Rhamnose-inducible gene expression in Listeria monocytogenes

Acid production from rhamnose is a characteristic phenotype of Listeria monocytogenes. We report the identification of the rhamnose transport and utilization operon located at lmo2846 to lmo2851, including the rhamnose-dependent promoter P(rha). Expression of reporter genes under control of P(rha) on a single copy integration vector demonstrated its suitability for inducible gene expression in L. monocytogenes. Transcription initiation from P(rha) is dose dependent, and a concentration as low as 100 µM rhamnose was found sufficient for induction. Moreover, P(rha) is subject to glucose catabolite repression, which provides additional options for strict control of expression. Infection of human THP1 macrophages revealed that P(rha) is repressed in intracellular L. monocytogenes, which is explained by the absence of rhamnose in the cytosol and possible interference by catabolite repression. The P(rha) promoter provides a novel and useful tool for triggering gene expression in extracellular L. monocytogenes, whereas intracellular conditions prevent transcription from this promoter.