In advance of the Society of Biology’s Policy Lates discussion on algal bioenergy, Rebecca Nesbit looks at some of the hurdles we need to overcome to produce liquid fuel from plants in a more sustainable manner.
First generation biofuels are made from starch, sugars, fats and oils, but often come from food plants. This has led to controversy over producing fuel on land which could otherwise be used to feed people.
Advanced generation biofuels use non-edible plant matter, whether this is from agricultural by-products or from alternative crops such as grasses or willow. Turning many of these plants into liquid fuel, however, is a much larger challenge than it is for first generation biofuels.
Sugars are locked up in cellulose, which is an essential structural component of the cell wall of green plants and many types of algae. Just as humans are unable to digest cellulose, it presents a problem when trying to turn biomass into a liquid fuel.
Some microorganisms produce cellulases, enzymes which break the celluose down into glucose, and these can then be used to make the energy from cellulose accessible. We haven’t yet overcome many of the hurdles to doing this efficiently for biofuels on a large scale, but the use of cellulases is a major area of research.
An alternative to researching enzymes which break down the cellulose is to produce a plant which is easier to turn into liquid biofuel. Research is taking place to make the stored carbon more available for conversion by increasing the oil content of the bioenergy crops, and using the energy from oils rather than cellulose.
Normally plants don’t store much oil in their leaves and other vegetative tissues, whereas seeds are high in oil because it is dense in energy, which is necessary for the developing embryo. Recent research in Arabidopsis identified genes for enzymes which break down oil. This raises the possibility, if these enzymes are inhibited, that crop plants could be modified so leaves and stems contain oil in the same concentration as seeds.
Another group of scientists achieved a 60-fold increase in leaf oil production by increasing the plant’s production of an enzyme involved in oil production.
Algal biofuels are another interesting option, and research is taking place to raise the oil content in algae for biofuels, both by identifying the optimum conditions for oil accumulation and manipulating lipid metabolism.
The economic and environmental challenges facing the biofuel industry are still large, but these are just a few examples of innovative ways scientists are tackling the problem. Our discussion about the future of algal biofuels on 28th November is open to everyone – please join us. I will be live tweeting with the hashtag #PolicyLates.
Kelly AA, van Erp H, Quettier AL, Shaw E, Menard G, Kurup S, & Eastmond PJ (2013). The sugar-dependent1 lipase limits triacylglycerol accumulation in vegetative tissues of arabidopsis. Plant physiology, 162 (3), 1282-9 PMID: 23686420