NASA Ames Research Center, Moffett Field, CA 94035-1000, USA.
J Photochem Photobiol B. 2011 Feb 7;102(2):140-5. doi: 10.1016/j.jphotobiol.2010.10.002. Epub 2010 Oct 23.
The halophilic archaeon Halococcus hamelinensis was isolated from living stromatolites in Shark Bay, Western Australia, that are known to be exposed to extreme conditions of salinity, desiccation, and UV radiation. Modern stromatolites are considered analogues of very early life on Earth and thus inhabitants of modern stromatolites, and Hcc. hamelinensis in particular, are excellent candidates to examine responses to high UV radiation. This organism was exposed to high dosages (up to 500 J/m(2)) of standard germicidal UVC (254 nm) radiation and overall responses such as survival, thymine-thymine cyclobutane pyrimidine dimer formation, and DNA repair have been assessed. Results show that Hcc. hamelinensis is able to survive high UVC radiation dosages and that intact cells give an increased level of DNA protection over purified DNA. The organism was screened for the bacterial-like nucleotide excision repair (NER) genes uvrA, uvrB, uvrC, as well as for the photolyase phr2 gene. All four genes were discovered and changes in the expression levels of those genes during repair in either light or dark were investigated by means of quantitative Real-Time (qRT) PCR. The data obtained and presented in this study show that the uvrA, uvrB, and uvrC genes were up-regulated during both repair conditions. The photolyase phr2 was not induced during dark repair, yet showed a 20-fold increase during repair in light conditions. The data presented is the first molecular study of different repair mechanisms in the genus Halococcus following exposure to high UVC radiation levels.
嗜盐古菌盐球菌（Halococcus hamelinensis）从澳大利亚西部鲨鱼湾的活体叠层石中分离出来，这些叠层石已知处于极端盐度、干燥和紫外线辐射条件下。现代叠层石被认为是地球早期生命的类似物，因此现代叠层石的居民，特别是 Hcc. hamelinensis，是研究对高紫外线辐射的响应的优秀候选者。该生物体暴露于高剂量（高达 500 J/m(2)）的标准杀菌 UVC（254nm）辐射下，评估了总体反应，如存活、胸腺嘧啶-胸腺嘧啶环丁烷嘧啶二聚体形成和 DNA 修复。结果表明，Hcc. hamelinensis 能够在高剂量 UVC 辐射下存活，并且完整细胞比纯化 DNA 提供更高水平的 DNA 保护。该生物体被筛选出具有细菌样核苷酸切除修复（NER）基因 uvrA、uvrB、uvrC 以及光解酶 phr2 基因。发现了这四个基因，并通过定量实时（qRT）PCR 研究了在光或暗条件下修复过程中这些基因的表达水平变化。本研究获得的数据表明，uvrA、uvrB 和 uvrC 基因在两种修复条件下均上调。光解酶 phr2 在暗修复期间未被诱导，但在光修复条件下增加了 20 倍。所提出的数据是在高剂量 UVC 辐射暴露后，对属 Halococcus 中不同修复机制的首次分子研究。
