INDUCTION OF UNIQUE TANDEM-BASE CHANGE MUTATIONS IN BACTERIAL-SPORES EXPOSED TO EXTREME DRYNESS

Despite the remarkable resistance to desiccation, Bacillus subtilis sp ores manifest indications of DNA damage when being kept in an extremel y dry environment made by high vacuum. Spores of strain TKJ3422 (uvrA1 0 spl-1 recA4) with triple repair defects lost colony-forming capacity dependent on the duration and strength of the exposure. Mutations to rifampicin resistance were induced in the spores of the strain HA101 w ith wild-type repair capability and the strain TKJ6312 (uvrA10 spl-1) with double repair defects. The majority of nalidixic acid-resistant m utations induced by the exposure to high vacuum belonged to one partic ular allele gyrA12 carrying a tandem-base change, 5'-CA to 5'-TT, at c odon 84 of the gyrA gene coding for DNA gyrase subunit A. This allele has never been found among more than 500 mutants obtained by various t reatments other than vacuum exposure. These results indicate forced de hydration of DNA in the microenvironment of the spore core causes uniq ue damage leading to lethal and mutagenic consequences.