Nitrogen uptake kinetics of Prymnesium parvum (Haptophyte)

The uptake rates of different nitrogen (N) forms (NO₃⁻, urea, and the amino acids glycine and glutamic acid) by N-deficient, laboratory-grown cells of the mixotrophic haptophyte, Prymnesium parvum, were measured and the preference by the cells for the different forms determined. Cellular N uptake rates (ρ_cell, fmol N cell⁻¹ h⁻¹) were measured using ¹⁵N-labeled N substrates. P. parvum showed high preference for the tested amino acids, in particular glutamic acid, over urea and NO₃⁻ under the culture nutrient conditions. However, extrapolating these rates to Baltic Seawater summer conditions, P. parvum would be expected to show higher uptake rates of NO₃⁻ and the amino acids relative to urea because of the difference in average concentrations of these substrates. A high uptake rate of glutamic acid at low substrate concentrations suggests that this substrate is likely used through extracellular enzymes. Nitrate, urea and glycine, on the other hand, showed a non-saturating uptake over the tested substrate concentration (1–40 μM-N for NO₃⁻ and urea, 0.5–10 μM-N for glycine), indicating slower membrane-transport rates for these substrates.