Figure 4. PGRPs kill B. subtilis through the CssR-CssS two-component system.

(a) Killing of WT B. subtilis (closed symbols) or ΔcssS or ΔcssR mutants (open symbols) incubated with the indicated PGRPs (100 μg ml⁻¹) or BSA (control) measured by colony counts; means of 3 experiments; the average SEM were 5 – 19% and are not shown; all mutants had significantly reduced sensitivity to killing by all PGRPs (P<0.05 versus WT, t-test). (b) Complementation of PGRP-induced bacterial killing by cssS and cssR inΔcssS or ΔcssR mutants transfected with an empty vector (pGDL48) or pGDL48 containing cssS in forward orientation (cssS), cssS in reverse orientation (cssS-Rev), cssR in forward orientation (cssR), or cssR in reverse orientation (cssR-Rev) and incubated with PGLYRP-1 or PGLYRP-3:4 (100 μg ml⁻¹) for 4 h; the results are % of surviving bacteria in cssS- or cssR-transfected groups compared to groups transfected with control plasmids (empty vector or reverse sequence); means of 3 experiments ± SEM; *, P<0.05 versus control plasmid (t-test).