Abstract Extreme anoxic environments are hotspots of sulfur cycling and harbor numerous novel uncharacterized microbial lineages. Although the phylum Joyebacterota was recently proposed, its internal phylogenetic architecture and evolutionary adaptations remain poorly understood. Here, we significantly expand the genomic diversity and metabolic framework of this phylum by integrating recovered metagenome-assembled genomes (MAGs), and propose a novel genus, Cavimicrobium. Phylogenomic analysis placed Cavimicrobium as a distinct clade and further divided into four species-level subgroups associated with diverse anoxic sources, including sediments from the Salton Sea, the Eastern Gotland Basin, and the anoxic waters of the Sansha Yongle Blue Hole (SYBH). Unlike previous broad surveys, our study revealed that this lineage evolved from a facultatively anaerobic ancestor and underwent adaptive gene gain and loss through phylogenetic reconstruction. Genomic evidence suggested that this lineage harbored a previously overlooked anaerobic sulfite reduction (asrABC) pathway that likely mediating thiosulfate uptake and conversion to sulfite and sulfide. Notably, Cavimicrobium was particularly abundant in the anoxic waters of SYBH, comprising up to one-third of the bacterial community in particle-associated fraction below 100 m, where it is likely a major contributor to sulfide accumulation. Analysis of MAGs and global amplicon datasets revealed that Cavimicrobium is widespread across anoxic environments, comprising up to 0.32% of the bacterial community in 354,200 publicly available 16S rRNA gene amplicon samples. Together, these findings reveal a new lineage dominant in certain anoxic environments where they are likely important mediators of sulfur cycling, and broaden our understanding of biogeochemical potential of Joyebacterota.
Chen et al. (Fri,) studied this question.