FIG. 4.

Specificity of the QS response. Isogenic B. subtilis tester strains that do not produce ComX were grown in the presence of conditioned media prepared from isogenic producer strains. β-Galactosidase expressed from a srfA-lacZ reporter construct was assayed during growth. The following tester strains were used: BD2876 (derived from B. subtilis 168) (A), BD2877 (derived from B. natto NAF4) (B), BD2962 (derived from B. mojavensis RO-H-1) (C), and BD2963 (derived from B. mojavensis RO-C-2) (D). Conditioned media were from strain 168 (BD2833) (▴), RO-H-1 (BD2913) (▾), RS-B-1 (BD2914) (▿), B. natto NAF4 (BD2915) (⧫), RO-B-2 (BD2936) (▵), and RO-C-2 (BD2937) (■). The open circles in panels C and D show the effect of adding fresh medium to the tester (panel D) or conditioned medium from the tester itself (panel C). Time is in hours before or after the time of transition from exponential to stationary phase. Note that the ordinate scales differ in the four panels.