Living With Lignin

The trunks of trees are mostly composed of cellulose and another polymer lignin. The lignin adds strength to the wood and inhibits herbivores and microorganisms from utilizing the cellulose. Without lignin, trees would not exist and houses made of lignin free wood would not last long. Walk through a forest and you will see logs in various stages of decay. The decay process is prolonged by the lignin.

Lignin is not digestible by most animals. Some microorganisms produce lignases, enzymes that metabolize the lignin and make the cellulose available for use. Humans have developed industrial chemical processes for removing lignin from wood. Lignin removal is a necessary step for the production of paper or the use of wood cellulose for biofuels.

Termites are an important group of animals that are able to feed on wood because they have evolved a system that solves the lignin problem. Termites host microorganisms in their guts that metabolize lignin. The microorganisms benefit from termites first processing the wood by chewing it into small particles that facilitate the enzymatic degradation. The termites provide their microorganisms with a warm moist environment and plenty of small particles of wood that can be used as a source of energy. The microorganisms use the energy from the cellulose to produce a variety of materials including vitamins that are important to the termites. By working together as symbionts, termites and their microorganisms can exploit abundant wood as a food source.

Reticulitermes flavipes, Eastern Subterranean Termite
Source of enzymes for biofuel production?

Humans have historically used wood as a biofuel by combusting it in fires. However, combustion is inefficient. Enzymatic processes are available that can efficiently produce electricity in fuel cells from cellulose. The a major obstacle is making the cellulose free of lignin. This is currently an expensive process. However, many scientists are studying termites and their microorganisms to unlock the enzymatic mechanisms that are more efficient. The strategy is to identify key enzymes responsible for lignin degradation and to simulate this process on an industrial scale. This would allow humans to use wood, a renewable resource to generate electricity in a manner that is more carbon neutral than our current use of fossil fuels.