Genetic Engineering for Cheaper Cellulosic Ethanol?

Grass BiofuelIn the June 2008 issue of the journal Nature Reviews Genetics, internationally renowned biofuels researcher Mariam Sticklen proposes that future production of cellulosic biofuels will be made infinitely more efficient and affordable through genetic modification of cellulosic feedstocks such as cereal grains and perennial grasses. Citing the impossibility of fueling the world on starch-based ethanol, such as that from corn, Sticklen argues that cellulosic biofuels are the only viable option for future commercial production.

Certainly this isn’t a new position, but there are still some major hurdles left in making cellulosic ethanol affordable and environmentally efficient:

  • Firstly, current feedstocks need to be pretreated to remove lignin and enrich cellulose prior to conversion to ethanol. This pretreatment process is very expensive. By manipulating feedstocks to reduce the amount of lignin in their biomass, the need for pretreatment could be largely eliminated.
  • Secondly, the cellulose left after pretreatment needs to be turned into something fermentable. This involves the use of microbial cellulases – enzymes that convert the various cellulosic components of the feedstock into fermentable sugars. The current methods of producing these enzymes are still quite expensive and, therefore, drive up the cost of producing cellulosic ethanol. Future genetic manipulation of feedstocks could be used to make the plants themselves produce copious amounts of these enzymes in various structures within their biomass. This could eliminate the need to produce these enzymes separately, which, in turn, would greatly reduce ethanol costs.
  • Lastly, Sticklen also points out that genetic modification could make it much easier to ferment butanol out of cellulosic biomass. On a practical level, butanol is a much better fuel source than ethanol: it contains more energy per unit, is less corrosive and volatile (meaning easier transportation), and could be used in an unmodified gasoline vehicle. Currently it is extremely difficult to produce butanol from biomass because of its toxicity to the organisms that ferment it, but the discovery of microrganisms tolerant to butanol, combined with the genetic modification of various feedstocks, could make biobutanol production a true option.

Cell StructureI’m not completely opposed to the use of genetic engineering to solve some problems, but manipulation of wind pollinated plants like grasses can pose serious threats. Those of us that suffer from allergies know full well how far grass pollen can be blown. Imagine if the genes that were engineered to make grasses more ethanol friendly also made the grasses less resistant to certain diseases, or caused them to have reduced seed yield. On the surface this may not seem like such a bad thing, but if these genes were to become ubiquitous in the world’s grasses through wind-driven cross pollination, it might have a deleterious effect on grassland ecosystems or grass seed farmers. In fact, in places like Oregon, where approximately 85% of all grass seed sold in the US is grown (PDF), the effect on farmers could be catastrophic. Already it looks as if the US Department of Agriculture is not going to cozy up to the idea of genetically engineered grasses, which, in and of itself, may make Sticklen’s suggestions a failure before they’ve even gotten off the paper.

What do you think? Do the potential benefits of genetic engineering of cellulosic feedstocks outweigh the potential risks? Can the process of creating and marketing genetically modified grasses be done in a way that eliminates risk? Would genetic modification of other types of cellulosic feedstocks (such as woody biomass) be more acceptable?

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Image credit: the cell structure graphic was taken from the Nature Reviews Genetics article by Mariam Sticklen.

Nick Chambers

Not your traditional car guy.