Production of superoxide anion and hydrogen peroxide associated with cell growth of Chattonella antiqua

The production of reactive oxygen species (ROS) by the red tide flagellate Chattonella antiqua (Raphidophyceae) was investigated. Flagellates were grown in an NIES (National Institute for Environmental Studies) culture tank containing 1 m 3 of f/2 medium under synchronized light conditions (12:12 h, L:D period). Raphidophycean flagellates are known to form ROS, such as the superoxide anion (O 2 -) and hydrogen peroxide (H 2 O 2 ) under normal growth conditions. We confirmed that C. antiqua generated O 2 -depending on the cell growth phase by chemiluminescence responses. O 2 -production had a maximum value during the exponential growth phase and subsequently decreased in the stationary phase. However, the maximum production of H 2 O 2 occurred in the early stationary growth phase. These results showed that O 2 -and H 2 O 2 generation pathways were different from each other in C. antiqua. The highest activity rates of both O 2 -and H 2 O 2 per carbon content (g carbon -1 ) were observed during the exponential growth phase, but the pattern of ROS generation was significantly different between O 2 -and H 2 O 2 during cell growth. Two sets of intensive observations (at 3 h intervals) were conducted for diel phasing of the cell cycle in the exponential and stationary growth phases. In the exponential growth phase, O 2 -and H 2 O 2 production rates increased during the light period and decreased during the dark period, in spite of the increase in cell density due to cell division, indicating that the rates were affected by photosynthesis. The patterns of ROS production during the stationary growth phase were similar to those in the exponential phase, although the growth rate had less effect during the stationary than in the exponential phase.