The Betaproteobacteria comprise over 75 genera and 400 species.[2] Together, they represent a broad variety of metabolic strategies and occupy diverse environments, ranging from obligate pathogens living within host organisms to oligotrophic groundwater ecosystems. Whilst most members of the Betaproteobacteria are heterotrophic, deriving both their carbon and electrons from organocarbon sources, some are photoheterotrophic, deriving energy from light and carbon from organocarbon sources. Other genera are autotrophic, deriving their carbon from bicarbonate or carbon dioxide and their electrons from reduced inorganicions such as nitrite, ammonium, thiosulfate or sulfide[1] — many of these chemolithoautotrophic.
Betaproteobacteria are economically important, with roles in maintaining soil pH and in elementary cycling. Some economically important members of the Betaproteobacteria use nitrate as their terminal electron acceptor and can be used industrially to remove nitrate from wastewater by denitrification. A number of Betaproteobacteria are diazotrophs, meaning that they can fix molecular nitrogen from the air as their nitrogen source for growth – this is important to the farming industry as it is a primary means of ammonium levels in soils rising without the presence of leguminous plants.
Four orders of Betaproteobacteria are currently recognised — the Burkholderiales, the Neisseriales, the Nitrosomonadales and the Rhodocyclales.[3] The name "Procabacteriales" was also proposed for an order of endosymbionts of Acanthamoeba, but since they cannot be grown in culture and studies have been limited, the name has never been validly or effectively published, and thus is no more than a nickname without any standing in nomenclature.[4][5]
An extensive reclassification of families and orders of the class based on a polyphasic analysis (including 16S rRNA gene analyses and 53-protein ribosomal protein concatamer analyses using the rMLSTMultilocus sequence typing system) was published in 2017, that removed the order Hydrogenophilales from the class and into a novel class of the "Pseudomonadota", the Hydrogenophilalia.[3] The same study also merged the former order Methylophilales into the Nitrosomonadales.[3]
Betaproteobacteria play an important role in denitrification, removal of phosphorus, and xenobiotic degradation from waste.[7] Various human activities, such as fertilizer production and chemical plant usage, release significant amounts of ammonium ions into rivers and oceans.[8] Ammonium buildup in aquatic environments is potentially dangerous because high ammonium content can lead to eutrophication.[8] Biological wastewater treatment systems, as well as other biological ammonium-removing methods, depend on the metabolism of various Bacteria including members of the Nitrosomonadales of the Betaproteobacteria that perform nitrification to remove excessive ammonia from wastewater. The ammonia is first oxidized into nitrite, further oxidized to nitrate. A variety of other organisms then reduces nitrate into molecular nitrogen gas (denitrification), which leaves the ecosystem and is carried into the atmosphere.[9]
^ abSlonczewski JL, Foster JW (2014). Microbiology: An Evolving Science (3rd ed.). W. W. Norton & Company. pp. 742–3. ISBN9780393123678.
^ abDworkin M, Falkow S, Rosenberg E, Schleifer KH, Stackebrandt E, eds. (2006). The Prokaryotes, Volume 5 - Proteobacteria: Alpha and Beta Subclasses (3rd ed.). Springer. pp. 15–18. doi:10.1007/0-387-30745-1. ISBN9780387254951.
^Dworkin M, Falkow S, Rosenberg E, Schleifer KH, Stackebrandt E, eds. (2006). The Prokaryotes, Volume 5 - Proteobacteria: Alpha and Beta Subclasses (3rd ed.). Springer. p. 11. doi:10.1007/0-387-30745-1. ISBN9780387254951.
^ abBonnet, C.; Volat, B.; Bardin, R.; Degranges, V.; Montuelle, B. (March 1997). "Use of immunofluorescence technique for studying a Nitrobacter population from wastewater treatment plant following discharge in river sediments: First experimental data". Water Research. 31 (3): 661–664. doi:10.1016/S0043-1354(96)00094-2.
