CORKSCREW-shaped bacteria that live in termite intestines curb the insects鈥�
output of methane, microbiologists have found. The discovery hints at possible
ways of preventing other microbial ecosystems from releasing methane, which is
an important greenhouse gas.
Termites鈥� guts teem with hundreds of species of protozoans, bacteria and
archaeans. Among the most abundant of these single-celled inhabitants are the
spiral bacteria known as spirochaetes. But for decades, no one knew what they
did, because efforts to grow them in laboratory cultures always failed.
鈥淲e鈥檝e been working for 25 years on termite gut microbes, and the
spirochaetes were always the big prize,鈥� says John Breznak, a microbiologist at
Michigan State University in East Lansing. 鈥淔inally, that persistence paid off.鈥�
Working in Breznak鈥檚 lab, Jared Leadbetter hit on the right combination of
nutrients and antibiotics in which two spirochaete species grew but other
bacteria did not (Science, vol 283, p 686).
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The newly cultured bacteria turn out to have a key position in the intricate
microbial food chain within the termite gut. Various microbes, together with
enzymes secreted by the termites themselves, break down the cellulose and other
large molecules in wood fibres into acetate鈥攖he insects鈥� main energy
source鈥攑lus hydrogen gas and carbon dioxide. Studies of the spirochaete
cultures show that the bacteria convert these gases into more acetate. This
process yields about a third of the acetate available to the termites.
But the spirochaetes may have an even further reaching effect, because they
prevent other microbes from using the hydrogen and carbon dioxide to make
methane, which is an important contributor to global warming. This finding could
lead to ways of reducing methane production in other important microbial
ecosystems, such as those in the guts of cattle and other ruminant grazers, says
Breznak.