Program 3: Cell Wall Interactions

Optimising energy release from sugars in plant cell walls to provide energy for humans, animals and vehicles.

Cell wall sugars are used by humans and animals to provide energy, dietary fibre and, more recently, to produce bioethanol for transport fuel. The methods by which plant cell walls are converted into usable substrates for these processes are surprisingly similar. There is an initial physical grinding step, either by chewing with your teeth or by chopping up plants into small, manageable pieces. Chemical treatment follows, such as exposure to stomach acid or industrial acids, alkali, ammonia or super-heated water, in order to relax the tight structure of the cell wall and make the long sugars accessible for hydrolysis. Finally, the sugars are exposed to enzymes, either in the gut or added to the plant slurry. Enzyme digestion completes the deconstruction of the cell wall into short-chain or individual sugars. Gut bacteria convert sugars into energy and health-promoting signalling molecules for animals; whereas yeast or bacteria can ferment glucose into bioethanol for use as transport fuel.

Remodelling the cell wall allows us to vary its composition to optimise performance for each use. In the case of humans, we would like to increase the amount of soluble and insoluble fibre to alleviate major health problems such as cardiovascular disease, colorectal cancer, diabetes and arthritis. Conversely, the feed and brewing industries would prefer grain with minimal fibre. Finally, biofuel stocks ideally maximise glucose-containing sugars and minimise other components that hinder ethanol conversion.