Comparative studies of flocculation and deflocculation of Saccharomyces uvarum and Kluyveromyces bulgaricus

Summary

Flocculation of Kluyveromyces bulgaricus and Saccharomyces uvarum occurred when these yeasts were grown in a peptone glucose medium enriched with calcium ions. K. bulgaricus and S. uvarum flocculated at the beginning and at the end, respectively, of the exponential growth phase. After growth, both yeasts were washed with an EDTA solution, flocculated again in an acetate buffer, and optimum flocculation was obtained at pH 4.5 in the presence of 3.75 mM Ca⁺⁺. K. bulgaricus flocculation was irreversibly suppressed by incubation at 80° C for 6 min. S. uvarum needed an incubation at 100° C for 20 min to be irreversibly deflocculated. For both yeasts, flocculation stability depended on the presence of sugars. Mannose, mannose 6P and oligosaccharides bearing a mannose in a terminal non-reducing position reversed flocculation of S. uvarum, while galactose, galactose 6P and oligosaccharides bearing a galactose in a terminal nonreducing position reversed flocculation of K. bulgaricus. It is suggested that sugars specifically reverse flocculation because cell-to-cell aggregation of these yeasts is a lectin-carbohydrate-linked mechanism; not any sugar is capable of deflocculating any yeast, but the mechanism is specific.