Membrane Stability and Salt Tolerance in Gram-negative Bacteria

Abstract

THE ability of a bacterium to tolerate any particular set of ionic conditions is likely to be determined in part by the outermost permeability barrier of the organism. This barrier, which is usually a lipoprotein membrane, is in contact with the extracellular environment and must remain functional under all conditions which permit growth of the organism. It has already been shown that the cell envelopes (or membranes) of two Gram-negative bacteria, one a marine organism (N.C.M.B. 845) requiring moderate concentrations of salt and the other a halophil (Halobacterium halobium) requiring high concentrations of salt, are unstable at low ionic strengths. The structural integrity of these two types of envelope depends, to a different degree in each case, on ionic strength or the concentration of bivalent cations^1,2. The work recorded here was undertaken to determine if cation-sensitive instability of bacterial membranes is a general phenomenon and if there is evidence of a correlation between membrane properties and salt tolerance of the growing organism.