Bugs Can Ward Off The 'Bends'

April 28, 1999

FOOD supplements laced with bacteria could protect deep-sea divers from the ravages of decompression sickness. Experiments with pigs have shown that methane-producing microorganisms that live in the gut can help ward off the dreaded "bends".

As divers descend to greater depths, more gas from their scuba tanks dissolves in their blood. If they ascend too quickly, the sudden drop in pressure causes bubbles to form, in the same way that a bottle of carbonated drink froths when the cap is removed. This can cause limb paralysis, headaches, blurred vision and tingling skin. In severe cases it is fatal.

Recreational divers-who should not descend deeper than about 45 metres-can breathe compressed air without risk, provided they stay within safe limits for the duration of dives, observe the correct intervals between them and don't ascend too fast. But professional divers descend to depths of up to 600 metres to repair oil rigs or conduct scientific studies, and can suffer the bends even if they meticulously follow slow ascent procedures and take repeated decompression stops. At such extreme depths, air becomes so dense that it can't be breathed-so divers breathe oxygen mixed with helium or hydrogen.

Susan Kayar and her colleagues at the Naval Medical Research Center in Bethesda, Maryland, reasoned that deep dives would be made safer if more dissolved hydrogen could be removed from the divers' blood. They turned to a bacterium called Methanobrevibacter smithii, which lives in the gut and metabolises hydrogen to form methane. They injected cultures of the bacteria into the intestines of pigs, then shut the animals in a hyperbaric chamber to simulate the effects of ascending from a three-hour dive at around 240 metres below the surface.

Pigs that were not given the bacterial cultures were nearly twice as likely to show symptoms of decompression sickness. The treated pigs were also more flatulent, releasing large quantities of methane-and the more bacteria that were added to their guts, the more methane they produced. Kayar says the bacterial supplements appear as harmless as live yogurt. "These are microbes that you have in your intestine right now," he says. The treated pigs seemed to suffer no ill effects and their altered gut microflora later returned to normal.

Lawrence Martin, a specialist in diving medicine at the Mount Sinai Medical Center in Cleveland, Ohio, describes Kayar's app-roach as "exciting and exotic". He says it may provide a cheaper alternative to pressurised scuba suits, which can eliminate the risk of the bends. Although their price may come down, these currently cost hundreds of thousands of dollars.
Author: Nell Boyce
New Scientist issue 1 May 1999


New Scientist

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