Sarcina (bacterium)
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Sarcina is the name of a genus of obligately anaerobic , gram-positive , coconut (spherical), acid-tolerant bacteria from the family of Clostridiaceae .
features
While many genera from the Clostridiaceae family are rod-shaped bacteria , the cell shape of Sarcina is round, it is cocci . Their appearance in the microscope is typical, which is caused by a special pattern of cell division: the cells do not separate completely after each division. The division itself takes place in alternating planes, each perpendicular to the plane of the previous division. So cubic packages arising out eight or more contiguous cocci, called Paketkokken or sarcinse (see figure).
In the case of the genus Sarcina ventricula , a cellulose layer is also produced around the cell wall , which, similar to an adhesive, holds the cells that have just been divided together, so that packets of up to 64 cocci can be observed attached to one another. The cell size of this genus is also striking; the cocci have a diameter of 4 µm. The generic name can be traced back to these special cell associations (aggregates) ( sarcina from Latin means “bundle”).
Typical representatives of clostridiaceae grow sarcinse obligate anaerobic , with Sarcina ventricula can cultivate microaero- tolerant. They are therefore catalase negative and oxidase negative. The cells are immobile and able to form endospores under unfavorable environmental conditions . The low GC content in the bacterial DNA is noticeable, at 28–31 mol percent. The acid tolerance of this bacterial species should also be emphasized . In order for Sarcina to grow , sugars must be present, which the bacterium ferment under anaerobic conditions in order to generate energy from it.
metabolism
The utilization of carbohydrates takes place in a fermentation . The first step is the gradual breakdown of monosaccharides (simple sugars) such as B. D - Glucose (grape sugar) in glycolysis to pyruvate . Under anaerobic conditions, the NAD + (nicotinamide adenine dinucleotide) consumed in the process must be regenerated, this is done through alcoholic fermentation . One molecule of carbon dioxide is split off from each molecule of pyruvate by the enzyme pyruvate decarboxylase ( EC 4.1.1.1 ). The acetaldehyde produced in this step is very toxic for the organism and is immediately further converted in the following step. The catalyzing enzyme alcohol dehydrogenase ( EC 1.1.1.1 ) reduces acetaldehyde to ethanol , thereby regenerating the NAD + . This metabolic pathway is common in yeasts (such as Saccharomyces cerevisiae ), but actually unusual in bacteria, but was found in Sarcina ventricula . Zymomonas is another genus of bacteria that produces ethanol, but here the degradation of the monosaccharides takes place according to the Entner-Doudoroff path . Other types of Sarcina carry out fermentations similar to the butyric acid fermentation of the Clostridia , in addition to butyric acid , carbon dioxide and elemental hydrogen (H 2 ) are the main products of fermentation.
Occurrence
The bacteria are widespread in the soil and can also be isolated from mud, feces and the stomach . The bacterium can tolerate pH values up to 2, so that it can survive in the acidic environment of the stomach, where S. ventriculi was first found in 1842. In people with certain digestive tract diseases (e.g. doorman's ulcers ), increased bacterial growth can be observed. However, Sarcina is not considered to be pathogenic.
proof
Sarcina can be cultivated well in a nutrient medium that contains peptone , yeast extract and glucose and has a slightly acidic pH of 6.0. Incubation takes place anaerobically at a temperature of 37 ° C. The pH value can be reduced further for selective enrichment. Sediment growth (with a clear supernatant) can be observed in liquid media, which can be attributed to the anaerobic growth. Through anaerobic metabolism, sarcines form mainly ethanol and carbon dioxide in media containing glucose .
The following features are used to differentiate the two Sarcina species S. ventriculi and S. maxima : The cellulose detection in S. ventriculi is positive, in S. maxima negative. S. ventriculi forms ethanol and acetoin , S. maxima butyric acid .
Individual evidence
- ↑ a b c d Hans G. Schlegel: General microbiology. 7th edition. Thieme Verlag, Stuttgart / New York 1992, ISBN 3-13-444607-3 .
- ↑ Horst Bayrhuber, Eckhard R. Lucius (Ed.): Microorganisms in lessons. (= Handbook of practical microbiology and biotechnology. Volume 3). 1st edition. Metzler-Schulbuchverlag, Hanover 1992, ISBN 3-8156-3351-6 .
- ↑ a b c d Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel, 1st edition. Spectrum Academic Publishing House, Heidelberg / Berlin 2000, ISBN 3-8274-0566-1 .
- ↑ a b Catalog of microorganisms on the website of the Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures GmbH. Retrieved February 25, 2013 .