Heavy metals contribute to oxidative stress in algae Enue Sicairos Fresh Water and Marine Algae

Metals in the Environment Occur naturally: part of organisms and food chain Occur naturally: part of organisms and food chain - Essential (Cu, Zn) - Toxic (Hg, Pb) Increase level due to anthropogenic activities: -Industrial effluents -Agricultural fungicide runoff -Mining operations -Urban runoff Aquatic ecosystems are being affected -Chlamydomonas photosyntesis inhibited -Massachusetts bay

Mechanism of toxicity 1.- Binding to sulphydryl groups in proteins 2.-Displacement of an essential element 3.-Induction of oxidative stress a) Increasing of reactive oxygen species (ROS) b) Reducing the cellular antioxidant capacity

Reactive Oxygen Species (ROS)  Small and highly reactive molecules (unpaired electrons) -oxygen ions, free radicals and peroxides  They are normal byproducts of oxidative metabolism (respiration, photosynthesis)  Environmental factor can increase ROS -Light -Light -Heavy metal -Heavy metal O 2.- H 2 O 2. OH

Cellular defense vs ROS Production of antioxidants Low molecular weight - ascorbate - ascorbate - carotenoids - flavonoids - phenolics - antioxidant glutathione High molecular weight - catalase - glutathione peroxidase (GPX) - ascorbate peroxidase (APX ) - lipid peroxidase - superoxide dismutase (SOD) Flavonoid Catalase APX

Scientific evidence 1.-Algae treated with Cd -Increased SOD activity in green algae Tetraselmis gracilis and Ditylum brightwellii (diatom). -Increased APX activity Selenastrum capricornutum(green unicellullar alga) -Decreased GSH content in the marine dinoflagellate L. polyedrum 2-Reductions in growth rates - Red algal species Asparagopsis armata (at 0.31 ppm Cd and ppm Cu ) - Red algal species Asparagopsis armata (at 0.31 ppm Cd 2+ and ppm Cu 2+ )

Conclusions Algae are the basis of the food web in all aquatic ecosystems. Algae are the basis of the food web in all aquatic ecosystems. Stress treatments like high illumination, suddenly changes in temperatures increase of metal concentration affects an algal cell’s biochemical composition Stress treatments like high illumination, suddenly changes in temperatures increase of metal concentration affects an algal cell’s biochemical composition At high levels of metal pollutant damage to algal cells occurs because ROS exceed the antioxidant response. At high levels of metal pollutant damage to algal cells occurs because ROS exceed the antioxidant response. At low or chronic levels algae accumulate heavy metals and can pass them along the food chain. At low or chronic levels algae accumulate heavy metals and can pass them along the food chain.