The Lactococcus lactis nisin-sucrose conjugative transposon Tn5276

The aim of the research described in this thesis was to identify and characterize the genetic element carrying the information for nisin biosynthesis and sucrose proficiency, the nisin-sucrose element. The thesis has the following outline. Chapter 2 describes our current knowledge of nisin genetics and the recent advances in the protein engineering of nisin. The cloning and analysis of several parts of the nisin-sucrose element of L. lactis strain NIZO R5 are described in the next two chapters. Chapter 3 deals with the prenisin gene, nis A, and its surrounding region, which includes the insertion sequence IS 1068 . In Chapter 4, the organization and transcription of the sucrose ( sac ) operon and the characterization of the gene for sucrose-6-phosphate hydrolase are described. The different parts of the nisin-sucrose element were used as DNA probes to investigate the nature and location of this element (Chapter 5). It was shown that the nisin-sucrose element of L. lactis NIZO R5 is a large (70 kb), conjugative transposon, designated Tn 5276. Chapter 6 describes the isolation and analysis of the genes that encode the transposition functions of Tn 5276. The experiments leading to a model for excision and insertion of Tn 5276 are described in Chapter 7. Chapter 8 deals with the distribution and evolution of nisin-sucrose elements in L. lactis . The thesis is completed with the summary and concluding remarks (Chapter 9) and a Dutch summary (Chapter 10).