The PVC superphylum is a superphylum of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

named after its three important members,

Planctomycetota The Planctomycetota are a phylum of widely distributed bacteria, occurring in both aquatic and terrestrial habitats. They play a considerable role in global carbon and nitrogen cycles, with many species of this phylum capable of anaerobic ammoniu ...

Verrucomicrobiota Verrucomicrobiota is a phylum of Gram-negative bacteria that contains only a few described species. The species identified have been isolated from fresh water, marine and soil environments and human faeces. A number of as-yet uncultivated species ...

, and

Chlamydiota The Chlamydiota (synonym Chlamydiae) are a bacterial phylum and class whose members are remarkably diverse, including pathogens of humans and animals, symbionts of ubiquitous protozoa, and marine sediment forms not yet well understood. All of th ...

. Cavalier-Smith postulated that the PVC bacteria probably lost or reduced their

peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

twice. It has been hypothesised that a member of the PVC clade might have been the host cell in the

endosymbiotic event An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualism (biology), mutualistic relationship. (The term endosymbiosis is from the Greek language, G ...

that gave rise to the first proto-

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

cell.

Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...

calls the same group Planctobacteria and considers it a

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

. However, this is not followed by the larger scientific community. In the Cavalier-Smith bacterial megaclassification, it is within the bacterial

Gracilicutes Gracilicutes (Latin: ''gracilis'', slender, and ''cutis'', skin, referring to the cell wall) is a clade in bacterial phylogeny. Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of ...

infra-kingdom and comprises the phyla

Lentisphaerota Lentisphaerota is a phylum of bacteria closely related to Chlamydiota and Verrucomicrobiota. It includes two monotypic orders Lentisphaerales and Victivallales. Phylum members can be aerobic or anaerobic and fall under two distinct phenotyp ...

Molecular signatures

, and

in the traditional molecular phylogeny view are considered as phyla and also cluster together in the PVC superphylum, along with the

candidate phyla A candidate division, candidate phylum or candidate division-level is a lineage of prokaryotic organisms for which until recently no cultured representatives have been found, but evidence of the existence of the clade has been obtained by 16S rRN ...

Omnitrophica (previously OP3) and the Poribacteria. An important molecular marker in the form of a conserved signature protein has been found to be consistently shared by PVC members, with the exception of

Poribacteria Poribacteria are a candidate phylum of bacteria originally discovered in the microbiome of marine sponges (''Porifera''). Poribacteria are Gram-negative primarily aerobic mixotrophs with the ability for oxidative phosphorylation, glycolysis, and ...

. The conserved signature protein may be a marker that represents a synapomorphic quality and a means to distinguish this bacterial group. Recent studies have characterized this protein and it has been attributed to play an important housekeeping function in DNA/RNA binding. This observation not only provides a means to demarcate the PVC superphylum, but it supports strongly supports an evolutionary relationship shared by this clade that is distinct from other bacteria.

Conserved signature indels Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers ...

(CSIs) have also been found specific for the

, and

that distinguish each respective phylum from one another, and from other bacteria. A three-amino-acid insert in the RNA polymerase protein

RpoB The ''rpoB'' gene encodes the β subunit of bacterial RNA polymerase and the homologous plastid-encoded RNA polymerase (PEP). It codes for 1342 amino acids in ''E. coli'', making it the second-largest polypeptide in the bacterial cell. It is targe ...

has been found that is shared by all sequenced Verrucomicrobia, Chlamydiae, and

Lentisphaerae Lentisphaerota is a phylum of bacteria closely related to Chlamydiota and Verrucomicrobiota. It includes two monotypic orders Lentisphaerales and Victivallales. Phylum members can be aerobic or anaerobic and fall under two distinct phenotypes ...

species. The CSI is absent from neighbouring Planctomycetes' and Poribacteria, suggesting common ancestry among the groups for which the CSI is specific. Additional lines of evidence for the existence of this clade have been found. These include the presence of membrane coat-like proteins,

tubulin Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoske ...

, sterol synthesis, and the presence of condensed DNA.

Notes

References

{{Taxonbar, from=Q845152 Superphyla