinococcus-Thermus.Soil clay particle had a significantly positive correlation with Gemmatimonadetes,and its correlation with Firmicutes increased gradually with the increase in soil particle size.The soil chemical properties showing high correlations with bacterial community were in the order of AK>TP>SOC>TN>AN>AP>pH.[Conclusion] Proteobacteria was the most abundant bacterial phylum in Ordos salt marshes experiencing vegetation succession,and Actinomycetes,Alphaproteobacteria,and Blastomonas were the classes with stronger salt tolerance.The diversity and abundance of bacteria in S3 were the highest,and the adaptability of bacterial community varied regarding the soil particle size in salt-alkali areas.AK was the most significant soil factor affecting the bacterial community structure in the salt marshes of Ordos platform.

Abstract:[Background] In view of the high mortality of live pigs due to diseases in China,it is particularly important to establish an efficient harmless method for treating diseased pig carcasses.[Objective] In order to improve the harmless treatment efficiency of compost on diseased pig carcasses.[Methods] We screened out the strains with protein and fat degradation functions and formulated the compound bacterial agents.Single factor experiments and response surface method were employed to optimize the strain ratio and degradation conditions.The degradation performance of compound bacterial agents on diseased pig carcasses and sawdust compost were evaluated.[Results] Strain DB1 was identified as Serratia marcescens with a protease activity of 36.76 U/mL and a degradation rate of 72.17% for pig carcass.Strain ZF2 was Bacillus velezensis,with a lipase activity of 12.33 U/mL and a degradation rate of 70.83% for pig carcass.The optimal ratio of DB1 to ZF2 in compound bacterial agent was 2.55:1,and the optimal degradation conditions obtained by response surface optimization were as follows:temperature at 31.65℃,inoculation amount of 3.11%,pH 6.0,salinity of 0.75%,and Mn²⁺ concentration of 1 mmol/L.A degradation test was carried out under the optimum conditions,which showed a degradation rate of 90.61% after 7 days.The composting test showed that the peak temperature of compost in the control group and the low-,medium-,and high-amount inoculation groups could reach 60,64,69,and 62℃,respectively.The group with an inoculation amount of 3% had the best treatment performance,with the high temperature period lasting for 19 days and the carcass degradation rate of 98.06%.All the indicators of this group were superior to those of the control group (p<0.01).[Conclusion] In this study,we designed the degradation test according to the fat/lean ratio of pig carcass for the first time to evaluate the performance of functional bacteria,which was superior to the previous methods.Taking the degradation rate as the evaluation index,we optimized the strain ratio of functional bacteria.Compared with those in previous studies,the compound bacterial agent designed in this study can well accelerate the temperature rise of composting and the degradation of pig carcass.

Abstract:[Background] Saccharin sodium wastewater,one type of organic industrial wastewater with high salt,is difficult to be treated.[Objective] To improve the biodegradation of this wastewater,it is in urgent need to study the characteristics of the saccharin sodium wastewater degrading bacteria.[Methods] A bacterial strain A20 capable of degrading saccharin sodium wastewater was isolated by pure culture technology from the activated sludge in the multistage biological contact oxidation system.It was identified based on morphological characteristics,physiological and biochemical properties,and 16s rRNA gene sequence analysis.The optimum conditions for strain A20 to degrade saccharin sodium wastewater were investigated by single factor experiment and response surface method.[Results] The strain A20 belonged to Halomonas.When the salinity of saccharin sodium wastewater in 5%,pH 8.0,and the temperature of 30℃,inoculum ratio at 15%,the chemical oxygen demand (CODcr) removal efficiency was more than 60%.Through the optimization with response surface method,the optimum conditions for Halomonas sp.A20 to degrade the saccharin sodium wastewater:pH 8.0,temperature of 30.3℃,and inoculum ratio of 14.1%.Under this optimum condition,the CODcr removal efficiency was 65.4%.[Conclusion] The salt-tolerant strain A20 obtained in this study can efficiently degrade the organic matter in saccharin sodium wastewater,which can provide excellent microbial strain resources for the treatment of high-salt and high-concentration saccharin sodium wastewater.

Abstract:[Background] The complicated genetic transformation methods hinder the gene cloning and gene function characterization of Trichoderma.[Objective]To establish a convenient and efficient genetic transformation system for Trichoderma atroviride HB20111.[Methods] Magnesium aminoclay was used as a carrier to adsorb the filamentous fungal expression vector pCAMBIA1303-gpdA-GFP-TrpC-Hygro containing the fluorescent protein gene gfp to form a plasmid-magnesium aminoclay complex.The conidia of T. atroviride HB20111 were then genetically transformed under ultrasonic conditions.[Results] Under the conditions of the conidial suspension at a concentration of 10⁶ CFU/mL,culture time of 12 h,magnesium aminoclay concentration of 100 mg/L,and ultrasonic treatment for 30 s (the ultrasonic output power was 100 W/cm²,and the emission frequency was 50 kHz),the transformation efficiency of HB20111 was the highest,which reached 124 CFU/μg-DNA.[Conclusion] Using magnesium aminoclay as a carrier can realize convenient and efficient genetic transformation of T. atroviride HB20111,and the resistance gene and reporter gene can be inherited stably in the transformant.

Abstract:[Background] Norovirus is the primary foodborne pathogen causing acute gastroenteritis in humans.There are currently no licensed vaccines and drugs available for this virus.RNA-dependent RNA polymerase (RdRp) of norovirus is a major target for the development of antivirals.[Objective] This study intended to express the RdRp of norovirus recombinant GII.P12/GII.3 and systematically study its replication characteristics.[Methods] The high-purity soluble RdRp of GII.P12/GII.3 was expressed and purified in Escherichia coli.The effects of temperature,template,substrate,and salt concentration on the function of RdRp were determined by in vitro RNA synthesis experiments.[Results] The RdRp of GII.P12/GII.3 showed the highest activity at 30℃ and 1 mmol/L MnCl₂.The K_m values of RdRp binding substrate GTP and template polyC were 79.0µmol/L and 10.6µg/mL,respectively.In vitro inhibitory assays indicated that ribavirin,favipiravir,and NF023 in the micromolar range inhibited RdRp,with half-maximal inhibitory concentrations of 23µmol/L,59µmol/L,and 11µmol/L,respectively.[Conclusion] This study firstly reported the RdRp properties of norovirus recombinant genotype GII.P12/GII.3.Fluorescence-based enzyme activity tests showed that RdRp had catalytic activity in vitro,which provided technical and theoretical support for the screening of norovirus RdRp inhibitors and the treatment of norovirus infections.

Abstract:Background]The infection of entomopathogenic fungi is a complex process resulted from the joint action of multiple genes.The Isaria fumosorosea isolate IFCF01 has high pathogenicity to Plutella xylostella.However,there are few reports on the genes related to the pathogenicity of I. fumosorosea to P. xylostella.[Objective]This study aims to explore the genes related to the infection of I. fumosorosea to P. xylostella,so as to reveal the pathogenic mechanism of I. fumosorosea and provide reference for the application of I. fumosorosea in the control of P. xylostella.[Methods] We performed high-throughput RNA sequencing to compare the transcriptomes of I. fumosorosea pure culture (control group) and the mixed samples of 2nd–3rd instar larvae of P. xylostella infected by I. fumosorosea for 4,8,12,16,24,30,and 36 h (treatment group) and mined the differentially expressed genes (DEGs) between the two groups.The functional modules and signaling pathways involving the DEGs were analyzed by bioinformatics method.[Results]A total of 28 384 DEGs were screened out,including 274 significant DEGs (118 up-regulated and 156 down-regulated ones).The significant DEGs screened out in this study,especially the up-regulated ones,were related to the infection.We conducted GO annotation to analyze the DEGs and found 36 GO terms,which included 18 biological processes,9 cellular components,and 9 molecular functions.There were 171 DEGs enriched in 132 KEGG pathways,of which 66 DEGs were significantly enriched in 14 pathways.Further analysis showed that many DEGs were virulence-associated genes during the infection.[Conclusion]The findings generated from this study provide a bioinformatic database for screening the pathogenic genes related to the infection of I. fumososea in P. xylostella and lays a theoretical foundation for elucidating the mechanism of I. fumosorosea infecting P. xylostella.

Abstract:[Background] Star anise anthracnose is a fungal disease caused by Colletotrichum horii,which has caused serious economic losses to star anise industry in China. [Objective]To isolate and screen out the actinomycetes strains with inhibitory effect on C. horii from the rhizosphere soil of star anise trees.[Methods]Actinomycetes strains were isolated by dilution-plating method,and a plate confrontation experiment was conducted to screen out the strains with antagonistic effects on C. horii.The antagonistic strain was identified based on morphological,physiological,and biochemical characteristics combined with 16S rRNA gene sequence analysis.The antagonistic activity was evaluated based on the mycelial growth rate.The biocontrol effect of the cell-free fermentation broth was tested with detached star anise leaves.[Results]An actinomycetes strain RX2-2 was isolated from the rhizosphere soil of star anise trees,which had a strong antagonistic effect against C. horii, with the inhibition rate of 95.48%.RX2-2 had a broad antimicrobial spectrum,with strong inhibitory effects on other seven plant pathogenic fungal species and five common bacterial species.The antibacterial substances in the fermentation broth of RX2-2 have good thermal stability.The cell-free fermentation broth showed the biocontrol effect up to 47.62% on detached star anise leaves infected with C. horii.RX2-2 was identified as Streptomyces lunalinharesii based on the morphological,physiological,and biochemical characteristics in combination with 16S rRNA gene sequence.[Conclusion]RX2-2 has a promising prospect in the biological control of star anise anthracnose and other plant diseases.

Abstract:[Background] The key to promoting green agriculture is microbial fertilizer.Siderophore is a low molecular iron chelate produced by rhizosphere microorganisms,which can promote plant growth by chelating Fe³⁺.Therefore,it is of great significance to screen out the strains with high-yield siderophore.[Objective] In order to provide germplasm resources for the development of plant growth-promoting bacteria,we isolated high-yielding siderophore microorganisms from rhizosphere soil.[Methods] A fungal strain with high yield of siderophore was isolated and purified by chrome azurol sulfonate (CAS) overlay plate method.The strain was identified based on morphological observation and 18S rRNA gene analysis.The culture conditions for siderophore production were optimized by single factor experiment,and the growth-promoting effect of the strain was preliminarily investigated by hydroponic experiment of Chinese cabbage.[Results] Four strains of siderophore-producing fungi were isolated,one of which with strong siderophores-producing ability was numbered RL1 and preliminarily identified as Aspergillus niger.The optimal culture conditions for siderophore production of strain RL1 were as follows:initial pH 5.0,carbon source of glucose at 5 g/L,temperature at 20℃,culture time of 5 days,and rotational speed of 60 r/min.The fresh weight and photosynthetic pigment content of Chinese cabbage increased with the increase in the concentration of RL1 suspension.When the maximum concentration (3.2×10⁸ CFU/mL) of suspension was applied,the total fresh weight and the aboveground weight of Chinese cabbage increased by 75.0% and 74.4%,respectively,and the content of chlorophyll a,chlorophyll b,and carotenoid increased by 49.8%,70.9% and 26.7%,respectively.[Conclusion]In this study,a fungal strain RL1 with high-yield siderophore was isolated.High siderophore production of the strain was achieved at optimized culture conditions,and the strain could effectively promote the growth of Chinese cabbage seedlings.

Abstract:[Background] Potato late blight is a devastating disease caused by Phytophthora infestans(Mont.) de Bary.When environmental conditions are suitable,the P. infestans remaining in the soil will infect potato plants and cause late blight.[Objective] To clarify the bacterial community structure and diversity of the rhizosphere soil of healthy and diseased potato plants.[Methods] The rhizosphere soil samples of healthy (M2J) and diseased (M2G) potato plants in a potato field with late blight occurrence were collected.The metagenomic high-throughput sequencing was performed on the Illumina MiSeq platform to analyze the bacterial communities in the soil samples.[Results] The soil samples of diseased plants had 1 747 fewer high-quality sequences and 1 466 fewer OTUs than those of healthy plants.At the phylum level,the microorganisms in the rhizosphere soil had similar community composition while different abundance between healthy plants and diseased plants.After the occurrence of late blight,the relative abundance of Proteobacteria and Chloroflexi in the rhizosphere soil increased by 17.70% and 1.58%,respectively,while that of Acidobacteria,Actinobacteria,Gemmatimonadetes,and Verrucomicrobia decreased by 6.13%,4.28%,1.41%,and 3.11%,respectively.At the genus level,the relative abundance of Rhodanobacter and Sphingomonas in the rhizosphere of diseased plants increased by 8.63% and 3.51% compared with healthy plants;while the Vicinamibacteraceae,norank_f__norank_o__Vicinamibacterales,norank_f__Gemmatimonadaceae,Chujaibacter and Flavobacterium have lower species abundance than healthy plants.[Conclusion] The community structure and diversity of bacteria in the rhizosphere soil of plants infected with P. infestans were significantly lower than those of healthy plants,and the proportions of some dominant bacterial phyla and genera changed after disease occurrence.

Abstract:[Background] The quality of pit mud (PM) is one of the critical factors affecting the quality of Luzhou-flavor Baijiu.The physicochemical properties,microbiome,and volatiles determine the quality of PM.[Objective] To reveal the relationship between physicochemical properties,microbiome,and volatiles of PM at different ages.[Methods] The physicochemical properties of growing PM (10 years) and mature PM (30 years) were compared.Volatiles were analyzed by headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS).PacBio SMRT high-throughput sequencing was conducted to analyze the microbiome.Spearman’s correlation analysis was performed with the obtained data.[Results] Moisture,available phosphorus and potassium,and the key flavor volatiles (caproic acid,ethyl caproate,and ethyl butyrate) in mature PM were higher than those in growing PM,whereas lactic acid and hexanol showed the opposite trend.Proteiniphilum and Petrimonas(Bacteroidia) were most abundant in growing PM,whereas Caproiciproducens and Clostridium(Clostridia) were most abundant in mature PM.The relative abundance of Clostridia(Caproiciproducens and Clostridium) was positively correlated with the content of caproic acid and ethyl caproate,and negatively correlated with the content of lactic acid.The physicochemical properties of PM influenced most species of Clostridia in PM.Moisture and available phosphorus and potassium were positively correlated with the content of key volatiles and the relative abundance of Clostridia.[Conclusion] Moisture,available phosphorus and potassium are the key factors affecting both the composition of Clostridia and the content of key volatiles (caproic acid and ethyl caproate) in Luzhou-flavor Baijiu.These findings improve our understanding of the microbial succession and volatile profile in PM,which facilitates the fermentation regulation and PM quality improvement of Luzhou-flavor Baijiu.

Abstract:[Background] Frequent occurrence of pneumonia in foxes and raccoon dogs has resulted in huge economic losses for farmers.[Objective] In order to investigate the causes of pneumonia attacking foxes and raccoon dogs in Heilongjiang,Jilin,Hebei,and Shandong provinces,we isolated,identified,and characterized the pathogenic bacteria.[Methods] The bacteria were isolated aseptically from the lung tissues of diseased foxes and raccoon dogs.Gram staining,biochemical test,PCR identification of specific genes,susceptibility test by disk diffusion method,virulence gene detection,and mouse pathogenicity test were then conducted for the isolates.[Results] All the 136 isolates were Gram-negative bacilli and were identified as Escherichia coli based on biochemical characteristics and specific gene PCR.The isolates had multiple drug resistance and 29 virulence gene combinations.The main virulence genes were yijP,fimC,fimH,fyuA,iutA,papC, irp2,and astA.The isolates carrying more virulence genes had stronger pathogenicity to mice.[Conclusion] E. coli was identified as the pathogen causing pneumonia of foxes and raccoon dogs,and the number of virulence genes was related to the pathogenicity.

Abstract:[Background] Under the high-temperature and-pressure condition,crude oil presents as a single-phase liquid.However,due to variations in temperature,pressure,and flow conditions during the mining and transportation processes,paraffin wax is continuously precipitated from the crude oil and deposits in the wellbore and pipelines.As an emerging technology,microbial wax removal has attracted wide attention.Nevertheless,the specific consortium applied needs to be determined according to the site conditions.[Objective] This study aims to use the consortium QZ-10 screened out from the saline-alkali reservoir environment in Qinghai oilfield to solve the problem of wax deposition in oil wells and investigate the mechanism.[Methods] The performance of QZ-10 was characterized based on surface tension/interfacial tension,EI₂₄ value,viscosity reduction rate,wax prevention rate,and hydrocarbon conversion ability.Finally,field trial was carried out to verify its actual effect on paraffin removal.[Results] The fermentation broth of QZ-10 could reduce the water-kerosene interfacial tension to 1.21 mN/m,and the EI₂₄ value was 91.11%.Besides,the viscosity reduction rate was measured as 92.90%,and the wax prevention rate could reach 90.00%.Furthermore,QZ-10 could degrade the heavy hydrocarbons in the crude oil,and increase the light hydrocarbon components,which would improve the quality of the crude oil.The results of laboratory experiments showed that the consortium QZ-10 reduced the viscosity of crude oil and emulsified the oil,and showed the potential to be applied in wax removal and prevention of oil well.The oil wells with severe wax deposition in Qinghai oilfield were selected for the field trial.After the injection of QZ-10 broth,paraffin wax was removed obviously in 80.95% of the tested oil wells after 140 days,and many of the tested oil wells had a significant increment in oil production,with a cumulative oil increment of 1 100 tons.[Conclusion] we demonstrated that the consortium QZ-10 could effectively remove paraffin wax deposited in oil wells and increase the oil production,which exhibited a broad application prospect.

Abstract:[Background] The bacteriophage qdvp001 has a great potentiality in preventing Vibrio parahaemolyticus contamination.However,the phage is highly sensitive to temperature and will be deactivated under high temperature.[Objective] We encapsulated qdvp001 in cationic liposomes to improve its thermal stability and explored the antibacterial activities of the cationic liposomes encapsulating qdvp001.[Methods] The cationic liposomes encapsulating qdvp001 were prepared and characterized,and their thermal stability and bactericidal activity were investigated.[Results] Compared with the neutral liposome without octadecylamine (ODA,a positively charged amine compound),the addition of ODA contributed to the positive charging of the liposome surface.The average particle size of liposomes decreased with the increase in the absolute value of surface charge.The polydispersity index (PDI) of different liposomes were all below 0.7,indicating the good uniformity of these liposomes.Besides,the cationic liposomes encapsulating qdvp001 showed good thermal stability at 50,60 and 70℃.The heat preventive effects of liposomes to bacteriophage gradually improved with the increase in the surface positive charges of the liposomes.In addition,the cationic liposomes encapsulating qdvp001 had stronger antibacterial activities than the neutral liposomes encapsulating the bacteriophage.[Conclusion] The cationic liposomes encapsulating qdvp001 can protect the phage at high temperature and have good antibacterial activity.It makes qdvp001 have a better application prospect.

Abstract:[Background] Citri reticulatae pericarpium is a widely used Chinese medicinal material with both medical and edible values.The growing of fungi and the production of mycotoxins by fungi during storage at proper humidity and temperature pose a threat to the quality and safety of Citri reticulatae pericarpium.[Objective] In order to analyze the composition of exogenous fungi and the toxin-producing fungi on Citri reticulatae pericarpium.[Methods] The exogenous fungi were isolated by plate dilution method and identified based on the morphological characteristics and sequence analysis.The toxin-producing fungi were detected by ultra-high performance liquid chromatography coupled to tandem quadrupole mass spectrometry (UPLC-MS/MS).[Results] A total of 132 strains of exogenous fungi were isolated from Citri reticulatae pericarpium.They were identified to belong to Ascomycota(98.48%) and Mucoromycota(1.52%),including Eurotiomycetes(95.45%),Dothideomycetes(3.03%) and Mucoromycetes(1.52%).Seventy-seven strains belonged to Aspergillus spp.,which was dominant on Citri reticulatae pericarpium,followed by Penicillium spp.The strains of Aspergillus spp.and Penicillium spp.were detected by UPLC-MS/MS.One strain of toxin-producing fungi was screened out and identified as A.flavus JXCP1-3,which can produce 1.52 ng/mL aflatoxin B₁.[Conclusion] We comprehensively analyzed the exogenous fungi and toxin-producing fungi on the surface of Citri reticulatae pericarpium,which provided a basis for the prevention and control of the toxin-producing fungi.

Abstract:[Background] Stenotrophomonas maltophilia is an opportunistic pathogen that exists widely in hospitals and environments,with intrinsic antibiotic resistance.[Objective] This study aims to isolate virulent phages to provide an alternative therapeutic method for S.maltophilia infection.[Methods] A phage was isolated from hospital sewage with a clinical strain of S.maltophilia as the host.The phage genome was sequenced on Illumina platform and its morphology was observed with transmission electron microscopy.The one-step growth curve was established by double-layer plate method.[Results] The isolated phage vB_SmaS_P11 had an icosahedral head and a long tail,belonging to Siphoviridae of Caudovirales.The genome of the phage had a length of 44 600 bp and the G+C content of 63.7%,encoding 66 open reading frames (ORFs),with no tRNA,virulence genes or resistance-related regions.The phage vB_SmaS_P11 was able to lyse 7 strains among 18 clinical isolates of S.maltophilia.The one-step growth curve showed that the strain had the latent time less than 5 min,the lysis period of about 60 min,and the burst size of 100 plaque forming units per cell,which indicated high virulence.[Conclusion] The isolated phage vB_SmaS_P11 is a novel virulent phage targeting S.maltophilia,which provides a candidate phage for treating S.maltophilia infection in the future.

Abstract:Salmonella Kentucky,one of the major zoonotic pathogens that cause intestinal diseases in humans and livestock,has been widely concerned for its multidrug resistance.The global prevalence of Salmonella Kentucky has been increasing in recent years,brings seriously threatens to livestock and public health.This paper summarizes the prevalence status,drug resistance and prevention and control measures of Salmonella Kentucky domestic and abroad,with a view to providing reference for the prevention and control of Salmonella Kentucky.

Abstract:Plant host,together with all associated microorganisms living on or in it,constitute a plant holobiont,and the hologenome is comprised of the genomes of host and microbiota.In recent years,the structure and function of plant microbiota have gradually been elucidated.As a part of plant microbiota,endophytic bacteria colonize inside plant tissues.Therefore,endophytic bacteria have closer and more direct interaction with plants and are less affected by environmental changes than epiphytic or environmental bacteria.This review introduced endophytic bacteria and summarizes the research progress in the development of specific detection methods for endophytic bacteria.Improved and standard analytical methods will greatly facilitate the elucidation of the interaction and symbiosis mechanisms between plants and their endophytic bacteria,leading to new strategies for improving plant nutrition and disease resistance from the perspective of endophytic bacteria.

Abstract:Hydroxylamine oxidoreductase (HAO) is a multiheme protein,and each monomer consists of seven electron transfer hemes and one catalytic heme.HAO can catalyze the oxidation of hydroxylamine and hydrazin or the reduction of hydroxylamine,nitrite oxide,and nitrite.The optimum temperature,pH,substrate,product specificity,and inhibitor of HAO vary among different nitrifying bacteria.As a key enzyme in nitrification,HAO plays an important role in improving the biological nitrogen removal rate and eliminating the toxicity of nitrification intermediates (hydroxylamine).This article systematically reviewed the distribution,structure,expression regulation,and activity of HAO in denitrifying microorganisms,summarized the biochemical properties of HAO in different nitrifying bacteria,and finally put forward the future research directions of HAO.This review is helpful for understanding the biological denitrification process and the mechanism of hydroxylamine metabolism in microorganisms and will shed new light on the optimization of wastewater treatment.

Abstract:Human skin is colonized by diverse microorganisms,whose composition,distribution,and dynamic changes play an important role in regulating skin health and diseases.However,it is still unclear how skin microbial community influences human health.In-depth research on skin commensal bacteria can help discover beneficial strains and screen out new drug targets for corresponding skin diseases.In recent years,there has been an explosion of research on the interaction of skin commensal bacteria with host cells and the mechanism.This review aims to sum up the latest findings on skin commensal bacteria.First,we summarized the distribution and basic community composition of skin commensal bacteria and their antimicrobial,anti-inflammatory,immunomodulatory,and anticancer functions in maintaining skin health.Then we elaborated the latest discoveries on how skin microbiota dysbiosis is associated and involved in the pathogenesis of several skin diseases,including psoriasis,acne,rosacea,and systemic scleroderma.Finally,we discussed the close mutual regulation between skin commensal bacteria and intestinal flora through intestine-skin axis.In summary,balanced skin microbiota is crucial for skin health,and the host-skin commensal bacteria interaction mechanism should be comprehensively understood to design skin microorganisms-targeted drugs for skin diseases.

Abstract:The decomposition of soil organic matter requires the coordinated function of microbial guilds,including the preliminary breakdown by upstream microorganisms,the further decomposition by midstream guilds and the final metabolism by downstream organisms.The initial breakdown of complex organic polymers is a key step,which requires the activity of microbial exoenzymes.Significant progress has been achieved recently in the research on the organic matter decomposition in gut.In this review,we compared the organic matter decomposition in human intestine,ruminant rumen and soil,with a focus on the specific mechanisms of polysaccharide transport in Bacteroidetes and Clostridia.Bacteroidetes secrete a cocktail of extracellular hydrolases into the outer membrane via type IX secretion system (T9SS) and require a series of gene loci termed polysaccharide utilization loci (PUL) to metabolize glycans.Polysaccharides are degraded into oligosaccharides and then transported into the periplasmic space via Sus complex located in the outer membrane.Oligosaccharides are further degraded into simple sugars like glucose and imported into the cell via inner membrane transporter.Clostridia utilize cellulosomes to directly degrade glycans in the extracellular space.The monosaccharides are captured by sugar-binding proteins and transported into the cell via ABC transporters.The intracellular sugar concentration is regulated by two-component systems (TCSs) and carbon catabolite repression (CCR) mechanism.At the end of this review,we put forward the perspectives of the future research on the decomposition of complex organic matter in soil.

Abstract:Staphylococcus are common Gram-positive pathogens,including Staphylococcus epidermidis and Staphylococcus aureus.With the emergence of drug-resistant staphylococci,especially the spread of multidrug resistant strains,the morbidity and mortality of infectious diseases caused by Staphylococcus are increasing year by year.The high pathogenicity of Staphylococcus is associated with the large number of virulence factors.Phenol-soluble modulins (PSMs) are a group of amphipathic peptides with broad cytolytic activity,which are major virulence factors released by Staphylococcus.PSMs could contribute to inflammation,affect immune cell function,participate in bacterial immune escape,and play a role in the pathogenic mechanism of skin and soft tissue infections,sepsis,biofilm-related infections,bone tissue infections,and atopic dermatitis caused by staphylococci.This article briefly summarizes the impact of PSMs on the host immune system and the roles of PSMs in common infectious diseases caused by Staphylococcus.