赤潮プランクトンのＢ群ビタミン要求に関する研究 Ｉ Ｈｅｔｅｒｏｓｉｇｍａ ａｋａｓｈｉｗｏ ＨＡＤＡのＢ群ビタミン要求に関する増殖生理

Abstract

Physiological characteristics on the growth of Heterosigma akashiwo HADA (Raphidophyceae), a red tide phytoplankton, were examined with special reference to B group vitamin requirements in the axenic clonal culture. The alga was wide-range euryhaline, and preferred relatively high concentration of nutrients. It was found that only vitamin B12 was essential for the growth, and that growth rates and final cell yields were dependent on the vitamin B12 concentrations in the media. Vitamin B12 halfsaturation constants were very small: 0.37-0.60ng/l. However, it needed the higher concentration of 20ng/l to maintain maximum growth yields. Maximum specific growth rates were 0.62-0.82 day-1. The minimum cell quota of vitamin B12 was 8.9×10-5pg/cell or 24.2 molecules/μm3 of the cell volume. Cells grown in the vitamin B12-rich media were able to accumulate it up to 50-fold as much as the minimum quota. These results suggest that vitamin B12 in seawater may be one of the most principal factors controlling the growth of H. akashiwo, and consequently the development of its population to a red tide.