A Specific Mutation in the Promoter Region of the SilentcelCluster Accounts for the Appearance of Lactose-Utilizing Lactococcus lactis MG1363

Abstract

ABSTRACTTheLactococcus lactislaboratory strain MG1363 has been described to be unable to utilize lactose. However, in a rich medium supplemented with lactose as the sole carbon source, it starts to grow after prolonged incubation periods. Transcriptome analyses showed thatL. lactisMG1363 Lac+cells expressedcelB, encoding a putative cellobiose-specific phosphotransferase system (PTS) IIC component, which is normally silent in MG1363 Lac−cells. Nucleotide sequence analysis of thecelcluster of a Lac+isolate revealed a change from one of the guanines to adenine in the promoter region. We showed here that one particular mutation, taking place at increased frequency, accounts for the lactose-utilizing phenotype occurring in MG1363 cultures. The G-to-A transition creates a −10 element at an optimal distance from the −35 element. Thus, a fully active promoter is created, allowing transcription of the otherwise cryptic cluster. Nuclear magnetic resonance (NMR) spectroscopy results show that MG1363 Lac+uses a novel pathway of lactose utilization.