DEVELOPMENT OF XYLOSE-FERMENTING YEASTS FOR ETHANOL-PRODUCTION AT HIGH ACETIC-ACID CONCENTRATIONS

Mutants resistant to comparatively high levels of acetic acid were iso lated from the xylose-fermenting yeasts Candida shehatae and Pichia st ipitis by adapting these cultures to increasing concentrations of acet ic acid grown in shake-flask cultures. These mutants were tested for t heir ability to ferment xylose in presence of high acetic acid concent rations, in acid hydrolysates of wood, and in hardwood spent sulfite l iquor, and compared with their wild-type counterparts and between them selves. The P. stipitis mutant exhibited faster fermentation times, be tter tolerance to acid hydrolysates, and tolerance to lower pH.