MIT researchers are genetically engineering yeast to break down stubborn plant fibers into sugars that it can then ferment. This is a step towards a potentially cost-effective single-organism process for manufacturing cellulosic biofuels. The source of the genetic material: anaerobic fungi from the digestive system of a horse on a hay-only diet. By teaming up with genetic-sequencing experts at MIT, the researchers have developed a novel analytical approach that will enable them to determine which enzymes in gut fungi are key players in plant digestion and how those enzymes are made and assembled — information that will help them replicate the fungi’s cellulose-destroying capabilities in yeast. Their approach could reveal new enzymes that are champion cellulose degraders but naturally occur only in unknown organisms that cannot be grown in a lab.
One promising source of renewable fuels is biomass from agricultural residues, grasses, and other dedicated energy crops. Methods exist to convert such cellulosic biomass into energy-rich fuels that could substitute for petroleum, particularly in transportation systems. In general, those methods use enzymes and chemicals to break plant biomass down into sugars such as glucose, which are then fed to a microorganism to ferment the sugars to make ethanol, butanol and other end products. But such methods are not economically viable for widespread use, largely due to the expense associated with enzyme production and activity and the costs associated with separating cellulosic processing into so many steps. Chris Kaiser, MIT’s provost and the MacVicar Professor of Biology, believes that a better approach is to genetically engineer a single organism that can both break down the cellulose and ferment the product — and he believes that the best organism for the job is yeast. “We already know how to genetically modify yeast to control its metabolic pathways, and we have vast experience with using yeast to conduct fermentation on an industrial scale,” Kaiser says. The steps needed to implement his idea are known: Select an organism that naturally digests cellulose, identify the key enzymes involved in that process, determine which genes express those enzymes, retrieve those genes, and insert them into yeast. Such engineered yeast could readily be put into an industrial process and scaled up for biofuel production.
Reference: “Evaluating expression and catalytic activity of anaerobic fungal fibrolytic enzymes native topiromyces sp E2 inSaccharomyces cerevisiae” by Michelle A. O’Malley, Michael K. Theodorou and Chris A. Kaiser, 30 December 2011, Environmental Progress and Sustainable Energy.
This research was supported initially by a seed grant from the MIT Energy Initiative. Postdoctoral fellow Michelle O’Malley was subsequently supported by a Whiting Foundation Fellowship and a US Department of Agriculture–National Institute of Food and Agriculture Postdoctoral Fellowship. A travel fellowship from the Company of Biologists supported her work with Professor Michael Theodorou at Durham University and the Center for Process Innovation in the United Kingdom.
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