class members originating at sites within the Pacific Ring of Fire and other tectonically active locations and description of the novel genus '.

Recent studies have expanded the genomic contours of the , highlighting important lacunae in our comprehension of the phylogenetic space occupied by certain lineages of the class. One such lineage is ', a novel genus-level taxon, represented by ' VAN18-1 as its type species, along with two other uncultivated metagenome-assembled genomes (MAGs) originating from geothermally active sites across the Pacific Ring of Fire. In this study, we investigate the genetic and genomic diversity, and the distribution patterns of several uncharacterized class strains and sequence clones, which are ascribed to the same 16S rRNA gene sequence clade. By digging deeper into this data and contributing to novel MAGs emerging from environmental studies in tectonically active locations, the description of this novel genus has been consolidated. Using state-of-the-art genomic taxonomy methods, we added to already recognized taxa, an additional four novel () species, including ' Igneacidithiobacillus chanchocoensis' (mCHCt20-1), ' (S30A2), ' Igneacidithiobacillus taupoensis' (TVZ-G3 ), and ' Igneacidithiobacillus waiarikiensis' (TVZ-G4 ). Analysis of published data on the isolation, enrichment, cultivation, and preliminary microbiological characterization of several of these unassigned or misassigned strains, along with the type species of the genus, plus the recoverable environmental data from metagenomic studies, allowed us to identify habitat preferences of these taxa. Commonalities and lineage-specific adaptations of the seven species of the genus were derived from pangenome analysis and comparative genomic metabolic reconstruction. The findings emerging from this study lay the groundwork for further research on the ecology, evolution, and biotechnological potential of the novel genus ''.