Molecular and Enzymatic Responses of Chlorococcum dorsiventrale to Heavy Metal Exposure: Implications for Their Removal

Heavy metals are one of the main threats to marine life and ecosystems and any remedial action in that regard is urgently required. The aim of this work is to study the bioremoval of cadmium, chromium and lead in a microalgae strain Chlorococcum dorsiventrale isolated from Tunisian coastal waters along with assessing its enzymatic and molecular responses. The microalgae were tested in artificial seawater to evaluate their capacity for phycoremediation in an aquatic environment. This strain tolerated exposure to Cd (II), Cr (VI), and Pb (II) and was able to grow for 14 days. Cd and Cr exposures elicited a decrease in chlorophyll, lipid and polysaccharide contents, whereas no damages were detected following Pb treatment. For protein content, no significant changes were seen except after Pb exposure which induced a slight increase after treatment with 5 mg/L. The assessment of stress defense-related gene expression using qRT-PCR revealed that exposure to Pb and Cr induced an up-regulation of catalase, superoxide dismutase and photosystem II protein D1 encoding genes. Moreover, heat shock protein 70 was slightly overexpressed. Removal efficiencies for Cr and Pb attained 89% and 95%, respectively. The mechanisms by which C. dorsiventrale removed Cr involved both intracellular and extracellular biosorption, while Pb was predominantly removed through membrane adsorption. This study highlights the potential of C. dorsiventrale as an efficient agent for the bioremediation of heavy metal-contaminated water, including industrial wastewater, thus paving the way for practical and environmental applications in pollution control.