Cell Cycle and N Acquisition 1 Cell Cycle Implication on Nitrogen Acquisition and Synchronization in Thalassiosira Weissflogii (bacyllariophyceae)

The Michaelis-Menten model of nitrogen acquisition, originally used to represent the effect of nutrient concentration on the phytoplankton uptake rate, is inadequate when other factors show temporal variations. Literature generally links the diurnal oscillations of nitrogen acquisition to a response of the physiological status of microalgae to the photon flux density and to the substrate availability. This work aims at analyzing how the cell cycle also constitutes a significant determinant of nitrogen acquisition and, where appropriate, at assessing the impact of this property at the macroscopic level. For this purpose, we carried out continuous culture experiments of the diatom Thalassiosira weissflogii (Grunow) Fryxell & Hasle exposed to various conditions of light and nitrogen supply. Results revealed a decrease in nitrogen acquisition when a significant proportion of the population is in mitosis. This observation suggests that the nitrogen acquisition is incompatible with mitosis and thus is not continuous during the cell cycle. In addition, environmental conditions, such as the light signal and the nutrient supply, interfere with the cell cycle at the individual level, and finally affect the synchrony of the population.