Hyphomicrobiales


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