Preliminary Studies Demonstrating Acetoclastic Methanogenesis in a Rat Colonic Ring Model

Washed rat colonic rings were incubated in closed flasks under N(2) at physiologic pH and temperature levels. In the absence of an exogenous substrate, negligible H(2) but some CH(4) concentrations were detected in vitro after one hour of incubation, but high concentrations (H(2) > 100 ppm, CH(4) > 10 ppm) of both gases were found after 24 hours of culture. Production of H(2) and CH(4) by the washed colonic rings was stimulated by lactose addition. Maximum H(2) production occurred at about pH 7.0, while maximum CH(4) production occurred between pH 4.0 and 6.0. The increased production of both gases at 24 hours was associated with dramatic increases (10(4)-fold) in anaerobic bacteria colony counts on the colonic rings and in the incubation media, as well as dramatic increases (100-fold) in acetate concentrations in the media, while lactate concentrations first rose and then fell significantly. These results suggest that gas production in colonic ring preparations is subject to quantitative changes in microbiota, pH, and metabolite formation analogous to in vivo conditions. In addition, microbiota firmly attached to colonic tissue appears to utilize colonic tissue to support its growth in the absence of an exogenous substrate.