The fungus colonizes oral cavity surfaces and is carried by up to 60% of human populations. Biofilm development by may be modulated by oral streptococci, such as , or , so as to augment pathogenicity. In this study we sought to determine if the cell wall-associated secreted aspartyl proteinase Sap9 was necessary for hyphal adhesin functions associated with biofilm community development. A Δ mutant of SC5314 formed biofilms that were flatter, and contained fewer blastospores and more hyphal filaments than the parent strain. This phenotypic difference was accentuated under flow (shear) conditions and in the presence of Dual-species biofilms of Δ with , , , and all contained more matted hyphae and more bacteria bound to substratum compared to wild type. Δ mutant hyphae showed significantly increased cell surface hydrophobicity, ∼25% increased levels of binding cell wall protein Als3, and reduced interaction with Eap1, implicating Sap9 in fungal cell–cell recognition. These observations suggest that Sap9 is associated with protein–receptor interactions between fungal cells, and with interkingdom communication in the formation of polymicrobial biofilm communities.
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