We all know that we need to develop new renewable energy sources, that using plants as feedstock allows for a CO₂-neutral energy cycle and that competing with food crops should be avoided, which makes the use of cellulosic feedstocks essential. Eddy Rubin, director of the DoE (Department of Energy) Joint Genomics Institute in Walnut Creek, USA, quickly works through some well known facts in his keynote lecture. But he then rightly asks: “If we know all this, why aren’t cellulosic feedstocks here yet?”

Accelerate
That is because the need to develop alternative energy sources just wasn’t there. Now it is. Bearing in mind that it took humanity thousands of years to develop today’s efficient food crops, it is obvious that we need to accelerate this process for energy crops. Rubin proposes to use genetic modification as an accelerator and has applied that idea to the fast growing poplar. After identifying poplar genes relevant for domestication (e.g. growth, trunk thickness and drought resistance), auxin genes from model plant Arabidopsis were successfully used to, for example, generate transgenic poplar with clearly thicker trunks.

Termite guts

Rubin paints his vision of the future; forests of short, stubby trees. A forest of bio-batteries. “The leaves are the energy collectors, the trunks are the polysaccharide batteries.” But how do we tap into those batteries? Focus on organisms that are capable of digesting (hemi)cellulose. Termites have microbes in their guts that secrete cellulases and hemicellulases, which enable the termite to feed on wood. Subjecting termite guts to a metagenomics analysis resulted in a number of enzyme candidates. For the final step, fermentation of the sugars, a serious efficiency boost is needed. Rubin proposes to use synthetic biology to engineer organisms that are capable of fermenting all the different sugars and that are fuel tolerant, as ethanol is toxic to most microbes.

Political push

Clearly, much work needs to be done to make energy crops a feasible alternative to fossil energy sources. What we need now is a political drive towards developing new energy sources, says Rubin. The sequencing of the human genome largely happened because politicians pushed hard enough. As a result, a host of new technologies was developed that are relevant to other research areas as well. The same could happen if we push for a large bio-energy project, according to Rubin. Convincing politicians is hard, he admits, but there is an upside. “Fortunately, money is a huge factor now as well, that really helps.”

 

[Esther Thole]