Corkscrew bacteria in termite guts and natural waters help capture a key element

Microbiologists have discovered that a type of bacteria found in termite guts and in fresh and salt water plays a major role in the process of nitrogen fixation. All organisms require the element to survive.

In the June 29 issue of the journal Science, a team led by National Science Foundation (NSF)-funded microbiologist John Breznak of Michigan State University (MSU) reports that spirochetes - spiral and wavy-shaped bacteria - are important providers of nitrogen in termites, whose ability to thrive despite a nitrogen-poor diet of plant matter had posed a decades old puzzle.

Although nitrogen gas makes up 80 percent of the air we breathe, only certain microbes can capture and use it for growth - a process called nitrogen fixation. Once nitrogen gas becomes "fixed" by microbes, it enters the food chain and is ultimately used by plants and animals.

Scientists have known for about 30 years that nitrogen fixation occurs within termites and could furnish up to 60 percent of the insects' nitrogen needs. But the particular microbes performing that fixation had been unclear. With colleagues at MSU and the California Institute of Technology, Breznak isolated spirochetes from termite guts and grew them in test tubes where they could be examined in detail.

"The spirochetes not only contained the genes for nitrogen fixation," Breznak said, "they performed nitrogen fixation at rates consistent with those seen in living termites. This was very exciting, because nitrogen fixation had never been described before in these fascinating, widely distributed bacteria."

The researchers then examined other spirochetes and found that nitrogen fixation also occurs in free-living, aquatic spirochetes, implying that their impact is global. They also found genes for nitrogen fixation in spirochetes that inhabit the human mouth and the intes
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Contact: Tom Garritano
tgarrita@nsf.gov
703-292-8070
National Science Foundation
28-Jun-2001