Changes in O2– and H2O2 production by Chattonella antiqua during diel vertical migration under nutrient stratification

摘要

ABSTRACT: The red tide flagellate Chattonella antiqua produces high levels of reactive oxygen species (ROS) such as the superoxide anion (O₂^–) and hydrogen peroxide (H₂O₂). Production of ROS by this flagellate species depends on nutrient and water conditions during its growth phases. To clarify the effect of nutrient depletion on ROS production, we investigated the production pattern of ROS in a culture tank containing 1 m³ of medium with low nitrate and phosphate nutrient concentrations. The production of O₂^– and H₂O₂ by C. antiqua was lower when nutrients were limited than when they were fully supplied (f/2 medium), as indicated by reductions in nitrogen and phosphorus cell quotas. We also examined ROS formation by C. antiqua under stratified conditions subsequent to the nutrient depletion experiment. The vertical stratification of salinity (ΔS = 2.5 psu) and temperature (ΔT = 5°C) in the tank were analogous to natural conditions during red tides, and only the bottom layer was enriched with nutrients. C. antiqua showed clear diel vertical migration under stratified conditions. The ROS production due to photosynthesis was high during the light period at the surface, even though the ambient nutrient concentration of the surface was low, and it decreased in the dark bottom layer. The generation of H₂O₂ increased continuously for 4 d, but O₂^– generation peaked on the second day of stratification and then gradually decreased.