Preferential Assimilation of Ammonium Ion by Chlorella vulgaris

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Abstract
A pure culture of C. vulgaris was grown in an organic medium containing NH4NO3 having N15 in the ammonium radical. The cells were harvested and the cell-free medium resterilized and reinoculated. This process was repeated 3 more times. The algal cells preferred ammoniacal N to the nitrate form. There was evidence that N from a source other than the ammonium supplied in the medium was retained by the cells, even when a plentiful supply of ammoniacal N was present. When practically no NH4 was available, the cells grew according to a new selection of N.