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The candidate phyla radiation (also referred to as CPR group) is a large evolutionary radiation of bacterial lineages whose members are mostly uncultivated and only known from metagenomics and single cell sequencing. They have been described as nanobacteria (not to be confused with non-living nanoparticles of the same name) or ultra-small bacteria due to their reduced size (nanometric) compared to other bacteria.
Originally (circa 2016), it has been suggested that CPR represents over 15% of all bacterial diversity and may consist of more than 70 different phyla. However,
the Genome Taxonomy Database (2018) based on relative evolutionary divergence found that CPR represents a single phylum, with earlier figures inflated by the rapid evolution of ribosomal proteins. CPR lineages are generally characterized as having small genomes and lacking several biosynthetic pathways and ribosomal proteins. This has led to the speculation that they are likely obligate symbionts.
Earlier work proposed a superphylum called Patescibacteria which encompassed several phyla later attributed to the CPR group. Therefore, Patescibacteria and CPR are often used as synonyms. The former name is not necessarily obsolete: for example, the GTDB uses this name because they consider the CPR group a phylum.
The Candidate phyla radiation was found to be the most basal-branching lineage in bacteria according to some early phylogenetic analyses of this group based on ribosomal proteins and protein family occurrence profiles. These studies found the following phylogeny between phyla and superphyla. The superphyla are shown in bold.
However, several recent studies have suggested that the CPR belongs to Terrabacteria and is more closely related to Chloroflexota. The evolutionary relationships that are typically supported by these studies are as follows.
Most of the Tree of Life is a Complete Mystery
We know certain branches exist, but we have never seen the organisms that perch there. by Ed Yong, April 12, 2016, atlantic.com.
Ultra-Small, Parasitic Bacteria Found in Groundwater, Dogs, Cats — And You
on: SciTechDaily; July 21, 2020; source: Forsyth Institute * * {{Taxonbar, from=Q27110262 Bacteriology Candidatus taxa Bacteria phyla
Characteristics
Although there are a few exceptions, members of the candidate phyla radiation generally lack several biosynthetic pathways for several amino acids and nucleotides. To date, there has been no genomic evidence that indicates that they are capable of producing the lipids essential for cell envelope formation. Additionally, they tend to lack complete TCA cycles and electron transport chain complexes, including ATP synthase. This lack of several important pathways found in most free-living prokaryotes indicates that the candidate phyla radiation is composed of obligate fermentative symbionts. Furthermore, CPR members have unique ribosomal features. While the members of CPR are generally uncultivable, and therefore missed in culture-dependent methods, they are also often missed in culture-independent studies that rely on16S rRNA 16S rRNA may refer to:
* 16S ribosomal RNA
16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome ( SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure.
The g ...
sequences. Their rRNA genes appear to encode proteins and have self-splicing introns, features that are rarely seen in bacteria, although they have previously been reported. Owing to these introns, members of CPR are not detected in 16S-dependent methods. Additionally, all CPR members are missing the L30 ribosomal protein, a trait that is often seen in symbionts.
Many of its characteristics are similar or analogous to those of ultra-small archaea ( DPANN).
Phylogeny
The Candidate phyla radiation was found to be the most basal-branching lineage in bacteria according to some early phylogenetic analyses of this group based on ribosomal proteins and protein family occurrence profiles. These studies found the following phylogeny between phyla and superphyla. The superphyla are shown in bold.
However, several recent studies have suggested that the CPR belongs to Terrabacteria and is more closely related to Chloroflexota. The evolutionary relationships that are typically supported by these studies are as follows.
Provisional taxonomy
Because many CPR members are uncultivable, they cannot be formally put into the bacterial taxonomy, but a number of provisional, or '' Candidatus'', names have been generally agreed on. As of 2017, twosuperphyla
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 fo ...
are generally recognized under CPR, Parcubacteria and Microgenomates. The Phyla under CPR include:
* ?" Elulimicrobiota" Rodriguez-R et al. 2020
* Clade "Patescibacteria" Rinke et al. 2013
** " Wirthbacteria" Hug et al. 2016
** Microgenomates Cluster
*** " Dojkabacteria" Wrighton et al. 2016 (WS6)
*** " Katanobacteria" Hug et al. 2016b (WWE3)
*** Superphylum Microgenomates
**** " Woykebacteria" Anantharaman et al. 2016 (RIF34)
**** " Curtissbacteria" Brown et al. 2015
**** " Daviesbacteria" Brown et al. 2015
**** " Roizmanbacteria" Brown et al. 2015
**** " Gottesmanbacteria" Brown et al. 2015
**** " Levybacteria" Brown et al. 2015
**** " Shapirobacteria" Brown et al. 2015
**** Clade GWA2-44-7
***** ?" Genascibacteria" He et al. 2021
***** " Amesbacteraceaeia" Brown et al. 2015
***** " Blackburnbacteria" Anantharaman et al. 2016 (RIF35)
***** " Woesebacteria" Brown et al. 2015 (DUSEL-2, DUSEL-4)
**** Clade UBA1400
***** " Beckwithbacteria" Brown et al. 2015
***** " Collierbacteria" Brown et al. 2015
***** " Chazhemtonibacteraceae" corrig. Kadnikov et al. 2020
***** " Chisholmbacteria" Anantharaman et al. 2016 (RIF36)
***** " Cerribacteria" Kroeger et al. 2018
***** " Pacebacteria" Brown et al. 2015
** Gracilibacteria
Gracilibacteria is a bacterial candidate phylum formerly known as GN02, BD1-5, or SN-2. It is part of the Candidate Phyla Radiation and the Patescibacteria group.
The first representative of the Gracilibacteria phylum was reported in 1999 after ...
Cluster
*** " Absconditabacteria" Hug et al. 2016b (SR1)
*** "''Ca.'' Altimarinus" Rinke et al. 2013 (GN02)
*** " Abawacabacteria" Anantharaman et al. 2016 (RIF46)
*** " Peregrinibacteria" Brown et al. 2015 (PER)
*** "Fertabacteria
Fertabacteria is a candidate bacterial phylum of the Candidate Phyla Radiation, first proposed in 2017 after analysis of a genome from the mouth of a bottlenose dolphin. Members of this phylum are predicted to have been widely under-detected in 1 ...
" Dudek et al. 2017 (DOLZORAL124_38_8)
*** " Peribacteria" Anantharaman et al. 2016
** Saccharibacteria Cluster
*** " Berkelbacteria" Wrighton et al. 2014 (ACD58)
*** " Kazanbacteria" Jaffe et al. 2020 (Kazan)
*** " Howlettbacteria" Probst et al. 2018 (CPR2)
*** " Saccharibacteria" Albertsen et al. 2013 (TM7)
** Parcubacteria Cluster
*** " Andersenbacteria" Anantharaman et al. 2016 (RIF9)
*** " Doudnabacteria" Anantharaman et al. 2016 (SM2F11)
*** " Torokbacteria" Probst et al. 2018
*** Clade ABY1
**** " Kerfeldbacteria" Anantharaman et al. 2016 (RIF4)
**** " Veblenbacteria" Anantharaman et al. 2016 (RIF39)
**** ?" Brownbacteria" Danczak et al. 2017
**** " Uhrbacteria" Brown et al. 2015 (SG8-24)
**** " Magasanikbacteria" Brown et al. 2015
**** " Kuenenbacteria" Brown et al. 2015
**** " Jacksonbacteria" Anantharaman et al. 2016 (RIF38)
**** " Komeilibacteria" Anantharaman et al. 2016 (RIF6)
**** " Moisslbacteria" Probst et al. 2018
**** " Falkowbacteria" Brown et al. 2015
**** " Buchananbacteria" Anantharaman et al. 2016 (RIF37)
*** Superphylum Parcubacteria
**** ?" Montesolbacteria " He et al. 2021
**** " Moranbacteria" Brown et al. 2015 (OD1-i)
**** Clade UBA6257
***** " Brennerbacteria" Anantharaman et al. 2016 (RIF18)
***** " Wolfebacteria" Brown et al. 2015
***** " Jorgensenbacteria" Brown et al. 2015
***** " Liptonbacteria" Anantharaman et al. 2016 (RIF42)
***** " Colwellbacteria" Anantharaman et al. 2016 (RIF41)
***** " Harrisonbacteria" Anantharaman et al. 2016 (RIF43)
**** Clade UBA9983_A
***** ?" Hugbacteria" Danczak et al. 2017
***** ?" Llyodbacteria" Anantharaman et al. 2016 (RIF45)
***** " Vogelbacteria" Anantharaman et al. 2016 (RIF14)
***** " Yonathbacteria" Anantharaman et al. 2016 (RIF44)
***** "Nomurabacteria
Nomurabacteria is a candidate phylum of bacteria belonging to the CPR group so they are ultra-small bacteria. They have been found in a wide variety of environments, mainly in sediments under anaerobic conditions.Castelle, C., Brown, C., Thomas, B ...
" Brown et al. 2015
***** " Kaiserbacteria" Brown et al. 2015
***** " Adlerbacteria" Brown et al. 2015
***** " Campbellbacteria" Brown et al. 2015
***** " Taylorbacteria" Anantharaman et al. 2016 (RIF16)
***** " Zambryskibacteria" Anantharaman et al. 2016 (RIF15)
**** " Yanofskybacteria" Brown et al. 2015
**** " Azambacteria" Brown et al. 2015
**** " Sungbacteria" Anantharaman et al. 2016 (RIF17)
**** " Ryanbacteria" Anantharaman et al. 2016 (RIF10)
**** Clade UBA9983
***** " Giovannonibacteria" Brown et al. 2015
***** " Niyogibacteria" Anantharaman et al. 2016 (RIF11)
***** " Tagabacteria" Anantharaman et al. 2016 (RIF12)
**** " Terrybacteria" Anantharaman et al. 2016 (RIF13)
**** " Spechtbacteria" Anantharaman et al. 2016 (RIF19)
**** " Parcunitrobacteria" Castelle et al. 2017 (GWA2-38-13b)
**** " Portnoybacteria" Anantharaman et al. 2016 (RIF22)
**** Clade "Paceibacteria"
***** " Wildermuthbacteria" Anantharaman et al. 2016 (RIF21)
***** " Paceibacteria"
***** " Nealsonbacteria" Anantharaman et al. 2016 (RIF40)
***** " Gribaldobacteria" Probst et al. 2018
***** " Staskawiczbacteria" Anantharaman et al. 2016 (RIF20)
The current phylogeny is based on ribosomal proteins (Hug et al., 2016). Other approaches, including protein family
A protein family is a group of evolutionarily related proteins. In many cases, a protein family has a corresponding gene family, in which each gene encodes a corresponding protein with a 1:1 relationship. The term "protein family" should not be c ...
existence and 16S ribosomal RNA
16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure.
The genes coding for it are referred to as 16S rRNA ...
, produce similar results at lower resolutions.
See also
* for some of the phyla in CPR.References
External links
Most of the Tree of Life is a Complete Mystery
We know certain branches exist, but we have never seen the organisms that perch there. by Ed Yong, April 12, 2016, atlantic.com.
Ultra-Small, Parasitic Bacteria Found in Groundwater, Dogs, Cats — And You
on: SciTechDaily; July 21, 2020; source: Forsyth Institute * * {{Taxonbar, from=Q27110262 Bacteriology Candidatus taxa Bacteria phyla