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.
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.| Phylum | Alternative names | Group | Known classes | Notes |
| "Abditibacteriota" | FBP | 1 | ||
| Acidobacteriota | "Acidobacteria" | 5 | ||
| Actinomycetota | "Actinobacteria" | Bacillati | 6 | |
| Armatimonadota | "Armatimonadetes", OP10 | Bacillati | 3 | |
| Atribacterota | OP9, JS1 | 1 | ||
| Aquificota | "Aquificae" | 3 | ||
| Bacteroidota | "Bacteroidetes" | FCB group | 6 | |
| Balneolota | 1 | |||
| Bdellovibrionota | 3 | |||
| Caldisericota | OP5, "Caldiserica" | FCB group | ||
| Calditrichota | FCB group | |||
| Campylobacterota | 2 | |||
| Chlamydiota | "Chlamydiae" | PVC group | 1 | |
| Chlorobiota | "Chlorobi" | FCB group | 1 | |
| Chloroflexota | "Chloroflexi" | Bacillati | ||
| Chrysiogenota | "Chrysiogenetes" | |||
| Coprothermobacterota | ||||
| Cyanobacteriota | Cyanobacteria | Bacillati | 2 | |
| Deferribacterota | Deferribacteres | |||
| Deinococcota | Deinococcus–Thermus | Bacillati | 1 | |
| Dictyoglomota | Dictyoglomi | |||
| Elusimicrobiota | Elusimicrobia, OP7, Termite Group 1 | |||
| Fibrobacterota | "Fibrobacteres" | FCB group | ||
| Bacillota | "Firmicutes" | Bacillati | 9 | |
| Fusobacteriota | "Fusobacteria" | 1 | ||
| Gemmatimonadota | Gemmatimonadetes | FCB group | ||
| Ignavibacteriota | "Ignavibacteria", ZB1 | FCB group | ||
| Kiritimatiellota | ||||
| Lentisphaerota | "Lentisphaerae", vadinBE97 | PVC group | ||
| "Marinimicrobia" | SAR406, Marine Group A | FCB group | ||
| Myxococcota | 3 | |||
| Nitrospinota | "Nitrospinae" | |||
| Nitrospirota | "Nitrospirae" | |||
| Planctomycetota | "Planctomycetes" | PVC group | ||
| Pseudomonadota | "Proteobacteria" | |||
| Rhodothermota | ||||
| "Saccharibacteria" | TM7 | CPR; Saccharibacteria-related CPR | ||
| Spirochaetota | "Spirochaetes" | |||
| Synergistota | "Synergistetes" | |||
| Mycoplasmatota | "Tenericutes" | |||
| Thermodesulfobacteriota | "Thermodesulfobacteria" | |||
| Thermomicrobiota | "Thermomicrobia" | |||
| Thermotogota | "Thermotogae", OP2, EM3 | |||
| Verrucomicrobiota | "Verrucomicrobia" | PVC group |
The following is a list of candidate phyla that have not been cultured.
| Phylum | Alternative Names | Group | Notes |
| "Absconditabacteria" | SR1 | CPR; Gracilibacteria-related CPR | |
| ABY1 | OD1-ABY1 | CPR; Parcubacteria | |
| "Aerophobota" / "Aerophobetes" | CD12, BHI80-139 | ||
| "Andersenbacteria" | RIF9 | CPR; Parcubacteria; Parcubacteria 4-related | |
| "Aminicenantota" | OP8 | ||
| "Berkelbacteria" | ACD58 | CPR; Saccharibacteria-related CPR | |
| "Bipolaricaulota" | OP1, "Acetothermia" | ||
| "Blackburnbacteria" | RIF35 | CPR; Microgenomates | |
| "Brennerbacteria" | RIF18 | CPR; Parcubacteria; Parcubacteria 3 | |
| "Brownbacteria" | CPR; Parcubacteria; unclassified Parcubacteria | ||
| "Buchananbacteria" | RIF37 | CPR; Parcubacteria; Parcubacteria 1 | |
| "Campbellbacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 4 | Seems to be polyphyletic; 2 clades | |
| "Cloacimonetes" | WWE1 | FCB group | |
| "Coatesbacteria" | RIF8 | ||
| "Collierbacteria" | CPR; Patescibacteria; Microgenomates | ||
| "Colwellbacteria" | RIF41 | CPR; Parcubacteria; Parcubacteria 3 | |
| "Curtissbacteria" | CPR; Patescibacteria; Microgenomates | ||
| "Dadabacteria" | No | ||
| "Daviesbacteria" | CPR; Patescibacteria; Microgenomates | No | |
| "Delphibacteria" | FCB group | No | |
| "Delongbacteria" | RIF26, H-178 | No | |
| "Dependentiae" | TM6 | ||
| "Dojkabacteria" | WS6 | CPR; Microgenomates-related CPR | |
| "Dormibacteraeota" | AD3 | ||
| "Doudnabacteria" | SM2F11 | CPR; Parcubacteria; Parcubacteria 1-related | |
| "Edwardsbacteria" | RIF29, UBP-2 | ||
| "Eisenbacteria" | RIF28 | FCB 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" | RIF5 | No | |
| "Giovannonibacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 4-related | No | |
| "Gottesmanbacteria" | CPR; Patescibacteria; Microgenomates | No | |
| "Gracilibacteria" | GN02, BD1-5, SN-2 | CPR; Patescibacteria; Gracilibacteria-related CPR | No |
| "Gribaldobacteria" | CPR; Parcubacteria; Parcubacteria 2 | No | |
| "Handelsmanbacteria" | RIF27 | No | |
| "Harrisonbacteria" | RIF43 | CPR; Parcubacteria; Parcubacteria 3 | No |
| "Howlettbacteria" | CPR; Saccharibacteria-related CPR | No | |
| "Hugbacteria" | CPR; Parcubacteria; unclassified Parcubacteria | ||
| "Hydrogenedentes" | NKB19 | ||
| "Jacksonbacteria" | RIF38 | CPR; Parcubacteria; Parcubacteria 1 | |
| "Jorgensenbacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 3 | ||
| "Kaiserbacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 4 | ||
| "Katanobacteria" | WWE3 | CPR; Microgenomates-related | |
| "Kazanbacteria" | Kazan | CPR; Saccharibacteria-related CPR | |
| "Kerfeldbacteria" | RIF4 | CPR; Parcubacteria; Parcubacteria 1 | |
| "Komeilibacteria" | RIF6 | CPR; Parcubacteria; Parcubacteria 1 | |
| "Kryptonia" | |||
| "Krumholzibacteriota" | |||
| "Kuenenbacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 1 | ||
| "Lambdaproteobacteria" | RIF24 | Proteobacteria | |
| "Latescibacteria" | WS3 | FCB group | |
| "Levybacteria" | CPR; Patescibacteria; Microgenomates | No | |
| "Lindowbacteria" | RIF2 | CPR; Saccharibacteria-related CPR | No |
| "Liptonbacteria" | RIF42 | CPR; Parcubacteria; Parcubacteria 3 | No |
| "Lloydbacteria" | RIF45 | CPR; Parcubacteria; Parcubacteria 4 | No |
| "Magasanikbacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 1 | No | |
| "Margulisbacteria" | RIF30 | No | |
| "Melainabacteria" | |||
| "Microgenomates" | OP11 | CPR; Patescibacteria | |
| "Modulibacteria" | KSB3, GN06 | ||
| "Moranbacteria" | OD1-i | CPR; Patescibacteria; Parcubacteria; unclassified Parcubacteria | |
| "Muproteobacteria" | RIF23 | Proteobacteria | |
| NC10 | |||
| "Nealsonbacteria" | RIF40 | CPR; Parcubacteria; Parcubacteria 2 | |
| "Niyogibacteria" | RIF11 | CPR; Parcubacteria; Parcubacteria 4-related | |
| "Nomurabacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 1 | ||
| "Omnitrophica" | OP3 | PVC group | |
| "Pacebacteria" | CPR; Patescibacteria; Microgenomates | ||
| "Parcubacteria" | OD1 | CPR | |
| "Parcubacteria" 1 | CPR; Parcubacteria | ||
| "Parcubacteria" 2 | CPR; Parcubacteria | ||
| "Parcubacteria" 3 | CPR; Parcubacteria | ||
| "Parcubacteria" 4 | CPR; Parcubacteria | ||
| "Parcunitrobacteria" | CPR; Parcubacteria; unclassified Parcubacteria | ||
| PAUC34f | sponge‐associated unclassified lineage | FCB group | |
| "Peregrinibacteria" | PER | CPR; Gracilibacteria-related CPR | |
| "Peribacteria" | CPR; Gracilibacteria-related CPR | ||
| "Poribacteria" | PVC group | ||
| "Portnoybacteria" | RIF22 | CPR; Parcubacteria; Parcubacteria 4-related | |
| "Raymondbacteria" | RIF7 | ||
| Riflebacteria | RIF32 | ||
| "Roizmanbacteria" | CPR; Patescibacteria; Microgenomates | ||
| "Rokubacteria" | |||
| "Ryanbacteria" | RIF10 | CPR; Parcubacteria; Parcubacteri 4-related | |
| "Saltatorellota" | |||
| "Schekmanbacteria" | RIF3 | Proteobacteria | |
| "Shapirobacteria" | CPR; Patescibacteria; Microgenomates | ||
| "Spechtbacteria" | RIF19 | CPR; Parcubacteria; Parcubacteria 2 | |
| "Staskawiczbacteria" | RIF20 | CPR; Parcubacteria; Parcubacteria 2 | |
| "Sumerlaeota" | BRC1 | ||
| "Sungbacteria" | RIF17 | CPR; Parcubacteria; Parcubacteria 4-related | |
| TA06 | |||
| "Tagabacteria" | RIF12 | CPR; Parcubacteria; Parcubacteria 4-related | |
| "Taylorbacteria" | RIF16 | CPR; Parcubacteria; Parcubacteria 4 | |
| "Tectomicrobia" | |||
| "Terrybacteria" | RIF13 | CPR; Parcubacteria; Parcubacteria 2 | |
| "Torokbacteria" | CPR; Parcubacteria; unclssified Parcubacteria | ||
| UBP-1 | |||
| "Uhrbacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 1 | ||
| "Veblenbacteria" | RIF39 | CPR; Parcubacteria; Parcubacteria 1-related | |
| "Vogelbacteria" | RIF14 | CPR; Parcubacteria; Parcubacteria 4 | |
| "Wallbacteria" | RIF33 | ||
| "Wildermuthbacteria" | RIF21 | CPR; Parcubacteria; Parcubacteria 2 | |
| "Wirthbacteria" | CPR-related bacteria | ||
| "Woesebacteria" | CPR; Patescibacteria; Microgenomates | ||
| "Wolfebacteria" | CPR; Patescibacteria; Parcubacteria; Parcubacteria 3 | ||
| "Woykebacteria" | RIF34 | CPR; Microgenomates | |
| "Yanofskybacteria" | CPR; Patescibacteria; Parcubacteria; unclassified Parcubacteria | ||
| "Yonathbacteria" | RIF44 | CPR; Parcubacteria; Parcubacteria 4 | |
| "Zambryskibacteria" | RIF15 | CPR; Parcubacteria; Parcubacteria 4 | |
| ZB2 | OD1-ZB2 | CPR; 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, Parcubacteria, and Gracilibacteria. More recent phylogenetic analyses show that the last common ancestor of these taxa is the same node as that of CPR.Sphingobacteria
The Sphingobacteria 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 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 and several accepted phyla 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.When bacterial nomenclature was controlled under the Botanical Code, the term division was used, but now that bacterial nomenclature is controlled under the Bacteriological Code, the term phylum is preferred.
In 1987, Carl Woese, regarded as the forerunner of the molecular phylogeny revolution, divided Eubacteria into 11 divisions based on 16S ribosomal RNA sequences, listed below.
- Purple Bacteria and their relatives
- *alpha subdivision
- *beta subdivision
- *gamma subdivision
- *delta subdivision
- Gram-positive Eubacteria
- *High-G+C species
- *Low-G+C species
- * Photosynthetic species
- * Species with Gram-negative walls
- Cyanobacteria and chloroplasts
- Spirochetes and relatives
- * Spirochetes
- * Leptospiras
- Green sulfur bacteria
- Bacteroides, Flavobacteria and relatives
- * Flavobacterium group
- Planctomyces and relatives
- * Planctomyces group
- * Thermophiles
- Chlamydiae
- Radioresistant micrococci and relatives
- * Deinococcus group
- * Thermophiles
- Green non-sulfur bacteria and relatives
- * Chloroflexus group
- * Thermomicrobium group
- Thermotogae
The advent of molecular sequencing technologies has allowed for the recovery of genomes directly from environmental samples, leading to rapid expansion of our knowledge of the diversity of bacterial phyla. These techniques are genome-resolved metagenomics and single-cell genomics.