Effect of iturin A, a lipopeptide from Bacillus subtilis on morphology and ultrastructure of human erythrocytes.

Iturin A, a lipopeptide from Bacillus subtilis, induced morphological modifications of human erythrocytes and a concomitant release of exovesicles. The modifications depended on the lipopeptide concentration and on the incubation time. Crenation of cells occurred while invaginations appeared when the incubation time was increased. This suggested that iturin A was gradually translocated from the outer layer into the inner half of the bilayer. For one lipopeptide concentration, heterogeneity in the form of the erythrocytes was observed which could result from heterogeneity in the self-association of iturin A. The lipid composition of exovesicles was markedly different from that of the native erythrocytes; they were enriched in cholesterol, sphingomyelin and phosphatidylcholine. Freeze-fracture showed that the ultrastructure of the protoplasmic face of the membrane was not modified by iturin A but, when erythrocytes were prefixed with glutaraldehyde prior to iturin A treatment, irregular smooth protuberances appeared with a decrease of intramembranous particles density. These protuberances which covered the complete area of the cell may have been complex associations of iturin A, phospholipids and cholesterol.