Happy New Year! Last year I blogged about the challenges and promises of second-generation biofuels (those made from agricultural by-products such as straw or from woody plants such as poplar). If these crops are going to be a relatively cheap and sustainable alternative to fossil fuels, we will have to think seriously about genetic modification.
Rice is one of the most important food resources in the world. Its cultivation means about 800 million metric tons of rice straw is also produced annually, which is normally burned or decayed in the field. Getting rid of the straw in this way produces greenhouse gasses such as methane. But what if we could use straw, currently a polluting by-product, as a source of energy?
Woody plants, including the inedible part of food crops, get their strength from lignin and cellulose. Cellulose is basically lots of glucose molecules joined together, so a perfect energy source. But the problem is how to turn it into ethanol to use as biofuel.
The process currently relies on enzymes from bacteria or fungi, but it is extremely expensive. If these enzymes could be produced by GM plants rather than by micro-organisms, the production of ethanol would be cheaper and quicker.
Scientists from Taiwan genetically modified rice plants to contain a gene from a bacteria which produces an enzyme that breaks down cellulose. The enzyme they chose has the advantage that it works best at high temperatures, and doesn’t work well to break down cellulose in conditions found in the field.
They managed to produce rice straw with high levels of the enzyme in it, so with potential to increase the efficiency of biofuel production. The enzyme remains stable in the straw long after the rice has been harvested, and becomes active at higher temperatures.
By choosing an enzyme that only breaks down cellulose at high temperatures, this shouldn’t stop the plant growing normally. However, they found some evidence that the genetically modified plants were shorter, so more experiments are needed to work out whether adding the gene for the enzyme disrupts the growth of the rice.
There are clear environmental benefits to using agricultural waste as a replacement for fossil fuels and to making the process of biofuel production more efficient. But is genetic modification a viable, sensible, or even essential option? As always, I’ll be interested to hear your views.
Chou, H., Dai, Z., Hsieh, C., & Ku, M. (2011). High level expression of Acidothermus cellulolyticus beta-1, 4-endoglucanase in transgenic rice enhances the hydrolysis of its straw by cultured cow gastric fluid Biotechnology for Biofuels, 4 (1) DOI: 10.1186/1754-6834-4-58