【Extremophiles】Effects of cadmium exposure on expression of glutathione synthetase system genes in Acidithiobacillus ferrooxidans

Zheng CL, Zhang L, Chen MJ, Zhao XQ, Duan YZ, Meng Y, Zhang XF, Shen RF. Effects of cadmium exposure on expression of glutathione synthetase system genes in Acidithiobacillus ferrooxidans. Extremophiles, doi: 10.1007/s00792-018-1046-3

Abstract

The glutathione synthetase system (GSS) is an important pathway of glutathione synthesis and plays a key role in heavy metal resistance. In this work, the response of Acidithiobacillus ferrooxidans to extracellular Cd²⁺ was investigated, and the interplay between Cd²⁺ resistance and the expression of GSS related-genes was analyzed by reverse-transcription quantitative PCR (RT-PCR). During growth in the presence of 5, 15 and 30 mM Cd²⁺, the transcript levels of eight GSS pathway genes were affected between 0.81- and 7.12-fold. Increased transcription was also reflected in increased enzyme activities: with those of glutathione reductase (GR) increased by 1.10-, 2.26- and 1.54-fold in the presence of 5, 15 and 30 mM Cd²⁺, respectively. In contrast, the activities of catalase (CAT) and superoxide dismutase (SOD) were decreased in the presence of Cd²⁺. At the metabolite level, intracellular methane dicarboxylic aldehyde (MDA) content was increased 1.97-, 3.31- and 1.92-fold in the presence of 5, 15 and 30 mM Cd²⁺, respectively. These results suggest that Cd²⁺ directly inhibits the activities of CAT and SOD, breaks the redox balance of the cells, which leads to the activation of the other antioxidant pathway of GSS. Resistance of A. ferrooxidans to Cd²⁺ may involve modulation of expression levels of glutathione S-transferase (GST), GR, and glutathione synthetase, which may protect against oxidative damage.