Chemoreception in a marine cryptophyte: Behavioral plasticity in response to amino acids and nitrate

The behavioral responses of Chroomonas sp. to ammonium, nitrate, and 19 ind ividual amino acids were examined by computer-assisted video motion analysi s. Cells were cultured with either glycine or nitrate as the sole nitrogen source. Relative to seawater, rates at which glycine-grown cells stopped an d turned were significantly reduced in response to 10(-6) and 10(-7) M glut amate, methionine, alanine, and aspartate. This response was akin to the tu mbling behavior (chemotaxis) displayed by flagellated bacteria. When cultur ed in nitrate, Chroomonas sp. did not react to amino acids and ammonium but did significantly reduce stopping and turning in response to 10(-6) M nitr ate. These results are the first to demonstrate chemoreception in any crypt ophyte species. Because Chroomonas sp. commonly lives in habitats where lig ht and inorganic nutrients are limiting, behavioral mechanisms that maximiz e use of both amino acids and nitrate would seem particularly adaptive.