The production of bioluminescent lactic acid bacteria suitable for the rapid assessment of starter culture activity in milk

Promoter elements from Lactobacillus casei were isolated with an Escherichia coli promoter probe vehicle and inserted 5' to the luxA/B genes from Vibrio fischeri located within a pCK1-based shuttle vector. Three independent promoter- lux constructs were each used to transform Lactobacillus casei, Lactococcus lactis and Lactococcus lactis subsp. diacetylactis by electroporation. Transformants of all three bacteria which expressed a bioluminescent phenotype in the presence of exogenous dodecanal were obtained. By virtue of monitoring changes in light production, these recombinant micro-organisms could form the basis of a rapid monitoring system for antimicrobial substances in milk active against starter culture bacteria. In addition, the research potential of in vivo bioluminescence for monitoring gene expression in lactic acid bacteria in situ within fermentation systems can now be addressed.