The indicated point mutations were introduced into the E. coli O9a Wzt–Wzm transporter and O-antigen transport was assayed by silver staining of the whole-cell lysate. Ag, silver-stained SDS–PAGE. Wzt and MBP were detected immunologically to monitor transporter expression and as a loading control, respectively. All results showing a phenotype have been confirmed at least three times as technical replicates. Time, period after inducing Wzt–Wzm expression in minutes.