Genetics of lactic acid bacteria with special reference to lactococci.

Lactic acid bacteria play an important role in the manufacture of fermented foods. Genetic studies have made these microorganisms, particularly lactococci, accessible to genetic manipulation. The instability of key metabolic traits of lactococci has been explained by the presence of plasmid DNA species. Most genetic interest has been focused to solve the quoted instability and the sensitivity to bacteriophage infection. At the same time, gene transfer systems have been developed and specific genes with commercial significance have been identified and cloned. Lactic acid bacteria can be also used as production organisms of heterologous proteins, e.g. chymosin, lysozyme.