Response of the marine diatom Thalassiosira weissflogii to iron stress1

The coastal diatom Thalassiosira weissflogii responds to iron limitation with decreasing growth rate, decreasing quotas of cellular iron, and increasing rates of maximum short term uptake. Growth response to steady iron limitation can be modeled according to the equations of Droop and Monod. The cellular iron quota varies from about 2 to 25 × 10 −5 mol iron per liter‐cell with increasing iron; the half‐saturation constant for growth, K µ , is 1.1 × 10 −21 M (free ferric ion). In contrast, the half‐saturation constant for iron uptake, K p , is about 3 × 10 −19 M; the maximum iron uptake rate ( ρ max ) is increased several‐fold under iron limitation, resulting in a potential short term uptake rate that is a few hundred times the steady state rate. At a fixed concentration of free manganese ion, the cellular manganese quota is increased several‐fold in iron‐limited cultures compared to iron‐sufficient cultures.