sac A and nis A genes are not always linked in Lactococcus lactis subsp. lactis strains

Sixty-seven lactococcal strains arising from dairy habitat were screened for the presence of the sucrose 6-phosphate hydrolase gene by polymerase chain reaction. Of the strains tested, 35.8% were able to ferment sucrose as well as to harbour the sucrose- 6-phosphate hydrolase gene, even though they were unable to produce nisin as well as to show the nisin structural gene. After pulsed-field gel electrophoresis and hybridisation all Suc‡Nis3 strains exhibited physical linkage between sacA gene and the left end of lactococcal transposons (Tn5276 or Tn5301) without linkage to nisin genes. However, we were unable to transfer the sacA gene as well as to detect Suc3 derivatives from Suc‡Nis3 strains after conjugation and curing experiments.