Effect of heavy metals on the antioxidant system of the acid-tolerant microalga Coccomyxa onubensis

Coccomyxa onubensis (C. onubensis) is an acid -tolerant microalga whose ecosystem (Tinto River, Huelva, Spain) contains high amounts of different heavy metals. However, the potential of this microalga to remove these pollutants from the environment has still not been studied. Thus, this work evaluates the tolerance and physiological response of this microalga in the presence of three heavy metals, copper, cadmium, and mercury, and the metalloids As (III) and As (V). The results demonstrated that C. onubensis is able to improve its growth parameters with the presence of copper in the culture medium until concentrations of 2 mM Cu2+ and also shows high tolerance to other heavy metals and metalloids tested, such as Cd2+, As(III), As(V) or Hg2+. Moreover, this microalga seems to be a high arsenic accumulator organism, showing its high potential for arsenic bioremediation processes. Finally, the characterization of three antioxidant enzymes and their evaluation under heavy metal stress was performed. The results showed that ascorbate peroxidase (APX, EC:1.11.1.11), catalase (CAT, EC:1.11.1.6), and glutathione reductase (GR, EC:1.6.4.2) were upregulated to different degrees when C. onubensis was cultivated under heavy metal stress.