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''Lactococcus lactis'' is a Gram-positive bacterium used extensively in the production of buttermilk and cheese, but has also become famous as the first genetically modified organism to be used alive for the treatment of human disease. ''L. lactis'' cells are cocci that group in pairs and short chains, and, depending on growth conditions, appear ovoid with a typical length of 0.5 - 1.5 µm. ''L. lactis'' does not produce spores (nonsporulating) and are not motile (nonmotile). They have a homofermentative metabolism and have been reported to produce exclusive L-(+)-lactic acid.〔ROISSART, H. and Luquet F.M. Bactéries lactiques: aspects fondamentaux et technologiques. Uriage, Lorica, France, 1994, vol. 1, p. 605. ISBN 2-9507477-0-1〕 However,〔 〕 reported D-(−)-lactic acid can be produced when cultured at low pH. The capability to produce lactic acid is one of the reasons why ''L. lactis'' is one of the most important microorganisms in the dairy industry.〔(Integr8 - Species search results: )〕 Based on its history in food fermentation, ''L. lactis'' has generally recognized as safe (GRAS) status with few case reports of being an opportunistic pathogen.〔Facklam RR, Pigott NE, Collins MD. Identification of Lactococcus species from human sources. Proceedings of the XI Lancefield International Symposium on Streptococci and Streptococcal Diseases, Siena, Italy. Stuttgart: Gustav Fischer Verlag; 1990:127〕 ''L. lactis'' is of 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 (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.〔(Lactococcus_lactis )〕 Other uses that have been reported for this bacterium include the production of pickled vegetables, beer or wine, some breads, and other fermented foodstuffs, such as soymilk kefir, buttermilk, and others.〔(Lactococcus lactis uses )〕 ''L. lactis'' is one of the best characterized low GC Gram positive bacteria with detailed knowledge on genetics, metabolism and biodiversity. ''L. lactis'' is mainly isolated from either the dairy environment or plant material. Dairy isolates are suggested to have evolved from plant isolates through a process in which genes without benefit in the rich medium milk were either lost or down-regulated.〔 This process, also called genome erosion or reductive evolution is also described in several other lactic acid bacteria. The proposed transition from the plant to the dairy environment was reproduced in the laboratory through experimental evolution of a plant isolate that was cultivated in milk for a prolonged period. Consistent with the results from comparative genomics (see references above) this resulted in ''L. lactis'' losing or down-regulating genes which are dispensable in milk and the up-regulation of peptide transport. ==Cheese production== ''L. lactis'' subsp. ''lactis'' (formerly ''Streptococcus lactis'') is used in the early stages for the production of many cheeses, including Brie, Camembert, Cheddar, Colby, Gruyère, Parmesan, and Roquefort. The state Assembly of Wisconsin, also the number one cheese-producing state in the United States, voted in 2010 to name this bacterium as the official state microbe. It would have been the first and only such designation by a state legislature in the nation, however the legislation was not picked up by the Senate.〔(【引用サイトリンク】url=http://www.npr.org/templates/story/story.php?storyId=126370268 )〕 The use of ''L. lactis'' in dairy factories is not without issues. Bacteriophages specific to ''L. lactis'' cause significant economic losses each year by preventing the bacteria from fully metabolizing the milk substrate.〔 Several epidemiologic studies showed the phages mainly responsible for these losses are from the species ''936'', ''c2'', and ''P335'' (all from the family Siphoviridae). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lactococcus lactis」の詳細全文を読む スポンサード リンク
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