QUORUM SENSING-CONTROLLED GENE-EXPRESSION IN LACTIC-ACID BACTERIA

Quorum sensing in lactic acid bacteria (LAB) involves peptides that ar e directly sensed by membrane-located histidine kinases, after which t he signal is transmitted to an intracellular response regulator. This regulator in turn activates transcription of target genes, that common ly include the structural gene for the inducer molecule. The two-compo nent signal-transduction machinery has proven to be indispensable for transcription activation and production of several autoinducers found in LAB, which are predominantly bacteriocins or bacteriocin-like pepti des. In the nisin autoregulation process in Lactococcus lactis the Nis K protein acts as the sensor for nisin and the NisR protein as the res ponse regulator, activating transcription of target genes. The cis-act ing elements for NisR were identified as the nisA and nisF promoter fr agments and these were further analysed for inducibility. Based on thi s knowledge efficient nisin-controlled expression (NICE) systems were developed for several different lactic acid bacteria. A promising appl ication of the NICE system is the development of autolytic starter lac tococci, which will lyse in an early stage during cheese ripening ther eby facilitating the release of intracellular enzymes which can contri bute to flavour formation. (C) 1998 Elsevier Science B.V. All rights r eserved.