Our analysis supports the increasing experimental evidence that competition for host-derived sialic acid is a key phenotype for successful colonization of complex mucosal microbiomes, such that a strong evolutionary selection has occurred for the emergence of sialic acid specificity within existing transporter architectures.ĪbstractMicrobial parasites adapted to thrive at mammalian mucosal surfaces have evolved multiple times from phylogenetically distant lineages into various extracellular and intracellular life styles. Two subfamilies of transporters stand out in being fused to the sialic acid mutarotase enzyme, NanM, and these transporter fusions are enriched in bacteria present in gut microbial communities. , many of which are species that have not been previously recognized to have sialometabolic capacities. The new transporters discovered occur in diverse bacteria, including Our phylogenetic analysis suggests that sialic acid-specific transport has evolved independently at least eight times during the evolution of bacteria, from within four of the major families/superfamilies of bacterial transporters, and we propose a robust classification scheme to bring together a myriad of different nomenclatures that exist to date. Here, we present the first comprehensive genomic and phylogenetic analysis of bacterial sialic acid transporters, leading to the identification of multiple new families and subfamilies. These bacteria rely on specific transporters for the acquisition of host-derived sialic acids. Located at the tip of cell surface glycoconjugates, sialic acids are at the forefront of host–microbe interactions and, being easily liberated by sialidase enzymes, are used as metabolites by numerous bacteria, particularly by pathogens and commensals living on or near diverse mucosal surfaces. Our analysis supports the increasing experimental evidence that competition for host-derived sialic acid is a key phenotype for successful colonisation of complex mucosal microbiomes, such that a strong evolutionary selection has occurred for the emergence of sialic acid specificity within existing transporter architectures.
We also provide evidence for a possible function of a sialic acid transporter component in chemotaxis that is independent of transport. The new transporters discovered occur in diverse bacteria including Spirochaetes, Bacteroidetes, Planctomycetes, and Verrucomicrobia, many of which are species that have not been previously recognised to have sialometabolic capacities. Our phylogenetic analysis suggests that sialic acid-specific transport has evolved independently at least 8 times during the evolution of bacteria, from within 4 of the major families/superfamilies of bacterial transporters, and we propose a robust classification scheme to bring together a myriad of different nomenclatures that exist to date. AbstractLocated at the tip of cell surface glycoconjugates, sialic acids are at the forefront of host-microbe interactions and, being easily liberated by sialidase enzymes, are used as metabolites by numerous bacteria, particularly by pathogens and commensals living on or near diverse mucosal surfaces.
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