Everything about The Proteobacteria totally explained
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. 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.
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.
Cavalier-Smith has postulated that Proteobacteria is part of the bacterial clade
Gracilicutes.
Sections/Classes
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 isn't so.
Alphaproteobacteria
The Alphaproteobacteria comprise most phototrophic genera, but also several genera metabolising C1-compounds (for example
Methylobacterium), symbionts of plants (for example
Rhizobia) and animals, and a group of dangerous pathogens, the
Rickettsiaceae. Moreover the precursors of the
mitochondria of eukaryotic cells are thought to have originated in this bacterial group. (See
endosymbiotic theory.)
Betaproteobacteria
The Betaproteobacteria consist of several groups of aerobic or facultative bacteria which are often highly versatile in their degradation capacities, but also contain chemolithotrophic genera (for example the ammonia-oxidising genus
Nitrosomonas) and some phototrophs (genera
Rhodocyclus and
Rubrivivax). Beta Proteobacteria play an important role in nitrogen fixation in various types of plants, oxidizing ammonium to produce nitrite- an important chemical for plant function. Many of them are found in environmental samples, such as waste water or soil. Pathogenic species within this class are the
Neisseriaceae (
gonorrhea and meningoencephalitis) and species of the genus
Burkholderia.
Gammaproteobacteria
The Gammaproteobacteria comprise several medically and scientifically important groups of bacteria, such as the
Enterobacteriaceae,
Vibrionaceae and
Pseudomonadaceae. An exceeding number of important pathogens belongs to this class, for example
Salmonella (
enteritis and
typhoid fever),
Yersinia pestis (plague),
Vibrio (cholera),
Pseudomonas aeruginosa (lung infections in hospitalized or
cystic fibrosis patients), and (food poisoning).
Deltaproteobacteria
The Deltaproteobacteria comprise a branch of predominantly aerobic genera, the fruiting-body-forming
myxobacteria, and a branch of strictly anaerobic genera, which contains most of the known
sulfate- (
Desulfovibrio,
Desulfobacter,
Desulfococcus,
Desulfonema, etc.) and
sulfur-reducing bacteria (for example
Desulfuromonas) alongside several other anaerobic bacteria with different physiology (for example ferric iron-reducing
Geobacter and syntrophic
Pelobacter and
Syntrophus species).
Epsilonproteobacteria
The Epsilonproteobacteria consist of only a few genera, mainly the curved to spirilloid
Wolinella,
Helicobacter, and
Campylobacter. Most of the known species inhabit the digestive tract of animals and humans and serve as
symbionts (
Wolinella in
cows) or
pathogens (
Helicobacter in the stomach,
Campylobacter in the duodenum). There have also been numerous environmental sequences of epsilons recovered from
hydrothermal vent and
cold seep habitats.
Further Information
Get more info on 'Proteobacteria'.
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