Bioaccumulation kinetics of arsenite and arsenate in Dunaliella salina under different phosphate regimes

Dunaliella salina is a potential candidate for the phycoremediation of saline water contaminated with arsenic (As) due to its strong tolerance of salt and this toxic metalloid. However, the efficiency of As removal by this microalga varies under different phosphate regimes and the underlying mechanisms remain unresolved. Therefore, more detailed studies are needed to optimize As remediation using D. salina. Here, we investigated the dynamic processes of arsenite (As(III)) and arsenate (As(V)) uptake, transformation, and excretion by D. salina under phosphate-deficient (-P) and phosphate-enriched (+P) conditions through short-term and long-term uptake experiments. In the short-term uptake experiment, the absorption of As(III) or As(V) by D. salina was significantly suppressed by an increased phosphate supply. The V-max values for As(III) and As(V) decreased by 2- and 2.5-fold, respectively, under +P conditions, although the Michaelis constants (K-m ) were similar irrespective of the phosphate supply. Long-term uptake experiments also revealed enhanced As(III)/As(V) absorption and efflux rates and As(V) reduction by D. salina under -P conditions. This study quantified the kinetic processes of As metabolism in D. salina. More importantly, the results imply that the optimal As remediation by this microalga may be achieved by regulating the phosphate level in the culture.