Localized, positive charge mediates adhesion of Rhodosporidium toruloides to barley leaves and polystyrene

The physicochemical forces that mediate attachment of yeasts to the phyllop lane are unknown. Cell surface charge and hydrophobicity and adhesion to po lystyrene, glass, and barley were assessed for wild-type Rhodosporidium tor uloides and attachment-minus (Att(-)) mutants. Cells were grown under condi tions promoting (excess carbon) or not promoting (excess nitrogen) capsule production. Hydrophobicity was measured by adhesion to xylenes, and surface charge characteristics were assessed by attachment to either DEAE (positiv e)or carboxymethyl (CM) (negative)-Sephadex ion-exchange beads. Hydrophobic ity and adhesiveness of nonencapsulated, wild-type R. toruloides decreased from mid-log to late stationary phase. Encapsulated wild-type R. toruloides cells were more hydrophobic and more adhesive than nonencapsulated cells. However, two encapsulated Att(-) mutants were more hydrophobic than the wil d type and levels of adhesion of R. toruloides were similar on polystyrene and less hydrophobic glass surfaces. Adhesion of wild-type yeast to barley and polystyrene was correlated with attachment to CM-Sephadex beads, indica ting a positive cell surface charge. Sixteen Att(-) mutants did not exhibit a positive cell surface charge, and wild-type yeast cells that did not att ach to CM-Sephadex did not adhere to either polystyrene or barley. Wild-typ e R. toruloides attached to CM-Sephadex beads by the poles of the cells, in dicating a localization of positive charge which was also visualized with I ndia ink We conclude that localized, positive charge, and not hydrophobic i nteractions, mediates attachment of R. toruloides to barley leaves.