Proteobacteria are a genetic domain of Gram-negative bacteria that share few phenological similarities and are characterized by extreme heterogeneity. Many classes of Proteobacteria perform anaerobic photosynthesis for energy or are known to be nitrogen oxidizers. The bacterial domain includes some pathogens, such as the causative agent of gonorrhea.
What are proteobacteria?
The bacterial world consists of many individual strains, some of which are more extensive than others. Proteobacteria form one of the most extensive bacterial strains known to date. The bacterial domain encompasses numerous pathogens as well as various nitrogen oxidizers, i.e., nitrogen-oxidizing bacteria. The name Proteobacteria is derived from the Greek god Proteus. According to legend, Proteus was a shape changer. The variety of shapes also makes the Proteobacteria. They do not form a morphological group, but a genetic grouping. They are of entirely different phenotype. However, their genotype has a genetic commonality through related RNA sequences. Above all, the systematics of the RNA strands is the decisive criterion for the genetic classification as a bacterial family. In addition, the common characteristic of the bacterial domain is considered to be the cell walls, which consist of low-layered murein with lipopolysaccharides. All species of the domain are gram-negative. Through their flagella, some of the species are capable of locomotion. Others move along in a gliding manner. Proteobacteria generally do not possess a nucleus and are thus classified as prokaryotes.
Occurrence, distribution, and characteristics
The bacterial domain of Proteobacteria is divided into five classes: alphaproteobacteria, betaproteobacteria, gammaproteobacteria, deltaproteobacteria, and epsilonproteobacteria. The former class includes non-sulfur processing purple bacteria and acetic acid bacteria. Gammaproteobacteria, in turn, include sulfur purpure bacteria. Some subgroups from the Proteobacteria division perform anoxygenic photosynthesis as a metabolic pathway under anoxic conditions, such as the purple bacteria and sulfur purple bacteria. They produce high-energy substances from low-energy substances using light energy. This enables them to live in environments in the absence of oxygen. As starting materials, the bacteria use sulfur, hydrogen, hydrogen sulfide, or other organic molecules as so-called electron donors. The reaction does not rely on elemental oxygen. Nor is elemental oxygen formed during the reaction. The Proteobacteria subgroup Myxobacteria is so far the only known group in the domain that is intermediate between unicellular and multicellular life. These bacteria form multicellular fruiting bodies by spores. The fruiting bodies converge with slime molds. For example, the alpha group of Proteobacteria occurs in nutrient-poor waters. Beta-Proteobateria such as Neisseria are partly pathogens of sexually transmitted diseases and inflammations and another part naturally colonize the mucous tract. The class of Gamma-Proteobacteria includes pathogens for animals, humans, and plants, such as the species Pseudomonas. Epsilonproteobacteria, such as Helicobacter pylori, are found in the stomach of humans, where they are involved in the development of gastric ulcers. The heterogeneity of the bacterial domain is extremely broad. At this point, reference should also be made to the so-called endosymbiont hypothesis. According to this, endosymbiont proteobacteria should correspond to the common descent of all mitochondria from eukaryotes. According to this hypothesis, eukaryotes evolved by symbiosis of their prokaryotic precursor organisms. Chemotrophic and phototrophic bacterial species of prokaryotic cells are hypothesized to have undergone uptake by phagocytosis and to have continued to live inside the cells, becoming endosymbionts. These endosymbionts are hypothesized to have progressed to become cell organelles within host cells. The complex of host cell and organelles within it is understood to be a eukaryote. 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 would thus owe their life to proteobacteria.
Diseases and ailments
Proteobacteria, although not consistently pathogens, include an unusually large number of bacteria that are pathogenic to humans. The alpha species Neisseria gonorrhoeae is also called gonococcus and is the causative agent of gonorrhea, making it one of the best-known STDs. The bacteria live in the mucous membranes of the urinary and genital organs and are transmitted with sexual intercourse. For men, the infection can be accompanied by urethritis, itching, purulent discharge, pain when urinating, and inflammation of the epididymis or prostate. Women can also become infertile due to gonorrhea when the lining of the uterus and fallopian tubes become bacterially stuck together. In many cases, symptoms do not develop. However, carriers still pass on the bacteria with sexual intercourse. Gonococci are also transmitted through oral and anal sex when they have colonized the mucosa of the throat or rectum. The related Proteobacteria Neisseria meningitidis are the most common pathogens of purulent meningitis. They physiologically colonize the nasal and pharyngeal cavities. Pseudomonads from the class of Gammaproteobacteria are opportunistic pathogens that occur on weakened animals and plants. On fish, for example, they cause spotted fever. For humans, infections with Helicobacter pylori are also worth mentioning, as they can result in various gastric diseases and cause increased gastric acid secretion. In addition to type B gastritis, gastric carcinoma is now also associated with the bacteria. Thus, the infections are thought to be a risk factor for gastric ulcers, duodenal ulcers, and their degeneration into malignant cancer.
