Bacterial catabolism of nonulosonic (sialic) acid and fitness in the gut

The term nonulosonic acid or sialic acid encompasses a varied group of nine-carbon amino sugars widely distributed among mammals and higher metazoans. Among bacteria, the ability to synthesize sialic acid was first examined in a small number of human pathogenic species that deposit sialic acid on their outer surface. New phylogenomic data suggest that the ability to synthesize sialic acid and sialic acid-like compounds is not a novel bacterial innovation but a much more widespread ancient trait. In contrast, the genes required for the catabolism of sialic acid are found only among pathogenic and commensal bacterial species. This ability to utilize sialic acid as a carbon source is correlated with bacterial virulence, especially, in the sialic acid rich environment of the gut. In this article, we present the most recent findings in sialobiology with a focus on sialic acid catabolism.