Calcium-mediated amelioration of profenofos toxicity in the Cyanobacteria Fischerella and Anabaena

Profenofos is a widely used organophosphate pesticide with environmental persistence and toxic effects on non-targeted organisms. Being natural inhabitant of agricultural fields, cyanobacteria are regularly exposed to pesticides and can be used for bioremediation citing their resilience and metabolic plasticity. But, their physiological response against profenofos remains unstudied. Therefore, assessing their tolerance and potential enhancers that can amplify resistance is essential for effective application. Hence, we investigated the detrimental effects of profenofos on two paddy field dwelling cyanobacteria, Fischerella sp. lmga1 and Anabaena sphaerica, and evaluated their physiological responses to the profenofos. Further, we observed calcium mediated amelioration of profenofos stress in cyanobacteria. Both strains possessed ophB-like genes encoding organophosphate hydrolases. Fischerella showed 1.8-fold transcriptional induction of ophB and stronger profenofos binding (-6.1 kcal mol^-1) compared to Anabaena (-5.8 kcal mol^-1). Under 0.5 μM profenofos, Fischerella retained 26 % higher viability, 24 % more chlorophyll a, and higher antioxidant enzyme activity. It also preserved unsaturated fatty acids and produced hydrocarbons, supporting membrane integrity. Anabaena was more sensitive but responded well to calcium co-treatment. With 5 mM CaCl₂, viability increased by 27 %, photosynthetic efficacy improved by 33 %, and ROS levels decreased by 60 %. Calcium also restored phycocyanin, proline, and glutathione levels in Anabaena. In contrast, Fischerella relied on intrinsic defense and remained relatively less responsive to calcium. These findings demonstrate distinct stress response strategies. Fischerella exhibited stronger tolerance, while Anabaena benefits from calcium mediated resilience. This study provides physiological insights into cyanobacteria-assisted detoxification of organophosphates and lays the foundation for developing sustainable, calcium-augmented bioremediation systems.