摘 要 台灣地熱區中的各種不同嗜熱性細菌，在先前的研究已被分離出來，而且有些嗜熱菌具有輻射抗性。本研究自台灣溫泉中的嗜熱菌，經過迦瑪射線處理後，篩選出數株具抗輻射特性的菌株，並進一步探討其輻射抗性的機制。根據16S rDNA 序列分析的結果顯示，六株新分離的抗輻射特性的菌株被歸為 Meiothermus 屬，進一步研究發現它們與標準株Meiothermus silvanus DSM 9946T 最相似。此外也分析其形態、生化、生理及遺傳的特性，以作為系統學的研究。結果顯示，六株Meiothermus 屬新的抗輻射菌株為桿狀形態且為革蘭氏陰性菌。經由 ICP-MS 分析的結果顯示，分離株中的NTU-716G、NTU-1574G、NTU-1573G之Mn/Fe比值，較標準株 Meiothermus silvanus DSM 9946T 與其他三株分離株(NTU-1113G、NTU-1115G、NTU-1575G)為低。有趣的是，含有較低Mn/Fe比值的菌株，同樣顯示其過氧化氫的活性比較低以及耐乾旱與耐紫外線的能力較低。此外，這些菌株經過紫外光照射後，會產生較多量的過氧化氫，而且過氧化氫酶活性會下降更加明顯。文獻指出在Deinococcus radiodurans 抗輻射菌珠中，較多的Mn累積是增加其抗迦瑪射線能力的機制。而本論文結果顯示，在嗜熱性Meiothermus spp.菌珠中，較高的Mn/Fe比值也與其抗紫外線與抗乾旱能力具有正相關性，而此種抗性可能與菌體本身具有較高過氧化氫酶活性有關。 Abstract In previous studies, various thermophilic bacteria living in Taiwan’s geothermal environments were isolated and showed radiation resistant. In this study, several thermophilic radiation resistant bacteria isolated from hot springs in Taiwan, were selected for further characterization of resistant mechanism. Radiation resistant bacteria were isolated from water samples after gamma irradiation. According to 16S rDNA sequence analysis, these isolates were all grouped into the genus of Meiothermus spp. Six strains were selected for further studying and found these strains were most similar with Meiothermus silvnus DSM9946T. Several analyses, including morphological, biochemical, physiological and genetic tests, were applied for systematic study. The results showed that the six novel radiation resistant strains of genus Meiothermus were rod-shaped and gram-negative. The isolates NTU-716G, NTU-1574G and NTU-1573G showed lower Mn/Fe ratio (as indicated by ICP-MS analysis) than that of type strain Meiothermus silvnus DSM 9946T and other isolates (NTU-1113G, NTU-1115G and NTU-1575G). Interestingly, the lower Mn/Fe ratio strains also showed either lower level of catalase activity or lower resistance to desiccation and UV. Moreover, UV-irradiation also significantly induced H2O2 production and attenuated catalase activity in these strains. Higher Mn accumulation has been shown to facilitate gamma-radiation resistance in Deinococcus radiodurans. The current results suggested that higher Mn in thermophilic Meiothermus spp. might be also correlated to UV and/or desiccation resistance, and this resistance in part is contributed by higher catalase activity.