Ammonium Transport in the Alkalophilic Diazotrophic Cyanobacterium Nostoc calcicola: Influence of Phosphate Limitation and Metabolic Inhibitors

Abstract

Ammonium transport in the diazotrophic cyanobacterium Nostoc calcicola was investigated in phosphate-sufficient and deficient conditions. Cells grown under phosphate-deficient conditions were characterized by a decrease in specific growth rate, phycocyanin content (50 %), oxygen evolution (50 %), reduced ATP pool and derepressed alkaline phosphatase activity. Under these conditions ammonium transport exhibited no change in Km (10.0 µM) in comparison to phosphate-sufficient cells, but a change in Vmax (41.0 nmol mg-1 protein min-1) was observed. The reduced rate of ammonium transport was attributed to unavailability of sufficient energy. Conditions that lowered or abolished the ATP pool (dark incubation or treatment with metabolic inhibitors DCMU, DCCD or CCCP) also reduced ammonium transport via two transport systems. The results indicated that unavailability of phosphate in the immediate environment may limit ammonium transport by a diazotrophic cyanobacterium. © 1991, Gustav Fischer Verlag, Stuttgart. All rights reserved.