Sporulation
The sporulation describes the process of spore formation in microorganisms such as bacteria and fungi .
In Bacillus subtilis , nutrient deficiency and cell density are the main factors that trigger sporulation. Metabolic activities cannot be measured in such spores, and they are remarkably resistant to heat (> 100 ° C), drought , UV and X-rays , organic solvents and lytic enzymes and can last for several thousand years and germinate again with improved nutrient supply.
In Bacillus subtilis , sporulation takes place in seven phases, in which up to 200 genes in the organism become active or inactive. The time required for this is around 7–8 hours. In the course of sporulation, dipicolinic acid (pyridine-2,6-dicarboxylic acid) is increasingly formed as a spore-specific substance that is not formed in normal vegetative cells. In addition, more calcium ions are absorbed. The process of sporulation is still not exactly understood today. Many different conditions can lead to sporulation, including insufficient supply or the composition of the medium. For example, manganese in the medium promotes spore formation.
Regulation of sporulation in B. subtilis
Membrane-bound and cytoplasmic histidine kinases are u. a. activated by nutrient deficiency, quorum sensing and DNA damage and phosphorylate the central regulator of sporulation spo0A via a phosphorelay, which activates it. During vegetative growth, the repressor abrB inhibits the sporulation genes. Spo0A now activates genes that are important for sporulation and also inactivates the repressor abrB.
A septum now forms in the mother cell. The phosphatase spoIIE is formed by spo0A, which then activates spoIIAA by removing a phosphate residue. The sigma factor σF is initially inactive and is linked to spoIIAB (anti-σ factor). SpoIIAA now binds to SpoIIAB whereby σF is released. A total of four sigma factors are required for endospore formation . σF and σG activate genes in the developing spore and σE and σK which regulate genes in the mother cell surrounding the spore. The free σF now binds to the RNA polymerase and promotes the transcription of early endopore genes and induces the production of σE in the mother cell. Signals are generated by σE which cause the synthesis of σG in the spore. In addition, σE leads to the production of σK in the mother cell. The last available factors σG (spore) and σK (mother cell) are required for the transcription of the late genes of the sporulation process. Triggered by σK it comes a. for the formation of dipicolinic acid and proteins that lyse nearby cells that have not yet entered the sporulation phase in order to use their cell debris as building materials for the spore. Through σG genes are transcribed in the spore which are important for DNA protection, later germination and the formation of SASP proteins.
literature
- Madigan et al .: Brock Biology of Microorganisms . 13th Edition, Pearson Verlag
- Fuchs (ed.): General microbiology . Thieme Verlag, 2006
Web links
Individual evidence
- ↑ Archived copy ( memento of the original from June 25, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
