Kluyveromyces marxianus, a yeast naturally assimilating but not
fermenting xylose, was genetically engineered to produce ethanol from xylose
efficiently. Genetic engineering included replacing the natural xylose
utilization pathway via xylose reductase and xylitol dehydrogenase to
xylulose by a fungal xylose isomerase converting xylose directly to xylulose.
Furthermore xylulokinase was overexpressed to improve efficiency of xylose
to ethanol fermentation. The resulting strain produced 37 g/L ethanol with a
yield of 0.4 g/g xylose used and an ethanol production rate of 0.94 g/L*h in
shake flask fermentation tests. The original strain produced xylitol very
efficiently in these conditions but did not produce any ethanol. The above
strain was further engineered to produce lactic acid from xylose by
expressing the L-lactate dehydrogenase (LDH) from Lactobacillus helveticus.
The resulting strain produced lactate from xylose in shake flask test
conditions with 77% yield and 1 g/L*h productivity. Lactobacillus helveticus
LDH was also introduced to Pichia stipitis, a yeast naturally fermenting
xylose. Lactate was the main product from xylose in shake flask test and was
produced with about 60% yield and 0.4 g/L*h productivity.
|Conference||International Specialised Symposium on Yeasts, ISSY 25 |
|Abbreviated title||ISSY 25|
|Period||18/06/06 → 21/06/06|