Ammonia/potassium exchange in methanogenic bacteria.

Area of Science:

• Microbiology
• Biochemistry
• Cell Physiology

Background:

• Methanogenesis is a vital microbial process.
• Cellular ion gradients, particularly potassium (K+), are crucial for microbial function.
• Ammonia (NH3) transport across cell membranes is a key factor in microbial environments.

Purpose of the Study:

• To investigate the mechanism and consequences of ammonia-induced potassium (K+) loss in Methanospirillum hungatei.
• To determine the role of ammonia/K+ exchange in cellular ion homeostasis and its effect on methanogenesis.
• To assess the sensitivity of methanogenesis to pH gradients and ammonia exposure in various microorganisms.

Main Methods:

• Exposure of Methanospirillum hungatei to ammonia in potassium-free buffer.
• Measurement of intracellular potassium (K+) loss.
• Analysis of transmembrane pH gradient and membrane potential changes.
• Testing methanogenesis inhibition across a range of external pH values in multiple species.

Main Results:

• Methanospirillum hungatei lost up to 98% of cytoplasmic K+ through immediate ammonia/K+ exchange.
• Ammonia (NH3) was identified as the likely species crossing the membrane, particularly at alkaline pH.
• The exchange dissipated the transmembrane pH gradient and affected membrane potential.
• Methanogenesis was significantly inhibited at external pH < 6.5 or > 7.5 in M. hungatei and Methanosarcina barkeri.
• Ammonia-induced K+ depletion was observed in Escherichia coli and Bacillus polymyxa, but not in all methanogens.

Conclusions:

• Ammonia/K+ exchange is a significant mechanism for K+ loss in M. hungatei, influenced by pH.
• Methanogenesis is highly sensitive to both cytoplasmic and external pH, with optimal activity within a narrow range.
• The observed ammonia/K+ exchange and its impact on methanogenesis vary among different microbial species.