Studies on cellular characteristics and phylogeny of chromistan algae.

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This study was intended to understand mixotrophic activity of were surveyed for haptophytes inhabiting in polar waters. Samples from Antarctic and Greenland were examined. It was found that only three taxa, Chrysochromulina hirta, C.spinifera and Balaniger sp.were mixotrophic, and other haptophytes such as Phaeocystis, Pappomonas and Chrysochromulina parkeae were not able to uptake food particles. Because density of haptophytes was very low, polar water samples were not suitable for examination of mixotrophy. So, culture strains mostly collected and isolated from Japanese coastal waters were used. Mixotrophic uptake rate increased as density of food particles (latex beads) increased. However, it decreased at the concentration of over 10^7 particles/ml. This was interepreted as that in such high density, the aggregate of food particles formed on the haptonema surface became bigger than 5 mum which was the maximum size of food particle C.hirta could uptake. Clearance rate of C.hirta was 0.07nl/cell/min under the condition that particle density is less than 10^7 (when 0.88 mum beads were used). This is about three times higher than that of Dinobryon, the most common member of freshwater algae that is able to uptake food particles. Variations of methods in food capturing were also surveyed for Chrysochromulina species. New type of food capture was found in C.aff brevifilum, C.asteroplastida sp.nov.and C.strobilus, that is, they form tubular structure and capturing food particle and suck it. This is different from capturing method previously known in other species, C.hirta and C.spinifera, in which the haptonema is involved in the capturing process.