Challenges in Engineering Microbes for Biofuels Production
Author: Stephanopoulos, Gregory
Author Affiliation: Science Magazine
Submitted: Mon, 07/07/2008 - 21:49
Edited: Mon, 07/07/2008 - 21:50
Published in: Science Magazine on February, 9th 2007
Copyright Status: Pay to Download Link to source material: Full Article Here Description:
Recent discoveries in Microbiology have made cellulosic transportation fuel a not-so-distant reality. However, significant advancements must still be made before the processing of cellulosic biomass to a liquid transportation fuel can be profitable at any scale.
The author outlines how the genomics revolution and improvements in metabolic engineering could create the technologies required to overcome many current obstacles. A complete description of a basic biomass-to-biofuels system is explored step-by-step, from biomass pre-treatment (the loosening of lignin-celulose fibers to increasing surface area), to saccrification/hydrolysis (the enzymatic treatment of cellulose and hemicellulose to produce six- and five-carbon sugars), and fermentation (the processing of hydrolyzed sugars by alcohol producing microorganisms).
Improvements that must be addressed include: reducing the cost of enzymes from 30 cents per gallon of alcohol fuel to 3 cents per gallon, engineer for the expression of cellulases in fermenting organisms (such as yeast), engineer for both hydrolysis and fermentation pathways inside one individual organism, design bioreactors to reduce sugar-degrading side reactions during hydrolysis, investigate the possible use of ionic liquid solvents to reduce lignin buildup on filters, engineer for alcohol tolerant strains of microorganisms (2% concentrations are usually lethal), further explore non-enzymatic physiochemical hydrolysis methods (high-temp pre treatments and acid-baths), engineer fermenting organisms to process all sugars released from hydrolysis (mainly pentose from hemicellulose hydrolysis), investigate how to collect and convert the CO2 byproduct into a usable liquid fuel via Fischer-Tropsch, and improve the energy-intensive distillation technique used to separate the end-product.
Many obstacles still remain for cellulosic biofuels. Capital costs must be reduced by at least half (currently $4 per gallon), feedstock costs must be significantly reduced through improvements in yield, and a ten-fold reduction in the cost of enzymes per volume must also be met before economic viability can be achieved. However, the author reminds us that the current state of technology was reached with a rather minimal investment directly into biofuels research, and that the full potential of biofuel production from cellulosic biomass will be obtainable in the next 10 to 15 years at current research levels.
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