Cell-cycle effects on the kinetics of silicic acid uptake and resource competition among diatoms

Current models of nutrient utilization by planktonic algae generallyassume that cells transport nutrients continuously. This assumptionis violated in the case of Si utilization by diatoms. Silicicacid transport is confined to specific portions of the cellcycle such that only a fraction of the cells in a populationare likely to be transporting silicic acid at any given time.A theoretical framework for describing the growth and nutrient-uptakekinetics of populations of cells exhibiting cell-cycle-dependentnutrient uptake is presented. Thalassiosira weissflogii wasused as a model organism. Kinetic parameters determined at steadystate, assuming cells take up Si continuously, underestimatedboth the V_m and K_s of individual cells by nearly an order ofmagnitude. Likewise, kinetic constants determined from short-termexperiments assuming continuing uptake were shown to be dependenton the initial physiological state of the population and todramatically underestimate the kinetic parameters of individualcells. The response of steady-state populations to large pulsesof dissolved Si was also examined. The ratio of the averagemaximum specific uptake rate of the culture to the average maximumobservable specific growth rate (V' _mavg/