Proposal of <i>Patescibacterium danicum</i> gen. nov., sp. nov. in the ubiquitous bacterial phylum <i>Patescibacteriota</i> phyl. nov.

<i>Candidatus</i> Patescibacteria is a diverse bacterial phylum that is notable for members with ultrasmall cell size, reduced genomes, limited metabolic capabilities, and dependence on other prokaryotic hosts. Despite the prevalence of the name <i>Ca</i>. Patescibacteria in the scientific literature, it is not officially recognized under the International Code of Nomenclature of Prokaryotes and lacks a nomenclatural type. Here, we rectify this situation by describing two closely related circular metagenome-assembled genomes and by proposing one of them (ABY1^TS) to serve as the nomenclatural type for the species <i>Patescibacterium danicum</i> ^TS gen. nov., sp. nov. according to the rules of the SeqCode. Rank-normalized phylogenomic inference confirmed the stable placement of <i>P. danicum</i> ^TS in the <i>Ca.</i> Patescibacteria class ABY1. Based on these results, we propose <i>Patescibacterium</i> gen. nov. to serve as the type genus for associated higher taxa, including the phylum <i>Patescibacteriota</i> phyl. nov. We complement our proposal with a genomic characterization, metabolic reconstruction, and biogeographical analysis of <i>Patescibacterium</i>. Our results confirm small genome sizes (<1 Mbp), low GC content (>36%), and the occurrence of long gene coding insertions in the 23S rRNA sequences, along with reduced metabolic potential, inferred symbiotic lifestyle, and a global distribution. In summary, our proposal will provide nomenclatural stability to the fourth-largest phylum in the bacterial domain.