A simple expression system for Lactococcus lactis and Enterococcus faecalis

Abstract

A new expression system that can be employedin Lactococcus lactis and Enterococcus faecalis has beenconstructed. It is based on the use of the chromosomalpH-controllable promoter region of the citMCDEFXGoperon and the replicon of pCIT264 plasmid from L. lactisCRL264. Six regions reported as pH-inducible in L. lactiswere evaluated for their ability to drive the expression ofthe lacLM reporter genes of pAK80 vector in order toselect the expression system promoter. The highest levelsof transcriptional activity and acid pH enhancement wereobtained from lactococcal Pcit region. Therefore, thisregion was selected to design an expression system forL. lactis, and the capacity of this system was analized byexpressing the soluble lactococcal enzyme CitM and therotavirus spike-protein subunit VP8*. While in L. lactis theexpression of the different genes was enhanced by the pHdecrease (pH), in E. faecalis we obtained constitutiveexpression levels for the tested genes. Our results confirmthe great potential of this expression system as an alternativeand economic tool for the heterologous proteinproduction of therapeutical or technological interest withoutinducer addition.