Lipotechoic acid in lactobacilli: D-alanine makes the difference.

T he intestinal tract is colonized by a myriad of mainly Grampositive microbes that show considerable spatial and temporal diversity (1–3). These intestinal microbiota reach astronomical numbers, and it has been estimated that the collective microbial genomes in our gut may contain 100 times more genes than the human genome (3). A prime function of the intestinal microbiota includes the processing of dietary components and host-produced polymers, such as mucus, leading to the production of short-chain fatty acids and a wealth of other metabolites. Moreover, several intestinal microbes develop an intimate relation with the host and modulate nutrient processing, immune function, and a variety of other host activities (4).