The Hyphomicrobiale' (synonym Rhizobiales) are an order of

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

Alphaproteobacteria ''Alphaproteobacteria'' or ''α-proteobacteria'', also called ''α-Purple bacteria'' in earlier literature, is a class of bacteria in the phylum '' Pseudomonadota'' (formerly "Proteobacteria"). The '' Magnetococcales'' and '' Mariprofundales'' ar ...

. The

rhizobia Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. I ...

, which fix nitrogen and are

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

with plant roots, appear in several different families. The four families '' Nitrobacteraceae'', '' Hyphomicrobiaceae'', '' Phyllobacteriaceae'', and '' Rhizobiaceae'' contain at least several genera of nitrogen-fixing, legume-nodulating, microsymbiotic bacteria. Examples are the genera '' Bradyrhizobium'' and ''

Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant ce ...

''. Species of the '' Methylocystaceae'' are

methanotroph Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to ...

s; they use

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

(CH₃OH) or

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

(CH₄) as their sole energy and carbon sources. Other important genera are the human pathogens '' Bartonella'' and ''

Brucella ''Brucella'' is a genus of Gram-negative bacterium, bacteria, named after David Bruce (microbiologist), David Bruce (1855–1931). They are small (0.5 to 0.7 by 0.6 to 1.5 μm), non-Bacterial capsule, encapsulated, non-motile, facultatively ...

'', as well as ''

Agrobacterium ''Agrobacterium'' is a genus of Gram-negative bacteria established by Harold J. Conn, H. J. Conn that uses horizontal gene transfer to cause tumors in plants. ''Agrobacterium tumefaciens'' is the most commonly studied species in this genus. ''Agr ...

,'' an important tool in

genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of Genetic engineering techniques, technologies used to change the genet ...

Taxonomy

Accepted families

* '' Aestuariivirgaceae'' Li ''et al''. 2019 * '' Afifellaceae'' Hördt ''et al''. 2020 * '' Ahrensiaceae'' Hördt ''et al''. 2020 * '' Alsobacteraceae'' Sun ''et al''. 2018 * '' Amorphaceae'' Hördt ''et al''. 2020 * '' Ancalomicrobiaceae'' Dahal ''et al''. 2018 * '' Aurantimonadaceae'' Hördt ''et al''. 2020 * '' Bartonellaceae'' Gieszczykiewicz 1939 (Approved Lists 1980) * '' Beijerinckiaceae'' Garrity ''et al''. 2006 * '' Blastochloridaceae'' Hördt ''et al''. 2020 * '' Boseaceae'' Hördt ''et al''. 2020 * '' Breoghaniaceae'' Hördt ''et al''. 2020 * '' Brucellaceae'' Breed ''et al''. 1957 (Approved Lists 1980) * '' Chelatococcaceae'' Dedysh ''et al''. 2016 * '' Cohaesibacteraceae'' Hwang and Cho 2008 * '' Devosiaceae'' Hördt ''et al''. 2020 * '' Hyphomicrobiaceae'' Babudieri 1950 (Approved Lists 1980) * '' Kaistiaceae'' Hördt ''et al''. 2020 * '' Lichenibacteriaceae'' Pankratov ''et al''. 2020 * '' Lichenihabitantaceae'' Noh ''et al''. 2019 * '' Methylobacteriaceae'' Garrity ''et al''. 2006 * '' Methylocystaceae'' Bowman 2006 * '' Nitrobacteraceae'' corrig. Buchanan 1917 (Approved Lists 1980) * '' Notoacmeibacteraceae'' Huang ''et al''. 2017 * '' Parvibaculaceae'' Hördt ''et al''. 2020 * '' Phreatobacteraceae'' Hördt ''et al''. 2020 * '' Phyllobacteriaceae'' Mergaert and Swings 2006 * '' Pleomorphomonadaceae'' Hördt ''et al''. 2020 * '' Pseudoxanthobacteraceae'' Hördt ''et al''. 2020 * '' Rhabdaerophilaceae'' Ming ''et al''. 2020 * '' Rhizobiaceae'' Conn 1938 (Approved Lists 1980) * '' Rhodobiaceae'' Garrity ''et al''. 2006 * '' Roseiarcaceae'' Kulichevskaya ''et al''. 2014 * '' Salinarimonadaceae'' Cole ''et al''. 2018 * '' Segnochrobactraceae'' Akter ''et al''. 2020 * '' Stappiaceae'' Hördt ''et al''. 2020 * '' Tepidamorphaceae'' Hördt ''et al''. 2020 * '' Xanthobacteraceae'' Lee ''et al''. 2005

Unassigned Genera

The following genus has not been assigned to a family: * '' Flaviflagellibacter'' Dong ''et al''. 2019

Provisional Taxa

These taxa have been published, but have not been validated according to the Bacteriological Code: * "''Nordella''" La Scola ''et al''. 2004 * "''Propylenellaceae''" Liu ''et al''. 2021 ** "''Propylenella''" Liu ''et al''. 2021 *** "''Propylenella binzhouense''" Liu ''et al''. 2021 * "''Thermopetrobacter''" Sislak 2013

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 and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclatu ...

and the phylogeny is based on whole-genome sequences.

Natural genetic transformation

Natural genetic transformation has been reported in at least four ''Hyphomicrobiales'' species: ''

Agrobacterium tumefaciens ''Agrobacterium tumefaciens'' (also known as ''Rhizobium 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-negative soil bacterium. Symptoms are cause ...

'', '' Methylobacterium organophilum'', '' Ensifer adhaerens'', and '' Bradyrhizobium japonicum''. Natural genetic transformation is a sexual process involving DNA transfer 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 ...

Taxonomy

Accepted families

Unassigned Genera

Provisional Taxa

Phylogeny

Natural genetic transformation

See also

Notes

References

Further reading