title: Negative control of Listeria monocytogenes virulence genes by a diffusible autorepressor.
abstract: Virulence genes from the facultative intracellular pathogen Listeria monocytogenes are controlled by the transcriptional regulator PrfA. Although PrfA synthesis is activated at 37 degrees C, PrfA-dependent expression remains low in rich medium. However, a strong induction of the PrfA regulon is observed when L. monocytogenes is cultured in the presence of activated charcoal. Here, we show that the 'charcoal effect' results from the adsorption of a diffusible autorepressor substance released by L. monocytogenes during exponential growth. Analyses using an L. monocytogenes strain in which the prfA gene is expressed constitutively at 37 degrees C from a plasmid indicate that the autoregulatory substance represses PrfA-dependent expression by inhibiting PrfA activity. PrfA presumably functions via an allosteric activation mechanism. The inhibitory effect is bypassed by a PrfA* mutation that locks PrfA in fully active conformation, suggesting that the autorepressor interferes with the allosteric shift of PrfA. Our data indicate that the listerial autorepressor is a low-molecular-weight hydrophobic substance. We suggest that this diffusible substance mediates a quorum-sensing mechanism by which L. monocytogenes restricts the expression of its PrfA virulence regulon. This autoregulatory pathway could serve L. monocytogenes to ensure the silencing of virulence genes during extracellular growth at 37 degrees C. It may also play a role during intracellular infection, by limiting the damage to the host cell caused by an excess production of cytotoxic PrfA-dependent virulence factors in the PrfA-activating cytosolic compartment.
authors.affiliation: Grupo de Patogénesis Molecular Bacteriana, Unidad de Microbiología e Inmunología, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Ermolaeva
authors.forename: Susana
authors.initials: S
authors.lastname: Novella
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Vega
authors.forename: Maria-Teresa
authors.initials: MT
authors.lastname: Ripio
authors.forename: Mariela
authors.initials: M
authors.lastname: Scortti
authors.forename: José A
authors.initials: JA
authors.lastname: Vázquez-Boland
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002606:Charcoal / Q000494:pharmacology*; D003470:Culture Media; D015964:Gene Expression Regulation, Bacterial; D008089:Listeria monocytogenes / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity*; D010454:Peptide Termination Factors; D011401:Promoter Regions, Genetic / Q000235:genetics; D012329:RNA, Bacterial / Q000032:analysis; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014774:Virulence / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D010454:Peptide Termination Factors; D012329:RNA, Bacterial; D015534:Trans-Activators; D002606:Charcoal