No abstract

A methanogenic bacterium, present in bovine rumen contents at concentrations of approximately 2 X 108 cells per ml, has been isolated in pure culture. The organism is a strictly anaerobic, weakly motile, nonsporeforming, gram-negative rod (0.7 ,u X 1.5 to 2.0 u) 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 by the organism. 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.

Bacteriophage populations in an activated-sludge sewage treatment plant were enumerated. A newly developed assay for quantitation of total phages, employing direct electron microscopic counts, was used in conjunction with the plaque assay. The total concentration of phages was significantly higher in reactor mixed liquor and effluent than in influent sewage, indicating a net production of phages within the reactor. Maximum total phage concentrations in the fluid phase of sewage, activated-sludge mixed liquor, and reactor effluent were 2.2 x 107, 9.5 x 107, and 8.4 x 107/ml, respectively. Conditions were optimized for isolation of predominant heterotrophic aerobic bacteria from sewage and mixed liquor. Blending at ice water temperatures was superior to ultrasound or enzyme treatments for maximum release of viable bacteria from microbial floc. A solidified extract of mixed liquor was superior to standard media for cultivating maximum numbers of heterotrophic bacteria. The highest culture counts for sewage and mixed liquor were 1.4 x 107 and 1.3 x 109/ml, respectively, which represented only 3 and 6.8%

The mechanism of propionate formation by two strains of Selenomonas ruminantiurn has been investigated using substrates specifically labelled by 14C. Both strains behaved similarly. When [2-14C] lactate was fermented, the label in propionate was completely randomized in carbons 2 and 3. When cells were grown on lactate in the presence of 14C02, label was fixed exclusively into propionate carboxyl. The results are consistent with propionate being formed by the ' succinate' pathway.

Six morphological types of bacteriophage were found in bovine rumen contents. Minimal total phage count was 5 X 107 per ml of rumen fluid.