Effects of micronutrients on the detection of extracellular superoxide produced by the harmful raphidophyte Chattonella antiqua in culture

Abstract

Abstract Noxious Chattonella species cause many red tides and fish kills. The detection of extracellular O2− produced by these algae will be critical for the development of a rapid toxicity-evaluation method; however, such a development has been prevented by the mismatch of the extracellular O2− detection level between field and laboratory experiments. The aim of this study was to identify impediments to detect extracellular O2− in laboratory experiments. Our results indicate that Mn and Co in the medium decreased the detection levels of extracellular O2− produced by Chattonella antiqua, and the effect by Mn was stronger than that by Co. IC50 of the radical-scavenging activity of Mn was 17.5 μM, and little activity was detected at 8.75 μM or less. Furthermore, the level of extracellular O2− production by C. antiqua in Mn-depleted medium varied greatly under various culture conditions; the extracellular O2− production level of C. antiqua was high under conditions similar to those under which blooms develop in the field. Therefore, Mn is a key scavenger of extracellular O2−, and amounts of Mn must be carefully considered whenever extracellular O2− production levels of phytoplankton cultured with other kinds of media are measured.