Flagellar Adherence ofCrithidia fasciculataCells in Culture1

Occurrence of N-acetyl- and N-O-diacetyl-neuraminic acid derivatives in wild and mutant Crithidia fasciculata

The cell-surface expression of sialic acids in wild-type Crithidia fasciculata and three drug-resistant mutants (FU(R)11, TR3, and TFRR1) was analyzed using fluorescein-labeled Limulus polyphemus agglutinin (LPA) binding, glycosidase of known sugar specificity, and thin-layer chromatography (TLC). Gas-liquid chromatography-mass spectrometry (GC-MS) analysis using both electron-impact (EI-MS) and chemical ionization (CI-MS) by isobutane with selected ion monitoring (SIM) was also used. The surface location of sialic acid was inferred from LPA binding to whole cells abrogated by previous treatment with neuraminidase. An exception occurred with the TFRR1 strain, which after incubation with neuraminidase showed increased reactivity with the fluorescent lectin. Both N-acetyl- and N-O-diacetyl-neuraminic acids were identified in the flagellates by TLC, with a clear predominance being noted for the former derivative. However, the content of N-O-diacetyl-neuraminic acid was preferentially found in the TFRR1 strain. The GC-MS analysis of the acidic component of the TFRR1 mutant strain confirmed the occurrence of N-acetyl-neuraminic acid (Neu5Ac) by the presence of the diagnostic ions (m/z values: 684 and 594 for CI-MS and 478, 298, and 317 for EI-MS) and also by comparison with the standard Neu5Ac retention time. GC-MS analysis also showed fragments (m/z values: 654 and 564 for CI-MS and 594, 478, 298, and 317 for EI-MS) expected for the 7-O- and 9-O-acetyl-N-acetyl-neuraminic acids (Neu5,7Ac2 and Neu 5,9Ac2, respectively).

Surface charge and hydrophobicity of wild and mutant Crithidia fasciculata

Surface charge of wild-type Crithidia fasciculata and three drug-resistant mutants (TR3, TFRR1, and FUR11) was studied by direct zeta-potential determination and ultrastructural cytochemistry. Surface tension was also investigated by measurements of the advancing contact angle formed by the protozoa monolayers with drops of liquids of different polarities. The individual zeta potential varies markedly among the C. fasciculata cells. The wild and FUR11 mutant strains displayed lower negative surface charge (-12.5 and -9.5 mV, respectively) as compared with the TR3 (-14.8 mV) and TFRR1 (-14.7 mV) mutant strains. Binding of cationized ferritin (CF) was observed at the cell surface of wild and mutant strains of C. fasciculata. Neuraminidase treatment reduced the negative surface charge in the TFRR1 and TR3 mutants in about 37 and 29%, respectively, whereas no significant change was observed with the wild and FUR11 mutant strains. These findings suggest that sialic acid residues are the major anionogenic groups on the surface of C. fasciculata. The density of sialic acid residues per cell in wild and mutant strains of C. fasciculata falls in a range of 1.4 x 10(4) to 3.6 x 10(4). Marked differences of hydrophobicity were also observed. For example, the TFRR1, FUR11, and TR3 drug-resistant mutant strains showed higher contact angle values (55.4, 54.2, and 49.3, respectively) than the wild-type (35.6), as assessed by alpha-bromonaphtalene.