σ B ‐dependent protein induction in Listeria monocytogenes during vancomycin stress

Listeria monocytogenes is a food‐borne pathogen that can survive under a wide range of environmental and energy stress conditions. The general stress response controlled by σ B largely contributes to stress resistance in L. monocytogenes . Moreover, the bacterial cell wall is the first defense against cellular stress and as such is the target of numerous antibiotics. We therefore hypothesize that σ B contributes to monitoring the integrity of cell walls. We evaluated σ B activity in wild type and Δ sigB mutant L. monocytogenes containing reporter fusions (σ B ‐dependent opuCA promoter and a lacZ reporter gene) during the early exponential growth phase by measuring the specific activity of β‐galactosidase after vancomycin (2 μg mL −1 final concentration) stress. σ B activity is significantly induced only in the wild‐type strain by addition of vancomycin. In addition, we identified σ B ‐dependent vancomycin‐inducible proteins using LC‐ESI‐MS/MS analysis. Two independent proteomic analyses confirmed the minimum twofold upregulation of 18 vancomycin‐inducible σ B ‐dependent stress response proteins in the wild‐type strain compared with the Δ sigB mutant. The functions of these proteins are associated with cell wall biogenesis, intracellular transport, general stress response, cell metabolism and virulence. These results suggest that the σ B protein may contribute to the monitoring of cell wall integrity.