The uptake of guanine and hypoxanthine by marine microalgae

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Abstract
Guanine and hypoxanthine were excellent sole nitrogen sources for several microalgal species grown in axenic culture. Of the algae studied onlyChlorella stigmatophoragrew well on pyrimidines. Freshly harvested nitrate or ammonium-grown organisms generally lacked ability to take up guanine or hypoxanthine but this ability developed during several hours of photosynthesis in nitrogen-free medium. Nitrate-grown (but not ammonium-grown)Tetraselmis subcordiformisandChlorella fuscacould take up guanine, the initial rate of uptake increasing when the cells were also nitrogen-deprived. Of the algae studied onlyChlorella vulgarisandAttheya decorarequired prior incubation with guanine before being able to take it up.Porphyridium purpureumdid not take up guanine. Factors affecting the development of ability to take up guanine and the characteristics of guanine transport were studied. The transport systems showed Michaelis-Menten type kinetics with K s values ranging from 05 to 3–7/IM guanine. In marine species, guanine uptake was dependent on the presence of Nations in the medium butChlorella stigmatophorashowed less dependence on Na+ than other species.

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