Gene-specific PCR amplification of technologically important lactococcal genes

Abstract

A set of gene-specific PCR techniques were used to characterize lactococcal cultures from the LBB collection. Initially the species identification of lactococci was confirmed by targeting the glutamate decarboxylase gene (gadB). PCR amplification of the genes for membrane proteinase (prtP) and citrate permease (citP) was used to select strains which grow rapidly in milk and/or ferment citrate. The prtP + and citP + phenotype was confirmed using differentiating microbiological media. It was proved that the citP + phenotype was always associated with strains of L. lactis ssp. lactis biovar. diacetylactis – an important aroma forming variety of dairy lactococci. In all diacetylactis strains the citP gene was localized on a 8.2 kbp plasmid. The lactococcal cultures were also tested for the presence of nisin synthesis (nisA/Z) genes. Potentially lysogenic lactococcal cultures which carry in their genome the gene of prophage integrase (int) were detected. From the tested strains nearly one third were int-positive. The thermal induction of prophage activity was demonstrated for the int + strain L. lactis ssp. lactis LBB.C1/6.