Inducible promoter-repressor system from the Lactobacillus casei phage φFSW

With the aim to extend the presently available inducible gene expression systems for lactobacilli, we have isolated a thermoinducible promoter-repressor cassette from the temperate Lactobacillus casei phage phiFSW-T1 in Escherichia coli. The phiFSW-T1 promoter fragment was abutted to the plasmid-borne promoterless beta-glucuronidase (gusA) reporter gene and shown to direct its transcription in L. casei. In addition, the functionality of the promoter-repressor system was verified in the L. casei phiFSW-T1 lysogen by showing that the gus4 reporter gene, controlled by the isolated phiFSW-T1 promoter, was repressed at 28degreesC and expressed at 42degreesC. Moreover, a homology search revealed that the C terminus of the isolated phiFSW repressor shows a high similarity to the small mutS-related domain of the MutS2 protein family that is unprecedented for phage-encoded repressor proteins.