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).
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.
List of bacterial phyla
The following is a list of bacterial phyla that have been validly published as of December 2023. +Published PhylaPhylumAlternative namesGroupKnown classesNotes"Abditibacteriota"FBP1Acidobacteriota"Acidobacteria"5Actinomycetota"Actinobacteria"Bacillati6Armatimonadota"Armatimonadetes", OP10Bacillati3AtribacterotaOP9, JS11Aquificota"Aquificae"3Bacteroidota"Bacteroidetes"FCB group6Balneolota1Bdellovibrionota3CaldisericotaOP5, "Caldiserica"FCB groupCalditrichotaFCB groupCampylobacterota2Chlamydiota"Chlamydiae"PVC group 1Chlorobiota"Chlorobi"FCB group1Chloroflexota"Chloroflexi"BacillatiChrysiogenota"Chrysiogenetes"CoprothermobacterotaCyanobacteriotaCyanobacteriaBacillati2DeferribacterotaDeferribacteresDeinococcotaDeinococcus–ThermusBacillati1DictyoglomotaDictyoglomiElusimicrobiotaElusimicrobia, OP7, Termite Group 1 (TG1)Fibrobacterota"Fibrobacteres"FCB groupBacillota"Firmicutes"Bacillati9Fusobacteriota"Fusobacteria"1GemmatimonadotaGemmatimonadetesFCB groupIgnavibacteriota"Ignavibacteria", ZB1FCB groupKiritimatiellotaLentisphaerota"Lentisphaerae", vadinBE97PVC group"Marinimicrobia"SAR406, Marine Group AFCB groupMyxococcota3Nitrospinota"Nitrospinae"Nitrospirota"Nitrospirae"Planctomycetota"Planctomycetes"PVC groupPseudomonadota"Proteobacteria"Rhodothermota"Saccharibacteria"TM7CPR; Saccharibacteria-related CPRSpirochaetota"Spirochaetes"Synergistota"Synergistetes"Mycoplasmatota"Tenericutes"Thermodesulfobacteriota"Thermodesulfobacteria"Thermomicrobiota"Thermomicrobia"Thermotogota"Thermotogae", OP2, EM3Verrucomicrobiota"Verrucomicrobia"PVC group The following is a list of candidate phyla that have not been cultured. +Candidate PhylaPhylumAlternative NamesGroupNotes"Absconditabacteria"SR1CPR; Gracilibacteria-related CPRABY1OD1-ABY1CPR; Parcubacteria"Aerophobota" / "Aerophobetes"CD12, BHI80-139"Andersenbacteria"RIF9CPR; Parcubacteria; Parcubacteria 4-related"Aminicenantota"OP8"Berkelbacteria"ACD58CPR; Saccharibacteria-related CPR"Bipolaricaulota"OP1, "Acetothermia""Blackburnbacteria"RIF35CPR; Microgenomates"Brennerbacteria"RIF18CPR; Parcubacteria; Parcubacteria 3"Brownbacteria"CPR; Parcubacteria; unclassified Parcubacteria"Buchananbacteria"RIF37CPR; Parcubacteria; Parcubacteria 1"Campbellbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 4Seems to be polyphyletic; 2 clades"Cloacimonetes"WWE1FCB group"Coatesbacteria"RIF8"Collierbacteria"CPR; Patescibacteria; Microgenomates"Colwellbacteria"RIF41CPR; Parcubacteria; Parcubacteria 3"Curtissbacteria"CPR; Patescibacteria; Microgenomates"Dadabacteria"No"Daviesbacteria"CPR; Patescibacteria; MicrogenomatesNo"Delphibacteria"FCB groupNo"Delongbacteria"RIF26, H-178No"Dependentiae"TM6"Dojkabacteria"WS6CPR; Microgenomates-related CPR"Dormibacteraeota"AD3"Doudnabacteria"SM2F11CPR; Parcubacteria; Parcubacteria 1-related"Edwardsbacteria"RIF29, UBP-2 "Eisenbacteria"RIF28FCB group"Eremiobacteraeota"WPS-2, Palusbacterota"Falkowbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 1"Fermentibacteria"Hyd24-12"Fertabacteria"CPR; Gracilibacteria-related CPR"Firestonebacteria"RIF1"Fervidibacteria"OctSpa1-106"Fischerbacteria"RIF25"Fraserbacteria"RIF31"Glassbacteria"RIF5No"Giovannonibacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 4-relatedNo"Gottesmanbacteria"CPR; Patescibacteria; MicrogenomatesNo"Gracilibacteria"GN02, BD1-5, SN-2CPR; Patescibacteria; Gracilibacteria-related CPRNo"Gribaldobacteria"CPR; Parcubacteria; Parcubacteria 2No"Handelsmanbacteria"RIF27No"Harrisonbacteria"RIF43CPR; Parcubacteria; Parcubacteria 3No"Howlettbacteria"CPR; Saccharibacteria-related CPRNo"Hugbacteria"CPR; Parcubacteria; unclassified Parcubacteria"Hydrogenedentes"NKB19"Jacksonbacteria"RIF38CPR; Parcubacteria; Parcubacteria 1"Jorgensenbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 3"Kaiserbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 4"Katanobacteria"WWE3CPR; Microgenomates-related"Kazanbacteria"KazanCPR; Saccharibacteria-related CPR"Kerfeldbacteria"RIF4CPR; Parcubacteria; Parcubacteria 1"Komeilibacteria"RIF6CPR; Parcubacteria; Parcubacteria 1"Kryptonia""Krumholzibacteriota""Kuenenbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 1"Lambdaproteobacteria"RIF24Proteobacteria"Latescibacteria"WS3FCB group"Levybacteria"CPR; Patescibacteria; MicrogenomatesNo"Lindowbacteria"RIF2CPR; Saccharibacteria-related CPRNo"Liptonbacteria"RIF42CPR; Parcubacteria; Parcubacteria 3No"Lloydbacteria"RIF45CPR; Parcubacteria; Parcubacteria 4No"Magasanikbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 1No"Margulisbacteria"RIF30No"Melainabacteria""Microgenomates"OP11CPR; Patescibacteria"Modulibacteria"KSB3, GN06"Moranbacteria"OD1-iCPR; Patescibacteria; Parcubacteria; unclassified Parcubacteria"Muproteobacteria"RIF23ProteobacteriaNC10"Nealsonbacteria"RIF40CPR; Parcubacteria; Parcubacteria 2"Niyogibacteria"RIF11CPR; Parcubacteria; Parcubacteria 4-related"Nomurabacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 1"Omnitrophica"OP3PVC group"Pacebacteria"CPR; Patescibacteria; Microgenomates"Parcubacteria"OD1CPR"Parcubacteria" 1CPR; Parcubacteria"Parcubacteria" 2CPR; Parcubacteria"Parcubacteria" 3CPR; Parcubacteria"Parcubacteria" 4CPR; Parcubacteria"Parcunitrobacteria"CPR; Parcubacteria; unclassified ParcubacteriaPAUC34fsponge‐associated unclassified lineage (SAUL)FCB group"Peregrinibacteria"PERCPR; Gracilibacteria-related CPR"Peribacteria"CPR; Gracilibacteria-related CPR"Poribacteria"PVC group"Portnoybacteria"RIF22CPR; Parcubacteria; Parcubacteria 4-related"Raymondbacteria"RIF7RiflebacteriaRIF32"Roizmanbacteria"CPR; Patescibacteria; Microgenomates"Rokubacteria""Ryanbacteria"RIF10CPR; Parcubacteria; Parcubacteri 4-related"Saltatorellota""Schekmanbacteria"RIF3Proteobacteria"Shapirobacteria"CPR; Patescibacteria; Microgenomates"Spechtbacteria"RIF19CPR; Parcubacteria; Parcubacteria 2"Staskawiczbacteria"RIF20CPR; Parcubacteria; Parcubacteria 2"Sumerlaeota"BRC1"Sungbacteria"RIF17CPR; Parcubacteria; Parcubacteria 4-relatedTA06"Tagabacteria"RIF12CPR; Parcubacteria; Parcubacteria 4-related"Taylorbacteria"RIF16CPR; Parcubacteria; Parcubacteria 4"Tectomicrobia""Terrybacteria"RIF13CPR; Parcubacteria; Parcubacteria 2"Torokbacteria"CPR; Parcubacteria; unclssified ParcubacteriaUBP-1"Uhrbacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 1"Veblenbacteria"RIF39CPR; Parcubacteria; Parcubacteria 1-related"Vogelbacteria"RIF14CPR; Parcubacteria; Parcubacteria 4"Wallbacteria"RIF33"Wildermuthbacteria"RIF21CPR; Parcubacteria; Parcubacteria 2"Wirthbacteria"CPR-related bacteria"Woesebacteria"CPR; Patescibacteria; Microgenomates"Wolfebacteria"CPR; Patescibacteria; Parcubacteria; Parcubacteria 3"Woykebacteria"RIF34CPR; Microgenomates"Yanofskybacteria"CPR; Patescibacteria; Parcubacteria; unclassified Parcubacteria"Yonathbacteria"RIF44CPR; Parcubacteria; Parcubacteria 4"Zambryskibacteria"RIF15CPR; Parcubacteria; Parcubacteria 4ZB2OD1-ZB2CPR; Parcubacteria"Zixibacteria"FCB group
Supergroups 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. The LPSN recognizes four kingdoms of bacteria as validly published: Bacillati, Fusobacteriati, Pseudomonadati and Thermotogati.
Candidate phyla radiation (CPR)
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.
Patescibacteria The superphylum Patescibacteria was originally proposed to encompass the phyla Microgenomates (OP11), Parcubacteria (OD1), and Gracilibacteria (GNO2 / BD1-5). More recent phylogenetic analyses show that the last common ancestor of these taxa is the same node as that of CPR.
Sphingobacteria
The Sphingobacteria (FCB group) includes Bacteroidota, Calditrichota, Chlorobiota, candidate phylum "Cloacimonetes", Fibrobacterota, Gemmatimonadota, Ignavibacteriota, candidate phylum "Latescibacteria", candidate phylum "Marinimicrobia", and candidate phylum "Zixibacteria".
Microgenomates Microgenomates was originally thought to be a single phylum although evidence suggests it actually encompasses over 11 bacterial phyla, including Curtisbacteria, Daviesbacteria, Levybacteria, Gottesmanbacteria, Woesebacteria, Amesbacteria, Shapirobacteria, Roizmanbacteria, Beckwithbacteria, Collierbacteria, Pacebacteria.
Parcubacteria Parcubacteria was originally described as a single phylum using fewer than 100 16S rRNA sequences. With a greater diversity of 16S rRNA sequences from uncultured organisms now available, it is estimated it may consist of up to 28 bacterial phyla. In line with this, over 14 phyla have now been described within the Parcubacteria group, including Kaiserbacteria, Adlerbacteria, Campbellbacteria, Nomurabacteria, Giovannonibacteria, Wolfebacteria, Jorgensenbacteria, Yanofskybacteria, Azambacteria, Moranbacteria, Uhrbacteria, and Magasanikbacteria.
Proteobacteria It has been proposed that some classes of the phylum Proteobacteria may be phyla in their own right, which would make Proteobacteria a superphylum. For example, the Deltaproteobacteria group does not consistently form a monophyletic lineage with the other Proteobacteria classes.
Planctobacteria
The Planctobacteria (PVC group) includes Chlamydiota, Lentisphaerota, candidate phylum "Omnitrophica", Planctomycetota, candidate phylum "Poribacteria", and Verrucomicrobiota.
Bacillati
The kingdom Bacillati, includes Actinomycetota, "Cyanobacteria/Melainabacteria clade", Deinococcota, Chloroflexota, Bacillota, and candidate phylum OP10.
Cryptic superphyla Several candidate phyla (Microgenomates, Omnitrophica, Parcubacteria, and Saccharibacteria) and several accepted phyla (Elusimicrobiota, Caldisericota, and Armatimonadota) have been suggested to actually be superphyla that were incorrectly described as phyla because rules for defining a bacterial phylum are lacking or due to a lack of sequence diversity in databases when the phylum was first established. For example, it is suggested that candidate phylum Parcubacteria is actually a superphylum that encompasses 28 subordinate phyla and that phylum Elusimicrobia is actually a superphylum that encompasses 7 subordinate phyla.
Historical perspective
Given the rich history of the field of bacterial taxonomy and the rapidity of changes therein in modern times, it is often useful to have a historical perspective on how the field has progressed in order to understand references to antiquated definitions or concepts.