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 φFSW-TI in Escherichia coli. The φFSW-TI promoter fragment was abutted to the plasmid-borne promoterless β-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 φFSW-TI lysogen by showing that the gusA reporter gene, controlled by the isolated φFSW-TI promoter, was repressed at 28°C and expressed at 42°C. Moreover, a homology search revealed that the C terminus of the isolated φFSW repressor shows a high similarity to the small mutS-related domain of the MutS2 protein family that is unprecedented for phage-encoded repressor proteins.