Rhamnose-inducible gene expression in Listeria monocytogenes

Abstract

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 Prha. Expression of reporter genes under control of Prha on a single copy integration vector demonstrated its suitability for inducible gene expression in L. monocytogenes. Transcription initiation from Prha is dose dependent, and a concentration as low as 100 μM rhamnose was found sufficient for induction. Moreover, Prha is subject to glucose catabolite repression, which provides additional options for strict control of expression. Infection of human THP1 macrophages revealed that Prha is repressed in intracellular L. monocytogenes, which is explained by the absence of rhamnose in the cytosol and possible interference by catabolite repression. The Prha promoter provides a novel and useful tool for triggering gene expression in extracellular L. monocytogenes, whereas intracellular conditions prevent transcription from this promoter. © 2012 Fieseler et al.