Six putative two-component regulatory systems isolated from Lactococcus lactis subsp cremoris MG1363

The genetic elements specifying six putative two-component regulatory syste ms (2CSs) were identified on the chromosome of Lactococcus lactis MG1363. T hese 2CSs appear to represent distinct loci, each containing a histidine ki nase and response-regulator-encoding gene pair. Transcriptional analysis of the six 2CSs was performed either by generating transcriptional fusions to a reporter gene or by primer extension. Two of the systems appeared to be expressed constitutively at a high level, whilst the remaining four exhibit ed growth-phase-dependent expression. insertional mutagenesis established t hat the two constitutively expressed 2CSs are necessary for normal cell gro wth and/or survival. Mutational analysis of the remaining four systems reve aled that they are implicated in susceptibility to extreme pH. osmotic or o xidative conditions, or the regulation of phosphatase activity in L. lactis .