The Hyphomicrobiales (synonym Rhizobiales) are an order of Gram-negative Alphaproteobacteria.
The rhizobia, which fix nitrogen and are symbiotic 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. Species of the Methylocystaceae are methanotrophs; they use methanol (CH<sub>3</sub>OH) or methane (CH<sub>4</sub>) as their sole energy and carbon sources. Other important genera are the human pathogens Bartonella and Brucella, as well as Agrobacterium, an important tool in genetic engineering.
Taxonomy
Accepted families
- Aestuariivirgaceae <small>Li et al. 2019</small>
- Afifellaceae <small>Hördt et al. 2020</small>
- Ahrensiaceae <small>Hördt et al. 2020</small>
- Alsobacteraceae <small>Sun et al. 2018</small>
- Amorphaceae <small>Hördt et al. 2020</small>
- Ancalomicrobiaceae <small>Dahal et al. 2018</small>
- Aurantimonadaceae <small>Hördt et al. 2020</small>
- Bartonellaceae <small>Gieszczykiewicz 1939 (Approved Lists 1980)</small>
- Beijerinckiaceae <small>Garrity et al. 2006</small>
- Blastochloridaceae <small>Hördt et al. 2020</small>
- Boseaceae <small>Hördt et al. 2020</small>
<!-- Bradyrhizobiaceae was reclassified as Nitrobacteraceae. -->
- Breoghaniaceae <small>Hördt et al. 2020</small>
- Brucellaceae <small>Breed et al. 1957 (Approved Lists 1980)</small>
- Chelatococcaceae <small>Dedysh et al. 2016</small>
- Cohaesibacteraceae <small>Hwang and Cho 2008</small>
- Devosiaceae <small>Hördt et al. 2020</small>
- Hyphomicrobiaceae <small>Babudieri 1950 (Approved Lists 1980)</small>
- Kaistiaceae <small>Hördt et al. 2020</small>
- Lichenibacteriaceae <small>Pankratov et al. 2020</small>
- Lichenihabitantaceae <small>Noh et al. 2019</small>
<!-- Mabikibacteraceae was reclassified as Notoacmeibacteraceae. -->
- Methylobacteriaceae <small>Garrity et al. 2006</small>
- Methylocystaceae <small>Bowman 2006</small>
- Nitrobacteraceae <small>corrig. Buchanan 1917 (Approved Lists 1980)</small>
<!-- Nitrobacteriaceae is a misspelling of Nitrobacteraceae. -->
- Notoacmeibacteraceae <small>Huang et al. 2017</small>
- Parvibaculaceae <small>Hördt et al. 2020</small>
- Phreatobacteraceae <small>Hördt et al. 2020</small>
- Phyllobacteriaceae <small>Mergaert and Swings 2006</small>
- Pleomorphomonadaceae <small>Hördt et al. 2020</small>
- Pseudoxanthobacteraceae <small>Hördt et al. 2020</small>
- Rhabdaerophilaceae <small>Ming et al. 2020</small>
- Rhizobiaceae <small>Conn 1938 (Approved Lists 1980)</small>
- Rhodobiaceae <small>Garrity et al. 2006</small>
- Roseiarcaceae <small>Kulichevskaya et al. 2014</small>
- Salinarimonadaceae <small>Cole et al. 2018</small>
- Segnochrobactraceae <small>Akter et al. 2020</small>
- Stappiaceae <small>Hördt et al. 2020</small>
- Tepidamorphaceae <small>Hördt et al. 2020</small>
- Xanthobacteraceae <small>Lee et al. 2005</small>
Unassigned genera
The following genus has not been assigned to a family:
- Flaviflagellibacter <small>Dong et al. 2019</small>
Provisional taxa
These taxa have been published, but have not been validated according to the Bacteriological Code:
- "Nordella" <small>La Scola et al. 2004</small>
- "Propylenellaceae" <small>Liu et al. 2021</small>
- "Propylenella" <small>Liu et al. 2021</small>
Phylogeny
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature and the phylogeny is based on whole-genome sequences. 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.
See also
- Lar1