ETHANOL-PRODUCTION FROM A MIXTURE OF GLUCOSE AND XYLOSE BY COCULTURE OF PICHIA-STIPITIS AND A RESPIRATORY-DEFICIENT MUTANT OF SACCHAROMYCES-CEREVISIAE

The effect of oxygenation on ethanol production from xylose or glucose by Pichia stipitis in batch culture was investigated, The fermentatio n parameters with respect to ethanol production by P. stipitis were st rongly dependent on the oxygen transfer rate (OTR). On the basis of OT R values, the relationship between the optimum specific oxygen uptake rate (qO(2)) and maximum specific ethanol production rate ((q(p))(max) was evaluated. The optimum qO(2) for ethanol production was 14.3 or 6 6.7 mg.(g cell)(-1).h(-1) when xylose or glucose was used as a carbon source, respectively. When a mixture of glucose and xylose was used as the carbon source in a culture of P. stipitis alone, the yield and pr oductivity of ethanol were significantly enhanced when qO(2) was adjus ted to an optimum level dependent upon the type of sugar consumed. In a co-culture of Saccharomyces cerevisiae and P. stipitis, it was impos sible to control qO(2) at an optimum value for xylose fermentation by P. stipitis because oxygen was consumed by the S. cerevisiae. In a co- culture of P. stipitis and a respiratory-deficient mutant of S. cerevi siae, the optimum qO(2) for xylose fermentation by P. stipitis was suc cessfully maintained due to the low oxygen consumption of the mutant y east strain. Co-culture of these two strains resulted in the maximum y ield and the highest productivity of ethanol from a mixture of glucose and xylose.