Lactococcus is a genus of lactic acid bacteria that were formerly included in the genus Streptococcus Group N1. They are known as homofermentors meaning that they produce a single product, lactic acid in this case, as the major or only product of glucose fermentation. Their homofermentative character can be altered by adjusting cultural conditions like pH, glucose concentration, and nutrient limitation. They are gram-positive, catalase negative, non-motile cocci that are found singly, in pairs, or in chains. The genus contains strains known to grow at or below 7˚C.
Five species of Lactococcus are currently recognized along with three subspecies. They are:
L. lactis
L. lactis subsp. lactis
L. lactis subsp. cremoris
L. lactis subsp. hordniae
L. garvieae
L. plantarum
L. raffinolactis
L. piscium
These organisms are commonly used in the dairy industry in the manufacture of fermented dairy products like cheeses. They can be used in single strain starter cultures, or in mixed strain cultures with other lactic acid bacteria such as Lactobacillus and Streptococcus. Special interest is placed on the study of L. lactis subsp. lactis and L. lactis subsp. cremoris as they are the strains used as starter cultures in industrial dairy fermentations. Their main purpose in dairy production is the rapid acidification of milk; this causes a drop in the pH of the fermented product which prevents the growth of spoilage bacteria. The bacteria also play a role in the flavor of the final product. Lactococci are currently being used in the biotechnology industry. They are easily grown at industrial scale up on cheap whey based media. As food grade bacteria they are used in the production of foreign proteins that are applied to the food industry.
Lactococcus lactis is a Gram-positive bacteria used extensively in the production of buttermilk and cheese. L. lactis are cocci that group in pairs and short chains, and depending on growth conditions appears ovoid with typically 0.5 - 1.5 µm in length. L. lactis do not produce spores (non-sporulating) and are not motile (non-motile). They have a homo-fermentative metabolism and have been reported to produce exclusively L(+) lactic acid.However, reported that D(-) lactic acid can be produced when cultured at low pH. The capability to produce lactic acid is one of the reasons why Lactococcus lactis is one of the most important micro-organisms involved in the dairy industry. Generally, it has been considered as an opportunistic pathogen. Even though, the number of clinical cases associated with infections by these microorganisms has increased in the last decade in both humans and animals. L. lactis is a bacterium which has a crucial importance for manufacturing dairy products such as buttermilk and cheeses. When L. lactis ssp. lactis is added to milk, the bacterium uses enzymes to produce energy molecules, called ATP, from lactose.The byproduct of ATP energy production is lactic acid. The lactic acid produced by the bacterium curdles the milk that then separates to form curds, which are used to produce cheese.
Other uses that have been reported for this bacteria include the production of pickled vegetables, beer or wine, some breads and other fermented food-stuffs such as soymilk kefir, buttermilk, .... Nowadays, researchers believe that understanding the physiology and genetic make-up of this bacterium will provide food manufacturers as well as the pharmaceutical industry with invaluable benefits
Lactococcus lactis
Scientific classification
Kingdom: Bacteria
Division: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Lactococcus
Species: L. lactis
Binomial name
Lactococcus lactis
(Lister 1873)
Schleifer et al. 1986
Subspecies
L. l. cremoris
L. l. hordniae
L. l. lactis
L. l. lactis bv. diacetylactis
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