FIGURE 5.

The proposed mechanism for survival of E. coli in glutaraldehyde. (A) % Glutaraldehyde conversion (degradation) by the evolved strains, knockouts, and their respective parental strains. The standard error is shown for duplicates. The p-values are shown above the brackets for each comparison (one-tailed t-test for independent means). (B) Growth of evolved strains, knockouts, and their respective parental strains in 250 μM of non-toxic 1,5-pentanediol. Such concentration was four to six times higher than the maximum concentration of glutaraldehyde in which evolved strains were able to grow at the otherwise same growth conditions. The standard error is shown for duplicates. (C) Michaelis-Menten kinetics of YqhD at different glutaraldehyde concentrations. K_M of YqhD for glutaraldehyde was calculated to be 0.55 ± 0.09 mM (SEM; n = 3 biological replicates). 0.6 mM NADPH and 10 μg of purified YqhD was used. Inset figure shows purified YqhD on native PAGE. (D) Mechanism of glutaraldehyde tolerance in E. coli MG1655: ALE selected for mutated versions of the transcription factor yqhC, which increased expression of the operon containing yqhD and dkgA. Increased expression of yqhD contributed to the survival of E. coli cells in the presence of glutaraldehyde due to the conversion of such toxic chemical to the innocuous corresponding alcohol, 1,5 pentanediol, by the aldehyde dehydrogenase YqhD.