Biomethylation and volatilization of arsenic by the marine microalgae Ostreococcus tauri

•O. tauri could tolerate 100 μM As(III) or As(V).•O. tauri is able to biomethylate and biovolatilize As.•As(V) reduction was speculated to be the rate-limiting factor for As methylation and volatilization.

Ostreococcus tauri is a marine green microalga, recognized as a model organism of the marine phytoplankton assemblage and widely distributed from coastal to oligotrophic waters. This study showed it could tolerate both arsenite and arsenate concentrations of up to 100 μM, and cellular As concentration increased significantly (P < 0.01) with increasing concentration of As(V) in the medium (0–50 μM). It was revealed that As biotransformations were mediated by algal cells. Volatilized As was detected and the ability of As biovolatilization by O. tauri was demonstrated. The reduction of As(V) to As(III) might be the limiting step for As methylation and volatilization from seawater since the treatment with As(III) yielded five times more volatile As as compared to that with As(V). Arsenic biogeochemical cycle in the marine environment might play an important role based on the huge surface area of ocean (71%) and the massive number of marine phytoplankton.