Treponema bryantii sp. nov., a rumen spirochete that interacts with cellulolytic bacteria

Abstract

A saccharolytic spirochete that associated and interacted with cellulolytic bacteria was isolated from bovine rumen fluid. Isolation was accomplished by means of a procedure involving serial dilution of a sample of rumen fluid into a cellulose-containing agar medium. Clear zones appeared within the medium as a result of cellulose hydrolysis by rumen bacteria. The saccharolytic spirochete and a cellulolytic bacterium later identified as a strain of Bacteroides succinogenes were isolated from the clear zones. The spirochete did not utilize cellulose, but grew in coculture with the cellulolytic bacterium in cellulose-containing media. When cocultured in these media the spirochete used, as fermentable substrates, soluble sugars released from cellulose by the cellulolytic bacterium. In cellulosecontaining agar medium the spirochete enhanced cellulose breakdown by the B. succinogenes strain. Electron microscopy showed that the helical spirochete cells possessed an outer sheath, a protoplasmic cylinder, and two periplasmic fibrils. Under a CO₂ atmosphere, in a reduced medium containing inorganic salts, rumen fluid, glucose, and NaHCO₃, the spirochete grew to a final density of 1.9×10⁹ cells/ml. Succinate, acetate, and formate were products of the fermentation of glucose by growing cells. CO₂ (HCO₃ ^-), branched short-chain fatty acids, folic acid, biotin, niacinamide, thiamine, pyridoxal, and a carbohydrate were required for growth of the spirochete. The results of this study indicated that the rumen spirochete represents a new species of Treponema. It is proposed that the new species be named Treponema bryantii.