Enhancement of nisin production in milk by conjugal transfer of the protease-lactose plasmid pLP712 to the wild strainLactococcus lactisUQ2

Lactococcus lactisUQ2 is a wild nisin A producer isolated from a Mexican cheese that grows poorly in milk. Conjugal matings withL. lactisNCDO712 to transfer the Lac+ Prt+ plasmid pLP712 and selection with nisin and lactose yieldedL. lactisNCDO712 NisA+. Naturally rifampicin resistantL. lactisUQ2Rif was isolated to provide an additional selective marker. The identity of a transconjugantL. lactisUQ2Rif Lac+ was confirmed by RAPD-PCR fingerprinting,nisAPCR amplification, nisin production, presence of pLP712 and phospho-β-galactosidase activity. This strain performed well in milk and synthesised 200IU/mL nisin, 40 times more than the original strain. [PUBLICATION ABSTRACT]