Leuconostoc mesenteroides
| Leuconostoc mesenteroides | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Leuconostoc mesenteroides | ||||||||||||
| ( Tsenkovskii , 1878) Van Tieghem , 1878 |
Leuconostoc mesenteroides is a widespread species of lactic acid bacteria belonging to the genus Leuconostoc . These are gram-positive bacteria thatappearas cocci in the microscopic image; they occur individually, as diplococci and as short chains of cocci, whereby oval cell shapes can also be observed in addition to the spherical cell shape typical of cocci. Leuconostoc species are widespread in the natural environment; they playan important rolein various industrial and food fermentations .
Occurrence
Leuconostoc mesenteroides can be isolated from many plant surfaces, whereby this is the case with intact, but also with decomposing plant parts; its occurrence on white cabbage is responsible for the fermentation of sauerkraut .
features
As typical representatives of lactic acid bacteria , they are microaerophilic (aerotolerant) or strictly anaerobic, but are catalase- negative and oxidase- negative. However, they are able to form cytochromes when cultured on nutrient media containing heme or blood . In this case they show a positive reaction in the oxidase test . Another characteristic of lactic acid bacteria is the need for complex growth factors and amino acids during cultivation.
Leuconostoc mesenteroides does not form endospores and is immobile. These bacteria can use numerous carbohydrates for energy, e.g. B. glucose , fructose , galactose , sucrose and maltose , although interestingly they cannot utilize lactose well. Although they are counted among the lactic acid bacteria because they form lactic acid in fermentation , they can not grow well in milk . The formation of dextran from the sucrose substrate is also typical .
The genus name can be traced back to the appearance of the colonies ( leukos from ancient Greek means "white"), the species name refers to the arrangement of the cells in chains (from ancient Greek mesenterion "mesentery" and eidos "appearance"). The genome of the subspecies Leuconostoc mesenteroides ssp. cremoris (strain ATCC 19254) was completely sequenced in 2009.
The optimum temperature for the cultivation of Leuconostoc mesenteroides is in the range of 20-25 ° C, so the bacterium is one of the mesophilic organisms with a tendency to psychrotolerance . The optimal pH for growth is in the range of pH 6.2 to 6.5.
metabolism
A heterofermentative lactic acid fermentation is carried out under aerobic , anaerobic and microaerophilic conditions . Glucose and other hexoses are converted to an equimolar amount of D - lactic acid , ethanol and carbon dioxide via the pentose phosphate pathway .
Other metabolic pathways include the conversion of acetyl-CoA to acetoin and diacetyl , the latter being important in the production of lactic acid foods.
proof
The bacterium can be cultivated well in MRS broth, which is incubated at temperatures of up to 30 ° C. Biochemical tests for identification include, as already described, the catalase and oxidase test , as well as typical tests from a "colorful series" , Leuconostoc mesenteroides urease behaves negatively, negative in nitrate reduction , negative in indole formation and positive in the Voges-Proskauer reaction if it is a subspecies that forms acetoin and diacetyl. A rapid determination system based on this in miniature format ( Analytical Profile Index ) for the determination of streptococci is commercially available and also includes the detection of Leuconostoc species.
Industrial importance
Bacteria of the species Leuconostoc mesenteroides play an important role in various industrial and food fermentations . In the production of silage and sauerkraut , fermentation is usually carried out by bacterial strains naturally present on the parts of the plant; In order to avoid incorrect fermentation, Leuconostoc mesenteroides is often added to the industrial production of sauerkraut .
The subspecies Leuconostoc mesenteroides ssp. cremoris is specifically used as a starter culture in cheese and butter production. In heterofermentative lactic acid fermentation , acetyl-CoA is a metabolite from which ethanol can be produced. Another metabolic pathway of Leuconostoc mesenteroides ssp. However, cremoris also enables the conversion to diacetyl , which is a flavoring substance that is responsible for the typical butter smell. This is why this subspecies is added to the industrial production of butter and buttermilk - but also yoghurt - for flavoring purposes in order to naturally produce diacetyl.
The formation of dextran slime leads to problems in extracting cane sugar (sucrose) from the plant when sugar cane is infested with Leuconostoc mesenteroides . In the sugar industry, Leuconostoc mesenteroides is therefore feared as a "frog spawn bacterium", since sucrose-containing solutions are transformed into a jelly-like mass by the formation of dextran . On the other hand, dextrans offer many uses, e.g. B. as blood plasma substitute, so that this exo - polysaccharide can be obtained industrially from cultures of this type of bacteria.
When brewing beer, Leuconostoc mesenteroides is generally undesirable, as the dextrans formed lead to the beers "stretching", i.e. to increased viscosity.
Individual evidence
- ↑ a b c d e f g h Hans G. Schlegel: General microbiology. 7th edition. Thieme Verlag, Stuttgart / New York 1992, ISBN 3-13-444607-3 .
- ↑ a b c d e f g h i j Horst Bayrhuber, Eckhard R. Lucius (Ed.): Microorganisms in the classroom. (= Handbook of practical microbiology and biotechnology. Volume 3). 1st edition. Metzler-Schulbuchverlag, Hanover 1992, ISBN 3-8156-3351-6 .
- ↑ Halil Dündar: CHARACTERIZATION AND PURIFICATION OF A BACTERIOCIN PRODUCED BY LEUCONOSTOC MESENTEROIDES SUBSP. CREMORIS. THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY, September 2006, accessed on February 1, 2020 .
- ↑ Leuconostoc mesenteroides cremoris ATCC 19254 on the website of the Genoms Online Database (GOLD). Retrieved February 24, 2013 .
- ↑ Catalog Microorganisms on the website of the Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures GmbH. Retrieved February 24, 2013 .
- ^ ID 32 biochemical identification; Streptococci on the website of bioMérieux Deutschland GmbH. (No longer available online.) Archived from the original on January 5, 2014 ; Retrieved February 24, 2013 . 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.
- ^ Back, Werner .: Demolition of the beer brewery . 7th, act. and exp. WILEY-VCH, Weinheim 2005, ISBN 3-527-31035-5 .
