INFLUENCE OF INTRA-AMEBIC AND OTHER GROWTH-CONDITIONS ON THE SURFACE-PROPERTIES OF LEGIONELLA-PNEUMOPHILA

The surface properties of Legionella pneumophila were examined by anal yzing outer membrane (OM) proteins, lipopolysaccharides (LPS), and cel lular fatty acids after growth within Acanthamoeba polyphaga and in vi tro under various nutrient-depleted conditions. Intra-amoeba-grown leg ionellae were found to differ in several respects from cells grown in vitro; most notably, they contained a 15-kDa OM protein and a monounsa turated straight-chain fatty acid (18:19). These compounds were also f ound in abundant quantities in the host amoeba. Immunoblot analysis of intra-amoeba-grown legionellae with antiacanthamoebic serum revealed that both the bacterial whole cells and Sarkosyl-extracted OMs contain ed amoebic antigens. The findings suggest that the 15-kDa OM protein i s likely to be of amoebic origin and associates with the OM of the bac terium. It is proposed that disruption of amoebic membranes, as a resu lt of intra-amoebic infection, may liberate macromolecules, including a 15-kDa polypeptide, a major constituent of the amoebic membrane, whi ch adhere to the surface of the legionellae. Growth under specific nut rient depletions also had a significant effect on the surface composit ion of L. pneumophila. Cells grown under phosphate depletion were mark edly sensitive to protease K digestion and contained lower levels of L PS, as observed by silver staining of the digests on polyacrylamide ge ls. Intra-amoeba-grown cells contained more bands than the in vitro-gr own organisms, reflecting further differences in the nature of the LPS . The whole-cell fatty acids of the phosphate-depleted cells were appr eciably different from those of cells grown under other nutritional co nditions. We found no evidence for expression of iron-regulated OM pro teins under iron depletion.