Tartrolon sensing and detoxification by theListeria monocytogenes timABRresistance operon

Abstract

AbstractListeria monocytogenesis a foodborne bacterium that naturally occurs in the soil. Originating from there, it contaminates crops and infects farm animals and their consumption by humans may lead to listeriosis, a systemic life-threatening infectious disease. The adaptation ofL. monocytogenesto such contrastive habitats is reflected by the presence of virulence genes for host infection and other genes for survival under environmental conditions. Among the latter are ABC transporters for excretion of antibiotics produced by environmental competitors, however, most of these transporters have not been characterized. Here, we generated a collection of promoter-lacZfusions for genes encoding ABC-type drug transporters ofL. monocytogenesand screened this reporter strain collection for induction using a library of natural compounds produced by various environmental microorganisms. We found that thetimABRlocus (lmo1964-lmo1962) was induced by the macrodiolide antibiotic tartrolon B, which is synthesized by the soil myxobacteriumSorangium cellulosum. Tartrolon B resistance ofL. monocytogeneswas dependent ontimAB, encoding the ATPase and the permease component of a novel ABC transporter. Moreover, transplantation oftimABwas sufficient to confer tartrolon B resistance toBacillus subtilis. Expression of thetimABRlocus was found to be auto-repressed by the TimR repressor, whose repressing activity was lost in the presence of tartrolon B. We also demonstrate that tartrolon sensitivity was suppressed by high external potassium concentrations, suggesting that tartrolon acts as potassium ionophore. Our results help to map the ecological interactions of an important human pathogen with its co-residing species within their joint natural reservoir.ImportanceListeria monocytogenesis an environmental bacterium that can cause listeriosis in humans when ingested. The genome of this bacterium contains many genes encoding putative ATP binding cassette transporters with unknown function. Presumably, these transporters serve the excretion of antimicrobial compounds produced by co-residing species competing withL. monocytogenesfor nutrients and habitats. We here fused thelacZreporter gene to the promoters of these transporter genes and screened a natural compound library for activating substances. We discovered that tartrolon B activates expression of theL. monocytogenes timABRoperon, encoding the TimAB exporter and the TimR repressor. Tartrolon B is an antibiotic produced by the soil-dwelling myxobacteriumSorangium cellulosum. We elucidate how thetimABRgenes mediate sensing and detoxification of this antibiotic. This represents the first known mechanism of tartrolon resistance and may help to better define the natural reservoir ofL. monocytogenes.