Mutation induced by drying of Escherichia coli on a hydrophobic filter membrane
Applied and Environmental Microbiology
Drying of Escherichia coli to a required cellular water level was conducted on a hydrophobic membrane at the corresponding relative humidity. Mutation from an arginine auxotroph to the prototroph was induced by drying to a water activity (au,) of 0.53 and below, but not to an a" of 0.75 and above. The critical a". below which mutation occurred in the course of drying was similar to that for induction of deoxyribonucleic acid (DNA) strand breakage in the bacteria. Some ultraviolet or
... olet or -y-irradiation-sensitive strains, e.g., strains carrying recA, recB, and uvrA recA were more sensitive to drying than the wild-type strains or strains carrying uvrA and polA. The DNA strand breakage of every strain was observed to be to a similar extent after drying to an a". of <0.53. The drying-resistant strains repaired the damaged DNA partially during postdrying incubation in a growth medium but not in phosphate buffer solution, while the drying-sensitive strains could not at all. Significant mutation on drying occurred in the wild-type strains, strains carrying uvrA andpolA, but not in strains carrying recA. It is, therefore, concluded that the mutation is caused by errors in rec-dependent repair of the dryinginduced breakage in DNA.