|Transmission electron micrograph of Wolbachia within an insect cell.
Credit:Public Library of Science / Scott O'Neill
Garrity et al. 2006
The Alphaproteobacteria comprise most phototrophic genera, but also several genera metabolising C1-compounds (e.g., Methylobacterium spp.), symbionts of plants (e.g., Rhizobium spp.) and animals, and a group of pathogens, the Rickettsiaceae. Moreover the precursors of the mitochondria of eukaryotic cells are thought to have originated from Rickettsia spp. (See endosymbiotic theory.). Because of their symbiotic properties, scientists often use Alphaproteobacteria of the genus Agrobacterium to transfer foreign DNA into plant genomes, and they also have many other biotechnological properties. Aerobic anoxygenic phototrophic bacteria are alphaproteobacteria that are a widely distributed marine plankton that may constitute over 10% of the open ocean microbial community.
Evolution and genomics
The Class Alphaproteobacteria comprises ten orders (viz. Magnetococcales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales, Caulobacterales, Kiloniellales, Kordiimonadales, Parvularculales and Sneathiellales)., In phylogenetic trees based upon concatenated sequences for large datasets of proteins, the species from these orders whose genomes have been sequenced branch in the following order from earliest branching to most recent: Magnetococcales-Rickettsiales-Rhodospirillales-Sphingomonadales-Rhodobacterales-(Caulobacterales-Parvularculales)- Rhizobiales.,,. Comparative analyses of the sequenced genomes have also led to discovery of many conserved 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.,
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)  and National Center for Biotechnology Information (NCBI) and the phylogeny is based on 16S rRNA-based LTP release 106 by 'The All-Species Living Tree' Project 
♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LSPN)
- "www.ncbi.nlm.nih.gov". Retrieved 2009-03-19.
- Heribert Hirt - Lab times 2008 - Intruder Alert
- Don J. Brenner; George Garrity; James T. Staley (2005). The Proteobacteria: Part A Introductory Essays. シュプリンガー・ジャパン株式会社. pp. 172–. ISBN 978-0-387-24143-2. Retrieved 4 November 2010.
- J.P. Euzéby. "Alphaproteobacteria". List of Prokaryotic names with Standing in Nomenclature (LPSN) . Retrieved 2011-11-17.
- Gupta, R.S. and Mok, A. (2007) Phylogenomics and signature proteins for the alpha Proteobacteria and its main groups. BMC Microbiol. 2007 Nov 28;7(1):106; PMID 18045498
- Williams KP, Sobral BW, Dickerman AW: A robust species tree for the Alphaproteobacteria. J Bacteriol. 2007 Jul;189(13):4578-86. PMID 17483224
- Bazylinski DA, Williams TJ, Lefèvre CT, Berg RJ, Zhang CL, Bowser SS, Dean AJ, Beveridge TJ. (2012) Magnetococcus marinus gen. nov., sp. nov., a marine, magnetotactic bacterium that represents a novel lineage (Magnetococcaceae fam. nov.; Magnetococcales ord. nov.) at the base of the Alphaproteobacteria. Int J Syst Evol Microbiol. doi: 10.1099/ijs.0.038927-0
- Gupta RS: Protein signatures distinctive of Alphaproteobacteria and its subgroups and a model for Alpha proteobacterial evolution. Crit Rev Microbiol 2005, 31: 135. PMID 15986834
- Gupta, R.S. (2000) Phylogeny of Proteobacteria: Relationships to other eubacterial phyla and to eukaryotes. FEMS Microbiol. Rev. 24: 367-402.
- Gupta, R.S. and Sneath, P.H.A. (2007) Application of the Character compatibility approach to generalized molecular sequence data: Branching order of the Proteobacterial subdivisions. J. Mol. Evol. 64: 90-100.
- Sayers et al. "Alphaproteobacteria". National Center for Biotechnology Information (NCBI) taxonomy database . Retrieved 2011-06-05.
- 'The All-Species Living Tree' Project."16S rRNA-based LTP release 106 (full tree)". Silva Comprehensive Ribosomal RNA Database . Retrieved 2011-11-17.
- Alphaproteobacteria at the US National Library of Medicine Medical Subject Headings (MeSH)
- Bacterial (Prokaryotic) Phylogeny Webpage: Alpha Proteobacteria.