The Thiotrichales are an order of Proteobacteria, including Thiomargarita namibiensis , the largest known bacterium.
Proteobacteria is a major phylum of gram-negative bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, Yersinia, Legionellales and many other notable genera. Others are free-living (non-parasitic) and include many of the bacteria responsible for nitrogen fixation.
Thiomargarita namibiensis is a Gram-negative coccoid Proteobacterium, found in the ocean sediments of the continental shelf of Namibia. It is the largest bacterium ever discovered, as a rule 0.1–0.3 mm (100–300 μm) in diameter, but sometimes attaining 0.75 mm (750 μm). Cells of Thiomargarita namibiensis are large enough to be visible to the naked eye. Although the species holds the record for the largest bacterium, Epulopiscium fishelsoni – previously discovered in the gut of surgeonfish – grows slightly longer, but narrower.
They also include certain pathogens, such as Francisella tularensis which causes tularemia (rabbit fever).
Francisella is a genus of pathogenic, Gram-negative bacteria. They are small coccobacillary or rod-shaped, nonmotile organisms, which are also facultative intracellular parasites of macrophages. Strict aerobes, Francisella colonies bear a morphological resemblance to those of the genus Brucella.
Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium Francisella tularensis. Symptoms may include fever, skin ulcers, and enlarged lymph nodes. Occasionally, a form that results in pneumonia or a throat infection may occur.
The Rhodospirillales are an order of Proteobacteria, with two families: the Acetobacteraceae and the Rhodospirillaceae.
The Campylobacterales are an order of Proteobacteria which make up the epsilon subdivision, together with the small family Nautiliaceae. Like all Proteobacteria, they are Gram-negative. Most of the species are microaerophilic.
Caulobacteraceae is a family of proteobacteria, given its own order (Caulobacterales) within the alpha subgroup. Like all Proteobacteria, the Caulobacteraceae are gram-negative. Caulobacteraceae includes the genera Asticcacaulis, Brevundimonas, Phenylobacterium and Caulobacter.
The Burkholderiales are an order of Proteobacteria. Like all Proteobacteria, they are Gram-negative. They include several pathogenic bacteria, including species of Burkholderia, Bordetella, and Ralstonia. They also include Oxalobacter and related genera, which are unusual in using oxalic acid as their source of carbon.. Other well-studied genera include Alcaligenes, Cupriavidus, Achromobacter, Comamonas, Delftia, Massilia, Duganella, Janthinobacterium, Polynucleobacter, non-pathogenic Paraburkholderia, Caballeronia, Polaromonas, Thiomonas, Collimonas, Hydrogenophaga, Sphaerotilus, Variovorax, Acidovorax, Rubrivivax and Rhodoferax, and Herbaspirillum.
The Legionellales are an order of Proteobacteria. Like all Proteobacteria, they are Gram-negative. They comprise two families, typified by Legionella and Coxiella, both of which include notable pathogens. For example, Q fever is caused by Coxiella burnetii and Legionella pneumophila causes Legionnaires' disease and Pontiac fever.
The Rhodocyclales are an order of the class Betaproteobacteria in the phylum "Proteobacteria". Following a major reclassification of the class in 2017, the previously monofamilial order was split into three families:
The Methylococcaceae are a family of bacteria that obtain their carbon and energy from methane, called methanotrophs.
Sphingomonadaceae are a family of the Alphaproteobacteria. An important feature is the presence of sphingolipids in the outer membrane of the cell wall. The cells are ovoid or rod-shaped. Others are also pleomorphic, i.e. the cells change the shape over time. Some species are phototrophic.
Desulfovibrionales belong to the Phylum of Proteobacteria, with four families. Like all Proteobacteria, they are Gram-negative. The majority are sulfate-reducing, with the exception of Lawsonia and Bilophila. All members of this order are obligately anaerobic. Most species are mesophilic, but some are moderate thermophiles.
The Syntrophobacterales are an order of Proteobacteria, with two families. All genera are strictly anaerobic. Many of the family Syntrophobacteraceae are sulfate-reducing. Some species are motile by using one polar flagellum.
The Aeromonadales are an order of Proteobacteria, with 10 genera in two families. The species are anaerobic. The cells are rod-shaped. Some species of this order are motile by a single polar flagellum; others are not motile.
The Methylophilaceae are a family of Proteobacteria, given their own order. Like all Proteobacteria, they are Gram-negative. The cells are slightly curved or straight rod-shaped.
The Cardiobacteriaceae are a family of Proteobacteria, given their own order. They are Gram-negative and rod-shaped, with diameters around 0.5 to 1.7 µm and lengths from 1–6 µm.
The Alteromonadales are an order of Proteobacteria. Although they have been treated as a single family, the Alteromonadaceae, they were divided into eight by Ivanova et al. in 2004. The cells are straight or curved rods. They are motile by the use of a single flagellum. Most of the species are marine.
Oceanospirillaceae is a family of Proteobacteria. Most genera in this family live in environments with high concentrations of salt; they are halotolerant or halophilic. They are marine, except Balneatrix which is found in fresh water.
The Alteromonadaceae are a family of Proteobacteria. They are now one of several families in the order Alteromonadales, including Alteromonas and its closest relatives. Species of this family are mostly rod-like shaped and motile by using one polar flagellum.
Betaproteobacteria are a class of gram-negative bacteria, and one of the eight classes of the phylum Proteobacteria.
Alphaproteobacteria is a class of bacteria in the phylum Proteobacteria. Its members are highly diverse and possess few commonalities, but nevertheless share a common ancestor. Like all Proteobacteria, its members are gram-negative and some of its intracellular parasitic members lack peptidoglycan and are consequently gram variable.
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.
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