Wednesday, June 09, 2004

Article: Vaccinating Livestock

Here is an article from the Economist.

An injection of innovation
Jun 3rd 2004
From The Economist print edition

Vaccinating livestock may be a way to slow global warming

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BURPING sheep and cattle may not sound much of a hazard, but their burps contain methane, and methane is a powerful greenhouse gas. In Australia, a place with a lot of livestock, this methane amounts to 13% of the country's greenhouse-gas emissions. That is a tempting target for politicians looking for ways to meet Kyoto protocol targets without having to curb consumer lifestyles.

But how do you stop a sheep burping? André-Denis Wright, of the Commonwealth Scientific and Industrial Research Organisation's laboratory in Perth, has an idea. The methane is generated not by the animals directly, but by bacteria that live in those animals' stomachs. So a vaccine against these methane-generating bacteria should switch off the gas supply. On top of that—and of more direct interest to farmers—methane-producing microbes consume over a tenth of the food the animals eat, making cattle less beefy.

In a forthcoming paper in Vaccine, Dr Wright and his colleagues describe the progress they are making towards such an inoculation. Most methanogens, as the gas-producing stomach bugs are known, are not true bacteria. They actually belong to a class of micro-organisms called the archaea, whose separate existence was recognised only recently. The archaea are not well understood, and are difficult to grow in a laboratory. And if a bug cannot be grown in a laboratory, then a vaccine against it cannot be made.

Indeed, Dr Wright's first attempt fell at this hurdle. Constrained by what he could grow, he made a vaccine against a mixture of seven of the methanogens that he was able to grow from cow and sheep guts. It did not work.

At that point he decided to try a different tack. Instead of restricting himself to those stomach bugs he could grow, he sought to identify the full range of what was there using a new technique called environmental genomics. This trick, pioneered by Craig Venter in the United States, breaks all of the DNA in a sample of liquid from, say, a stomach, up into small pieces. It then sequences each piece to establish the order of the genetic “letters” in it, and uses a computer to fit the pieces back together by matching the overlaps between the sequences of letters. That way, if all goes well, the genomes of the bugs in a sample will emerge from the soup of pieces, and the organisms can be identified without the need to grow them.

The researchers surveyed the microbial populations of 17 sheep stomachs in this way, and revealed several new species of methanogen, including some from a group of archaea not previously known to inhabit digestive tracts. Crucially, knowing the genomes of these ungrowable organisms allowed Dr Wright to identify close relatives that it was already known could be grown. He used three of these relatives to make a new vaccine, and got an 8% reduction in methane production from the sheep he vaccinated.

Not a bad start, and certainly enough to prove the point. Dr Wright is now extending his “library” of sheep methanogens by taking samples from around Australia, in order to discover how much variation there is. He is also planning to extend the work to cattle, which are ten times as gassy, but are too big to fit in the current generation of gas-collecting boxes. If he succeeds, he will be the toast of both environmentalists and ranchers—a rare and enviable coincidence of views.


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