FIG 8.

Effect of CdaAR on autolysis. (A) Autolysis assay of L. monocytogenes cdaAR mutant strains in the presence and absence of penicillin. Strains EGD-e (wild type), LMJR45 (ΔcdaR), LMJR46 (IcdaA), and LMJR65 (ΔcdaR IcdaA) were grown in BHI broth with or without 1 mM IPTG at 37°C until an OD₆₀₀ of 0.8. Cells were harvested and resuspended in 50 mM Tris-HCl (pH 8.0) with or without 25 μg/ml penicillin. The decline in optical densities was recorded photometrically and is expressed as relative average values. Standard deviations are calculated from an experiment performed in triplicate. *, P < 0.05, data points at which differences in autolysis rates in the presence of penicillin between LMJR46 without IPTG and LMJR46 with IPTG and between LMJR65 without IPTG and LMJR65 with IPTG were statistically different. (B) Autolysis of L. monocytogenes strains EGD-e (wt) and LMJR45 (ΔcdaR) in the presence of 2.5 μg/ml lysozyme. Average values and standard deviations were calculated from three independent experiments. *, P < 0.05, statistically significant differences. (C) Suppression of the cdaA-dependent growth defect by osmoprotection of growth conditions. Strains EGD-e (wild type) and LMJR46 (IcdaA) were pregrown in BHI broth (containing 1 mM IPTG for LMJR46) at 37°C and used to inoculate fresh BHI broth (without IPTG) containing or not containing 2% NaCl. OD₆₀₀ values were measured in hourly intervals.