Overexpression of Cu/Zn Superoxide Dismutase (Cu/Zn SOD) in Synechococcus elongatus PCC 7942 for Enhanced Azo Dye Removal through Hydrogen Peroxide Accumulation

SIMPLE SUMMARY: Synthetic azo dyes are used in various industries like apparel, food, paper, etc. The improper discharge of these recalcitrant dyes poses a serious threat to the environment. However, in nature, certain microorganisms including cyanobacteria can degrade these recalcitrant compounds by producing various reactive oxygen species (ROS), particularly by hydrogen peroxide (H(2)O(2)). This study aimed at developing a genetically modified cyanobacterium for better H(2)O(2) accumulation that results due to superoxide radicals dismutation by enzyme superoxide dismutase (SOD). The modified strain (MS-sodC(+)) was created by integrating Cu/Zn SOD gene (sodC) from another cyanobacterium, and its expression was driven by a strong constitutive psbA gene promoter. The modified strain (MS-sodC(+)) resulted in over-accumulation of H(2)O(2) during azo dye treatment with a higher rate of dye removal than the wild-type strain (WS-sodC). Therefore, to encourage cyanobacteria for biodegradation of toxic azo dyes faster than the natural rate enhanced H(2)O(2) accumulation through SODs, overexpression may serve as a valuable bioremediation tool. ABSTRACT: Discharge of recalcitrant azo dyes to the environment poses a serious threat to environmental health. However certain microorganisms in nature have developed their survival strategies by degrading these toxic dyes. Cyanobacteria are one such prokaryotic, photosynthetic group of microorganisms that degrade various xenobiotic compounds, due to their capability to produce various reactive oxygen species (ROS), and particularly the hydrogen peroxide (H(2)O(2)) when released in their milieu. The accumulation of H(2)O(2) is the result of the dismutation of superoxide radicals by the enzyme superoxide dismutase (SOD). In this study, we have genetically modified the cyanobacterium Synechococcus elongatus PCC 7942 by integrating Cu/Zn SOD gene (sodC) from Synechococcus sp. PCC 9311 to its neutral site through homologous recombination. The overexpression of sodC in the derivative strain was driven using a strong constitutive promoter of the psbA gene. The derivative strain resulted in constitutive production of sodC, which was induced further during dye-treated growth. The genetically engineered Synechococcus elongatus PCC 7942 (MS-sodC(+)) over-accumulated H(2)O(2) during azo dye treatment with a higher dye removal rate than the wild-type strain (WS-sodC(−)). Therefore, enhanced H(2)O(2) accumulation through SODs overexpression in cyanobacteria may serve as a valuable bioremediation tool.