Poster: Nutrient Biology

Abs # 405: Function of iodine in marine phytoplankton: effect of iodine on growth and identification of iodine-containing proteins

Presenter:	Iwamoto, Koji , ivanov@anet.ne.jp
Authors	Iwamoto, Koji  (A)   Obata, Toshihiro  (A)   Seki, Riki  (A)   Shiraiwa, Yoshihiro  (A)
Affiliations:	(A): University of Tsukuba

Iodine is the most abundant non-conservative, biophilic and redox-sensitive trace element in the oceans. Recently, marine phytoplankton is implied to play an important role in the iodine-evaporation from the ocean into the atmosphere, iodine-migration to the sub-oceanic sediment and iodine-supply to aquatic lower animals. However, role of iodine in phytoplankton remains unclear due to the lack of basic data on its physiology. In this study, we report some physiological effects of iodine in marine phytoplankton. The growth of diatom Chaetoceros was suppressed by iodate even at 0.1 mM, whereas that of the coccolithophorids, Emiliania and Gephyrocapsa, was stimulated at 1 mM. Other marine algae, such as green alga Dunaliella, raphydophycean alga Heterosigma, diatoms Bellerochea and Skeletonema and haptophyte Isochrysis were not influenced by such high concentration of iodate and iodide. This is the first report on the stimulation of algal growth by iodine. The stimulatory effect in Emiliania huxleyi was obvious in cells at the stationary phase but not at logarithmic and linear growth phases. Such stimulating effect was specific to iodate, but not to iodide. The radioactivation analysis indicated that the internal concentration of iodine was 4.4, 140 and 530 mM, respectively, in cells grown in the presence of 0.4 mM KI, 1 mM KI and 1 mM KIO3. We also revealed that 42 kD iodine-containing protein is synthesized in E. huxleyi and 55 kD and 65 kD iodine-containing proteins were additionally induced under the selenium-deficient condition. As selenium was found to be an essential element for E. huxleyi, such iodine-containing proteins, may be induced for the stimulation of growth or cell viable, suggesting the importance of iodine for coccolithophorids.