Hyphomicrobiales

Hyphomicrobiales
	Agrobacterium (SEM image)
Scientific classification
Domain:	Bacteria
Phylum:	Pseudomonadota
Class:	Alphaproteobacteria
Order:	Hyphomicrobiales; Douglas 1957 (Approved Lists 1980)
Families
	See text
Synonyms
	Rhizobiales Kuykendall 2006;

The Hyphomicrobiales (synonom 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 (CH₃OH) or methane (CH₄) as their sole energy and carbon sources. Other important genera are the human pathogens Bartonella and Brucella, as well as Agrobacterium (useful in genetic engineering).

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^[3]

Provisional Taxa

These taxa have been published, but have not been validated according to the Bacteriological Code:

"Nordella" La Scola et al. 2004^[4]
"Propylenellaceae" Liu et al. 2021^[5]
- "Propylenella" Liu et al. 2021^[5]
  - "Propylenella binzhouense" Liu et al. 2021^[5]
"Thermopetrobacter" Sislak 2013^[6]

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature^[7] and the phylogeny is based on whole-genome sequences.^[2]^[a]

Hyphomicrobiales

Parvibaculaceae

Hyphomicrobiaceae

Amorphaceae

	Rhodobiaceae

	Afifellaceae

Cohaesibacteraceae

	Breoghaniaceae

	Stappiaceae

Devosiaceae

Aurantimonadaceae

Ahrensiaceae

	Notoacmeibacteraceae

	Phyllobacteriaceae

Rhizobiaceae

Bartonellaceae

	Phyllobacterium ^[b]

	Brucellaceae

Tepidamorphaceae

Kaistiaceae

Pseudoxanthobacteraceae

	Prosthecomicrobium ^[c]

	Pleomorphomonadaceae

	Blastochloridaceae

	Xanthobacteraceae

	Phreatobacteraceae

	Nitrobacteraceae

Beijerinckiaceae

	Roseiarcaceae

	Methylocystaceae

Chelatococcaceae

Boseaceae

	Salinarimonadaceae

	Methylobacteriaceae

outgroups

Rhodobacterales

	Parvularculales

	Caulobacterales

Natural genetic transformation

Natural genetic transformation has been reported in at least four Hyphomicrobiales species: Agrobacterium tumefaciens,^[8] Methylobacterium organophilum,^[9] Ensifer adhaerens,^[10] and Bradyrhizobium japonicum.^[11] 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.

Notes

^ Aestuariivirgaceae, Alsobacteraceae, Ancalomicrobiaceae, Lichenibacteriaceae, Lichenihabitantaceae, Rhabdaerophilaceae, and Segnochrobactraceae are not included in this phylogenetic tree.
^ Phyllobacterium is separate from the rest of Phyllobacteriaceae.
^ Prosthecomicrobium is separate from the rest of Hyphomicrobiaceae.