Oral
Presentation 2-04
New
Xylose-growing Saccharomyces cerevisiae
Strain
for
Biofuel Ethanol Production
Kaisa Karhumaa, Bärbel Hahn-Hägerdal and
Marie-F. Gorwa-Grauslund*
Department
of Applied Microbiology
SE-22100
Phone: 046-222 06 19
Fax: 046-222 42 03
E-mail: Marie-Francoise.Gorwa@tmb.lth.se
Ethanol
production from renewable material is a sustainable alternative to the use of
fossil fuels. Efforts are being made to ferment lignocellulose hydrolysates to
ethanol. Saccharomyces cerevisiae is
a candidate for this purpose, since it efficiently produces ethanol from
hexoses. However, it is unable to ferment pentose sugars such as xylose. Sustainable
production of biofuel ethanol from wood hydrolysates requires the fermentation
of both the hexose and the pentose fractions.
Previously,
xylose utilisation has been achieved by the heterologous expression of
NAD(P)H-dependent xylose reductase (XR) and NAD+-dependent xylitol
dehydrogenase (XDH) from Pichia stipitis.
However, the cofactor imbalance between the two enzymes generated low ethanol
yield and productivity. Attempts to express bacterial xylose isomerase (XI)
genes have also given limited results due to a low enzyme expression and to the
inhibition of XI by xylitol. Xylose utilisation can also be limited by
transport, by a low xylulokinase level and low level of the pentose phosphate
pathway.
We have
constructed a novel recombinant S.
cerevisiae strain engineered for several of these parameters. The new strain
grows aerobically on xylose and can ferment xylose to ethanol in anaerobic
batch fermentations.