Non-proton-motive-force-dependent sodium efflux from the ruminal bacterium Streptococcus bovis: bound versus free...

Area of Science:

• Microbiology
• Cellular Physiology
• Biochemistry

Background:

• Intracellular sodium concentration is critical for bacterial cell function.
• The mechanisms of sodium transport and its regulation in bacteria are not fully understood.
• Streptococcus bovis JB1 is a relevant model organism for studying bacterial ion transport.

Purpose of the Study:

• To investigate the intracellular sodium content and transport mechanisms in Streptococcus bovis JB1.
• To determine the relationship between sodium efflux, cellular energy status, and ATP synthesis.
• To explore the potential for a bound sodium pool within bacterial cells.

Main Methods:

• Measurement of intracellular sodium content in growing and stationary phase cells.
• Analysis of sodium efflux under various conditions, including glucose energization and ionophore treatment.
• Assessment of ATP levels and ATP synthesis driven by artificial sodium gradients.
• Use of specific inhibitors targeting glycolysis and proton-motive force.

Main Results:

• Growing S. bovis JB1 cells exhibit high intracellular sodium content, with a significant portion being bound and exchangeable for potassium.
• Sodium expulsion from stationary phase cells is rapidly induced by glucose and directly correlated with ATP hydrolysis.
• Inhibitors of proton-motive force had minimal impact on sodium efflux, suggesting a non-canonical mechanism.
• Sodium-driven ATP synthesis was observed, independent of the H+-ATPase inhibitor dicyclohexylcarbodiimide (DCCD).

Conclusions:

• Streptococcus bovis JB1 possesses a substantial pool of bound intracellular sodium.
• Sodium expulsion is directly coupled to ATP hydrolysis, indicating a novel energy-dependent mechanism.
• The findings challenge conventional models of bacterial sodium transport and highlight a unique energy coupling strategy.