CELLULAR CHARGE OF CRYPTOCOCCUS-NEOFORMANS - CONTRIBUTIONS FROM THE CAPSULAR POLYSACCHARIDE, MELANIN, AND MONOCLONAL-ANTIBODY BINDING

Cryptococcus neoformans is a human pathogenic fungus which is unusual in two respects: it has a polysaccharide capsule similar to that found in encapsulated bacteria and it can produce melanin, Capsular and mel anization phenotypes are associated with virulence. In this study we a nalysed the contributions of the capsular polysaccharide, melanization , and antibody binding to the capsule to the cellular charge of C. neo formans. Cell charge was inferred from measurements of zeta potential. The results indicate that (i) C. neoformans cells are significantly m ore negatively charged than Saccharomyces cerevisiae cells, (ii) the p olysaccharide capsule of C. neoformans is responsible for the high neg ative charge of the cells, (iii) C. neoformans melanin is negatively c harged, (iv) melanization in C. neoformans is associated with an incre ased negative charge per cell and (v) antibody binding to the capsule of C. neoformans significantly alters the cell charge, These results s uggest that alterations in cell charge attributable to polysaccharide capsule formation, melanisation, and antibody binding may affect C. ne oformans virulence given that macrophage phagocytosis is effected by t he zeta potential of microorganisms.