Abstract
The Gram-positive bacterium Listeria monocytogenes occurs ubiquitously in the environment and infects humans upon ingestion. It encodes four PadR-like repressors, out of which LftR has been characterized previously and was shown to control gene expression in response to the antibiotic aurantimycin produced by other environmental bacteria. To better understand the PadR regulons of L. monocytogenes, we performed RNA-sequencing with mutants of the other three repressors LadR, LstR and Lmo0599. We show that LadR is primarily responsible for the regulation of the mdrL gene, encoding an efflux pump, while LstR and Lmo0599 mainly regulate their own operons. The lstR operon contains the lmo0421 gene, encoding a homolog of the RodA/FtsW protein family. However, this protein does not possess such functionality, as we demonstrate here. The lmo0599 operon contains two additional genes coding for the hypothetical trans-membrane proteins lmo0600 and lmo0601. A striking phenotype of the lmo0599 mutant is its impaired growth at refrigeration temperature. In light of these and other results we suggest that Lmo0599 should be renamed and propose LltR (listerial low temperature regulator) as its new designation. Based on the nature of the PadR target genes we assume that these repressors collectively respond to compounds acting on the cellular envelope.
Highlights
The Gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, which is one of the most serious foodborne bacterial infections in humans
In L. monocytogenes, the PadR-type repressor LftR controls the expression of the lieAB genes encoding another antibiotic efflux pump[20]
We demonstrated that this efflux pump is expressed when L. monocytogenes comes into contact with aurantimycin A21, a depsipeptide antibiotic with very potent bactericidal activity against Gram-positive bacteria and produced by soil-dwelling Streptomyces aurantiacus[22]
Summary
The Gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, which is one of the most serious foodborne bacterial infections in humans. L. monocytogenes frequently enters the food chain due to its wide-spread presence in the soil, in surface waters, on plants and in the gut of various animals[4]. Aggravating this situation, the bacterium has a profound capacity to resist many conditions used to prevent food spoilage. Www.nature.com/scientificreports converts the toxic phenolic acids into less toxic products, thereby conveying resistance to high levels of phenolic acids[12,13] Another well-studied PadR-type repressor, LmrR from Lactococcus lactis, activates expression of the lmrCD multi drug efflux pump genes upon exposure to small toxic compounds like the antibiotic daunorubicin[14,15]. In light of the results obtained we suggest to rename Lmo0599 as LltR (listerial low temperature regulator)
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