Abstract:[Background] Short chain fatty acids (SCFA) produced by ruminal bacteria fermentation of carbohydrates can be used as the fuels and chemical precursors. Ethanol plays an important role in the production of caproic acid by carbon chain extension, but the effect of ethanol on the caproic acid production capacity of feed with different fibers fermented in rumen is rarely reported. [Objective] To reveal the difference in SCFA yield of ethanol on rumen fermentation of fiber feed in vitro, and to explore the potential bacteria producing C5 and C6 fatty acids. [Methods] In vitro continuous passage culture technology and Illumina HiSeq sequencing technology were used to compare the effects of ethanol on SCFA-producing capacity of six feeds, as well as the differences in bacterial community structure. [Results] The total SCFA yield of 6 kinds of fiber feed was ryegrass straw>triticale straw>oat straw>corncob>rice straw>stevia straw. The yield of valeric acid and caproic acid of triticale straw and ryegrass straw was significantly increased by adding ethanol. Firmicutes and Bacteroidetes were the dominant bacteria phylum, and ethanol significantly increased the relative abundance of Actinobacteria and Tenericutes phylum in oat straw and triticale straw group. At the species level, the relative abundance of dominant bacteria of stevia straw, rice straw and corncob was different from that of oat straw, triticale straw and ryegrass straw. Among the bacteria with the top 10 relative abundance, the relative abundance of Prevotella sp. DJF CP65, Clostridium butyricum and Bifidobacterium thermophilum showed significant positive correlation with the yield of valeric acid. C. butyricum relative abundance was significantly positively correlated with caproic acid yield. [Conclusion] More valeric acid and caproic acid can be produced by fermentation of fiber feed with ethanol in vitro. The results provide reference data for screening ruminal bacteria that can be cultured for in vitro fermentation to increase the yield of valeric acid and caproic acid, and to explore the functions of ruminal bacteria.

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Abstract:In order to investigate molecular diversity of bacteria community from both a normal arable soil (Nor-1) and an arsenic and sulphate polluted soil (Sul-1). Environmental total DNA was directly extracted from two soil samples. The 16S rRNA genes were amplified from the total DNA and construction a clone library. Positive clones were randomly selected from the library and identified by amplified ribosomal DNA restriction analysis (ARDRA) and sequencing, then constructed phylogenetic tree. 23 unique clone sequences from Nor-1 soil were classified into 5 bacterial phylum including Acidobacteria (12.3%, 8/65), Actinobacteria(3.1%, 2/65), Firmicutes (21.5%, 14/65), Nitrospira (3.1%, 2/65) and Proteobacteria (60%, 39/65), while 19 unique clone sequences from Sul-1 soil were classified into 2 bacterial phylum including Firmicutes (29.5%, 13/44), and Proteobacteria (70.5%, 31/44). The result suggested that the high concentration of arsenic and sulphate influenced the bacterial population of Sul-1 soil leading to construction of obviously specific bacteria community. Interestingly, a lot of Acinetobacter related sequences have been detected in Sul-1 soil bacteria community including clone Sul11/15, Sul12/7 and Sul12/11. Because Acinetobacter strains are often ubiquitous, exhibit metabolic versatility, those related strains may be good targets for exploiting novel arsenic detoxification bacteria.

Abstract:[Background] Triploid Populus tomentosa is suitable for the ecological and economic development of the Yellow River and serves as an important tree species for forestry extension projects in China. Endophytic bacteria of triploid P. tomentosa play a role in the disease prevention, growth promotion, nitrogen fixation, and biological repair. [Objective] The objective was to analyze the diversity of endophytic bacteria and fully explore the microbial resources in triploid P. tomentosa. [Methods] In this study, the diversity of endophytic bacterial community in the roots, stems and leaves of P. tomentosa from the research base of Beijing Forestry University in Guanxian county, Shandong province was analyzed via 16S rRNA gene high-throughput sequencing and plate streaking. The variation trends and rules of endophytic bacterial diversity in different tissues of triploid P. tomentosa were clarified to lay a theoretical foundation for the further application of endophytic bacteria. [Results] The endophytic bacteria of triploid P. tomentosa had the highest richness and diversity in the roots while the lowest in the leaves. Pseudomonas and Actinobacteria were the dominant phyla, and Burkholderia, Pseudonocardia, and Acidovorax were the dominant genera. The structure of endophytic bacterial community varied among different tissues. The functions of the endophytic bacteria mainly involved amino acid metabolism, vitamin metabolism, degradation of aromatic compounds, and glycolysis. A total of 217 endophytic bacterial strains were isolated, belonging to 44 species of 23 genera. Among them, four strains shared the 16S rRNA gene sequence similarity below 97.5%, which might be new taxa. [Conclusion] In conclusion, the diversity of endophytic bacteria in the roots, stems and leaves of triploid P. tomentosa was significant. The diversity and richness of endophytic bacteria were higher in the roots than in the stems than in the leaves. Some endophytic bacterial resources were obtained by traditional isolation and culture methods, including 4 strains with 16S rRNA gene sequence similarity less than 97.5%. However, the results of high-throughput sequencing showed that a large number of endophytic bacterial strains had not been cultured in this experiment. It was necessary to further develop new high-throughput isolation, culture and identification methods to fully explore more uncultured and difficult endophytic bacterial strains.

Abstract:[Background] The natural forest dominated by Picea purpurea plays an important role in maintaining ecological security in the upstream of Taohe river. It is still unclear how altitude influences the bacterial diversity and nutrients in rhizosphere and non-rhizosphere soil of P. purpurea, and how the altitude, soil nutrients, and bacterial diversity interact with each other. [Objective] To explore the community structures of bacteria in rhizosphere and non-rhizosphere soil of P. purpurea and the influencing factors.[Methods] Illumina Miseq was employed for sequence analysis of the rhizosphere and non-rhizosphere bacteria in the natural P. purpurea forest at different elevations in the upper reaches of Taohe river. The changes of soil physical and chemical factors and bacterial diversity with altitude were analyzed. Correlation and redundancy analysis was performed to elucidate the effect of some environmental factors on bacterial community. [Results] The nutrients of rhizosphere and non-rhizosphere soil samples of P. purpurea increased first and then decreased with the rise of altitude. The intergroup difference was significant for rhizosphere soil nutrients (P<0.05) but insignificant for non-rhizosphere soil nutrients (P>0.05). The rhizosphere species diversity index (H), evenness index (E), richness index (Chao1/ACE), and number of operational taxonomic units (OTU) demonstrated a unimodal trend with the increase in altitude. The non-rhizosphere bacteria diversity showed a bimodal variation trend with the rise of elevation. Bacteria diversity was in close correlation with soil nutrients, particularly in positive correlation with organic matter, total nitrogen, and available nitrogen (P<0.05) but in negative correlation with pH and available phosphorus (P>0.05). The community structures of bacteria in the forest at different elevations were highly consistent. A total of 7 159 bacterial OTUs were identified from 30 samples, which belonged to 37 phyla. The dominant bacteria phyla were Actinobacteria, Proteobacteria, Acidobacteria, and Chloroflexi, respectively. The response of different bacteria phyla to soil nutrients was different, and organic matter, total nitrogen, and available nitrogen were in positive correlation with Proteobacteria (P<0.05). [Conclusion] Composition and diversity of rhizosphere and non-rhizosphere soil bacteria of P. purpurea are significantly influenced by soil physical and chemical factors. The driving effects of environmental factors such as altitude and hydrothermal conditions on plants and soil are important reasons for the stable bacterial community structure. This study is expected to help gain a clearer insight into the variation of soil bacteria diversity of P. purpurea and the driving mechanism, which is expected to provide a reference for natural forest restoration in the upstream of Taohe river.