Cytoskeletal Actin Binding Is Related to Cadmium Tolerance and Accumulation of <i>Dunaliella parva</i>

This study investigates the cadmium (Cd) tolerance and accumulation capacity of Dunaliella parva, a halophilic microalga, for effective Cd bioremediation. It has the capacity to tolerate and continuously accumulate Cd within its cells during growth, retaining 80% of Cd intracellularly. The average bioaccumulation is 64.62 ± 1.54 fg of Cd per cell, with concentrations reaching 1499 ± 65 mg/kg of dry weight. Subcellular fractionation and chemical speciation analysis revealed that approximately 75% of the accumulated Cd is associated with heat-stable proteins, indicating a key detoxification mechanism. A Cd-binding protein was isolated via column gel electrophoresis-inductively coupled plasma mass spectrometry (GE-ICP-MS) and identified as cytoskeletal actin (42 kDa). This protein significantly increases in algal cells with maximal Cd accumulation, effectively sequestering the metal and mitigating its toxicity. Heterologous expression of the actin gene in Escherichia coli BL21 (DE3) resulted in a 40–60% enhancement in Cd accumulation. These results suggest that cytoskeletal actin contributes to D. parva’s high-level Cd tolerance and accumulation under hypersaline conditions. This finding highlights the potential of D. parva for treating saline wastewater and its application in Cd bioremediation through synthetic biology approaches.