Sarcina (genus)
- Sarcina maxima Lindner 1888
- Sarcina Goodsir ventriculi 1842
Sarcina is the name of a genus obligate anaerobic, gram-positive, coccoid ( spherical ), acid-tolerant bacteria from the family of Clostridiaceae.
Features
While it is in many genera of the family of Clostridiaceae is rod-shaped bacteria, the cell shape of Sarcina is round, it is cocci. Typical is their appearance under the microscope that comes through a particular pattern of cell division into existence: the cells do not separate completely after each division. The pitch itself is, however, in alternate layers are perpendicular to the preceding partition level. This results in cubical packets of eight or more contiguous cocci, so-called Paketkokken or sarcinse ( see figure).
In the genus Sarcina ventricula also takes place around the production of a cellulose layer around the cell wall, similar to a glue holding together the just divided cells, so that you can watch stapled packets of up to 64 cocci together. Further striking is the cell size of this genus, the cocci have a diameter of 4 microns. The genus name can be attributed to this particular cell aggregates (aggregates ) attributed ( sarcina from the Latin meaning " bundle ").
As a typical representative of the Clostridiaceae grow sarcinse obligate anaerobes, with Sarcina ventricula can also cultivate microaerophilic tolerant. They are thus catalase negative and oxidase negative. The cells are immobilized and capable of forming endospores under unfavorable environmental conditions. In the bacterial DNA of low GC content is striking, he is 28-31 mole percent. These is also the acid tolerance of this bacterial genus. For the growth of Sarcina sugar must be present, which ferments the bacteria under anaerobic conditions, in order to extract energy.
Metabolism
The utilization of carbohydrates takes place in a fermentation. Initially carried out for the phasing of monosaccharides ( simple sugars ) such as D -glucose (dextrose ) in glycolysis to pyruvate. The consumed here NAD ( nicotinamide adenine dinucleotide ) must again be regenerated under anaerobic conditions, this is done by the alcoholic fermentation. From each molecule of pyruvate, one molecule of carbon dioxide by the enzyme pyruvate decarboxylase ( EC 4.1.1.1 ) is cleaved. The heat generated in this step, acetaldehyde is highly toxic to the organism and is further reacted immediately in the following step. The catalyzing enzyme alcohol dehydrogenase ( EC 1.1.1.1 ) reduces acetaldehyde to ethanol, while the NAD is regenerated. This pathway is in yeasts ( such as Saccharomyces cerevisiae) common, but is actually unusual in bacteria, but was found in Sarcina ventricula. Zymomonas is another genus of bacteria that produces ethanol, however, takes place here the degradation of monosaccharides by the Entner- Doudoroff pathway. Other Sarcina species cause similar fermentations of butyric acid fermentation by clostridia, in addition to butyric acid are carbon dioxide and elemental hydrogen ( H2), here the main products of fermentation.
Occurrence
The bacteria are common in soil and also can be isolated even from mud, feces and stomach. The bacteria can tolerate up to pH 2, so that the survival in the acidic environment of the stomach is possible here p ulcer was found for the first time in 1842. In people with certain diseases of the digestive tract (eg ulcers porter ) is sometimes increased growth of bacteria detected. However, Sarcina is not considered pathogenic.
Evidence
Sarcina is easy to cultivate in a nutrient medium containing peptone, yeast extract and glucose and which has a slightly acidic pH of 6.0. The incubation is carried out anaerobically at a temperature of 37 ° C. Selective enrichment of the pH can be further reduced. In liquid media, a sediment growth is observed ( in clear supernatant), which can be traced back to the anaerobic growth. Through anaerobic metabolism sarcinse form in glucose-containing media, especially ethanol and carbon dioxide.
To differentiate the two Sarcina species S. ulcer and S. maxima following features are used: the cellulose proof in S. ulcer is positive, in S. maxima negative. S. ulcer forms of ethanol and acetoin, S. maxima butyric acid.