In previous studies, gram-positive bacteria which grew rapidly with peptides or an amino acid as the sole energy source were isolated from bovine rumina. Three isolates, strains C, FT (T = type strain), and SR, were considered to be ecologically important since they produced up to 20-fold more ammonia than other ammonia-producing ruminal bacteria. On the basis of phenotypic criteria, the taxonomic position of these new isolates was uncertain. In this study, the 16s rRNA sequences of these isolates and related bacteria were determined to establish the phylogenetic positions of the organisms. The sequences of strains C, FT, and SR and reference strains of Peptostreptococcus anaerobius, Clostridium sticklandii, Cbstridium coccoides, Cbstridium aminovalericum, Acetomaculum ruminis, Cbstridium leptum, Cbstridium lituseburense, Cbstridium acidiurici, and Clostridium barkeri were determined by using a modified Sanger dideoxy chain termination method. Strain C, a large coccus purported to belong to the genus Peptostrep#ococcus, was closely related to P. anaerobius, with a level of sequence similarity of 99.670. Strain SR, a heat-resistant, short, rod-shaped organism, was closely related to C. sticklandii, with a level of sequence similarity of 99.%. However, strain FT, a heat-resistant, pleomorphic, rod-shaped organism, was only distantly related to some clostridial species and P. anaerobius. On the basis of the sequence data, it was clear that strain FT warranted designation as a separate species. The closest known relative of strain FT was C. coccoides (level of similarity, only 90.6%). Additional strains that are phenotypically similar to strain FT were isolated in this study. On the basis of phenotypic and phylogenetic differences, we believe that strain FT represents a new species of the genus Cbstridium, for which we propose the name Clostridium aminophilum.

When nonlactating Holstein cows (685 +/- 59 kg) were fed chopped timothy hay (9% CP, 7.0 kg/d) 12 times daily, the steady-state ruminal ammonia concentration was 2.6 mM, and the specific activity of ammonia production by mixed ruminal bacteria was 27.4 nmol/mg of protein-1.min-1. The addition of soybean meal (53% CP, 1 or 2 kg/d) to the basal diet caused a linear increase in ruminal ammonia (7.0 and 12.4 mM, respectively; P < .001), but there was only a small increase in the specific activity of ammonia production (30.7 and 33.8 nmol/mg of protein-1.min-1, respectively; P < .05). The addition of monensin (350 mg/d) to the diets caused more than a 30% decrease (P < .01) in ruminal ammonia at all levels of soybean supplementation, and there was a similar decrease (P < .001) in the specific activity of ammonia production. Before monensin addition, the most probable number of bacteria that could utilize peptides and amino acids, but not carbohydrates, as an energy source for growth was 5.8 to 7.0 x 10(6)/mL. When monensin was added to the diets, these bacteria decreased (P < .001) nearly 10-fold. Based on these results, it seemed that monensin inhibited highly active amino acid-fermenting ruminal bacteria, and this inhibition, in turn, decreased ruminal amino acid deamination and ammonia production. Because monensin did not increase soluble protein, peptides, or amino acids in ruminal fluid, it did not seem that the decrease in ammonia increased flow of dietary amino N to the lower gut.(ABSTRACT TRUNCATED AT 250 WORDS)

This study evaluated the effect of branched-chain volatile fatty acids (VFA; isobutyric acid, isovaleric acid), amino acids (valine, leucine), and dipeptides (valine-valine, leucine-leucine) on neutral detergent fiber (NDF) degradation by rumen microorganisms in vitro. The CP (%) and in situ NDF degradation rate (%/h) for alfalfa, bermudagrass, and pangolagrass hays, and napiergrass silage were 17.2 and 7.5, 4.7 and 3.1, 8.3 and 5.3, and 9.6 and 3.4, respectively. In vitro NDF digestibility was the lowest for bermudagrass; alfalfa and napiergrass were the highest. When the incubation contained more ammonia initially, digestibilities increased, but relative differences among forages were unchanged. Adding branched-chain VFA (2 mM) to incubations increased digestibilities more than controls on 15 out of 16 occasions. The effectiveness varied with isoacids and forages used. Amino acid (2 mM) or dipeptide (1 mM) addition consistently increased digestibility over controls. Amino acids further increased digestibility over corresponding isoacids on 14 occasions. Improvement in digestibility over control by leucine appeared to be greater than that by valine. Digestibilities with dipeptides were always greater than those with isoacids, except for one case. Dipeptide addition further increased digestibility significantly over corresponding amino acids on only six occasions, while percent improvement in digestibility numerically by dipeptides occurred in 10 cases. Valine-valine seemed to exert different effect than leucine-leucine, depending on initial ammonia availability. The results indicate that dipeptides could be more effective than isoacids and amino acids in improving NDF digestion. Forages with high CP content or rapid NDF degradation rate appeared to respond to additives to smaller degrees.