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.
Highlights
Listeria monocytogenes is a non-sporulating Gram-positive rod, and the causative agent of human Listeriosis, a severe infection transmitted via contaminated food
In L. monocytogenes serovar 1/2 strains, rhamnose is used as a carbon source, it is found as a decoration of the cell wall teichoic acids, and required for adsorption of A118 like bacteriophages [7]
Reporter genes encoding green fluorescent protein and drug resistance were placed under control of Prha on a single-copy integration vector. Employing both in vitro growth and intracellular infection models, we demonstrate that Prha enables quantitative expression of target genes, which can be modulated by the presence and concentration of rhamnose
Summary
Listeria monocytogenes is a non-sporulating Gram-positive rod, and the causative agent of human Listeriosis, a severe infection transmitted via contaminated food. The bacterium serves as a model organism for studies in cellular microbiology, bacterial pathogenicity and virulence, bacteriophage biology, and food safety [1,2,3,4]. Rhamnose is a naturally occurring L-6-deoxy hexose. It is present as a substituent of pectin in plant cell walls where it is periodically attached via a-1, 2-glycosylic linkages to galacturonic acid. In L. monocytogenes serovar 1/2 strains, rhamnose is used as a carbon source, it is found as a decoration of the cell wall teichoic acids, and required for adsorption of A118 like bacteriophages [7]
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