Uptake of Organic, Compounds by Two Facultatively Heterotrophic Marine Centric Diatoms1,2

SUMMARY Glucose and galactose uptake ability inCyclotella cryptica(clone WT‐1‐8) and glucose uptake ability inCoscinodiscussp. develop rapidly in the dark. Induction of sugar uptake ability in the dark does not require the presence of sugar in the medium. The sugars are taken up by carrier‐mediated systems. InC. crypticaglucose and galactose are probably taken up by the same system. The capacity of glucose uptake in this recently isolated clone ofC. crypticais nearly 5 times that of a previously studied clone (0‐3A). Other organic compounds, which by themselves do not support heterotrophic growth, can be taken up and respired by both diatoms at considerable rates compared, to glucose and galactose. Therefore, in nature, these diatoms may be able to utilize a variety of dissolved organic compounds as sources of intermediary metabolites and as respiratory substrates.