Hydrogen peroxide production by a marine phytoplankter 1

Hymenomonas carterae , a calcified marine phytoplankter, produces hydrogen peroxide extracellularly. Hydrogen peroxide production by a washed cell suspension occurs in the dark and is inhibited by cell‐impermeable protein modification reagents. A cell‐surface redox enzyme is thus likely responsible for production of H 2 O 2 . The physiological function of this potentially toxic compound is unknown. If the production rate of 1–2 × 10 −14 mol cell −1 h −1 measured in cultures of H. carterae could be generalized, marine phytoplankton would be an important source of the hydrogen peroxide found in the marine environment.