Optimization of copper bioremoval from hypersaline environments by the halophilic archaeon Halalkalicoccus sp. Dap5 via response surface methodology.

Copper pollution in hypersaline environments poses a significant challenge due to the inefficiency of conventional bioremediation strategies under high salinity and metal stress. Halophilic archaea represent a promising solution for heavy metal removal in saline environments due to their biocompatibility and cost-effectiveness. Here, we investigated the copper removal potential of a Halalkalicoccus sp. Dap5, a halophilic archaeon isolated from the Urmia Lake in Iran. This strain exhibited copper tolerance (MIC: 80 mg/L Cu²⁺) and tolerance to several other toxic metals, including cadmium (Cd²⁺), cobalt (Co²⁺), lead (Pb²⁺), zinc (Zn²⁺), and arsenite (As³⁺) under 15% (w/v) salinity. A Central Composite Design (CCD) was employed within the Response Surface Methodology (RSM) to optimize three key parameters: pH, initial copper concentration, and inoculum percentage, to maximize copper removal. The resulting model was statistically significant (R² = 0.9972, p < 0.0001) and attained a maximum copper removal efficacy of 90.8% at pH 8.1, 28.8 mg/L Cu²⁺, and 4.8% (v/v) inoculum. Microscopic and spectroscopic analyses revealed that copper removal occurred through both biosorption and bioaccumulation mechanisms, supported by increased extracellular polymeric substance (EPS) production and specific functional group interactions identified via FTIR. The results demonstrate that Halalkalicoccus sp. Dap5 exhibits marked tolerance to copper and efficiently removes copper ions from saline environments, making it a valuable candidate for sustainable bioremediation under extreme conditions. This is the first report on optimization of copper bioremoval in a Halalkalicoccus strain using RSM, underscoring its biotechnological significance for green environmental management.