Surface charge and surface carbohydrates of Cyptobia salmositica virulent and avirulent forms and of C. bullocki (Kinetoplastida: Cryptobiidae).

The surface charge and surface carbohydrate residues of the virulent (freshly isolated from the fish blood) and avirulent forms (from culture) of Cryptobia salmositica and one strain of C. bullocki were studied. Measurements of the zeta potential of parasites showed that C. bullocki and the virulent form of C. salmositica had a net negative surface charge of about -15 mV, whereas the attenuated form of C. salmositica showed a surface charge of -7.9 mV. Enzymatic treatments of parasites with neuraminidase, trypsin, or phospholipase C indicated the presence of sialic acid residues, phosphate groups, and protein glycoconjugates as components of the Cryptobia surface that accounted for their surface charge. Residues of alpha-D-man, alpha- and beta-D-gal, alpha-D-galNAc, alpha-L-fuc, and D-glcNAc could be detected on the surface of all parasites by specific fluorescein isothiocyanate (FITC)- and colloidal gold-labeled lectins. The cell surface of the avirulent form of C. salmositica showed the strongest reactivity to almost all lectins tested. A remarkable binding pattern of lectins in the anterior region of parasites was observed.