Abstract
奇異球菌屬(Deinococcus)有四個菌種，其中D.radiopugnans ATCC19172 只擁有一種catalase，此與其它我們所測試的三株奇異球菌種皆有兩種 catalase 包括(cat alaseA及catalaseB)的性質相異。經由的DNA的雜交 實驗，我們確認除了ATCC19172菌株外，其它我們所測試的三株奇異球 菌 皆有與D. radiodurans IR的catalaseA基因同源的DNA序列存在。在經N- methyl-N'-nitro-N-nitrosoguanidine突變處理的菌落中我們成功的分離 到一catalase活性完全缺失的突變株，並將之命名為D. radiopugnans KM 。此KM菌株對H2O2抗性遠低於野生株其LD90較野生株低了約39倍，然而其 高抗輻射性並沒有受到影響(包括對FUV(254nm),r-ray等的抗性)。另外在 superoxide dismutase及peroxidase的活性、突變頻率上，KM菌株也保存 了原親系的特質。 Catalase活性缺失的KM菌株較野生株在細胞生長效應 上有缺失。它生長時的菌數倍增時間，最大生長量及靜止期維持時間分別 只有野生株的2/3,1/2,1/7倍。而在加Mn(II)的培養中，顯著縮短了KM菌 株的靜止期，此種現象也發生在高氧濃度(40%)的培養中。我們推測在細 胞處於生長靜止期或是高氧化壓力的環境時，極需catalase的作用來幫助 細胞生理功能運作並延長細胞在靜止期的存活。另外我們發現菌株存在著 一種對抗性的細胞密度效應，即高細胞密度較低細胞密度有較高的抗性， 此現象卻不存在於菌株，我們認為此效應中可能扮演一很重要角色。 There are four species in Deinococcus, among which three have two types of catalase, and the other one, D.radiopugnans ATCC19172 has one catalase. Sourthern blot analysis showed that D.radiopugnans ATCC19172 had no homologous DNA sequence that can hybridize with the katA probe of D.radiodurans IR. After mutagenizing D.radiopugnans ATCC19172 strain with N-methyl-N'- nitro-N-nitroguanidine, a catalase-deficient mutant was isolated through secreening 10,000 colonies for a catalase minus phenotype . The catalase-deficient mutant was designated D.radiopugnans KM. The KM strain was hypersensitive to H2O2,but the radioresistance such as FUV, r-ray was as high as that of the wild type strain. The KM strain still retained the parental characters in its superoxide dismutase activity, peroxidase activity, and mutation frequency for Rifs to Rifr. The doubling time, maximum cell density, and the stationary phase duration time of KM strain were reduced by 0.67-, 0.5-and 0.14-fold, respectively, as compared to those of wild type. When incubated with Mn(II), the KM strain had shorter duration stationary phase. This phenomenon was also found when culture was under high oxygen concentration (40%). We counclude that catalase logical role when ATCC19172 cells are in the stationary phase or in a high oxidative stress. We also found that the wild type ATCC19172 strain, but not the KM strain, had cell density effect when treated with H2O2. This effect showed that higher cell density had higher H2O2 sensitivity. This result indicated that catalase may have some function in the cell density effect.