The bacterial world consists of many individual strains, some of which are more extensive than others. Proteobacteria are one of the most extensive bacterial strains known to date. The bacterial domain encompasses both numerous pathogens and various nitrogen oxidizers, ie nitrogen-oxidizing bacteria.
The term Proteobacteria derives from the Greek god Proteus. This was, according to say, a form changer. The variety of forms also makes the Proteobacteria. They do not form a morphological group but a genetic grouping. They are of a completely different phenotype. However, their genotype has a genetic similarity through related RNA sequences. Above all, the classification of RNA strands is the decisive criterion for the genetic classification as a bacterial family.
As a common characteristic of the bacterial domain, the cell walls, which consist of low-layered murein with lipopolysaccharides, also apply. All species of the domain are gram negative. With their flagella, some of the species are capable of locomotion. Others are moving on. Proteobacteria generally have no nucleus and thus belong to the prokaryotes.
The bacterial domain of Proteobacteria is divided into five classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria and Epsilonproteobacteria. The first class includes, among others, not sulfur-processing purple bacteria and acetic acid bacteria. The Gammaproteobacteria in turn include sulfur purple bacteria.
Some subgroups of the Proteobacteria Division have anoxigenic photosynthesis as the metabolic pathway under anoxic conditions, such as the purple bacteria and sulfur purple bacteria. They generate energy-rich substances by means of light energy from low-energy substances. This enables them to live in environments under the absence of oxygen.
As starting materials, the bacteria use sulfur, hydrogen, hydrogen sulfide, or other organic molecules as a so-called electron donor. On elemental oxygen, the reaction is not dependent. Also, no elemental oxygen is formed in the reaction.
The Proteobacteria subgroup Myxobacteria is so far the only known group of the domain, which stands between unicellular and multicellular way of life. These bacteria form multicellular fruiting bodies by spores. The fruiting bodies converge with slime molds. The alpha group of Proteobacteria occurs, for example, in nutrient-poor waters. Beta-proteobateria such as the Neisseria are partly pathogens of sexually transmitted diseases and inflammation and naturally colonize the mucus tracts to another part.
The class of gamma proteobacteria includes pathogens for animals, humans and plants, such as the species Pseudomonas. Epsilon proteobacteria, such as Helicobacter pylori, occur in the stomach of humans, where they are involved in the development of gastric ulcers. The heterogeneity of the bacterial domain is extremely broad.
Reference should also be made at this point to the so-called endosymbionten hypothesis. According to this, the endosymbiotic proteobacteria should correspond to the common descent of all mitochondria of eukaryotes. The eukaryotes are said to have arisen by their symbioses prokaryotic precursor organisms. Chemotrophic and phototrophic bacterial species of prokaryotic cells have been hypothesized to have been phagocytosed uptake and have persisted inside the cells, turning them into endosymbionts.
These endosymbionts are said to have evolved to cell organelles within the host cells. The complex of host cell and organelles therein is understood as eukaryotic. The individual cell organelles in this theory are the mitochondria and plastids. Thus, plant, animal and human cell complexes would have their origin in a fusion of prokaryotes. All living beings with a cell nucleus owe their lives to proteobacteria.
While proteobacteria are not all pathogens, they contain an unusually large number of bacteria that are pathogenic to humans. The alpha species Neisseria gonorrhoeae is also called gonococci and is the causative agent of gonorrhea and thus one of the best known sexually transmitted diseases. The bacteria live in the mucous membranes of the urinary and genital organs and are transmitted with sexual intercourse. For men, the infection may be associated with urethritis, itching, purulent discharge, painful urination, and inflammation of the epididymis or prostate gland. Women can also become infertile due to gonorrhea during bacterial adhesion of the uterine and fallopian tube mucosa. In many cases, the symptoms are gone. However, the carriers still pass on the bacteria with the sexual intercourse. Gonococci are also transmitted through oral and anal intercourse when they have colonized the pharynx or rectal mucosa.
The related Proteobacteria Neisseria meningitidis are the most common causative agents of purulent meningitis. Physiologically they colonize the nasopharynx.
Pseudomonads from the class Gammaproteobacteria are opportunistic pathogens that occur on weakened animals and plants. In fish, for example, they call out the spot disease.
For humans, Helicobacter pylori infections are also noteworthy, since they can lead to various gastric diseases and cause increased gastric acid secretion. In addition to the type B gastritis, a gastric carcinoma is now associated with the bacteria. Thus, the infections are a risk factor for stomach ulcers, duodenal ulcers and their degeneration to malignant cancer come into question.