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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. [2] Others are free-living, and include many of the bacteria responsible for nitrogen fixation. Because of the great diversity of forms found in this group, the Proteobacteria are named after Proteus, the Greek god of the sea, capable of assuming many different shapes.[1] [3]
[edit] CharacteristicsAll 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, chemautotrophs, 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. [edit] TaxonomyThe group is defined primarily in terms of ribosomal RNA (rRNA) sequences. 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 Gammaproteobacteria are paraphyletic to the Betaproteobacteria, recent molecular data suggests that this is not so. 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).[4].
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