Consolidated bioprocessing method using thermophilic microorganisms
The present invention is directed to a method of converting biomass to biofuel, and particularly to a consolidated bioprocessing method using a co-culture of thermophilic and extremely thermophilic microorganisms which collectively can ferment the hexose and pentose sugars produced by degradation of cellulose and hemicelluloses at high substrate conversion rates. A culture medium therefor is also provided as well as use of the methods to produce and recover cellulosic ethanol.
1. A method of converting biomass to biofuel which comprises co-culturing in a fermentation reactor biomass with a first cellulolytic, thermophilic microorganism and a second hemicellulolytic, extremely thermophilic, xylose-fermenting microorganism for a time and under conditions sufficient to ferment hexose and pentose sugars which are produced as said biomass is hydrolyzed and converted to biofuel and to ferment said sugars at a substrate conversion rate of at least 50% over a period of about 50 to about 150 hours, wherein said first microorganism is Clostridium thermocellum and said second microorganism is Caldicellulosiruptor obsidiansis and said co-culturing is conducted at 60° C.
2. The method of claim 1 , wherein said Clostridium species is C. thermocellum strain ATCC 27405 and said Caldicellulosiruptor species is C. obsidiansis strain OB47 T (ATCC BAA-2073).
3. The method of claim 1 , wherein biofuel comprises ethanol and/or acetate.
4. The method of claim 1 , wherein said pentose sugar is xylose.
5. A method of producing cellulosic ethanol which comprises:
(a) co-culturing in a fermentation reactor biomass with a first cellulolytic, thermophilic microorganism and a second hemicellulolytic, extremely thermophilic, xylose-fermenting microorganism for a time and under conditions sufficient to ferment hexose and pentose sugars to produce ethanol at a substrate conversion rate of at least 50% over a period of about 50 to about 150 hours, wherein said first microorganism is Clostridium thermocellum and said second microorganism is Caldicellulosiruptor obsidiansis and said co-culturing is conducted at 60° C.; and
(b) recovering said ethanol.
6. The method of claim 5 , wherein said ethanol is recovered by distillation.
7. The method of claim 5 , wherein said substrate conversion rate is at least 75%.
8. The method of claim 5 , wherein said Clostridium species is C. thermocellum strain ATCC 27405 and said Caldicellulosiruptor species is C. obsidiansis strain OB47 T (ATCC BAA-2073).