Dimorphic behaviour of Debaryomyces hansenii grown on barley bran acid hydrolyzates

Debaryomyces hansenii exhibited yeast-to-mycelium dimorphism in the continuous fermentation of xylose-containing media made from acid hydrolyzates of barley bran. The lower the dilution rate, the earlier the yeast-to-mycelia transition occurred. Within a selected range of dilution rates, the yeast morphology was reversibly affected by the dissolved O-2: low aeration caused the transition from oval cells to hyphae, and further increases in dissolved O-2 concentration resulted in recuperation of the oval shape. Under the operational conditions assayed, xylitol was the major fermentation product when the yeast was in both morphological forms, whereas the production of ethanol was increased when the yeast grew under hyphal morphology and oxygen limitation. The lower xylose consumption corresponded to the yeast-to-mycelia transition. In media made with commercial sugars (xylose or glucose), the yeast-to-mycelia transition was induced by adding selected amounts of acid-soluble lignin.