Abstract
高度抗輻射奇異球菌(Deinococcus radiodurans)不產孢,其對於高熱的致 死之抗性稍高於一般中溫菌,Tan & Maxcy曾報導, D. radiodurans 有一 不尋常的抗熱殘存曲線:當奇異球菌受到60 C 20分鐘處理後的殘存者可以 持續存活3小時以上仍保存活性,因而在 殘存曲線,第一個對數致死部份之 後出現一個水平的tailing o這種 對付致死處理的奇特現象似乎只由熱 所引發,故稱為thermo-tailing.比較處於thermo-tailing的存活者( TT cells )與處於第一個對數 致死期之細胞( EK cells )的特性,前者之耐 鹽性較後者為高,且重新培養之生長延滯時間亦較小,顯示TT cell較EK cells所受的熱傷 害要少o此外,這種奇特的現象會受到加熱時的溶液不同 而改變,若將 加熱的溶液由培養基改為蒸餾水或磷酸緩衝液,則thermo- tailing就 無法產生. Thermo- tailing可於55 C 及60 C 加熱處理而產 生,若將 加熱產生的TT cells ( 60 C 60 min,or 55 C 120 min ), 轉 移至室溫( 25 C )一段時間再回到原加熱溫度,則thermo-tailing的現象 就會受到影響而改變原有的熱抗性o另外,將不同溫度產生的tailing轉移 至產生tailing的溫度,發現tailing的細胞無法在其它溫度下繼續抗熱o綜 合結果,提出一可能的模式來解釋thermo- tailing的形成機制:thermo- tailing的形成必須有一持續的熱源供應,當達到一定熱量時,可引發 deinococcal bacteria 修飾其外圍結構或構形的改變,造成一個熱阻擋 物( heat barrier )o 在熱能引發之熱阻擋物( heat induced heat barrier: HIHB )未達到有效溫度前,細胞會因重要成份受熱而死亡o 若 HIHB已生成,使的熱能無法進入細胞內造成傷害細胞就能保持活性而形成 thermo-tailing這種特殊的熱殘存現象o A highly radiation resistant bacterium, Deinococcus radiodurans, has a higher resistance to lethal thermal stress than other mesophile bacteria,In 1982, Tan & Maxcy have reported that there was a unusual heat survival curve : when the cells of D. radiodurans were treated at lethal temperature, 60 C, for 20 min, the survivors could preseve their activities more than 3 hours. So there was a novel tailing in the survival curve after the first log killing. We called this special phenomenon as "thermo-tailing " which only induced by thermal stress. To compare the survivors at the thermo- tailing state ( TT cells : 60 C 60 min ) and at the first exponential killing state ( EK cells : 60 C 10 min ), we found that the salt-tolerance of TT cells was higher than the EK cells. The lag time of TT cells was shorter than that of EK cells after reculture at the fresh growth medium. These results suggested that the TT cells suffered less heat injury than EK cell. Our results suggested : If the cells of D. radiodurans were resuspended in phosphate buffer or distiled water, or in medium containing EDTA, heat survival curve had no thermo-tailing. It indicated that the formation of thermo- Thermo-tailing could be found in 55 C and 60 C treatment. The TT cells ( 60 C, 60 min, or 55 C 120 min) after shifted to room temperature ( 25 C ) for 10 min for the duration of thermo-tailing were disturbed and the survivors become more sensitive to heat. In addition, shifting the TT cells of 55 C and 60 C to 60 C and 55 C respectively, the thermo-tailing were also disturbed.