Effects of light on nitrate-limited Oscillatoria agardhii in chemostat cultures

Abstract

The effects of the average light irradiance (〈I〉) on growth and nitrate uptake kinetics of the cyanobacterium Oscillatoria agardhii, in nitrate-limited chemostat cultures, were studied. Light was nonsaturating for 〈I〉 <9.4 Wm−2, for all growth rates (μ) studied. However, μ was throughout limited by the availability of nitrate. Under light-saturating conditions the kinetics of nitrate-limited growth could be adequately described by both the Monod and Droop equations. Under light-non-saturating conditions the internal nitrogen content (Q) was a function of both μ and 〈I〉, for which new formulas were derived. The high uptake capacity (Vmax) of nitrate-limited cells was independent of μ, but was significantly increased for cells growing at 〈I〉 <9.4 Wm−2. The half-saturation constant for nitrate uptake (K s u ) increased with increasing μ, but was independent of the prevailing light conditions. The effects of light during nitrate-limited growth were associated with the regulation in the nitrogen-containing pigments.