Heavy metal contamination is a serious environmental problem. Understanding the toxicity mechanisms may allow to lower concentration of metals in the metal‐based antimicrobial treatments of crops, and reduce metal content in soil and groundwater. Here, we investigate the interplay between metal efflux systems and the superoxide dismutase (SOD) in the purple bacterium Rubrivivax gelatinosus and other bacteria through analysis of the impact of metal accumulation. Exposure of the Cd²⁺‐efflux mutant ΔcadA to Cd²⁺ caused an increase in the amount and activity of the cytosolic Fe‐Sod SodB, thereby suggesting a role of SodB in the protection against Cd²⁺. In support of this conclusion, inactivation of sodB gene in the ΔcadA cells alleviated detoxification of superoxide and enhanced Cd²⁺ toxicity. Similar findings were described in the Cu⁺‐efflux mutant with Cu⁺. Induction of the Mn‐Sod or Fe‐Sod in response to metals in other bacteria, including Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida, Vibrio cholera and Bacillus subtilis, was also shown. Both excess Cd²⁺ or Cu⁺ and superoxide can damage [4Fe‐4S] clusters. The additive effect of metal and superoxide on the [4Fe‐4S] could therefore explain the hypersensitive phenotype in mutants lacking SOD and the efflux ATPase. These findings underscore that ROS defence system becomes decisive for bacterial survival under metal excess.

中文翻译：

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金属过量和超氧化物（细菌中的剧毒混合物）的叠加作用。

重金属污染是一个严重的环境问题。了解毒性机理可能会降低农作物以金属为基础的抗菌处理中金属的浓度，并减少土壤和地下水中的金属含量。在这里，我们通过分析金属积累的影响，研究了紫色外生细菌Rubrivivax gelatinosus和其他细菌中金属外排系统与超氧化物歧化酶（SOD）之间的相互作用。CD的曝光²⁺ -efflux突变Δ的cadA对Cd ²⁺引起的量和细胞溶质的Fe-SOD SODB的活性的增加，因此表明SODB在打击Cd中的保护作用²⁺。为了支持这一结论，灭活了SODB在Δ基因的cadA细胞减轻超氧的解毒和增强镉²⁺毒性。类似的结果在铜被描述⁺ -efflux突变体的Cu ⁺。还显示了Mn-Sod或Fe-Sod对其他细菌（包括大肠杆菌，铜绿假单胞菌，恶臭假单胞菌，霍乱弧菌和枯草芽孢杆菌）中金属的响应。过量的Cd ²⁺或Cu ⁺超氧化物会损坏[4Fe-4S]团簇。因此，金属和超氧化物对[4Fe-4S]的累加作用可以解释缺乏SOD和外排ATPase的突变体的超敏表型。这些发现强调了ROS防御系统对于金属过量时细菌的存活起决定性作用。