Sigma B contributes to PrfA-mediated virulence in Listeria monocytogenes

Abstract

Transcription of the Listeria monocytogenes positive regulatory factor A protein (PrfA) is initiated from either of two promoters immediately upstream of prfA (prfAp(1) and prfAp(2)) or from the upstream plcA promoter. We demonstrate that prfAp(2) is a functional sigma(B)-dependent promoter and that a sigB deletion mutation affects the virulence phenotype of L. monocytogenes. Thus, the alternative sigma factor sigma(B) contributes to virulence in L. monocytogenes.

FIG. 1.

Map of the L. monocytogenes plcA-prfA region.

FIG. 2.

Intracellular growth of L. monocytogenes ΔsigB and prfA promoter mutant strains in mouse macrophage-like J774 cells. The data are shown as the mean CFU per coverslip and standard errors (bars) of six independent experiments. Equal numbers of viable cells were added to each well at infection initiation. At each time point, the numbers of recovered ΔsigB ΔprfAp₁ and ΔprfAp₁ ΔprfAp₂ strains were lower than those of wild-type 10403S, ΔprfAp₁, or ΔprfAp₂. ▪, 10403S; ○, ΔprfAp₂; •, ΔprfAp₁; ▵, ΔsigB ΔprfAp₁; ▴, ΔprfAp₁ ΔprfAp₂.