Effects of B group vitamins on the growth of toxic dinoflagellate Alexandrium catenella

Physiological growth characteristics of Alexandrium catenella (Whedon et Ko foid) Balech, toxic dinoflagellate,were examined in axenic, batch cultures with specific reference to B group vitamin requirements. A. catenella required essentially vitamin B-12 among the B group vitamins f or their growth. It was found that growth rates and final cell yields were dependent on the vitamin B-12 concentrations in the media. Under the condit ions of our batch culture experiments, the half-saturation constant for gro wth of vitamin B-12 (K mu) and maximum growth rate (mu 'm) were 0.22 ng/L a nd 0.55 day(-1), respectively. The minimum cell quota of vitamin B-12 was e stimated at 0.65 fg/cell or 27 molecules/mum(3) of the cell volume. In this experiment, A. catenella could grow at almost a maximum growth rate at hig h vitamin B-12 levels of eutrophied coastal waters. The comparison of K mu and mu 'm between A. catenella and other red-tide species suggests that thi s organism can win competition with some red-tide species under low B-12 co ncentrations.