Genome-resolved discovery of Candidatus Vitaminotrophota reveals carbon fixation and multi-vitamin biosynthetic potential in hot springs.

Abstract

Geothermal environments harbor abundant microbial diversity, yet rare lineages remain poorly resolved, limiting understanding of ecosystem function and evolutionary innovation under energy limitation. Here, we describe Candidatus Vitaminotrophota, a previously unrecognized bacterial phylum represented by 35 metagenome-assembled genomes (MAGs) from Tengchong hot spring sediments, China. Phylogenomic analyses support a coherent internal taxonomy comprising one order, two families and four candidate genera. Metabolic reconstruction indicates a predominantly anaerobic, mixotrophic lifestyle, with widespread carbon fixation potential via the Wood-Ljungdahl pathway and a noncanonical CODH/ACS architecture featuring divergent acsA paralogs. Nitrogenase structural genes (nifHDK) occur in two genera, suggesting diazotrophic potential in part of the lineage. All MAGs encode complete or near-complete cobalamin and pantothenate biosynthesis pathways, and most retain conserved thiamine pathway components, alongside transport systems consistent with corrinoid and metal acquisition. Ca. Vitaminotrophota dominated community-level cobalamin biosynthetic potential in several samples, reaching 99.11% and accounting for >50% in nearly half of the samples. Conserved flagellar and chemotaxis gene sets suggest capacity to navigate steep physicochemical gradients. These findings expand the phylogenetic and functional landscape of geothermal bacteria and identify Ca. Vitaminotrophota as a candidate contributor to carbon fixation and vitamin-mediated metabolic interactions in nutrient-limited hot springs.