Figure 3. Effect of ompA inactivation on chemical transformation with a series of concentrations of Ca²⁺.

Competent E. coli cells were prepared with CaCl₂ solution at serial concentrations (5, 10, 20, 30 and 60 mM). Transformation frequencies of BW25113 (solid square symbols) and the ompA mutant JW0940 (BW25113::ompA::kan, open circle symbols) were shown. Each point denotes an average of 2 samples. Error bars denote standard deviation. ^*P value ≦ 0.05; ^**P value ≦ 0.01.