Disruption of the cytochrome c gene in xylose-utilizing yeast Pichia stipitis leads to higher ethanol production

Abstract

The xylose-utilizing yeast, Pichia stipitis, has a complex respiratory system that contains cytochrome and non-cytochrome alternative electron transport chains in its mitochondria. To gain primary insights into the alternative respiratory pathway, a cytochrome c gene (PsCYC1, Accession No. AF030426) was cloned from wild-type P. stipitis CBS 6054 by cross-hybridization to CYC1 from Saccharomyces cerevisiae. The 333 bp open reading frame of PsCYC1 showed 74% and 69% identity to ScCYC1 and ScCYC7, respectively, at the DNA level. Disruption of PsCYC1 resulted in a mutant that uses the salicylhydroxamic acid (SHAM)-sensitive respiratory pathway for aerobic energy production. Cytochrome spectra revealed that cytochromes c and a*a3 both disappeared in the cyc1-D mutant, so no electron flow through the cytochrome c oxidase was possible. The cyc1-D mutant showed 50% lower growth rates than the parent when grown on fermentable sugars. The cyc1-D mutant was also found to be unable to grow on glycerol. Interestingly, the mutant produced 0*46 g/g ethanol from 8% xylose, which was 21% higher in yield than the parental strain (0.38 g/g). These results suggested that the alternative pathway might play an important role in supporting xylose conversion to ethanol under oxygen-limiting conditions.

Citation

Shi, Nian-Qing.; Davis, Brian.; Sherman, Fred.; Cruz, Jose.; Jeffries, Thomas W. 1999. Disruption of the cytochrome c gene in xylose-utilizing yeast Pichia stipitis leads to higher ethanol production. Yeast. Vol. 15 (1999).:p. 1021-1030 : ill.