Morphogen crosstalk. RH06 cells (expressing TEM1-BLA) or RH01 cells (expressing P99-BLA) were spread evenly on plates containing Tet (15 μg/ml) and IPTG (10 μM or 300 μM, respectively). The level of IPTG was different for the two strains so that their MIC for Amp was the same. Filter paper discs containing Amp or CA were placed at the indicated locations. Both clavulanic acid (CA) and ampicillin (Amp) can induce growth in the presence of Tet. However, CA's differential inhibitory effects of TEM1-BLA and P99-BLA result in different patterns of growth (not shown) and fluorescence.