HOME

TheInfoList




Alphaproteobacteria is a
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
of
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
in the
phylum In biology, a phylum (; plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken fr ...
Proteobacteria Proteobacteria is a major phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The pl ...
(See also
bacterial taxonomy Bacterial taxonomy is the Linnaean taxonomy, taxonomy, i.e. the Taxonomic rank, rank-based classification, of bacteria. In the scientific classification established by Carl Linnaeus, each species has to be assigned to a genus (binary nomenclature) ...
). Its members are highly diverse and possess few commonalities, but nevertheless share a common ancestor. Like all ''Proteobacteria'', its members are
gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), do ...
and some of its intracellular parasitic members lack
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidia ...

peptidoglycan
and are consequently gram variable.


Characteristics

The Alphaproteobacteria are a diverse taxon and comprises several
phototroph Terrestrial and aquatic phototrophs: plants grow on a fallen log floating in algae-rich water Phototrophs ('' Gr'': φῶς, φωτός = light, τροϕή = nourishment) are organism In biology, an organism (from Ancient Greek, Greek: ...
ic genera, several genera metabolising C1-compounds (''e.g.'', ''Methylobacterium'' ''spp.''), symbionts of plants (e.g., ''
Rhizobium ''Rhizobium'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circu ...
'' ''spp.''),
endosymbiont An endosymbiont or endobiont is any organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mol ...
s of arthropods (''
Wolbachia ''Wolbachia'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including their ...

Wolbachia
'') and intracellular
pathogen In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
s (''e.g.
Rickettsia ''Rickettsia'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circ ...
''). Moreover, the class includes (as an extinct member) the
protomitochondrion The proto-mitochondrion is the hypothetical ancestral bacterial endosymbiont from which all mitochondria in eukaryotes are thought to descend. Phylogeny The phylogenetic analyses of the few genes that are still encoded in the genomes of modern mit ...
, the bacterium that was engulfed by the eukaryotic ancestor and gave rise to the
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
, which are organelles in eukaryotic cells (See
endosymbiotic theory Symbiogenesis, endosymbiotic theory, or serial endosymbiotic theory, is the leading evolutionary theory of the origin of eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that fun ...

endosymbiotic theory
). A species of technological interest is ''
Rhizobium radiobacter ''Agrobacterium tumefaciens'' (updated scientific name ''Rhizobium radiobacter'', synonym ''Agrobacterium radiobacter'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram ...
'' (formerly ''Agrobacterium tumefaciens''): scientists often use this species to transfer foreign DNA into plant genomes. Aerobic anoxygenic phototrophic bacteria, such as ''
Pelagibacter ubique ''Pelagibacter'', with the single species ''P. ubique'', was isolated in 2002 and given a specific name, although it has not yet been described as required by the bacteriological codeThe International Code of Nomenclature of Prokaryotes (ICNP) fo ...
'', are alphaproteobacteria that are a widely distributed and may constitute over 10% of the open ocean microbial community.


Evolution and genomics

There is some disagreement on the
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram A diagram is a symbolic representation Representation may refer to: Law a ...

phylogeny
of the
orders Orders is a surname In some cultures, a surname, family name, or last name is the portion of one's personal name 300px, First/given, middle and last/family/surname with John Fitzgerald Kennedy as example. This shows a structure typical f ...
, especially for the location of the '' Pelagibacterales'', but overall there is some consensus. The discord stems from the large difference in gene content (''e.g.'' genome streamlining in ''Pelagibacter ubique'') and the large difference in
GC-content In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
between members of several orders. Specifically, ''Pelagibacterales'', ''Rickettsiales'' and ''Holosporales'' contain species with AT-rich genomes. It has been argued that it could be a case of
convergent evolution Convergent evolution is the independent evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; eit ...
that would result in an artefactual clustering. However, several studies disagree. Furthermore, it has been found that the GC-content of
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
(the traditional phylogenetic marker for prokaryotes) little reflects the GC-content of the genome. One example of this atypical decorrelation of ribosomal GC-content with phylogeny is that members of the '' Holosporales'' have a much higher ribosomal GC-content than members of the '' Pelagibacterales'' and ''
Rickettsiales The Rickettsiales, informally called rickettsias, are an order of small Alphaproteobacteria. Some are notable pathogens, including ''Rickettsia'', which causes a variety of diseases in humans, and ''Ehrlichia'', which causes diseases in livestock. ...
'', even though they are more closely related to species with high genomic GC-contents than to members of the latter two orders. The Class ''Alphaproteobacteria'' is divided into three
subclasses Subclass may refer to: * Subclass (taxonomy), a taxonomic rank below "class" * Subclass (computer science) * Subclass (set theory) See also

* Superclass (disambiguation), Superclass {{disambiguation ...
''Magnetococcidae'', ''Rickettsidae'' and ''Caulobacteridae''. The
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
group is ''Magnetococcidae'', which is composed by a large diversity of
magnetotactic bacteria Magnetotactic bacteria (or MTB) are a polyphyletic 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly">monophyly.html" ;"title="primates, showing a monophyly">primates, showing a monophyly (the simians, ...
, but only one is described, ''Magnetococcus marinus''. The ''Rickettsidae'' is composed of the intracellular ''Rickettsiales'' and the free-living ''Pelagibacterales''. The ''Caulobacteridae'' is composed of the ''Holosporales'', ''Rhodospirillales'', ''Sphingomonadales'', '' Rhodobacterales'', ''Caulobacterales'', ''Kiloniellales'', ''Kordiimonadales'', ''Parvularculales'' and ''Sneathiellales''. Comparative analyses of the sequenced genomes have also led to discovery of many conserved insertion-deletions (indels) in widely distributed proteins and whole proteins (i.e. signature proteins) that are distinctive characteristics of either all ''Alphaproteobacteria'', or their different main orders (viz. ''Rhizobiales'', ''Rhodobacterales'', ''Rhodospirillales'', ''Rickettsiales'', ''Sphingomonadales'' and ''Caulobacterales'') and families (viz. ''Rickettsiaceae'', ''Anaplasmataceae'', ''Rhodospirillaceae'', ''Acetobacteraceae'', ''Bradyrhiozobiaceae'', ''Brucellaceae'' and ''Bartonellaceae''). These molecular signatures provide novel means for the circumscription of these taxonomic groups and for identification/assignment of new species into these groups. Phylogenetic analyses and conserved indels in large numbers of other proteins provide evidence that ''Alphaproteobacteria'' have branched off later than most other phyla and Classes of Bacteria except ''Betaproteobacteria'' and ''Gammaproteobacteria''.


Phylogeny

The currently accepted taxonomy is based on the
List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature ('LPSN'') is an online database that maintains information on the naming Naming is assigning a name A name is a term used for identification by an external observer. They can identify a ...
(LPSN) and
National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine The United States National Library of Medicine (NLM), operated by the United States federal government The federal gov ...
(NCBI) and the phylogeny is based on
16S rRNA 16S rRNA may refer to: * 16S ribosomal RNA, the prokaryotic ribosomal subunit * Mitochondrially encoded 16S RNA, the eukaryotic ribosomal subunit {{Short pages monitor An updated phylogeny of the alphaproteobacteria was published in which the position of the Mitochondria is not clear yet.


Natural genetic transformation

Although only a few studies have been reported on natural genetic transformation in the ''Alphaproteobacteria'', this process has been described in ''
Agrobacterium tumefaciens ''Agrobacterium tumefaciens'' (updated scientific name ''Rhizobium radiobacter'', synonym ''Agrobacterium radiobacter'') is the causal agent of crown gall disease (the formation of tumour A neoplasm () is a type of abnormal and excessive gr ...

Agrobacterium tumefaciens
'', '' Methylobacterium organophilum'', and ''
Bradyrhizobium japonicum ''Bradyrhizobium japonicum'' is a species of legume-Root nodule, root nodulating, Symbiosis, microsymbiotic Nitrogen fixation, nitrogen-fixing bacteria. The species is one of many Gram-negative, Bacillus (shape), rod-shaped bacteria commonly refer ...

Bradyrhizobium japonicum
''. Natural genetic transformation is a sexual process involving
DNA transfer Deoxyribonucleic acid (; DNA) is a molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a cha ...
from one bacterial cell to another through the intervening medium, and the integration of the donor sequence into the recipient genome by
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

homologous recombination
.


References


External links

*
Bacterial (Prokaryotic) Phylogeny Webpage: Alpha Proteobacteria.
{{Taxonbar, from=Q306579 Bacteria classes