Pb toxicity at initial level is managed by Desmonostoc muscorum PUPCCC 405.10 by activating antioxidant defense system

Heavy metal pollution is one of the most severe ecological problems with Lead (Pb) being present in high concentrations. Cyanobacteria growing in polluted sites have evolved different mechanisms to avoid metal toxicity and continue to contribute to the biological activity of the site. The present study was undertaken to understand the mechanism of Pb tolerance in a common diazotroph Desmonostoc muscorum as it tolerated Pb up to 20 mg L -1 . During first 48 h, Pb toxicity in this organism resulted in 88% increase in superoxide radicals (SOR) which caused morphological alterations, 37–72% decrease in photosynthetic pigments leading to reduced growth of the organism. The cyanobacterium managed this toxicity by activating antioxidant enzymes superoxide dismutase (SOD) (187% increase) and peroxidase (POD) (181% increase). Simultaneously, increase in the levels of gluthathione (GSH) (53%) and proline (60%), and activity of glutathione reductase (GR) was observed. After 48 h, level of SOR, activities of SOD and POD decreased while the level of GSH and GR remained high. This indicated that Pb toxicity at initial level is managed by the organism by activating both SOD/POD and GSH/GR systems, while later on the organism adopts some other mechanism and is able to manage Pb toxicity by only GSH/GR system.