Attachment of the yeast Rhodosporidium toruloides is mediated by adhesiveslocalized at sites of bud cell development

The basidiomycetous yeast Rhodosporidium toruloides (anamorph, Rhodotorula glutinis) is a common phylloplane epiphyte with biocontrol potential. To un derstand how R. toruloides adheres to plant surfaces, we obtained nonadhere nt fungal mutants after chemical mutagenesis with methane-sulfonic acid eth yl eater. Sixteen attachment-minus (Att(-)) mutants were identified by thre e methods: (i) screening capsule-minus colonies for loss of adhesive abilit y; (ii) enrichment for mutants unable to attach to polystyrene; and (iii) s election for reduced fluorescence of fluorescein isothiocyanate-concanavali n A (Con A)-stained cells by fluorescence-activated cell sorting. None of t he 16 mutants attached to polystyrene or barley leaves. The lectin Con A el iminated adhesion in all of the wild-type isolates tested. Hapten competiti on assays indicated that Con A bound to mannose residues on the cell surfac e. Adhesion of wild-type R. toruloides was transient; nonadhesive cells sub sequently became adhesive, with bud development, All Att(-) mutants and non attaching wild-type cells lacked polar regions that stained intensely with fluorescein isothiocyanate-Con A and India ink. Lectin, enzyme, and chemica l treatments showed that the polar regions consisted of alkali-soluble mate rials, including mannose residues. Tunicamycin treatment reduced wild-type adhesion, indicating that the mannose residues could be associated with gly coproteins, We concluded that compounds, including mannose residues, that a re localized at sites of bud development mediate adhesion of R. toruloides to both polystyrene and barley leaf surfaces.