Microbial interaction between the succinate-utilizing bacteriumPhascolarctobacterium faeciumand the gut commensalBacteroides thetaiotaomicron

A large variety of microbes are present in the human gut, some of which are considered to interact with each other. Most of these interactions involve bacterial metabolites.Phascolarctobacterium faeciumhardly uses carbohydrates for growth and instead uses succinate as a substrate. This study investigated the growth behavior of the co-culture of the succinate-specific utilizerP.faeciumand the succinogenic gut commensalBacteroides thetaiotaomicron. Succinate production byB.thetaiotaomicronsupported the growth ofP.faeciumand concomitant propionate production via the succinate pathway. The succinate produced was completely converted to propionate. This result was comparable with the monoculture ofP.faeciumin the medium supplemented with 1% (w/v) succinate. We analyzed the transcriptional response (RNA-Seq) between the mono- and co-culture ofP.faeciumandB.thetaiotaomicron. Comparison of the expression levels of genes ofP.faeciumbetween the mono- and co-cultured conditions highlighted that the genes putatively involved in the transportation of succinate were notably expressed under the co-cultured conditions. Differential expression analysis showed that the presence ofP.faeciuminduced changes in theB.thetaiotaomicrontranscriptional pattern, for example, expression changes in the genes for vitamin B(12)transporters and reduced expression of glutamate-dependent acid resistance system-related genes. Also, transcriptome analysis ofP.faeciumsuggested that glutamate and succinate might be used as sources of succinyl-CoA, an intermediate in the succinate pathway. This study revealed some survival strategies of asaccharolytic bacteria, such asPhascolarctobacteriumspp., in the human gut.