FIG 7.

Alternate substitutions for amino acids in the ToxT unstructured region affect responses to bicarbonate. V. cholerae O395 ΔtoxT mutant with plasmid-borne WT or mutant MBP-ToxT was grown in the absence or presence of 36 mM bicarbonate (0.3%). (Top) β-Galactosidase activity from chromosomal tcpA::lacZ in classical strain O395 ΔtoxT produced in the absence or presence of bicarbonate was measured. Statistical significance of ToxT mutant activation of tcpA::lacZ under each condition compared to WT ToxT activation of tcpA::lacZ under the same condition was calculated using Student's t test. Statistical significance of activation by a ToxT mutant without or with effector is denoted by an asterisk or a plus sign, respectively (* or +, P < 0.05). (Bottom) Mean fold increase in activation of tcpA::lacZ upon the addition of bicarbonate is shown for each ToxT mutant. Statistical significance of fold change for an MBP-ToxT mutant compared to fold change for WT MBP-ToxT was determined by Student's t test (*, P < 0.05); the dashed line represents fold change for WT ToxT with the addition of effector. ToxT mutants with results above the line had increased sensitivity to effector, while results below the line represent decreased sensitivity to effector. Error bars represent ± SEM.