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 mu M 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.