197 Investigation of vitamin B12 sharing within the skin microbiome

The skin microbiome has a key role in supporting necessary functions that promote skin health, including protection from pathogens and immune homeostasis. To more fully understand microbiome function in the context of skin health, it is necessary to characterize the fundamental biological and ecological interactions that occur within the skin microbiome. Using comparative genomics across 71 species of the Corynebacterium genus, a dominant skin taxon, we identified that skin-associated species encode for de novo biosynthesis of cobamides (vitamin B12), a cofactor essential for enzymatic reactions across all domains of life. Because a much larger fraction of bacteria require B12 than are able to synthesize it, we hypothesize that B12 sharing occurs within the skin microbiome and that these interactions mediate microbial community composition. To assess B12 biosynthesis and use by skin microbiota, 906 skin metagenomes were queried for conserved sequences of B12 biosynthetic and dependent enzymes and B12 regulatory elements. Reads mapping to B12 dependent and regulatory sequences were classified to 1462 species, while de novo cobamide biosynthesis was restricted to 23 species. This suggests B12 is utilized throughout the phylogenetic diversity of the skin microbiome while only produced by a small number of taxa. In addition, we analyzed published relative abundance data from 594 skin metagenomes and found that in skin sites such as the occiput and inguinal crease, increased microbiome diversity was associated with a higher abundance of B12-producing Corynebacteria (rho=0.36-0.79, p<0.05). Loss of diversity is associated with dermatological disease, therefore our results suggest that B12 sharing plays a role in mediating microbiome structure and ultimately may promote skin health by promoting diversity. In the future, we will test this with ex vivo live human skin and synthetic skin microbial communities consisting of B12 producers and users to examine the effects on community dynamics when B12 biosynthesis is depleted.