B. Citrate synthase enzyme activity measurements performed on cellular lysates. An empty vector control (pCtrl) or vcdP expression plasmids (pVcdP and pVcdP*) were conjugated into V. cholerae wild-type, ΔvcdRP, ΔgltA or F383A GltA backgrounds. Cells were grown in LB medium to stationary phase and subsequently lysed. The protein concentrations of these cellular extracts were measured, and served as input for the assay. The resulting colorimetric product at 412nm was proportional to the enzymatic activity of citrate synthase present. The enzyme kinetics were assayed at 15 second intervals for at least 30 minutes and the activity per milligram of lysate was determined from the initial velocities. 