Effect of glucose or glycerol as the sole carbon source on gene expression from the Salmonella prpBCDE promoter in Escherichia coli.

We have developed an expression system (Salmonella-based pPro system) containing the Salmonella enterica prpBCDE promoter (PprpB) and prpR encoding the positive transcriptional regulator of this promoter. In this study, the transcriptional efficiency of the pPro expression system was measured by placing the gene encoding the green fluorescent protein (gfp) under the control of PprpB and growing cells containing this construct in minimal medium supplemented with glucose or glycerol as a sole carbon source. In wild-type Escherichia coli (E. coli) BL21, the system exhibited high induced expression as well as high background expression; however, in E. coli JSB, a sbm-ygfDGHI deletion mutant of E. coli BL21(DE3), the system showed low background expression and high induced expression. The system exhibited homogeneous expression at the single-cell level, highly regulatable expression over a wide range of propionate concentrations, and fully induced expression at a low propionate concentration relative to that needed to induce the system in rich, undefined medium. The expression system is comparable to the widely used T7 promoter-driven expression systems in glucose or glycerol minimal medium.