Enhancement of nisin production in milk by conjugal transfer of the protease-lactose plasmid pLP712 to the wild strain Lactococcus lactis UQ2

Lactococcus lactis UQ2 is a wild nisin A producer isolated from a Mexican cheese that grows poorly in milk. Conjugal matings with L. lactis NCDO712 to transfer the Lac+ Prt+ plasmid pLP712 and selection with nisin and lactose yielded L. lactis NCDO712 NisA+. Naturally rifampicin resistant L. lactis UQ2Rif was isolated to provide an additional selective marker. The identity of a transconjugant L. lactis UQ2Rif Lac+ was confirmed by RAPD-PCR fingerprinting, nisA PCR amplification, nisin production, presence of pLP712 and phospho-β-galactosidase activity. This strain performed well in milk and synthesised 200 IU/mL nisin, 40 times more than the original strain. © 2010 Society of Dairy Technology.This work was partially supported by grant BIO2007-65061(Ministerio de Eduación y Ciencia, Spain) and FOMIX CONACYT-QRO (México) grant Qro.-2008-C02-101687. Thanks are given to CONACYT for PhD scholarship to MDGP.Peer Reviewe