A propionate-inducible expression system for enteric bacteria

A series of new expression vectors (pPro) have been constructed for the regulated expression of genes in Escherichia coli. The pPro vectors contain the prpBCDE promoter (P-prpB) responsible for expression of the propionate catabolic genes (prpBCDE) and prpR encoding the positive regulator of this promoter. The efficiency and regulatory properties of the prpR-P-prpB, system were measured by placing the gene encoding the green fluorescent protein (gfp) under the control of the inducible P-prpB of E. coli. This system provides homogenous expression in individual cells, highly regulatable expression over a wide range of propionate concentrations, and strong expression (maximal 1,500-fold induction) at high propionate concentrations. Since the prpBCDE promoter has CAP-dependent activation, the prpR-PprpB system exhibited negligible basal expression by addition of glucose to the medium.