Osmotic effects on bacterial transport and energetics.

Paracoccus denitrificans suspended in media containing 20-300 mM NaCl swelled progressively as the salt concentration was decreased. The increase in intracellular water volume was accompanied by an enhancement of respiration and a stimulation of the rates of net potassium and alpha-aminoisobutyric acid accumulation. It is postulated that influx of water and consequent lowering of intracellular solute concentration trigger transport mechanisms which are destined to restore the original ion and metabolite balance. Since a number of transport reactions operate against the electrochemical gradient of their substrates, energy utilization increases. The increased ATP usage and lowering of [ATP] stimulates the activity of the respiratory chain and increases oxygen uptake and energy production.