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White ants could offer a solution to the problems of global warming. T.V. Jayan reports
It is one of the most destructive species ever known. It can turn houses to dust in a very short time and chomp its way through huge quantities of wood or paper at a frightening speed, posing an enormous threat to homes and offices. But although the termite problem causes billions of dollars in damage every year, the tiny insects — also called white ants — may actually help find a solution to a major problem mankind faces today — climate change.
Even as thousands of climate scientists and policy hawks from all over the world meet for yet another biennial jamboree on the beautiful island of Bali, trying to figure out better ways of cutting the emissions of carbon dioxide and other gases that heat up the earth, microbiologists working on termites — collected from the evergreen rain forests of Costa Rica — offer a glimmer of hope. The way to a greener biofuel future is through the tummy of termites, they claim in a recent issue of Nature.
The work, spearheaded by researchers at the California-based Joint Genome Institute — part of the US Department of Energy — reveals the remarkable metabolic machinery that helps termites digest hardy plant materials with amazing efficiency.
Termites can devour wood because their bellies harbour more than 200 unique microbes whose concerted action helps break down the stuff. This consortium of microbes works in tandem with chemicals generated in their gut to produce an ensemble of enzymes that are so far the most efficient biochemical means to digest wood.
If scientists can crack the genetic code and synthesise these novel enzymes on an industrial scale, it would make for one of the best available methods to efficiently convert wood or waste biomass into valuable biofuels.
A United Nations Development Programme report released last week touted biofuels such as ethanol and biodiesel as a viable energy option to mitigate the threat of climate change because, unlike fossil fuels like petroleum, they are carbon neutral. Carbon dioxide, released into the atmosphere by biofuel burning, is of recent origin and is hence part of the ongoing carbon cycle. Using fossil fuels, on the other hand, releases carbon dioxide that has been sequestered for millions of years as oil or coal, adding to the carbon dioxide build up in the atmosphere.
The rain forests of Costa Rica are a well known hotbed of biodiversity for termites. The “higher†termites that the scientists chose, to further the frontiers of science, belong to the genus Nasutitermes.
While termites have been the subject of keen scientific study for more than a century, the precise identity and role of the microbes in their digestive tract remained a mystery. The current work, a collaborative effort among scientists from the US, Costa Rica and Germany, is the first to throw light on the symbiotic orchestration that goes on in the belly of white ants.
Termites eat wood, but they can’t extract energy from the complex lignocellulose polymers within it. These polymers are broken down into simple sugars by fermenting bacteria in their gut, using enzymes that produce hydrogen as a byproduct. A second wave of bacteria uses the simple sugars and hydrogen to make the acetate the termites require for energy.
Another remarkable finding was that like cows, termites too have a series of stomachs, each home to a distinct community of microbes that have specifically assigned jobs along the conversion pathway of woody polymers to sugars. The real work is carried out in the rear portion of the gut, where the enzymatic juices exuded by the bacteria attack and break down cellulose and hemicellulose which along with lignin form the basic building blocks of wood.
Subsequently, the scientists extracted and purified the contents of the third paunch, or hindgut, of more than 150 worker termites, mapping the extract to ascertain their genetic content.
“Our analysis revealed that the hindgut is dominated by two major bacterial lineages — treponemes and fibrobacters,†said Philip Hugenholtz, who heads JGI’s microbial ecology research. While it was earlier known that treponemes exist in the termite gut, fibrobacters were an exciting new find, he remarked. Their relatives found in the cow rumen are excellent in degrading cellulose.
While experts feel that cellulose can be an excellent raw material for producing energy, as it is theoretically a great source of hydrogen, extracting hydrogen — the cleanest possible fuel — is difficult because it requires a huge amount of energy and money.
But termites do the job exceedingly well, without using harsh chemicals or excess heat, thanks to their microbial guests. Theoretically speaking, termites can convert a sheet of A4 paper into two litres of hydrogen, said Andreas Brune, a biogeochemist at Germany’s Max Plank Institute for Terrestrial Microbiology in Marburg. Cranking up such a large amount of hydrogen from a cellulose source (the main content of paper is cellulose) calls for unbelievably high efficiency. As a result, termites are often referred to as one of the most efficient bioreactors in Nature.
Figuring out which enzymes are used to create hydrogen and which genes produce them is the first step towards developing a process that can help generate hydrogen commercially from biomass.
“To get there, we must first define the set of genes with functional attributes for the breakdown of cellulose. This study represents an essential step along that path,†said Edward Rubin, JGI director.
Sources: The Telegraph (Kolkata, India)
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