Serological Studies on the Fimbriae of Yeasts and Yeastlike Species

Antisera prepared against pure fimbrial proteins of Ustilago violacea (antiserum U) and of Rhodotorula rubra (antiserum R) agglutinate cells carrying fimbriae of appropriate cross-reactivity. All except one of 24 species of smut fungi in the Ustilaginales agglutinated strongly with antiserum U and varied from no response to moderate agglutination with antiserum R. The exceptional species, Tilletia caries, has been shown to be afimbriate under tested conditions. A group of 42 strains of basidiomycetous yeasts varied in their response from no agglutination to either antiserum, agglutination with one antiserum, or agglutination with both antisera. Approximately one-quarter were afimbriate under the tested conditions. Fimbriated basidiomycetous yeasts, like the smut fungi, produce long flexuous fimbriae with a maximum length ca. 10-20 μm. Eleven ascomycetous yeasts produced a short fringe of fimbriae, usually ca. 0.5-1.0 μm long. Many of these species were agglutinated by one or both antisera, but none of five algal species responded to either antibody. No strains responded to control sera, and tests on a few species with purified antisera confirmed the results with crude sera. The agglutination response was correlated with visible fimbriation on all occasions, including studies with temperature-sensitive fimbriated strains. These results indicate that a family of relatively conserved proteins is common to many species of smut fungi, basidiomycetous yeasts, and ascomycetous yeasts.