Parasitism of yeasts by lignicolous Basidiomycota and other fungi

Abstract

On water agar, hyphae of certain fungi are able to attack microcolonies and even solitary cells of yeasts belonging to the genera Candida, Cryptococcus, Pichia, Rhodotorula, and Sporidiobolus. The ability to attack yeasts is particularly common among the Basidiomycota and 100 of 195 isolates tested positive. In the Ascomycota and Deuteromycota, only 12 of 128 isolates tested positive. Two species of the Oomycota and 10 species of the Zygomycota tested negative. Two types of initial responses were recorded: (i) a chemotropic response in which directional hyphae are attracted to microcolonies or solitary cells, and (ii) a contact response in which hyphae reach yeast colonies by chance and subsequently attack them. In both cases the invading fungus produces coralloid masses of branched assimilative hyphae within the yeast colonies. Yeast cells are utilized as a nutrient source by the invading fungus in either of two ways: (i) the walls of yeast cells are lysed releasing the contents that are absorbed by the coralloid hyphae or (ii) branched hyphae from the invading fungus attach to the yeast cells, penetrate the walls, and absorb the contents. Both methods involve necrotrophic mycoparasitism. Keywords: yeasts, Basidiomycota, necrotrophic mycoparasitism, wood decay, nitrogen requirements.