Limnol. Oceanogr., 44(6), 1999, 1571–1574

Fig. 1. Mean (6SEM [standard error of the mean]) stop-and-turn rates of glycine-grown cells in response to artificial seawater (ASW), ammonium (NH4), nitrate (NO3), and amino acids. Abbreviations for amino acids are standard three-letter codes. The Y-axis units are Hertz (Hz), the number of stops and turns per second. A minimum of 40 paths was analyzed for ASW and each chemical; compounds were presented at 1026 M. Relative to ASW, significant changes in stop-andturn rates were determined by a one-way ANOVA followed by pairwise comparisons using Bonferroni’s correction: * P , 0.05; ** P , 0.01. Abstract—The behavioral responses of Chroomonas sp. to ammonium, nitrate, and 19 individual amino acids were examined by computer-assisted video motion analysis. Cells were cultured with either glycine or nitrate as the sole nitrogen source. Relative to seawater, rates at which glycine-grown cells stopped and turned were significantly reduced in response to 1026 and 1027 M glutamate, methionine, alanine, and aspartate. This response was akin to the tumbling behavior (chemotaxis) displayed by flagellated bacteria. When cultured in nitrate, Chroomonas sp. did not react to amino acids and ammonium but did significantly reduce stopping and turning in response to 1026 M nitrate. These results are the first to demonstrate chemoreception in any cryptophyte species. Because Chroomonas sp. commonly lives in habitats where light and inorganic nutrients are limiting, behavioral mechanisms that maximize use of both amino acids and nitrate would seem particularly adaptive.