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Phosphate uptake in the obligately marine fungus Thraustochytrium roseum is maximally stimulated by sodium chloride in a range of concentrations (0.2 to 0.4 molar) similar to those commonly encountered in littoral habitats. The effectiveness of sodium chloride for phosphate transport extends beyond its osmotic function and can be attributed specifically to sodium. Increases in respiration in the presence of the salt can be ascribed primarily to an osmotic effect.

Investigations of a nonfilamentous fungus (Schizochytrium aggregatum gen. et sp. nov.) reveal that it proliferates zoosporangia by successive bipartitioning of the thallus. Thus, its vegetative reproduction differs from that of other fungi, but resembles that of some possibly primitive chlorosphaeracean algae. Organism development is described from growth on natural substrates and synthetic media. Inoculation experiments involving diverse algae and phanerogam materials suggest that S. aggregatum is largely a saprophyte of vascular plant detritus in the littoral zone—a conclusion consonant with the results of a survey of its apparent distribution in coastal waters. This obligately marine organism requires 2.5‐3.0% NaCl for optimal growth and does not develop in media which differ radically from sea water in potassium content. Neither KCl nor CaCl2 can replace NaCl, and increased levels of KC1 do not mitigate the inhibitory effects of high concentrations of NaCl. The fungus grows well at 12–25 C and gives maximal yields when provided with cellobiose or the cleavage products of starch as carbon sources.

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Phosphate uptake in the obligately marine fungus, Thraustochytrium roseum, is maximal at pH 7.5 to 7.8, is dependent on temperature, and varies with phosphate concentration. Pyruvate and succinate stimulate phosphate uptake, although they do not increase respiration. The uncoupling agents, 2,4-dinitrophenol and dicoumerol, inhibit phosphate uptake but stimulate oxygen consumption only in the presence of NaCl. Oligomycin inhibits both processes. Among the inhibitors of protein synthesis, chloramphenicol reduces phosphate uptake without affecting respiration. Puromycin is unique in that it greatly enhances phosphate uptake and abolished the lag period associated with this phenomenon. It does not affect respiration. Most fungi isolated from the sea are fortuitous invaders endowed with a broad salinity tolerance which permits them to adapt to a variety of other habitats (28). In contrast, phycomycetes re

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