EFFECT OF DIPICOLINIC ACID ON THE ULTRAVIOLET RADIATION RESISTANCE OF BACILLUS CEREUS SPORES

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Abstract— The ultraviolet radiation (UV) resistance of B. cereus spores was shown to depend on their content of dipicolinic acid (DPA). Wild‐type spores with decreasing amounts of DPA exhibited increased UV resistance. Similarly, spores devoid of DPA (DPA‐minus), produced by a mutant strain of B. cereus unable to synthesize DPA, were more resistant to UV than mutant spores (DPA‐plus) produced in the presence of exogenously supplied DPA. Resistance of both the wild type and mutant strains to ionizing radiation, however, was unaffected by DPA content. Comparison of the resistance of DPA‐minus and DPA‐plus mutant spores to UV of various wavelengths showed that the greater sensitivity of the latter DPA‐plus spores appeared at wavelengths corresponding to the region of the first molecular absorption band of the calcium chelate of DPA. In the wild type and mutant, thymine photoproducts were produced at a greater rate and to a greater extent in spores with high levels of DPA than in spores with low DPA.The data indicate that DPA transfers energy to DN A in vivo, which leads to the conclusion that DPA occurs in the spore protoplast.

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