Effect of chemical treatments on methane emission by the hindgut microbiota in the termiteZootermopsis angusticollis

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Abstract
Selective removal of symbiotic hindgut microorganisms by chemical treatments reduced methane emission by the termiteZootermopsis angusticollis. Methane emission from untreated termites incubated in 25% H2 increased 123%, from 10.3 nmol/termite/hour (U) to 22.9 U. Though linear with time, methane emission was not correlated with termite mass. Hyperbaric oxygen treatments reduced methane emission to unquantifiable levels and eliminated all but the protozoaTricercomitus andHexamastix. Exogenous H2 restored 5% of methane emission to 1.3 U. 2-bromoethanesulfonic acid, fed on filter papers to termites, eliminated methane production. Epifluorescence microscopy showed that this treatment selectively removed methanogens from symbioses withTricercomitus, Hexamastix, andTrichomitopsis, but the protozoa did not appear to be affected. The insect molting hormone 20-hydroxyecdysone reduced methane production 86% to 1.6 U from an initial level of 11.4 U. Hydrogen incubation increased this rate to 77% of the initial rate, 8.8 U. Hormone treatment reduced the number ofTrichonympha in the hindgut and induced sexuality in these protozoa. A model suggests thatTrichonympha evolve most of the hydrogen and that methanogenic bacteria symbiotic withTrichomitopsis produce most of the methane in this hindgut ecosystem.