Properties of Thymineless Strains of Bacillus megaterium1

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RESUMO

Both Bacillus megaterium KM:T-R1, a strain partially resistant to thymineless death, and strain KM:T-, the parent strain, can satisfy their thymine requirement with either thymidine, 5-methyldeoxycytidine, or 5-methyluridine. Neither strain can use 5-methylcytosine, 5-hydroxymethylcytosine, 5-hydroxymethyluracil, or 5-aminouracil for this purpose. Strain KM:T-R1 requires as little as 0.01 mM thymine for maximum growth, whereas strain KM:T- requires 0.10 to 0.20 mM thymine. Lysogenic KM:T-R1 dies more rapidly in the presence of mitomycin C than the corresponding phage-sensitive strain. Unexpectedly, the lysogenic strain was found to be less sensitive to thymineless death than the phage-sensitive strain. Lysogenic KM:T-R1 is induced by exposure to mitomycin C and by thymineless incubation. It is concluded that thymineless death occurs by a mechanism which is unrelated to phage induction and that a major lethal effect of mitomycin C is probably a consequence of phage induction.

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