Betaproteobacteria
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''Betaproteobacteria'' are a class of
Gram-negative bacteria Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...
, and one of the six classes of the
phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...
'' Pseudomonadota'' (synonym Proteobacteria).


Metabolism

The ''Betaproteobacteria'' comprise over 75
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
and 400 species. Together, they represent a broad variety of metabolic strategies and occupy diverse environments, ranging from obligate
pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
s 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 Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
and their electrons from reduced
inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...
ions such as nitrite,
ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
,
thiosulfate Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...
or
sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...
— 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 Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
as their terminal electron acceptor and can be used industrially to remove
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
from wastewater by denitrification. A number of ''Betaproteobacteria'' are diazotrophs, meaning that they can fix molecular
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
from the air as their nitrogen source for growth – this is important to the farming industry as it is a primary means of
ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
levels in soils rising without the presence of leguminous plants.


Phylogeny

The ''Betaproteobacteria'' are one of the eight classes that make up the '' Pseudomonadota'' ("Proteobacteria"). The ''Betaproteobacteria'' are most closely related to the '' Gammaproteobacteria'', ''
Acidithiobacillia ''Acidithiobacillia'' is a class of the phylum '' Pseudomonadota'' ("Proteobacteria"). Its type order, the ''Acidithiobacillales'', was formerly classified within the '' Gammaproteobacteria'', and comprises two families of sulfur-oxidising autot ...
'' and '' Hydrogenophilalia'', which together make up a
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
which has previously been called " Chromatibacteria". Four orders of ''Betaproteobacteria'' are currently recognised — the '' Burkholderiales'', the '' Neisseriales'', the '' Nitrosomonadales'' and the '' Rhodocyclales''. The name " Procabacteriales" was also proposed for an order of
endosymbiont An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualism (biology), mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), whi ...
s 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. 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 rMLST Multilocus 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''. The same study also merged the former order '' Methylophilales'' into the '' Nitrosomonadales''. The four orders of the ''Betaproteobacteria'' are: * '' Burkholderiales'' (type order) comprises the families '' Burkholderiacae'' (type family), '' Alcaliginaceae'', '' Comamonadaceae'', '' Oxalobacteraceae'' and '' Sutterellaceae''. They exhibit a range of morphologies, including rods, curved rods, cocci, spirillae and multicellular 'tablets'. Both heterotrophs and photoheterotrophs are found along with some facultative autotrophs. * '' Neisseriales'' comprises the families '' Neisseriaceae'' (type family) and '' Chromobacteriaceae''. Their morphologies include cocci, curved rods, spirillae, rods, multicellular ribbons and filaments. Most are heterotrophs with some facultative methylotrophs and chemolithoheterotrophs. * '' Nitrosomonadales'' comprises the families '' Nitrosomonadaceae'' (type family), '' Methylophilacae'', '' Thiobacillaceae'', '' Sterolibacteriacae'', '' Spirillaceae'' and '' Gallionellaceae''. Their morphologies include rods, spirillae and curved rods. Most are chemolithoautotrophs with some methylotrophs and heterotrophs * '' Rhodocyclales'' comprises the families '' Rhodocyclaceae'' (type family), '' Azonexaceae'' and '' Zoogloeaceae''. Morphologies include rods, curved rods, rings, spirillae and cocci. Most species are heterotrophs with some photoheterotrophs and chemolithoautotrophs.


Role in disease

Some members of the ''Betaproteobacteria'' can cause disease in various
eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
organisms, including humans. For example, '' Neisseria gonorrhoeae'' and '' N. meningitidis'' cause gonorrhea and
meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasion ...
respectively, while '' Bordetella pertussis'' causes whooping cough. Other members of the class infect plants, such as '' Ralstonia solanacearum'' which causes bacterial wilt disease of over 250 plant species, '' Burkholderia cepacia'' which causes bulb rot in onions, and '' Xylophilus ampelinus'' which causes necrosis of grapevines.


Economic importance

''Betaproteobacteria'' play an important role in denitrification, removal of phosphorus, and xenobiotic degradation from waste. Various human activities, such as fertilizer production and chemical plant usage, release significant amounts of ammonium ions into rivers and oceans. Ammonium buildup in aquatic environments is potentially dangerous because high ammonium content can lead to eutrophication. 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 Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
. A variety of other organisms then reduces nitrate into molecular
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
gas ( denitrification), which leaves the ecosystem and is carried into the atmosphere.


See also

* ''
Acidithiobacillia ''Acidithiobacillia'' is a class of the phylum '' Pseudomonadota'' ("Proteobacteria"). Its type order, the ''Acidithiobacillales'', was formerly classified within the '' Gammaproteobacteria'', and comprises two families of sulfur-oxidising autot ...
'' * '' Gammaproteobacteria'' * '' Hydrogenophilalia''


References


External links

* {{Taxonbar, from=Q136674 Bacteria classes