| Betaproteobacteria | |
|---|---|
 | |
| Colonies ofBurkholderia pseudomallei, one of many pathogenic Betaproteobacteria. | |
Scientific classification | |
| Domain: | Bacteria |
| Kingdom: | Pseudomonadati |
| Phylum: | Pseudomonadota |
| Class: | Betaproteobacteria |
| Orders | |
Burkholderiales | |
Betaproteobacteria are a class ofGram-negative bacteria, and one of the six classes of thephylumPseudomonadota (synonym Proteobacteria).[1]
TheBetaproteobacteria comprise over 75genera and 400 species.[2] Together, they represent a broad variety of metabolic strategies and occupy diverse environments, ranging from obligatepathogens living within host organisms to oligotrophic groundwater ecosystems. Whilst most members of theBetaproteobacteria areheterotrophic, deriving both their carbon and electrons from organocarbon sources, some arephotoheterotrophic, deriving energy from light and carbon from organocarbon sources. Other genera areautotrophic, deriving their carbon frombicarbonate orcarbon dioxide and their electrons from reducedinorganicions such asnitrite,ammonium,thiosulfate orsulfide[1] — many of thesechemolithoautotrophic.
Betaproteobacteria are economically important, with roles in maintainingsoil pH and in elementary cycling. Some economically important members of theBetaproteobacteria usenitrate as theirterminal electron acceptor and can be used industrially to removenitrate fromwastewater bydenitrification. A number ofBetaproteobacteria arediazotrophs, meaning that they can fix molecularnitrogen from the air as their nitrogen source for growth – this is important to the farming industry as it is a primary means ofammonium levels in soils rising without the presence ofleguminous plants.
TheBetaproteobacteria are one of the eight classes that make up thePseudomonadota ("Proteobacteria"). TheBetaproteobacteria are most closely related to theGammaproteobacteria,Acidithiobacillia andHydrogenophilalia, which together make up ataxon which has previously been called "Chromatibacteria".[2]
Four orders ofBetaproteobacteria are currently recognised — theBurkholderiales, theNeisseriales, theNitrosomonadales and theRhodocyclales.[3] The name "Procabacteriales" was also proposed for an order ofendosymbionts ofAcanthamoeba, 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 orderHydrogenophilales from the class and into a novel class of the "Pseudomonadota", theHydrogenophilalia.[3] The same study also merged the former orderMethylophilales into theNitrosomonadales.[3]
The four orders of theBetaproteobacteria are:
Some members of theBetaproteobacteria can cause disease in variouseukaryotic organisms, including humans. For example,Neisseria gonorrhoeae andNeisseria meningitidis causegonorrhea andmeningitis respectively, whileBordetella pertussis causeswhooping cough. Other members of the class infect plants, such asRalstonia solanacearum which causes bacterial wilt disease of over 250 plant species,Burkholderia cepacia which causes bulb rot in onions, andXylophilus ampelinus which causesnecrosis of grapevines.[6]
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 toeutrophication.[8] Biological wastewater treatment systems, as well as other biological ammonium-removing methods, depend on the metabolism of variousBacteria including members of theNitrosomonadales of theBetaproteobacteria that performnitrification to remove excessive ammonia from wastewater. The ammonia is first oxidized intonitrite, further oxidized tonitrate. A variety of other organisms then reduces nitrate into molecularnitrogen gas (denitrification), which leaves the ecosystem and is carried into the atmosphere.[9]