Utilization of L-lysine and L-arginine by the diatomPhaeodactylum tricornutum

The rate of growth ofPhaeodactylum tricornutum Bohlin with L-lysine as sole nitrogen source is about half that with ammonium or nitrate, and only one of the two nitrogen atoms in the lysine molecule appears to be used for growth. The organism cannot grow heterotrophically with lysine as carbon source. The rate of lysine metabolism is slow and most of that utilized is incorporated into protein, this process being faster in light than in darkness. The dark incorporation of lysine-carbon into protein is stimulated by addition of ammonium, whereas incorporation in light is unaffected. Arginine-carbon is also mainly incorporated into protein. Light has little effect on this incorporation, and addition of ammonium decreases it both in light and darkness. There is no appreciable conversion of the carbon of either amino acid to carbon dioxide. Although, under anaerobiosis, lysine is taken up and accumulated, negligible metabolism of lysine occurs.