Quorum sensing

As quorum sensing ability of individual learning is referred to be able to measure the cell density of the population on chemical communication. It allows the cells to a suspension of activating certain genes only when a certain cell density is exceeded or not. In itself, the term " quorum " dates from the time of the Roman Empire and called in the Senate needed for a vote smallest number of members.

On the study of quorum sensing in the 1990s, Bonnie L. Bassler American Professor was heavily involved.

Quorum sensing is used by bacteria to coordinate processes that would be inefficient if it would only be performed on individual cells, for example, bioluminescence, biofilm formation, or the secretion of virulence factors or antibiotics.

Bacteria that use the quorum sensing, produce and secrete signaling molecules that act as autoinducers or pheromones. This is in the case of autoinducer 1 (AI -1) to N-acyl homoserine lactone ( AHL ). AI-1 is used for intraspecific communication. Autoinducer -2 is a cyclic furanosyl borate diester and is used for communication between different types of bacteria. The nature of the autoinducer -3 is unknown. It is used among others by enterohemorrhagic Escherichia coli.

Autoinducer be continuously released into the medium and can easily pass through cell membranes because they are amphiphilic. When the concentration exceeds a threshold value, set for a specific receptor, the auto-induction and are activated different genes, including those that produce the autoinducer: There is a positive feedback which leads to a complete activation of the receptor, which in turn regulation of other genes result has ( on the right). For example, as the person responsible for the bioluminescence of luciferase is induced.

By Quorum sensing the movement of the bacteria of a species is coordinated in a confined space. Pseudomonas aeruginosa, a pathogen of pneumonia and other infections can live within its host without harming it. However, if it proliferates, he changes his " practice": the cells form biofilms and can lead to the disorder of the host.

The first organisms in which quorum sensing has been observed, the complex myxobacteria and species of the genus Streptomyces. The best known, however, is the bioluminescence of Vibrio fischeri, a bacterium that lives as a symbiont in the luminous organs of a sepia style. Free-living bacteria of this type do not reach the same concentration as within these bodies, so they do not shine there.

Streptococcus pneumoniae used quorum sensing in order to achieve competence.

In the dimorphic fungus Candida albicans farnesol acts as a quorum -sensing molecule. It inhibits hyphal growth at high population density.

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