Ethanol production using xylitol synthesis mutant of xylose-utilizing zymomonas
View Patent ↗Production of ethanol using a strain of xylose-utilizing Zymomonas with a genetic modification of the glucose-fructose oxidoreductase gene was found to be improved due to greatly reduced production of xylitol, a detrimental by-product of xylose metabolism synthesized during fermentation.
1. A process for producing ethanol comprising,
a) providing a recombinant Zymomonas strain which utilizes xylose to produce ethanol., said strain comprising at least one genetic modification which reduces glucose-fructose oxidoreductase activity, and
b) culturing the strain of (a) in a medium comprising xylose whereby xylose is converted to ethanol.
2. The process according to claim 1 , wherein the strain of (a) improves conversion of xylose to ethanol relative to a recombinant Zymomonas strain without at least one genetic modification which reduces glucose-fructose oxidoreductase activity.
3. The process of claim 2 , wherein the strain of (a) improves one or more of rate, titer or yield, of xylose conversion to ethanol relative to a recombinant Zymomonas strain without at least one genetic modification which reduces glucose-fructose oxidoreductase activity.
4. The process according to claim 1 , wherein the strain of (a) produces a reduced amount of xylitol when metabolizing xylose to ethanol as compared to a Zymomonas strain without at least one genetic modification which reduces glucose-fructose oxidoreductase activity.
5. The process according to claim 4 , wherein the strain of (a) produces substantially no xylitol when metabolizing xylose to ethanol.
6. The process according to claim 1 , wherein the recombinant Zymomonas strain of (a) is selected from the group consisting of ZW800, ZW801-4 and ZW801-6.
7. The process of claim 1 , wherein the medium comprises a mixture of sugars including xylose and a sugar alcohol selected from the group consisting of sorbitol, mannitol, galactitol, ribitol, and a mixture thereof, wherein the mixture of sugars is at a concentration of at least about 120 g/L and wherein the sugar alcohol is at a final concentration that is between about 2 mM and about 100 mM.
8. The process of claim 7 , wherein the sugar alcohol is in a concentration that is between about 5 mM and about 20 mM.