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( Proteobacteria)
Alpha Proteobacteria
&_160;&_160;&_160;Caulobacterales - e.g. Caulobacter
&_160;&_160;&_160;Kordiimonadales
&_160;&_160;&_160;Parvularculales
&_160;&_160;&_160;Rhizobiales - e.g. rhizobia
&_160;&_160;&_160;Rhodobacterales
&_160;&_160;&_160;Rhodospirillales - e.g. Acetobacter
&_160;&_160;&_160;Rickettsiales - e.g. Rickettsia
&_160;&_160;&_160;Sphingomonadales e.g. Sphingomonas
The Proteobacteria are a major group (phylum) of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera.[1] Others are free-living, and include many of the bacteria responsible for nitrogen fixation. The group is defined primarily in terms of ribosomal RNA (rRNA) sequences, and is named for the Greek god Proteus (also the name of a bacterial genus within the Proteobacteria), who could change his shape, because of the great diversity of forms found in this group.[2] All Proteobacteria are Gram-negative, with an outer membrane mainly composed of lipopolysaccharides. Many move about using flagella, but some are non-motile 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 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. The proteobacteria are divided into five sections, referred to by the Greek letters alpha through epsilon, again based on rRNA sequences. These are often treated as classes. Although it has been suggested previously that the Gamma Proteobacteria are paraphyletic to the Beta Proteobacteria, recent molecular data suggests that this is not so.
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