Effect of ethanol on in vitro short chain fatty acid yield by ruminal bacteria fermented on fiber substrate

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.