Abstract
The vitamin B12 family of cofactors known as cobamides are essential for a variety of microbial metabolisms. We used comparative genomics of 11,000 bacterial species to analyze the extent and distribution of cobamide production and use across bacteria. We find that 86% of bacteria in this data set have at least one of 15 cobamide-dependent enzyme families, yet only 37% are predicted to synthesize cobamides de novo. The distribution of cobamide biosynthesis varies at the phylum level, with 57% of Actinobacteria, 45% of Proteobacteria, and 30% of Firmicutes, and less than 1% of Bacteroidetes containing the complete biosynthetic pathway. Cobamide structure could be predicted for 58% of cobamide-producing species, based on the presence of signature lower ligand biosynthesis and attachment genes. Our predictions also revealed that 17% of bacteria that have partial biosynthetic pathways, yet have the potential to salvage cobamide precursors. These include a newly defined, experimentally verified category of bacteria lacking the first step in the biosynthesis pathway. These predictions highlight the importance of cobamide and cobamide precursor crossfeeding as examples of nutritional dependencies in bacteria.
