[Nature of lactate secretion by E. coli cells]

Area of Science:

• Microbiology
• Biophysics
• Ion Transport

Background:

• Escherichia coli (E. coli) are bacteria crucial for biological research.
• Understanding ion transport is key to comprehending cellular functions and homeostasis.
• The role of specific ion fluxes in bacterial electroneutrality requires further elucidation.

Purpose of the Study:

• To quantify the ion exchange stoichiometry in E. coli suspensions.
• To investigate the mechanism of maintaining intracellular electroneutrality during ion transport.
• To determine the role of lactate (Lac--) in conjunction with proton (H+) and potassium (K+) fluxes.

Main Methods:

• Utilizing ion-selective electrodes to measure ion fluxes.
• Studying ion transport in E. coli suspensions.
• Analyzing the stoichiometry of proton-potassium-lactate exchange.

Main Results:

• The study identified a specific stoichiometry for DCCD-sensitive ionic exchange: 2H+ : K+ : Lac--.
• Evidence suggests E. coli actively secretes Lac-- anions.
• This secretion occurs during the activity of a proton-potassium pump.

Conclusions:

• The proton-potassium pump exchanges intracellular H+ for extracellular K+.
• Bacteria maintain intracellular electroneutrality by secreting Lac-- anions.
• The identified ion exchange mechanism is critical for E. coli homeostasis.