Pseudomonas

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Pseudomonas
Pseudomonas aeruginosa (secondary electron microscope image, colored)

Pseudomonas aeruginosa
(secondary electron microscope image, colored)

Systematics
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Gammaproteobacteria
Order : Pseudomonadales
Family : Pseudomonadaceae
Genre : Pseudomonas
Scientific name
Pseudomonas
Migula 1894
species

Pseudomonas (fem .: the Pseudomonas, plural for the organisms belonging to the genus: pseudomonads , ancient Greek ψεῦδος = deception, μονᾶς = unit) is a genus of rod-shaped, with polar flagella actively moving, always anaerobic or aerobic respiratory, never fermenting bacteria , gram-negative bacteria . Spores are not formed. The genome of the species P. aeruginosa has been completely sequenced .

Characteristics and metabolism

The size varies between 0.5–1.0 × 1.5–5.0 µm. You can actively move with one or more polar flagella (they are motile). They react negatively in the Voges-Proskauer test and positive in the catalase test. The oxidase test is positive for most species , e.g. B. in Pseudomonas fluorescens , these species thus have a c-type cytochrome.

Pseudomonads are aerobic , meaning they usually need oxygen for their energy metabolism in order to grow. So they use an oxidative energy metabolism with oxygen as an electron acceptor . Sugar is broken down via the Entner-Doudoroff route to generate energy. In most species, nitrate can serve as an alternative electron acceptor instead of oxygen when breathing ( nitrate breathing ). In this case, nitrate (NO 3 - ) is reduced to elemental, molecular nitrogen (N 2 ) ( denitrification ). Since no oxygen is required for nitrate breathing, some species are also able to grow with the exclusion of freely dissolved oxygen ( anoxically ), but this is rarely the case. As representatives of the nitrate-reducing bacteria, the species Pseudomonas aeruginosa , Pseudomonas stutzeri and Pseudomonas denitrificans are used in waste treatment for nitrate elimination . One of the few species that are unable to breathe nitrate is Pseudomonas fluorescens .

Fermentation is not used by this genus as an energy metabolism, all types are so-called nonfermenters (non-fermenters).

Several Pseudomonas species produce siderophores when there is an iron deficiency ; at least 50 different pyoverdines were found, as well as ferrioxamines , which are otherwise only found in actinobacteria .

Cultures of P. aeruginosa are characterized by a blue-green color of the culture medium and a sweet, aromatic odor.

ecology

Pseudomonads are ubiquitous, so ubiquitous in the environment ("puddle germ"). They can be found in the soil, in water, in or on plants and animals. Pseudomonads often live saprotrophically , i.e. from dead organic material. They are also often found in the rhizosphere ; this environment, influenced by the plants, is a good habitat for pseudomonads, they are well adapted to the rhizosphere. Among other things, they move actively, are chemotaxic and resistant to special antibodies in plants. Although some are phytopathogenic , many species also help protect plants by displacing other microorganisms within the rhizosphere. Furthermore, some species such as Pseudomonas putida are associated with arbuscular mycorrhizal fungi and thus even promote the growth of plants. One speaks of plant-growth promoting rhizobacteria ( PGPR ) , in German plant growth-promoting rhizobacteria .

Pathogenicity

The pseudomonads are physiologically highly flexible and can also occur as opportunistic pathogens in already weakened plants and animals. Many Pseudomonas TYPES exist plant pathogenic strains, known as pathovars (phytopathogens). The species Pseudomonas marginalis causes soft rot, mostly on the stem axes. Pseudomonas syringae subsp. savastanoi pv. oleae caused the tubercular disease in the olive tree . Pseudomonas syringae pv. Aesculi is, along with the chestnut leaf miner and, more rarely, Phytophthora species ( Oomycetes ), an important cause of chestnut death , which damages the tree so severely that it becomes susceptible to opportunistic fungi. In animals, u. a. the spot disease of freshwater fish Pseudomonas caused. Species like Pseudomonas aeruginosa can be dangerous for people with compromised immune systems.

The virulence genes are mostly mobile ( plasmids ) and can easily be transferred from one Pseudomonas species to another, but also to more distantly related bacteria. The pseudomonads often have a so-called R-plasmid, which is used to transfer the resistance genes.

The highly dangerous nerve toxin tetrodotoxin (TTX) is produced by some Pseudomonas species. Anhydro-TTX, a variant with a slightly different molecular structure, was also detected in this genus. Pseudomonas and also various vibrions are held responsible for the high toxicity of various puffer fish . The fish presumably ingests the bacteria through food (for example various crustaceans, worms and red algae). Pseudomonas was detected in the puffer fish Takifugu poecilonotus (synonym: Fugu poecilonotus ). It is assumed that there is a symbiosis between the puffer fish and the bacteria. The puffer fish uses the poison for defense or deterrence against predators and in turn provides the bacteria with a suitable habitat. However, the ability of bacteria, especially vibrios, to produce tetrodotoxin has been questioned again.

Clinical significance

The genus is particularly important clinically because the majority of its members are resistant to antibiotics . They are also able to form biofilms (slime) at higher cell densities , which protect them against phagocytes and antibiotics. While bacteria of the genus Pseudomonas rarely cause diseases in people with an intact immune system, they can cause infections of wounds, respiratory and urinary tract, pneumonia , sepsis and heart disease in patients whose immune system is already weakened (for example in hospitals, so-called hospitalism germs ) . Wound infections caused by P. aeruginosa are characterized by their blue-green color and their sweet, aromatic odor. Patients with the hereditary disease cystic fibrosis ( cystic fibrosis ), in whom pneumonia caused by Pseudomonas is the most common cause of death, are particularly at risk .

Acylaminopenicillins such as piperacillin, cephalosporins from the third generation (especially ceftazidime and cefepime; however, ceftriaxone and cefotaxime are not effective), fluoroquinolones , aminoglycosides and carbapenems are suitable for therapy .

Clinical studies on Pseudomonas vaccinations have been carried out for some time, for example by the Austrian biotech company Intercell , which is already testing its vaccine in phase III. The referenced study did not come to the desired result.

literature

Web links

Commons : Pseudomonas  - collection of images, videos and audio files
Wiktionary: Pseudomonas  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Pseudomonas Genome Project
  2. ↑ SA Essén et al .: Siderophore production by Pseudomonas stutzeri under aerobic and anaerobic conditions. In: Applied and Environmental Microbiology , Volume 73, No. 18, September 2007, pp. 5857-5864, PMID 17675442 , PMC 2074896 (free full text). doi: 10.1128 / AEM.00072-07 .
  3. ↑ BJJ Lugt Mountain, GA Bloemberg: Life in the rhizosphere . In: JL Ramos (ed.): Pseudomonas. Kluwer Academic / Plenum Publishers, New York 2004, Volume 1, pp. 403-430.
  4. ↑ Veronica Artursson, Roger D. Finlay, Janet K. Jansson: Interactions between arbuscular mycorrhizal fungi and bacteria and their potential for stimulating plant growth. In: Environmental Microbiology , Volume 8, No. 1, 2006, pp. 1-10, PMID 16343316 .
  5. ^ UK Forestry Commission Joan Webber: Bleeding Canker of Horse Chestnut, accessed September 13, 2016
  6. ↑ Süddeutsche Zeitung Thomas Hahn: Kastaniensterben: My friend, bleeding tree from September 12, 2016, accessed on September 13, 2016
  7. ↑ AC Scoging: biotoxins Marine. In: Journal of Applied Microbiology Symposium Supplement , Volume 84, 1998, pp. 418-508. doi : 10.1046 / j.1365-2672.1998.0840s141S.x .
  8. ↑ M. Yotsu et al: Production of tetrodotoxin and its derivatives by Pseudomonas sp. isolated from the skin of a pufferfish. In: Toxicon , Vol. 25, 1987, pp. 225-228, PMID 3576639 .
  9. ↑ Kendo Matsumura: Reexamination of Tetrodotoxin Production by Bacteria. In: Applied and Environmental Microbiology , September 1995, pp. 3468-3470 ( online ).
  10. ↑ DS Kim, CH Kim: No ability to produce tetrodotoxin in bacteria - authors reply. In: Applied and Environmental Microbiology , May 2001, pp. 2393-2394 ( online ).
  11. ↑ Intercell starts a pivotal Phase II / III efficacy study with its Pseudomonas aeruginosa vaccine candidate ( Memento from February 16, 2013 in the web archive archive.today )
  12. ↑ Vaccine candidate against Pseudomonas aeruginosa vla43 has positive vaccine effect ... not confirmed