[Simultaneous reversion for genes thy, dra and drm in Bacillus thuringiensis]

The reversions of mutations in genes thy, dra (deoxyriboaldolase) and drm (phosphodeoxyribomutase) were studied in Bacillus thuringiensis var. galleriae 351. In this strain, both dra and drm mutants are sensitive to the presence of thymidine (Tds). In addition to the reversions for one of the properties (thymine requirement or sensitivity to thymidine), the simultaneous reversions for both properties (Thy + Tdr) were indicated. The frequency of Thy + Tdr revertants varied from 10(-4) to 10(-8), depending on both a selection method and the conditions of preliminary cultivation. The Thy + Tdr revertants had a rough (R) colony morphology in 100% of the cases, though the parental strains were of smooth (S) colony morphology. Selection for R variants, visually or by means of screening for Tg4 resistant or tetracycline resistant clones, resulted in detecting double Thy + Tdr revertants in 100% of the cases. The parental Thy - Tds phenotype restored after R leads to S conversion which occurred at the frequency 10(-7) to 10(-8) and might be detected by means of streptomycine selection.