Leuconostoc mesenteroides

Leuconostoc mesenteroides is a widely used lactic acid bacteria belonging to the genus Leuconostoc. It is gram- positive bacteria, which appear under the microscope as cocci, while they come individually, as diplococci and short chains of cocci as before, where in addition to the typical cocci spherical cell shape, oval cell shapes are observed. Leuconostoc species are widely distributed in the natural environment; they play an important role in various industrial and food fermentations.

Occurrence

Leuconostoc mesenteroides can be isolated from many plant surfaces, where this is the case in intact, but also in the decomposing plant parts, its occurrence on white cabbage is responsible for the sauerkraut fermentation.

Features

As a typical representative of the lactic acid bacteria grow facultative anaerobes ( aerotolerant ), are, however, catalase - negative and oxidase - negative. However, they are able to form cytochromes when cultured on nutrient media containing hemins or blood. In this case, they then exhibit a positive reaction in the oxidase test. Further, a typical lactic acid bacteria, the need for complex flag growth factors and amino acids in the culture.

Leuconostoc mesenteroides does not form endospores and is immobile. These bacteria can utilize many carbohydrates for energy, eg Glucose, fructose, galactose, sucrose, and maltose, and they can not apply the good interestingly lactose. Although they are included among the lactic acid bacteria, because they form lactic acid in the fermentation, but can not grow well in milk. Typical also is the formation of dextran from the sucrose substrate.

The genus name can be traced back to the appearance of colonies ( mean leukos from the Ancient Greek "white" ), the species name refers to the arrangement of the cells to form chains ( from Ancient Greek mesenterion " mesentery " and eidos "appearance "). The genome of the bacterium Leuconostoc mesenteroides subspecies ssp. cremoris ( strain ATCC 19254 ) was completely sequenced in 2009.

The optimum temperature for the cultivation of the bacterium Leuconostoc mesenteroides in the range 20-25 ° C, thus, the bacterium belongs to the mesophilic organisms, with a tendency to Psychrotoleranz. The optimum pH for growth is within the range of pH 6.2 to 6.5.

Metabolism

Under aerobic, anaerobic and microaerophilic conditions, a heterofermentative lactic acid fermentation is performed. Glucose and other hexoses are converted via the pentose phosphate pathway to an equimolar amount of D- lactic acid, ethanol, and carbon dioxide.

Other metabolic pathways involve the conversion of acetyl -CoA to acetoin and diacetyl, wherein the latter of the lactic acid in the preparation of food is important.

Evidence

The bacterium is well cultured in MRS broth is incubated at temperatures of up to 30 ° C. Biochemical tests for identification include, as already described, the catalase and oxidase test, and typical tests of a "colorful series", this is Leuconostoc behaves mesenteroides urease - negative, negative for nitrate reduction, negative for indole formation and positive Voges - Proskauer in the reaction, if it is a subspecies, the acetoin and diacetyl forms. A work based on the rapid determination system in miniature (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 a variety of industrial and food fermentations. In the production of silage and sauerkraut fermentation is usually done by naturally present in the plant parts strains of bacteria; to avoid faulty fermentation, Leuconostoc mesenteroides is in the industrial production of sauerkraut but also often added.

In dairies is the subspecies of Leuconostoc mesenteroides ssp. cremoris specifically used as a starter culture in cheese and butter production. In the heterofermentative lactic acid fermentation Acetyl -CoA is a metabolite that may result from the ethanol. Another pathway of Leuconostoc mesenteroides ssp. cremoris but also enables the conversion to diacetyl, this is a flavoring agent, which is responsible for the typical odor butter. Therefore, these subspecies, in the industrial production of butter and buttermilk - added to the aromatization to naturally produce diacetyl - but also of yogurt.

The formation of dextran gums leads sugarcane Infection with the bacterium Leuconostoc mesenteroides to problems in the extraction of cane sugar ( sucrose) from the plant. In the sugar industry Leuconostoc mesenteroides therefore feared as " frog spawn bacterium " because sucrose-containing solutions are transformed by the dextran formation in a jelly - like mass. On the other hand, offer dextrans many uses, such as so that this exo- polysaccharide can be industrially extracted from cultures of these bacteria as a blood plasma substitute.