In vivo gene transfer systems and transposons.

The continued development of our understanding and application of the in vivo gene transfer systems, transduction and conjugation, and the more recent use of transposons in lactic acid bacteria is reviewed. The discovery of transduction and its use as a tool for genetic analysis is described. The history of the use of conjugation in lactic acid bacteria is outlined, but more detailed discussion is reserved for in-depth analysis of the conjugation system associated with the lactose plasmids of Streptococcus lactis strains ML3 and C2. This system is notable for an unusual cell aggregation phenotype associated with variants of lactose plasmids capable of high frequency transfer and the complex DNA interactions associated with this property. Recent advances in the use of wide host range conjugation systems, such as that of plasmid pAM beta 1 are described, including the mobilisation of vectors by cointegrate formation and subsequent segregation after transfer. The successful exploitation of conjugation for the construction of bacteriophage-resistant starter cultures is highlighted. A description of transposable genetic elements in the lactic acid bacteria, both insertion sequences and transposons, puts emphasis on the elegant analysis of insertion sequence ISL1 in Lactobacillus casei and on the exploitation of the conjugative transposons Tn916 and Tn919. The latter is especially important for providing a technology to initiate analysis of the bacterial chromosome of the lactic acid bacteria.