中圧紫外線の微生物不活化と光・暗回復

本研究では芽胞を形成するB. subtilisにLPUVおよびMPUVを照射して,不活化力およびESS生成数を定量的に評価した。その結果,以下に示す知見が得られた。1)LPUVとMPUVの単位線量当たりのB. subtilis不活化力およびESS生成数はほぼ同じであった。2)紫外線照射したB. subtilis の ESS数およびCFAは光・暗回復するが,回復速度はE. coliなどの芽胞を形成しないほかの細菌と比べて遅かった。3)E. co1iで見られたMPUV照射による回復抑制効果はB. subtilisでは認められなかった。

Some microorganisms are known to possess the ability to repair the DNA lesion by mechanisms such as photoreactivation and dark repair. However, the ability of spore formed microorganisms to perform photoreactivation and dark repair has not been clarified yet in spite of the importance of these phenomena. In previous study, the photoreactivation and dark repair of E. coli were investigated by an endonuclease sensitive site (ESS) assay, which can determine the number of ultraviolet induced pyrimidine dimers in the genomic DNA. Then, in this study, Photoreactivation of Bucillus subtilis spore subsequent to an inactivation by low-pressure or medium-pressure UV lamps was investigated. An endonuclease sensitive site (ESS) assay was applied to determine UV-induced pyrimidine dimers in the genomic DNA of B. subtilis, while a conventional cultivation assay was also used to investigate the colony forming ability (CFA) of B. subtilis. The UV-induced pyrimidine dimers were gradually repaired as the exposure time to fluorescent light increased. Approximately 10% of the ESS were reduced after fluorescent light irradiation at a dose of 540 mJ/cm^2. After photoreactivation, finally achieved inactivation of the CFA ratio of B. subtilis was 1.5 log_<10> subsequent to a 2 log_<10> inactivation by LP or MP lamp. The UV-induced pyrimidine dimers were gradually repaired during storage in the dark. Nonetheless, the number of ESS decreased more slowly in the latter than during the photoreactivation process. Approximately 95% of the ESS were reduced after storage in the dark for 48 hours, indicating B. subtilis has the ability to repair the pyrimidine dimers in the genomic DNA during either exposure to fluorescent light or storage in the dark.

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