Bacterial phyla

Bacterial phyla constitute the major lineages of the domain Bacteria. While the exact definition of a bacterial phylum is debated, a popular definition is that a bacterial phylum is a monophyletic lineage of bacteria whose 16S rRNA genes share a pairwise sequence identity of ~75% or less with those of the members of other bacterial phyla. It has been estimated that ~1,300 bacterial phyla exist. As of May 2020, 41 bacterial phyla are formally accepted by the LPSN, 89 bacterial phyla are recognized on the Silva database, dozens more have been proposed, and hundreds likely remain to be discovered. As of 2017, approximately 72% of widely recognized bacterial phyla were candidate phyla (i.e. have no cultured representatives). There were no fixed rules to the nomenclature of bacterial phyla. It was proposed that the suffix "-bacteria" be used for phyla. The situation changed in 2021. The rank of phylum has been included in the rules of the International Code of Nomenclature of Prokaryotes, using the ending –ota for phylum names that must be based on the name of a genus as its nomenclatural type. The following is a list of bacterial phyla that have been proposed. Despite the unclear branching order for most bacterial phyla, several groups of phyla consistently cluster together and are referred to as supergroups or superphyla. In some instances, bacterial clades clearly consistently cluster together but it is unclear what to call the group. For example, the Candidate Phyla Radiation includes the Patescibacteria group which includes Microgenomates group which includes over 11 bacterial phyla. Candidate phyla radiation The CPR is a descriptive term referring to a massive monophyletic radiation of candidate phyla that exists within the Bacterial domain. It includes two main clades, the Microgenomates and Parcubacteria groups, each containing the eponymous superphyla and a few other phyla. The superphylum Patescibacteria was originally proposed to encompass the phyla Microgenomates (OP11), Parcubacteria (OD1), and Gracilibacteria (GNO2 / BD1-5).