Characterization of Methanobacterium mobilis , sp. n., Isolated from the Bovine Rumen

Abstract

A methanogenic bacterium, present in bovine rumen contents at concentrations of approximately 2 x 108 cells/ml, was isolated in pure culture. The organism is a strictly anaerobic, weakly motile, nonsporeforming, gram-negative rod (0.7 [mu] x 1.5 to 2.0 [mu]) with rounded ends. There is a single polar flagellum. The organism grows at temperatures between 30 and 45 C, with an optimum at 40 C, and at pH values between 5.9 and 7.7, with optimal growth between pH 6.1 and 6.9. Of the 17 substrates tested, only formate and H2 plus CO2 supported growth. An unidentified, heat-stable factor(s) was required. The factor which was not one of the common ones was present in rumen fluid, mixed rumen bacteria and yeast extract. On the basis of colony morphology, Gram reaction and motility the organism is classified as a new species of methanogenic bacterium, and the name Methanobacterium mobilis sp. n. is proposed.