乙醇对瘤胃细菌发酵纤维类饲料产短链脂肪酸能力的影响

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

摘要:

【背景】瘤胃细菌发酵碳水化合物产生的短链脂肪酸(Short Chain Fatty Acid，SCFA)，可作为燃料和化工产品的前体物。乙醇在碳链延伸产生己酸过程中具有重要作用，但对瘤胃发酵不同纤维类饲料产己酸能力的研究少有报道。【目的】揭示乙醇对纤维类饲料体外瘤胃发酵的SCFA产量差异，挖掘潜在的产C5和C6脂肪酸细菌。【方法】利用体外连续传代和Illumina HiSeq测序等技术，比较了添加乙醇对6种饲料产SCFA能力的影响以及细菌群落结构的差异。【结果】6种纤维类饲料的总SCFA产量顺序为黑麦草>小黑麦草>燕麦草>玉米芯>稻秸>甜叶菊。添加乙醇显著提高了小黑麦草、黑麦草的戊酸和己酸产量；细菌群落以厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)为优势菌门，乙醇显著提高了燕麦草组和小黑麦草组的放线菌门(Actinobacteria)和软壁菌门(Tenericutes)相对丰度；种水平上，甜叶菊、稻秸和玉米芯的优势菌与燕麦草、小黑麦草和黑麦草的优势菌相对丰度不同。相对丰度前10的细菌中，Prevotella sp. DJF CP65、Clostridium butyricum和Bifidobacterium thermophilum相对丰度与戊酸产量呈显著正相关，C. butyricum相对丰度与己酸产量呈显著正相关。【结论】瘤胃细菌体外发酵纤维类饲料并添加乙醇可生产更多戊酸和己酸，该结果为筛选可培养瘤胃细菌用于体外发酵提高戊酸和己酸产量、挖掘瘤胃细菌功能提供了参考数据。

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.