Potassium uptake and retention by Oceanomonas baumannii at low water activity in the presence of phenol

Oceanomonas baumannii^T (ATCC 700832) is a halotolerant bacterium capable of degrading phenol, which requires potassium in order for turgor growth to occur in minimal medium containing 5% NaCl (w/v). However, at this salinity growth can be inhibited by reduced potassium concentrations. The affinity for potassium (K_S) was determined to be 219 μM and 408 μM for cultures utilising phenol and succinate respectively as the sole carbon source for growth. Rubidium but not caesium could substitute for potassium in alleviating growth inhibition due to potassium limitation. The effect of elevated phenol on potassium retention was studied, and it was shown that contrary to expectations, as external phenol concentration was increased the levels of intracellular potassium were significantly elevated. This observation correlated with changes in the cytoplasmic membrane, particularly the increase in the saturated:unsaturated fatty acid ratio from 0.47 to 1.44, and the decrease in the zwitterionic:anionic phospholipid ratio from 2.23 to 1.22. Both these changes promote membrane bilayer configurations and increase lipid ordering of the membrane reducing its permeability and inhibiting cation efflux.