If only wood could be converted to biofuels, there would be no need to wait a million years for the trees to be buried and become oil. Wood is indeed convertible to useful chemicals, because termites do it every day, causing $1 billion of damage every year in the United States. But to live on a diet of wood is challenging, not least because wood contains so little nitrogen. So how do termites do it?
The trick lies in a cunning triple symbiosis, a team of Japanese scientists report in Friday’s issue of Science. In the termites’ gut lives an amoeba-like microbe called a protist, and inside each protist live some 10,000 members of an obscure bacterium.
The microbes in the termites’ gut are very hard to cultivate outside their termite host and so cannot be studied in the lab. The Japanese scientists, led by Yuichi Hongoh and Moriya Ohkuma at the RIKEN Advanced Science Institute in Saitama, have cut through this problem. They extracted the protist’s bacteria directly from a termite’s gut, collected enough to analyze their DNA, and then decoded the 1,114,206 units of DNA in the bacterium’s genome.
By comparing the DNA sequence of the bacterium’s genes with other decoded genes already in public databases, the Japanese team was able to figure out what each gene did. It could then reconstruct all the biochemical reactions of which the bacterium is capable, as shown in the figure above.
They found that in the bacterium’s biochemical repertoire is the ability to convert nitrogen (shown as N2 , to the right of center in the figure) into ammonium and hydrogen. Unlike nitrogen, which is very unreactive, ammonium is easily incorporated into biochemical reactions.
The bacterium can also import urea (shown in the yellow border, at 5 o’clock), a waste product produced by its protist host. Since it takes a lot of energy to fix nitrogen, the bacteria probably use urea as their main nitrogen source as long as their host is making enough, and switch to nitrogen as a backup, the Japanese scientists say.
The overall process whereby this troika of species makes a meal of wood is shown in the graphic at left: the termite chews the wood into particles that are absorbed by the amoeba. The amoeba breaks down the cellulose of the wood and gets the nitrogen it needs from its bacteria. The net result is that the two microbes digest wood into sugars and other nutrients of use to the termite.
Dr. Caroline Harwood, an expert on microbes and biofuels at the University of Washington, Seattle, said the new research was a “ tour de force of genome sequencing” that “solves the mystery of where the termite gets its nitrogen.” Understanding how the termite’s gut microbes digest cellulose would be of major significance for biofuels, she said, and the Japanese group’s whole genome approach could further this goal.
The trick lies in a cunning triple symbiosis, a team of Japanese scientists report in Friday’s issue of Science. In the termites’ gut lives an amoeba-like microbe called a protist, and inside each protist live some 10,000 members of an obscure bacterium.
The microbes in the termites’ gut are very hard to cultivate outside their termite host and so cannot be studied in the lab. The Japanese scientists, led by Yuichi Hongoh and Moriya Ohkuma at the RIKEN Advanced Science Institute in Saitama, have cut through this problem. They extracted the protist’s bacteria directly from a termite’s gut, collected enough to analyze their DNA, and then decoded the 1,114,206 units of DNA in the bacterium’s genome.
By comparing the DNA sequence of the bacterium’s genes with other decoded genes already in public databases, the Japanese team was able to figure out what each gene did. It could then reconstruct all the biochemical reactions of which the bacterium is capable, as shown in the figure above.
They found that in the bacterium’s biochemical repertoire is the ability to convert nitrogen (shown as N2 , to the right of center in the figure) into ammonium and hydrogen. Unlike nitrogen, which is very unreactive, ammonium is easily incorporated into biochemical reactions.
The bacterium can also import urea (shown in the yellow border, at 5 o’clock), a waste product produced by its protist host. Since it takes a lot of energy to fix nitrogen, the bacteria probably use urea as their main nitrogen source as long as their host is making enough, and switch to nitrogen as a backup, the Japanese scientists say.
The overall process whereby this troika of species makes a meal of wood is shown in the graphic at left: the termite chews the wood into particles that are absorbed by the amoeba. The amoeba breaks down the cellulose of the wood and gets the nitrogen it needs from its bacteria. The net result is that the two microbes digest wood into sugars and other nutrients of use to the termite.
Dr. Caroline Harwood, an expert on microbes and biofuels at the University of Washington, Seattle, said the new research was a “ tour de force of genome sequencing” that “solves the mystery of where the termite gets its nitrogen.” Understanding how the termite’s gut microbes digest cellulose would be of major significance for biofuels, she said, and the Japanese group’s whole genome approach could further this goal.
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