PHYSICOCHEMICAL PROPERTIES AND SURFACE COMPONENTS OF PHOTORHABDUS-LUMINESCENS INFLUENCING BACTERIAL INTERACTION WITH NON-SELF RESPONSE SYSTEMS OF NONIMMUNE GALLERIA-MELLONELLA LARVAE

Mutants of Photorhabdus luminescens with increased virulence for Galleria mellonella were used to determine the relationship of bacterial physicochemical properties, outer membrane composition, and interaction with the antibacterial systems of G. mellonella larvae to bacterial virulence. Insect serum slowed the growth of the wild type and both mutant bacteria. In part, this was attributed to increased spheroplast formation. Spheroplast formation was associated with increased sensitivity to insect lysozyme and reduction in bacterial cationic charge and was independent of bacterial hydrophobicity. Increased hydrophobicity of the PBr mutant resulted in increased attachment to the insect's hemocytes but not the accelerated removal of bacteria from the hemolymph. Attachment of both mutants to the insect hemocytes in vitro increased as the bacterial lipopolysaccharide content increased, and the level of inhibition of prophenoloxidase activation decreased and cationic charge decreased. Bacterial emergence into the hemolymph occurred in parallel with hemocyte damage but neither the level of the total lipopolysaccharides in the bacteria nor the rate of bacterial emergence was associated with virulence. The rate of lipopolysaccharides released into the hemolymph influenced the rate of hemocyte damage. The contribution of outer membrane proteins to lipopolysaccharide release, bacterial adhesion to hemocytes, and virulence is discussed. (C) 1995 Academic Press, Inc.