Discovery of potential genes contributing to the biosynthesis of short-chain fatty acids and lactate in gut microbiota from systematic investigation in E. coli

Microbiota play important roles in the internal environment and health of humans, livestock and wild animals. Short-chain fatty acids (SCFAs) and lactate are primary metabolites that can impact the composition and function of human microbiota. According to the well-characterized key synthesis genes, many SCFA- and lactate-producing bacteria have been identified in the gut microbiota. However, unknown genes may also contribute to the formation of SCFAs and lactate. The identification of such genes will provide new engineering targets and new strategies for maintaining a stable structure of beneficial microbiota. In this study, we used Escherichia coli as a model to analyze possible genes related to SCFAs and lactate production besides the well-characterized ones. The functions of nineteen candidate genes were studied by targeted gene deletion and overexpression. Results indicated thioesterase genes such as yciA, tesA, tesB, and men/ can contribute to acetate and/or butyrate formation. As for lactate, mgsA and lldD can function in addition to ldh gene. At the same time, the distribution of these functional genes in gut microbiota was investigated. Most bacteria contain the well-studied genes whereas some bacteria contain some of the described unusual ones. The results provide insights and genetic targets for the discovery of new SCFA- and lactate-producing bacteria in gut microbiota.