| Abstract: | Acriflavine-generated mutants of Streptococcus lactis 7962 with various combinations of plasmid molecular masses were screened for nisin production. Nisin was produced by both the wild type and mutants that contained a 17.5-megadalton plasmid, which was obscured by chromosomal fragments. No nisin was produced by plasmid-free mutants. Sucrose fermentation and nisin production were simultaneously expressed. A transconjugant obtained from nisin-producing donor S. lactis 7962 and recipient Leuconostoc dextranicum 181 was a "supernisin" producer. The L. dextranicum Nis+ transconjugant was resistant to S. lactis 7962 phage and vancomycin (greater than 1,000 micrograms/ml), and it contained an extra 17.5-megadalton plasmid. |
