V. harveyi TTS and V. cholerae H/A protease production are regulated by E. coli Lsr-mediated AI-2 transport. a, V. harveyi TTS expression was measured using a vopN-lacZ fusion (18 h co-culture). b, V. cholerae hapA expression was measured with a hapA-lux fusion (16 h co-culture). Activities were measured in the following vibrio strains: WT, black bars; LuxS-, striped bars; LuxQ-, white bars. Each vibrio strain was grown in co-culture with the following E. coli strains: WT, LsrR-, LsrK-, and LuxS-, LsrK- double mutant. β-gal units and RLU are as in Fig. 2 and 3. Error bars denote the standard deviations.