Bacillus subtilis
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Bacillus subtilis |
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| ( Ehrenberg 1835) Cohn 1872 |
Bacillus subtilis (Latin bacillum / bacillus , rods; subtilis , fine, plain) or hay bacillus is a widespread gram-positive , rod-shaped, flagellated bacterium . Like all bacteria of the genus Bacillus , B. subtilis is an aerobically growing endospore former .
features
The rod-shaped B. subtilis usually has a size of approx. 2 to 3 µm, the thickness is approx. 0.6 µm. The cells are peritrich , that is, flagellated several times and distributed over the whole cell and can therefore move quickly. The bacterium is surrounded by a gram-positive cell wall that can withstand an internal cell pressure of 20 atmospheres.
Lifestyle and Physiology
B. subtilis is ubiquitous and can be isolated from soil (especially compost ), water and air. Its natural location, however, is the upper layers of the soil. There it is almost constantly exposed to stress and hunger situations due to frequently changing environmental conditions, to which it has to adapt accordingly.
The name hay bacillus indicates that it can be easily enriched in a so-called hay infusion . The generation time is approx. 26 minutes with an optimal supply of nutrients, optimal oxygen supply and an optimal growth temperature of 40 ° C.
B. subtilis feeds chemoorgano-heterotrophic , d. This means that it uses nutrients produced by other living things to generate energy and the body's own substance. B. subtilis colonizes both the rhizosphere and the upper layers of the soil. As a typical putrefactive bacterium, it contributes to the return of organic matter into the food cycle. It has a large arsenal of glucan - (polymer-linked sugars) and protein- degrading enzymes , which are exported from the cell when required.
Dextrose ( glucose ) is the preferred source of carbon and energy . When in sufficient concentration, glucose prevents the activation of genes, the products of which introduce other carbon sources into the metabolism. In the absence of glucose, other sugars or carbon-containing substrates can also be used ( catabolite repression ).
Oxygen is used as the preferred terminal electron acceptor ( cellular respiration ) to generate energy . Here, too, the use of alternative possible substrates is suppressed when oxygen is admitted. Under anaerobic conditions, the cells can still generate enough energy for slow growth if glucose and nitrate are present. If no substrates that can be used as electron acceptors are available, B. subtilis is able to survive exclusively through fermentation metabolism with the production of lactic acid , ethanol , acetoin and 2,3-butanediol .
B. subtilis tries to evade adverse environmental conditions through active locomotion with the help of its scourge. Furthermore, as a vegetatively active cell , B. subtilis can deal with fluctuations in environmental factors via the so-called general stress response. Ultimately, B. subtilis can form endospores through an atypical cell division program that outlast long periods - albeit with the abandonment of the ecological niche and elimination from evolutionary processes. In the light microscope, spores or pre-spores in sporulating cells can be seen as highly light-refracting, oval structures even without coloring.
Another characteristic is the development of competence . Competence in bacteria means the ability to absorb extracellular (foreign) DNA and to integrate it for the purpose of expanding one's own genome or to use it for nutrition.
Systematics
Taxonomically , B. subtilis is one of the eubacteria ( Bacteria ), more precisely to the gram-positive Firmicutes . There it is assigned to the class of Bacilli (low GC content ). This class includes the order of the Bacillales and the Lactobacillales ( lactic acid bacteria ). The order of the Bacillales includes, inter alia, the family of the Bacillaceae with the genus Bacillus , which includes about 150 species (Claus & Berkeley, 1986). In addition, the families of the Staphylococcaceae and the Listeriaceae also belong to the order of the Bacillales. The phylogenetic proximity to pathogens such as staphylococci or listeria makes B. subtilis particularly interesting for research in molecular biology and medicine.
In 1999 the division into subspecies took place , of which three are currently (as of 2014) known:
- B. subtilis subsp. inaquosorum Rooney et al. 2009
- B. subtilis subsp. spizizenii Nakamura et al. 1999
- B. subtilis subsp. subtilis ( Ehrenberg 1835) Nakamura et al. 1999
B. subtilis was described in 1835 by Christian Gottfried Ehrenberg as Vibrio subtilis (curved rod). In 1872 it was renamed Bacillus subtilis (chopsticks) by Ferdinand Julius Cohn and in 1895 Fischer assigned it to a family of the same name.
Importance to humans
B. subtilis was previously used in human medicine to treat chronic skin diseases (dermatoses) or diarrhea , fermentation and putrefaction dyspepsia , gastrointestinal inflammation ( enteritis ) and enterocolitis. In the Red List of the finished medicinal products available in Germany from 2017 (Red List, 2017) only the homeopathic preparations Utilin and Utilin N are listed without indication .
Due to the high heat resistance of B. subtilis spores, they are also used as an indicator in appropriate sterilization processes in pharmacy, medicine and the food industry.
In agriculture, the B. subtilis strain QST 713 is also marketed as a "Serenade" and is used as a biological fungicide for seeds such as cotton, vegetables, peanuts and soybeans. B. subtilis colonizes the root system during germination and prevents fungal growth through competition. The bacteria also produce volatile organic compounds (VOC), which have a fungicidal effect. The production of fungicidal VOCs is very high, especially when glucose is present.
Due to its ability to secrete extracellular enzymes, B. subtilis is used in the biotechnological industry in particular for the production of detergent enzymes (e.g. subtilisin ), but also for the synthesis of riboflavin (vitamin B 2 ) and the antibiotic bacitracin .
The strain Bacillus subtilis var. Natto is used to produce the Japanese specialty natto and similar dishes.
B. subtilis can also be pathogenic under extremely rare circumstances, e.g. B. it can lead to blindness ( panophthalmia ) with eye injuries and penetration of the bacterium .
genetics
B. subtilis is considered to be the best-studied gram-positive bacterium. There are several reasons for this:
- The discovery of the competence by John Spizizen in 1961 made it possible to develop methods for mapping genes via transformation , so that gene maps were already available before the sequencing project began .
- Because of its ability to form endospores, B. subtilis is being investigated as a model system for simple cell differentiation : During sporulation , the regulation of gene expression must be spatially (in the forepore and mother cell) and temporally (it takes about 8 hours for a vegetative cell to turn into a spore arises) are coordinated.
- In contrast to other Bacillus species (e.g. anthracis or B. cereus ), B. subtilis can very rarely have a pathogenic effect - an ideal prerequisite for laboratory work.
- B. subtilis is of industrial importance.
Between 1990 and 1997, his genome was researched and completely sequenced , the sequencing strategy being based on existing gene maps . The circular DNA double strand comprises 4,214,810 base pairs ; the GC content is 43.52%. Of the total sequence , 86.87% of the nucleotides have a coding function, the remaining nucleotides are in z. T. Regions of regulatory importance between the genes. On average, a gene measures 893.41 nucleotides, the longest is 14,793 and the shortest predicted 63 nucleotides long.
literature
- M. Leaver, P. Domínguez-Cuevas, JM Coxhead, RA Daniel, J. Errington: Life without a wall or division machine in Bacillus subtilis . In: Nature . tape 457 , no. 7231 , p. 849-853 , doi : 10.1038 / nature07742 .
Web links
- Bacillus subtilis: description and characterization. ( Memento from March 5, 2005 in the Internet Archive ) Institute for Microbiology in Greifswald
- The Teflon biofilm. US researchers have revealed the secret of the dreaded biofilms, which are responsible for stubborn infections, among other things. Wissenschaft.de, January 11, 2011
Individual evidence
- ↑ a b c d Jean Euzéby, Aidan C. Parte: Genus Bacillus. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved August 9, 2014 .
- ↑ PMID 25653551
- ↑ Werner Köhler (Ed.): Medical Microbiology. 8th edition. Munich / Jena 2001, ISBN 978-3-437-41640-8 .