铜胁迫对苜蓿中华根瘤菌抗氧化酶系的影响

探讨铜胁迫对苜蓿中华根瘤菌抗氧化酶系的影响,揭示苜蓿中华根瘤菌对铜的生理抗性机制。以铜抗性菌株Sinorhizobium meliloti CCNWSX0020和铜敏感性S.meliloti CCNWSX0018为材料,测定其对铜的最小抑制浓度（MIC）和最大耐受浓度（MTC）及不同铜浓度对其抗氧化保护酶活性的变化。结果表明：（1）在YMA固体培养基上,S.meliloti CCNWSX0020和S.melilotiCCNWSX0018的MIC分别为0.5mmol·L^-1和0.2mmol·L^-1Cu^2＋,MTC分别为1.8mmol·L^-1和0.8mmol·L^-1Cu^2＋。（2）Cu^2＋浓度≤0.4mmol·L^-1时,S.meliloti CCNWSX0020菌体内的SOD、CAT和GPX活性变化不显著;S.meliloti CCNWSX0018菌体内的SOD、CAT和GPX活性显著升高;Cu^2＋浓度为0.6mmol·L^-1和0.8mmol·L^-1时,前者SOD、CAT和GPX活性显著升高,后者保护酶活性开始降低。随着Cu^2＋浓度升高,S.meliloti CCNWSX0020的GR活性增强,与对照相比,Cu^2＋浓度为0.8mmol·L^-1时GR活性提高了110.51%;而S.meliloti CCNWSX0018的GR活性则反之。（3）在Cu^2＋浓度≤0.8mmol·L^-1胁迫下,抗性菌株S.meliloti CCNWSX0020可通过提高SOD、CAT、GPX、GR的活性以降低Cu^2＋的毒害效应,为丰富根瘤菌抗铜机制提供了理论基础。

Effects of Copper Stress on Antioxidant Enzymes of Sinorhizobium Meliloti

The physiological mechanism of the resistance to heavy metal stress in rhizobium could be explored through the research on its antioxidative activity. Strain S. meliloti CCNWSX0020 exhibited high intrinsic tolerance to copper and therefore was used in this work to study the physiological mechanism of the bacterial responses to copper stress, and compared with copper-sensitive stain S. meliloti CCNWSX 0018. The results showed that the activities of SOD, CAT, GPX and GR in S. meliloti CCNWSX0020 significantly increased in 0.6 mmol·L-1 Cu2＋, and their activities reached the maximum levels in 0.8 mmol·L-1 Cu2＋. In comparison, the activities of SOD and CAT in S. meliloti CCNWSX 0018 significantly increased in 0.2 mmol·L-1 Cu2＋, and the activity of GPX increased in 0.4 mmol·L-1 Cu2＋, while the activity of GR decreased in copper-stress. These results indicated that copper-resistant strain S. meliloti CCNWSX0020 could reduce the damage of copper stress by enhancing the activities of SOD, CAT,GPX and GR, which could be the physiogical basis for the copper-resistance in rhizobium.