Nitrogen uptake by Microcystis aeruginosa in the San Francisco Estuary Delta

This study demonstrated that Delta Microcystis can utilize different forms o f inorganic and organic N, with the greatest capacity for NH4+ uptake and the least for glutamic acid uptake, though N uptake did not always follow the classic Michaelis-Menten hyperbolic relationship at substrate concentrations up to 31 |imol N L '1. Current ambient N concentrations in the Delta are often at sub-saturating levels for N uptake, indicating that if N loading (especially N H /) were to increase, Delta Microcystis assemblages have the potential for increased N uptake rates, and increased growth, assuming steady-state and balanced growth conditions. In culture, N uptake by non-toxigenic and toxigenic M. aeruginosa strains followed similar trends to those found in the field, and both strains did not show severe inhibition o f N0 3 ~ uptake by NH4 + or inhibition o f NHt+ uptake on NO3”, but did show some inhibition o f urea uptake by N H / ; however severity o f responses to N inhibition phenomena may be strain-specific.