Relationship of Cell Surface Hydrophobicity to Morphology of Monomorphic and Dimorphic Fungi

ABSTRACT

Germ tubes of the dimorphic human pathogenic fungus Candida albicans are hydrophobic, but the level of yeast cell wall hydrophobicity is dependent on growth temperature. Cell wall hydrophobicity of several other dimorphic fungi was assessed in order to determine whether this characteristic is a common feature of these organisms. Yeast and mycelial monomorphic fungi were also tested. Cell wall hydrophobicity was determined by the ability of unmodified polystyrene latex microspheres to attach to fungal cells. Mycelial forms of four dimorphic fungi, Histoplasma capsulatum, Blastomyces dermatitidis, Sporothrix schenckii, and Paracoccidioides brasiliensis, and two monomorphs, Aspergillus fumigatus and Penicillium chrysogenum, were hydrophobic. Expression of surface hydrophobicity of yeast cells was organism-specific. Growth temperature did not determine the level of surface hydrophobicity of two monomorphic yeasts, Saccharomyces cerevisiae and Cryptococcus neoformans. However, the general distribution of microspheres attached to S. cerevisiae differed depending on growth temperature. Attachment of microspheres to C. albicans was substantially lower at pH 9.0 than at pH 7.0. At higher pH, yeast cell clumps of H. capsulatum disaggregated suggesting that hydrophobic interactions may be involved. Elevated pH did not prevent microsphere attachment to several other fungi. A cell wall digest of C. albicans obtained by lyticase treatment inhibited microsphere attachment to hydrophobic yeast cells of C. albicans but was less effective with S. cerevisiae. Hydrophilic C. albicans yeast cells exhibited increased cell surface hydrophobicity before morphologic evidence of germination was observed. These results indicate that surface hydrophobicity may be an important feature of the mycelial form of fungi but the hydrophobic components of these fungi may differ.

Key Words:

• hydrophobicity
• polystyrene
• dimorphism
• Candida albicans