Decompression sickness risk in rats by microbial removal of dissolved gas

We present a method for reducing the risk of decompression sickness (DCS) in rats exposed to high pressures of H . Suspensions of the human colonic microbe Methanobrevibacter smithii were introduced via a colonic cannula into the large intestines of the rats. While the rats breathed H in a hyperbaric chamber, the microbe metabolized some of the H diffusing into the intestine, converting H and CO to methane and water. Rate of release of methane from the rats, which was monitored by gas chromatography, varied with chamber H pressure. This rate was higher during decompression than during compression, suggesting that during decompression the microbe was metabolizing H stored in the rats' tissues. Rats treated with M. smithii had a 25% (5 of 20) incidence of DCS, which was significantly lower ( P < 0.01) than the 56% (28 of 50) incidence of untreated controls, brought on by a standardized compression and decompression sequence. Thus using a microbe in the intestine to remove an estimated 5% of the body burden of H reduced DCS risk by more than one-half. This method of biochemical decompression may potentially facilitate human diving.