FIG 4.

Response of reporters to low PO₄ concentrations in other proteobacteria. Red and green fluorescence from colonies of V. fischeri, V. cholerae, E. coli, S. enterica, or R. pomeroyi carrying a promoterless parent vector (pJLS27 for vibrios or pJLS71 for nonvibrios) or a vector containing the PhoB-activated promoter (pJLS1088 for vibrios or pJLS137 for nonvibrios) are shown. Strains include V. fischeri ES114 and JLS9 (ΔphoB), V. cholerae AC2764 (ΔtcpA) and AC3236 (ΔphoB), E. coli MG1655, S. enterica MS1868, and R. pomeroyi DSS-3. Strains were grown on agar plates with defined medium containing low or high concentrations of added PO₄ (see Materials and Methods). Colonies of similar sizes were imaged by using a Nikon Eclipse E600 microscope with a 51005v2 filter, which enabled the simultaneous visualization of both the constitutive red fluorescence and the green fluorescence of the reporter.