Production of ethanol from thin stillage by metabolically engineered Escherichia coli.
Thin stillage is a by-product generated in large amounts during the production of ethanol that is rich in carbon sources like glycerol, glucose and maltose. Unfortunately, the fermentation of thin stillage results in a mixture of organic acids and ethanol and minimum utilization of glycerol, the latter a compound that can represent up to 80% of the available substrates in this stream. We report here the efficient production of ethanol from thin stillage by a metabolically engineered strain of Escherichia coli. Simultaneous utilization of glycerol and sugars was achieved by overexpressing either the fermentative or the respiratory glycerol-utilization pathway. However, amplification of the fermentative pathway (encoded by gldA and dhaKLM) led to more efficient consumption of glycerol and promoted the synthesis of reduced products, including ethanol. A previously constructed strain, EH05, containing mutations that prevented the accumulation of competing by-products (i.e. lactate, acetate, and succinate) and overexpressing the fermentative pathway for glycerol utilization [i.e. strain EH05 (pZSKLMgldA)], efficiently converted thin stillage supplemented with only mineral salts to ethanol at yields close to 85% of the theoretical maximum. Ethanol accounted for about 90% (w/w) of the product mixture. These results, along with the comparable performance of strain EH05 (pZSKLMgldA) in 0.5 and 5 l fermenters, indicate a great potential for the adoption of this process by the biofuels industry.
Gonzalez
Ramon
R
Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main Street, MS-362, Houston, TX, 77005, USA. Ramon.Gonzalez@rice.edu
Campbell
Paul
P
Wong
Matthew
M
D056804:Biofuels; D019149:Bioreactors / Q000382:microbiology; D004926:Escherichia coli / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005818:Genetic Engineering / Q000379:methods*; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D008320:Maltose / Q000378:metabolism; D013379:Substrate Specificity; D014866:Waste Products / Q000032:analysis*
D056804:Biofuels; D014866:Waste Products; D000431:Ethanol; D008320:Maltose; D005947:Glucose; D005990:Glycerol