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Uptake and metabolism of methylammonium by Pseudomonas aeruginosa
1Fachrichtung Mikrobiologie, Universität des Saarlandes, Im Stadtwald, Saarbrücken, F.R.G.
Abstract:
The mechanism of ammonium uptake was studied in Pseudomonas aeruginosa, measuring the uptake (transport and metabolism) of [14C]methylammonium (MA). This ammonium analogue was not utilized for growth, but unmetabolized MA was accumulated to intracellular concentrations about 30 times higher than those in the medium. Most of the MA taken up, however, was rapidly metabolized to gamma-N-methylglutamine, which could be removed from the cells by the addition of ammonium. Uptake of MA exhibited distinct optima at pH 7.0 and 35 to 40 degrees C and depended on metabolic energy, as indicated by the inhibitory effect of various metabolic poisons. Growth with ammonium as nitrogen source resulted in the repression of MA uptake, whereas high uptake rates were observed with nitrate or after incubation without nitrogen source. These results suggested that the ammonium/MA uptake system is subject to nitrogen control in P. aeruginosa.
Insights
Pseudomonas aeruginosa accumulates methylammonium (MA) via an energy-dependent system. This ammonium uptake mechanism is regulated by nitrogen availability, showing repression with ammonium and high rates without nitrogen.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Understanding nutrient transport mechanisms is crucial for microbial physiology.
- Ammonium uptake is a key process for bacterial growth and nitrogen assimilation.
- Pseudomonas aeruginosa is an opportunistic pathogen with complex metabolic capabilities.
Purpose of the Study:
- To elucidate the mechanism of ammonium uptake in Pseudomonas aeruginosa.
- To investigate the transport and metabolism of ammonium analogues.
- To determine the regulatory control of the ammonium uptake system.
Main Methods:
- Utilized [14C]methylammonium (MA) as an ammonium analogue to study uptake.
- Measured intracellular accumulation and metabolic conversion of MA.
- Assessed the effects of pH, temperature, metabolic inhibitors, and nitrogen sources on MA uptake.
Main Results:
- Unmetabolized MA accumulated intracellularly, while most was converted to gamma-N-methylglutamine.
- MA uptake showed optimal activity at pH 7.0 and 35-40°C, requiring metabolic energy.
- Ammonium uptake was repressed by growth on ammonium but enhanced by nitrate or nitrogen starvation.
Conclusions:
- The ammonium/methylammonium uptake system in P. aeruginosa is an active, energy-dependent process.
- The system exhibits specific physicochemical optima and is subject to nitrogen catabolite repression.
- These findings highlight the intricate nitrogen regulatory network in Pseudomonas aeruginosa.