Interaction of lipopolysaccharide with detergents and its possible role in the detergent resistance of the outer membrane of Gram-negative bacteria.

In the presence of MgCl2, amounts of detergents which disrupted phospholipid vesicles caused lipopolysaccharide I from Proteus mirabilis to aggregate and form vesicular, membrane-like structures. Vesicle formation with P. mirabilis lipopolysaccharide II containing longer O-polysaccharide chains was extremely poor. Lipopolysaccharides of Salmonella minnesota R mutants (chemotypes Ra, Rc and Re) displayed a growing tendency for vesicle formation with increasing deficiency of the R core polysaccharide. Lipopolysaccharides of chemotypes Rc and Re produced vesicles even in the absence of MgCl2 and detergent. Spherical aggregates consisting of P. mirabilis lipopolysaccharide I MgCl2 and detergent were unable to either entrap or retain [14C]-sucrose, [3H=inulin or [3H]dextran. On the other hand, S. minnesota R mutant lipopolysaccharides of chemotypes Rc and Re could entrap all three saccharides and retain them for at least short periods of time. Leakage of [3H]-inulin out of re-lipopolysaccharide vesicles was greatly retarded by addition of MgCl2 to the vesicle system. Incorporation of P. mirabilis lipopolysaccharide I or S. minnesota Rc lipopolysaccharide into phospholipid vesicles protected these model membranes from disruption by detergent. This suggested a similar protective function of lipopolysaccharide in the outer membrane of enteric bacteria against the action of surfactants occurring in their normal intestinal habitat.