Ammonium and methylammonium uptake in a fertilizer-degrading strain of Ochrobactrum anthropi

The transport of ammonium and methylammonium was studied in a strain of Ochrobactrum anthropi, a microorganism isolated from garden soil and able to degrade methyleneureas which are used as slow-release nitrogen fertilizer. The activity of both transport systems was determined using [14C]methylammonium. Differences between the two transport systems were observed with regard to their pH- and temperature dependence as well as their kinetic parameters and regulation during growth with various nitrogen sources. Ammonium transport was subject to repression by ammonium and to derepression in its absence, while the methylammonium carrier was induced in the presence of methylamine. The ammonium but not the methylammonium transport system was severely inhibited by ammonium, and metabolic poisons inhibited both uptake systems. The analysis of intracellular metabolites using thin-layer chromatography and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry indicated that methylammonium was rapidly metabolized to N-methylglutamate via gamma-N-methylglutamine.