Proteobacteria
Encyclopedia
The Proteobacteria are a major group (phylum
) of bacteria
. They include a wide variety of pathogen
s, such as Escherichia
, Salmonella
, Vibrio
, Helicobacter
, and many other notable genera.
Others are free-living, and include many of the bacteria responsible for nitrogen fixation
.
In 1987, Carl Woese
established this grouping, calling it informally the "purple bacteria and their relatives".
Because of the great diversity of forms found in this group, the Proteobacteria are named after Proteus
, a Greek god of the sea, capable of assuming many different shapes, and it is therefore not named after the genus Proteus
.
, with an outer membrane
mainly composed of lipopolysaccharide
s. Many move about using flagella
, but some are nonmotile or rely on bacterial gliding
. The last include the myxobacteria
, a unique group of bacteria that can aggregate to form multicellular fruiting bodies. There is also a wide variety in the types of metabolism
. Most members are facultatively or obligately anaerobic
, chemoautotrophs
, and heterotrophic, but there are numerous exceptions. A variety of genera, which are not closely related to each other, convert energy from light through photosynthesis
. These are called purple bacteria
, referring to their mostly reddish pigmentation.
(rRNA) sequences. The Proteobacteria are divided into six sections, referred to by the Greek letters alpha through zeta, again based on rRNA sequences. These are often treated as classes. The alpha, beta, delta, elpsilon sections are monophyletic, bar the Gammaproteobacteria
due to the Acidithiobacillus
genus is paraphyletic to Betaproteobacteria, according to multigenome alignement studies
, which if done correctly are more precise than 16S
(note that Mariprofundus ferrooxydans
sole member of the Zetaproteobacteria was previously missclassified on NCBI taxonomy). Acidithiobacillus contains 5 species and the sole genus in its order Acidithiobacillales
The divisions of the proteobacteria were once regarded as subclasses (e.g. α-subclass of the Proteobacteria), but are now regarded as classes (e.g. the Alphaproteobacteria).
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
) of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. They include a wide variety of pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s, such as Escherichia
Escherichia
Escherichia is a genus of Gram-negative, non-spore forming, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae. In those species which are inhabitants of the gastrointestinal tracts of warm-blooded animals, Escherichia species provide a portion of the...
, Salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
, Vibrio
Vibrio
Vibrio is a genus of Gram-negative bacteria possessing a curved rod shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Typically found in saltwater, Vibrio are facultative anaerobes that test positive for oxidase and do not form...
, Helicobacter
Helicobacter
Helicobacter is a genus of Gram-negative bacteria possessing a characteristic helix shape. They were initially considered to be members of the Campylobacter genus, but since 1989 they have been grouped in their own genus...
, and many other notable genera.
Others are free-living, and include many of the bacteria responsible for nitrogen fixation
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
.
In 1987, Carl Woese
Carl Woese
Carl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice. He was also the originator of the RNA world hypothesis in 1977,...
established this grouping, calling it informally the "purple bacteria and their relatives".
Because of the great diversity of forms found in this group, the Proteobacteria are named after Proteus
Proteus
In Greek mythology, Proteus is an early sea-god, one of several deities whom Homer calls the "Old Man of the Sea", whose name suggests the "first" , as protogonos is the "primordial" or the "firstborn". He became the son of Poseidon in the Olympian theogony In Greek mythology, Proteus (Πρωτεύς)...
, a Greek god of the sea, capable of assuming many different shapes, and it is therefore not named after the genus Proteus
Proteus (bacterium)
Proteus is a genus of Gram-negative Proteobacteria.-Clinical significance:Three species—P. vulgaris, P. mirabilis, and P. penneri—are opportunistic human pathogens. Proteus includes pathogens responsible for many human urinary tract infections. P. mirabilis causes wound and urinary...
.
Characteristics
All proteobacteria are Gram-negativeGram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
, with an outer membrane
Outer membrane
The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane includes a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's...
mainly composed of lipopolysaccharide
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
s. Many move about using flagella
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
, but some are nonmotile or rely on bacterial gliding
Bacterial gliding
Bacterial gliding is a process whereby a bacterium can move under its own power. This process does not involve the use of flagella, which is a more common means of motility in bacteria...
. The last include the myxobacteria
Myxobacteria
The myxobacteria are a group of bacteria that predominantly live in the soil. The myxobacteria have very large genomes, relative to other bacteria, e.g. 9-10 million nucleotides. Sorangium cellulosum has the largest known bacterial genome, at 13.0 million nucleotides...
, a unique group of bacteria that can aggregate to form multicellular fruiting bodies. There is also a wide variety in the types of metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
. Most members are facultatively or obligately anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...
, chemoautotrophs
Chemotroph
Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic or inorganic . The chemotroph designation is in contrast to phototrophs, which utilize solar energy...
, and heterotrophic, but there are numerous exceptions. A variety of genera, which are not closely related to each other, convert energy from light through photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. These are called purple bacteria
Purple bacteria
Purple bacteria or purple photosynthetic bacteria are proteobacteria that are phototrophic, that is capable of producing energy through photosynthesis...
, referring to their mostly reddish pigmentation.
Taxonomy
The group is defined primarily in terms of ribosomal RNARibosomal RNA
Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
(rRNA) sequences. The Proteobacteria are divided into six sections, referred to by the Greek letters alpha through zeta, again based on rRNA sequences. These are often treated as classes. The alpha, beta, delta, elpsilon sections are monophyletic, bar the Gammaproteobacteria
Gammaproteobacteria
Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria, such as the Enterobacteriaceae , Vibrionaceae and Pseudomonadaceae. An exceeding number of important pathogens belongs to this class, e.g...
due to the Acidithiobacillus
Acidithiobacillus
Acidithiobacillus is a genus of Proteobacteria. Like all Proteobacteria, Acidithiobacillus is Gram-negative. The members of this genus used to belong to Thiobacillus, before they were reclassified in the year 2000....
genus is paraphyletic to Betaproteobacteria, according to multigenome alignement studies
Phylogenomics
Phylogenomics can be regarded as the intersection between the fields of evolution and genomics. The term has been used in multiple ways to refer to some type of analysis involving genome data and evolutionary reconstructions. It is an expansion of earlier phylogenetics...
, which if done correctly are more precise than 16S
16S ribosomal RNA
16S ribosomal RNA is a component of the 30S subunit of prokaryotic ribosomes. It is approximately 1.5kb in length...
(note that Mariprofundus ferrooxydans
Mariprofundus ferrooxydans
Mariprofundus ferrooxydans is a neutrophilic chemolithotrophic gram-negative bacterium which can grow by oxidising ferrous to ferric iron. It is the sole member of the class Zetaproteobacteria in the phylum Proteobacteria...
sole member of the Zetaproteobacteria was previously missclassified on NCBI taxonomy). Acidithiobacillus contains 5 species and the sole genus in its order Acidithiobacillales
Acidithiobacillales
The Acidithiobacillales are a recently recognized order of Proteobacteria with only two genera, placed in separate families. Originally both were included in the genus Thiobacillus, but they are not related to the type species, which belongs to the beta proteobacteria....
The divisions of the proteobacteria were once regarded as subclasses (e.g. α-subclass of the Proteobacteria), but are now regarded as classes (e.g. the Alphaproteobacteria).
- AlphaproteobacteriaAlphaproteobacteriaAlphaproteobacteria is a class of Proteobacteria. Like all Proteobacteria, they are Gram-negative.-Characteristics:The Alphaproteobacteria comprise most phototrophic genera, but also several genera metabolising C1-compounds , symbionts of plants and animals, and a group of pathogens, the...
- BetaproteobacteriaBetaproteobacteriaBetaproteobacteria is a class of Proteobacteria. Betaproteobacteria are, like all Proteobacteria, gram-negative.The Betaproteobacteria consist of several groups of aerobic or facultative bacteria which are often highly versatile in their degradation capacities, but also contain chemolithotrophic...
- GammaproteobacteriaGammaproteobacteriaGammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria, such as the Enterobacteriaceae , Vibrionaceae and Pseudomonadaceae. An exceeding number of important pathogens belongs to this class, e.g...
- DeltaproteobacteriaDeltaproteobacteriaDeltaproteobacteria is a class of Proteobacteria. All species of this group are, like all Proteobacteria, gram-negative.The Deltaproteobacteria comprise a branch of predominantly aerobic genera, the fruiting-body-forming Myxobacteria which release myxospores in unfavorable environments, and a...
- EpsilonproteobacteriaEpsilonproteobacteriaEpsilonproteobacteria is a class of Proteobacteria. All species of this class are, like all Proteobacteria, gram-negative.The Epsilonproteobacteria consist of few known genera, mainly the curved to spirilloid Wolinella spp., Helicobacter spp., and Campylobacter spp...
- ZetaproteobacteriaZetaproteobacteriaZetaproteobacteria is a class of Proteobacteria, which is composed of a sole member, Mariprofundus ferrooxydans described in 2010, falling basal to the gamma and betaproteobacteria and confirmed by other studies...
External links
- http://www.palaeos.org/ProteobacteriaProteobacteria information from PalaeosPalaeosPalaeos.com is a web site on biology, paleontology, cladistics and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of vertebrate palaeontology in the Department of...
] - Proteobacteria – J.P. Euzéby: List of Prokaryotic names with Standing in Nomenclature