TAXONOMY: Bacteria -> Terrabacteria group -> Firmicutes -> Bacilli -> Lactobacillales -> Streptococcaceae -> Lactococcus
'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 such as 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 7o C., These organisms are commonly used in the dairy industry in the manufacture of fermented dairy products such as 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. Lactococci are currently being used in the biotechnology industry. They are easily grown at industrial scale on whey-based media. As food-grade bacteria, they are used in the production of foreign proteins that are applied to the food industry. Spheres or ovoid cells occur singly, in pairs, or in chains, and are often elongated in the direction of the chain. Gram-stain-positive. Endospores are not formed. Nonmotile. Not β-hemolytic. Facultatively anaerobic; catalase-negative. Growth at 10°C but not at 45°C. Usually grows in 4% (w/v) NaCl with the exception of Lactococcus lactis subsp. cremoris which only tolerates 2% (w/v) NaCl. Chemo-organotroph. Metabolism fermentative. The predominant end product of glucose fermentation is l(+)-lactic acid. May contain menaquinones. Most strains react with group N antisera (Lancefield, 1 9 3 3). Nutritional requirements are complex and variable. The peptidoglycan is of group A with l-lysine as diamino acid in position 3 of the peptide subunit. Typical inhabitants of plants, animals, and their products.
DNA G+C content (mol%): 34–43 (Tm).
Type species: Lactococcus lactis
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]