Transposable elements in Lactococci: a review.

Genetic studies have identified the presence of transposable elements within the genus Lactococcus, which includes industrially important microorganisms used in the production of fermented dairy products. Three insertion sequences have been fully characterized in addition to several reports of transpositionlike events. The three insertion sequence elements, ISS1, IS904, and IS981, exhibit the physical and genetic properties characteristic of known insertion sequences. They are closely related to insertion sequences isolated from a wide variety of microorganisms. In lactococci, insertion sequence elements are associated with lactose and sucrose metabolism, proteinase activity, nisin production and immunity, conjugal transfer determinants, and bacteriophage resistance, which are attributes significant for growth in a milk environment. The characteristics, involvement in lactococcal evolution, and recent developments as tools for genetic engineering of the lactococcal elements are discussed.