FIG. 5.

Competence pheromone produced in E. coli. The B. subtilis 168 tester strain (BD2876) was grown in the presence of supernatant prepared from E. coli (ED318) carrying a plasmid with the B. subtilis 168 comQ and comX genes. β-Galactosidase activities produced from a srfA-lacZ reporter construct were assayed during growth. BD2876 was grown in the presence of 10-fold (▵), 20-fold (▾), and 100-fold (□) dilutions of the E. coli supernatant. The activities of the B. subtilis producer (BD2833) (▴) and tester (○) strains grown in fresh medium are included for comparison. (The open circles are obscured by the solid squares). Conditioned medium from an isogenic E. coli strain (ED319) carrying the comQ and comX genes in reversed (nonexpressing) orientation (■) exhibited no activity.