The red tide flagellate Chattonella antiqua produces high levels of reactive oxygen species (ROS) such as the superoxide anion (O 2 -) and hydrogen peroxide (H 2 O 2 ). 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 m 3 of medium with low nitrate and phosphate nutrient concentrations. The production of O 2 -and H 2 O 2 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 (∆S = 2.5 psu) and temperature (∆T = 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 H 2 O 2 increased continuously for 4 d, but O 2 -generation peaked on the second day of stratification and then gradually decreased. KEY WORDS: Chattonella antiqua · Diel vertical migration · Hydrogen peroxide · Nutrient stratification · Reactive oxygen species · Superoxide anion Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 39: [183][184][185][186][187][188][189][190][191] 2005 division occurred almost once per day during the exponential growth phase (Kim et al. 2004).Chattonella antiqua is a motile phytoplankton characterized by diel vertical migration (DVM) and nocturnal nutrient uptake . The cells accumulate at the surface during the day for photosynthesis and sink to a deeper layer, where nutrients such as nitrate and phosphate are abundant, to take up the nutrients during the night. Under stratified conditions, the DVM ability gives the cells an ecological advantage over other non-motile phytoplankton species because the surface nutrients are generally almost depleted. The DVM of the flagellate population was examined in a culture tank at the National Institute for Environmental Studies (NIES), Japan (Kohata & Watanabe 1986, 1987, Kimura et al. 1999, in terms of nutrition and growth. Kim et al. (2004) suggested that the toxicity induced by ROS was presumably linked to cell migration through the cell cycle and nutrition although their study on ROS generation by C. antiqua was conducted in the NIES tank under fully mixed conditionsFor the present study, we grew Chattonella antiqua in the NIES culture tank under limited nitrate and phosphate nutrient conditions to clarify the effect of nutrient depletion on ROS production through the growth metabolism du...
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