Cobamide-producing microbes as a model for understanding general nutritional interdependencies in soil food webs

Nutrient crossfeeding critically governs microbiome-host interactions and ecosystem stability. Cobamides, synthesized only by prokaryotes, offer a powerful and tractable model for studying nutrient-mediated interdependencies in soil food webs; however, their ecological role in sustaining soil health remains unclear. Here, we construct the Soil Cobamide Producer database (SCP v.1.0) by integrating over 48,000 metagenomic and genomic datasets from 1,123 sampling sites. This database catalogs phylogenetically diverse prokaryotes (19 phyla, 302 genera) with cobamide biosynthetic potential. Using this resource, we identify host-specific colonization patterns of cobamide-producing microbes in fauna. These microbes also carry diverse functional traits that may contribute to trophic cascades and microbial community stability. In an Enchytraeid model, these colonizers support host development, modulate gene expression, and promote gut stability through transkingdom interactions, with cobamide biosynthesis serving as one representative trait among multiple microbial functions. At macroecological scales, cobamide-producing microbes occur across relatively high trophic levels, reflecting a broader principle of nutrient transfer that may also apply to other essential metabolites. This framework provides a general basis for studying nutritional microbes in soil food webs and advances One Health research.