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Nate Lo
Digestion of wood by termites, and the origins of cellulase genes
 Portion of cellulose chain |
Cellulose, the main component
of wood, is the most abundant organic compound on earth, with global annual
production estimated at 100 billion tonnes. Breakdown of cellulose by living
organisms helps the earth's carbon cycle to continue. It is widely believed
that such 'recycling' is done only by microbes such as bacteria, fungi and
protozoa, and that animals can't digest cellulose by themselves. My research
has shown that this belief is unfounded. |
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Termites are a text-book example of 'symbiosis': they provide a home (their lower intestines) to protozoa and/or bacteria, who, in return, convert the wood into products usable by the termite. Together with some Japanese colleagues, I identified the first animal cellulase gene, in a Japanese termite. The cellulase protein is expressed in the saliva, where microbes don't live. Thus termites have two sources of enzymes for cellulose breakdown, which helps to explain why they are among the few organisms on earth that can digest living wood - well known for its strength and durability. This discovery of termite genes has led to the determination of the three-dimensional structure of the enzyme, which will hopefully lead to the development of environmentally-friendly inhibitors of these enzymes that can be impregnated into wood to inhibit termite activity. |
 Structure of a termite cellulase. Source: Protein Data Bank |
Where did these genes come from?
If one looks through the genomes of humans, fly, nematode, rat, fish and
various other animals, no cellulase genes are present. On the other hand,
these genes are common in bacteria, fungi and protozoa. Did an ancestor
of termites 'pick up' the gene from a microbe by horizontal transfer? By
looking for cellulase genes in other insects, and scanning the DNA databases,
we have found evidence for the presence of these genes in very primitive
animals. Thus, these genes have been lost over evolutionary time by many
lineages, including that leading to vertebrates like ourselves, but retained
in some lineages, like that leading to insects. |
Publications relevant to this research:2,
3, 5, 6,
12, 13, 17
