Figure 9

Transcriptional regulation of cadBA by CadC in vitro or in vivo. A Expression profiles of cadBA operon in normal and acidic conditions. E. tarda TX01 and TX01ΔcadC in logarithmic growth phase was culture in normal LB (pH = 7.0) or in acidic LB (pH = 5.5) for 1 h, then the expression of cadB, cadA, and cadBA were examined by RT-qPCR. For convenience of comparison, the expression level of cadBA operon in wild type TX01 set as 1. B The promoter activity of cadBA operon was regulated by CadC in vitro. DH5α/pSC418/pJR21 and DH5α/pSC418/pJR21C were streaked and cultured on an X-gal plate at pH 5.5 in the presence of 5 mM L-lysin. The depth of blue indicates the strength of promoter activity. C The promoter activity of cadBA operon was regulated by CadC in vivo. The wild-type TX01 and TX01ΔcadC mutant carrying the reporter plasmid pJR21-418-lx were cultured to the exponential phase. Then strains were transferred acid LB media (pH = 5.5) supplemented with 5 mM l-lysine and grown for 1 h. The transcriptional regulation of promoter of cadBA was assessed by measuring luciferase activity. Data are the means of three independent experiments and presented as means ± SEM (N = 3). N, the number of times the experiment was performed. **, P < 0.01; *, P < 0.05.