Vegetative growth of Noctiluca scintillans containing the endosymbiont Pedinomonas noctilucae

Vegetative growth of Noctiluca scintillans containing the photosynthetic endosymbiont Pedinomonas noctilucae was investigated in culture and in natural populations. Clonal cultures of N. scintillans containing theendosymbiont, isolated from the inner Gulf of Thailand and Manila Bay, were of two types: one requiring an external food supply and the other not requiring an external food supply. The latter strain was neverthelessable to feed on phytoplankton, indicating facultative phagotrophy. Under optimal growth conditions there was no significant difference in growth rate between N. scintillans possessing the endosymbiont (0.33 day–1)and the heterotrophic N. scintillans (0.28 day–1), without the endosymbiont, isolated from the Seto Inland Sea, Japan. These observations support the hypothesis that the symbiont does not enhance the growth of Noctiluca, but phagotrophy does promote faster growth. Symbiosis is considered to secure survival of the host under food limitation. Cell cycle analysis conducted in a natural population in Manila Bay revealed a diurnal rhythm in cell division, peaking during early morning. The in situ specific growth rate of 0.16 day–1 was within the range reported for the heterotrophic N. scintillans in temperate waters

ISOLATION OF ASP TOXIN-PRODUCING NITZSCHIA FROM THAILAND

Nitzschia navis-varingica is recognized as the major ASP toxin producer other than Pseudo-nitzschia species. Surveys on the distribution and the toxin production of this diatom has been conducted in a few countries in eastern Asia and expanded to Thailand. Eighteen isolates from Thailand showed the positive result for the ASP toxin production is DA and IB, although the ratio of IB was much lower than those of the isolates from southern countries including Okinawa, Japan, the Philippines and Vietnam