The positive role of voids in the plasma membrane in growth and energeticsof Escherichia coli

Bacterial respiration, endogenous as well as induced respiration by glucose , lactose and glycine betaine, was found to be sensitive to external solute concentration. Permeability of hydrogen peroxide, a non-electrolyte of mol ecular size between water and urea, through the bacterial membranes changed directly with the rate of respiration (an activity residing in the bacteri al plasma membrane) in E. coli and the enhanced permeability and respirator y activity were highly correlated Hydrogen peroxide permeability and induct ion of voids (spaces in the matrix of the bilayer into which hydrophobic fl uorescent probes partition, which in turn were used to assess the modulatio n of these cavities) were shown to be a direct and excellent measure of lea k conductance. Fluorescence intensity and anisotropy of the extrinsic fluor escent probes (incorporated by growing bacteria in their presence) decrease d with increased respiration in bacteria, consistent with lowered molecular restriction and enhanced hydration in the membrane phase for these probes as seen in dimyristoylphosphatidylcholine bilayers due to phase transition. The physical basis of osmotic phenomena, as a relevant (thermodynamic) vol ume, could relate to water exchange or compression depending on the osmotic domain. In the domain of compression in bacteria, i.e. well above the isot onic range, the computed activation volume was consistent with voids in the membrane. This study emphasises a major role of leak conductance in bacter ial physiology and growth. (C) 2000 Elsevier Science B.V. All rights reserv ed.