Lactococcus lactis
Lactococcus lactis
Lactococcus lactis is a Gram-positive bacterium used for the production of buttermilk, sour milk, kefir, and cheese.
- 2.1 Outer systematics
- 2.2 Internal systematics
Features
Appearance
The cells are of Lactococcus lactis cocci forming pairs or short chains, and will appear in dependence on the growth conditions, oval with a length of 0.5-1.5 microns. They do not form Überdauerungsformen as endospores and are not motile.
Growth and metabolism
The optimum temperature of the growth and proliferation of Lactococcus lactis is in the range of 28-32 ° C, so the L. lactis one of mesophilic organisms. It grows even at 10 ° C but not at 45 ° C, it is used as a discriminating criterion to the more thermophilic strains of Streptococcus.
L. lactis performs a homofermentative lactic acid fermentation, producing thereby L-( ) -lactic acid. At a lower pH - value and the D-form can be prepared. Lactic acid produced during the lactic acid fermentation, which benefits the bacteria and their enzymes in the breakdown of lactose energy.
Genetics
The genome of several bacteria strains of the species Lactococcus lactis has already been completely sequenced. The size of the genome of all previously studied representative is 2370-2810 kilobase pairs (kb ), which is only 55 % of the genome size of Escherichia coli. There are about 2300-2600 proteins annotated.
System
Outer systematics
Lactococcus is a genus of Gram- positive coccus. The generic name is " Germanized " as Laktokokkus (plural: lactococci ) written. Lactococcus is closely related to the genus Streptococcus, both of which belong to the family Streptococcaceae. Previously they were - to the genus Streptococcus - together with the enterococci of faecal origin. To distinguish the common pathogenic species of the types used for human -hazardous, and partially also in the food industry, in 1986, a separation into the genera Streptococcus, Lactococcus, and Enterococcus. They belong together with other species of bacteria to the order of the lactic acid bacteria. However, even the old names still find use as Streptococcus lactis is the Basonym for Lactococcus lactis, as it was originally assigned to the genus Streptococcus.
Inside systematics
Currently (2013 ), four Lactococcus lactis subspecies ( subspecies ) of the Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures GmbH in the Prokaryotic Nomenclature up-to -date ( " Prokaryotic Nomenclature up to date " ) listed. This compilation includes all according to the Bacteriological Code validly published names and takes into account the validation list of the International Journal of Systematic and Evolutionary Microbiology.
- Lactococcus lactis (Lister 1873) Schleifer et al. 1986 comb. nov. (formerly Streptococcus lactis ) Lactococcus lactis subsp. cremoris ( Orla -Jensen 1919) Schleifer et al. 1986 comb. nov. (previously Streptococcus cremoris )
- Lactococcus lactis subsp. hordniae ( Latorre - Guzman et al., 1977) Schleifer et al. 1986 comb. nov. (previously Lactobacillus hordniae )
- Lactococcus lactis subsp. lactis (Lister 1873) Schleifer et al. 1986 comb. nov. (formerly Streptococcus lactis )
- Lactococcus lactis subsp. tructae Pérez et al. 2011 subsp. nov.
Industrial importance
The ability to produce lactic acid is one of the reasons why Lactococcus lactis one of the most important microorganisms in the production of dairy products. The lactic acid provides a coagulation of the milk and allows the separation of curd and whey. Using Lactococcus lactis subsp. lactis are made kefir, cottage cheese and other cheese products. Lactococcus lactis subsp. cremoris is used in the production of cultured milk ( sour milk ), sour cream products such as sour cream, sour cream butter, butter milk, curd and cheese. Other applications of L. lactis in food processing include the production of pickled vegetables, beer, wine or bread.
Furthermore, is obtained with L. lactis engineered the preservative nisin.
The use of L. lactis in dairies is not without problems. Specific bacteriophages cause by the inhibition of L. lactis significant economic losses.