Four strains of gram-negative, anaerobic, non-spore-forming bacteria that were curved rods which were motile by means of flagella originating from the concave side of the cells and which fermented succinate quantitatively to propionate were isolated from high dilutions of rumen ingesta obtained from cows on pasture. The bacteria were asaccharolytic and not proteolytic and did not ferment amino acids or peptides. Succinate was the only substrate fermented. Rumen fluid together with yeast extract was required for good growth on succinate. Growth on succinate was enhanced in the presence of fumarate. The strains did not grow at 22°C, and growth at 45°C was in all cases less than growth at 39°C. The cellular fatty acid compositions of all four strains were determined. The DNA base composition was about 46 mol% G+C. The complete 16S ribosomal DNA sequence of the type strain (strain S1–1) was determined, and the phylogenetic relationships were analyzed. The most closely related genera were the genera , and , whereas the recently described succinate-fermenting organism was distantly related. The name proposed for these strains is gen. nov., sp. nov.; the type strain is strain S1–1 (= DSM 10502). These organisms are common inhabitants of the rumina of cows on pasture.


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