Evidence for multiple K+ export systems in Escherichia coli.

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Potassium (K+) transport is crucial for bacterial cell homeostasis.
• The kefB and kefC genes in Escherichia coli encode proteins involved in K+ transport.
• Understanding K+ efflux mechanisms is vital for comprehending bacterial physiology.

Purpose of the Study:

• To investigate the role of KefB and KefC in Escherichia coli K+ efflux.
• To determine if KefB and KefC are involved in K+ efflux stimulated by various environmental factors.
• To identify alternative K+ efflux pathways in Escherichia coli.

Main Methods:

• Comparative analysis of K+ efflux rates in wild-type and mutant Escherichia coli strains.
• Utilizing null mutations in kefB and kefC genes.
• Stimulating K+ efflux using N-ethylmaleimide (NEM), increased turgor pressure, cytoplasmic alkalinization, and 2,4-dinitrophenol.

Main Results:

• KefB and KefC are the primary systems mediating NEM-stimulated K+ efflux.
• These systems do not significantly contribute to K+ efflux induced by high turgor pressure, cytoplasmic alkalinization, or 2,4-dinitrophenol.
• A spontaneous high rate of K+ efflux in the kefC121 mutant is further enhanced by NEM, indicating NEM-sensitive sites remain functional.

Conclusions:

• Escherichia coli possesses additional K+ efflux systems beyond KefB and KefC.
• The KefB and KefC systems are specifically involved in NEM-induced K+ efflux.
• The kefC121 mutation causes spontaneous efflux without eliminating NEM-sensitive efflux mechanisms.