Flocculation of the yeast Candida famata (Debaryomyces hansenii): An essential role for peptone

Aggregation of Candida famata (Debaryomyces hansenii) is consistent with being a form of lectin-mediated yeast flocculation. Flocculation of C, famata is unusual in that it requires the presence of peptone, either in the growth medium or added later to harvested cells in buffer. Flocculation after pep:one addition was rapid, being largely complete within 10 min. Heat-killed cells also flocculated, arguing for direct participation of peptone in the flocculation binding mechanism. Flocculent C. famata cells progressively lost the ability to flocculate when washed with EDTA. Flocculation was fully restored by peptone addition; calcium addition was without effect. C. famata cells were able to agglutinate erythrocytes in the presence or absence of peptone. Pronase E-treated yeast lost both the ability to haemagglutinate and self-flocculate. Haemagglutination was not diminished by progressive EDTA washing, suggesting that surface lectins remained present and active on the yeast cell walls. Non-flocculating C. famata cells mutually flocculated with non-flocculent Schizosaccharomyces cells, shown to have surface-exposed galactose residues. Mutual flocculation was lost following treatment of C. famata with Pronase E. It was concluded that the cell wall of C. famata contains lectins enabling haemagglutination and mutual flocculation but lacks carbohydrate receptors for these lectins. This yeast self-flocculates only via bridging multi-valent carbohydrates; these being present in peptone.