Evaluation of the genetic expression diversity in lactococci, development of tools and peptidases application.

The expression of a gene depends primarily, on the activity of its promoter . It can vary as a function of several parameters such as environmental con ditions and cellular factors. The cellular factors are sometimes different in independent isolates as a result of the genetic diversity. Few genetic t ools are available in lactococci to study the variability of gene expressio n and we have thus developed vectors for this purpose. These vectors contai n bacterial luciferase as reporter genes. The luciferase activity can be fo llowed by light emission in milk or other natural media. Moreover, these Ve ctors can be integrated on the chromosome in lactococci and are easily tran sferable by conjugation. Transcriptional fusions with peptidase promoters o f Lactococcus lactis have shown that general aminopeptidase gene promoters have stronger transcription than other promoters. The versatility of these genetic tools to study the variability of gene expression in Lactococcus la ctis is presented via the study of the pepC promoter.