Ruminant animals and ruminal microorganisms have a symbiotic relationship that facilitates fiber digestion, but domestic ruminants in developed countries are often fed an abundance of grain and little fiber. When ruminants are fed fiber-deficient rations, physiological mechanisms of homeostasis are disrupted, ruminal pH declines, microbial ecology is altered, and the animal becomes more susceptible to metabolic disorders and, in some cases, infectious disease. Some disorders can be counteracted by feed additives (for example, antibiotics and buffers), but these additives can alter the composition of the ruminal ecosystem even further.

Aims: To isolate predominant ruminal bacteria that produce trans-10, cis-12 conjugated linoleic acid (CLA) from linoleic acid (LA). Methods and Results: Mixed bacteria from ruminal contents of a cow fed grain were enriched with DL-lactate and trypticase. They produced more trans-10, cis-12 CLA than those that were not enriched (7 vs 2 lg mg protein )1 , P < 0AE05). Enrichments had an abundance of large cocci that produced trans-10, cis-12 CLA from LA. Strain YJ-4 produced the most trans-10, cis-12 CLA (approx. 7 lg mg protein )1 ) and 16S rDNA sequencing indicated that YJ-4 was a strain of Megasphaera elsdenii. Megasphaera elsdenii T81 produced approx. 4 lg trans-10, cis-12 CLA mg protein )1 while strains B159, AW106 and JL1 produced < 0AE5 lg mg protein )1 . The trans-10, cis-12 CLA production of YJ-4 was first order with respect to cell concentration (0-800 lg protein ml )1 ), but kinetics were not first order with respect to substrate concentration. Conclusions: Some M. elsdenii strains produce significant amounts of trans-10, cis-12 CLA. Significance and Impact of the Study: Trans-10, cis-12 CLA appears to cause milk fat depression in cattle fed diets supplemented with grain and polyunsaturated fatty acids, but predominant ruminal bacteria that produced trans-10, cis-12 CLA from LA had not previously been isolated.

Dopamine ␤-hydroxylase (DBH) catalyzes the production of norepinephrine, and its expression defines the noradrenergic phenotype. Transcription factors dHAND, a basic helix-loop-helix protein, and Arix/ Phox2a, a homeoprotein, have been demonstrated to play a role in the differentiation and maintenance of catecholaminergic neurons. Three Arix regulatory sites have been identified in the DBH promoter proximal region, but there is no such evidence for dHAND. Cotransfection with a DBH promoter-luciferase reporter construct plus dHAND or dHAND-E12 expression plasmids did not alter luciferase activity, whereas transfection with Arix resulted in a 2.5-fold stimulation of luciferase activity. However, a 5.5-fold increase was observed when Arix and dHAND were combined, and an 8-fold level of expression was observed when Arix was transfected with a dHAND mutant lacking the basic DNAbinding domain. When the homeodomain sites in the DBH promoter proximal region were mutated, all activity was lost, demonstrating dependence upon Arix-DNA interaction for transcriptional activation. In electrophoretic mobility shift assays, the addition of dHAND decreased the amount of Arix needed to elicit a mobility shift with the DBH homeodomain sites, and the dHAND basic mutant potentiated Arix binding in a manner similar to wild-type dHAND. The dHAND-Arix complex was dissociated upon the addition of an unlabeled competitor containing a homeodomain, but not upon the addition of a competitor containing E-boxes. Arix coprecipitated with antisera directed against recombinant dHAND, demonstrating direct protein-protein interactions. These results indicate that the activation of the DBH promoter by Arix is potentiated by dHAND via a mechanism independent of a direct interaction of dHAND with DNA.Cell-specific transcription is accomplished by the precise and transient interactions of numerous and complex molecular factors. Basic helix-loop-helix (bHLH) 1 proteins are transcription factors that play an important role in the development and differentiation of specific cell types such as neurons (1), appendages (2), and myocytes (3, 4). These bHLH proteins have been shown to bind to defined consensus sites, E-boxes (CANNTG), through the basic domain and require dimerization partners (via helices) to activate transcription. These proteins have been divided into several classes based on structure, function, and tissue specificity. Class I bHLH proteins (E12 and E47) are expressed ubiquitously in all tissues and can function as homodimers, but prefer to form heterodimers with other bHLH proteins (5). Class II proteins (dHAND, NeuroD, and MyoD) are expressed in specific tissues and are believed to be functionally active when complexed with a class I protein (5, 6). dHAND/HAND2 (deciduum, heart, autonomic nervous system, and neural crest cell derivatives) is a 30-kDa member of the class II bHLH protein family (7,8) and has been detected in Xenopus, zebrafish, chicks, mice, and humans (9). dHAND is required for cardiac (7), vascular (10), and craniofacial...

Three predominant ruminal cellulolytic organisms, Fibrobacter succinogenes S85, Ruminococcus albus 8, and R. flavefaciens FD-1, were cultured with a methanogen, Methanobrevibacter smithii. Growth rates, bacterial protein, organic acids, and methane production were measured. When grown in diculture with the methanogen, a fermentative advantage was observed with F. succinogenes S85 as seen by an increase in specific rate of ATP production and organic acid concentration. The introduction of the methanogen did not improve the growth rate, organic acid yield, or specific rate of ATP production for R. albus 8. The growth rate and amount of organic acid end products increased when R. flavefaciens FD-1 was cultured with the methanogen; however, the specific activity of ATP production did not increase.

When ruminal fluid from a cow fed timothy hay was serially diluted (10-fold increments into anaerobic broth containing 15 mg ml(-1) Trypticase), the low dilutions (< or =10(-6)) had optical densities greater than 2.0 and ammonia concentrations greater than 100 m M. The optical densities and ammonia concentrations of the 10(-8) and 10(-9) dilutions were very low, but large cocci were observed in the 10(-8) dilution. The large cocci were isolated and identified by 16S rDNA sequencing as Megasphaera elsdenii. The freshly isolated strain (JL1) grew well on Trypticase, but less than 4% of the amino acid nitrogen in Trypticase was converted to ammonia. Optical density and ammonia production were twice as great if Casamino acids were provided, and similar results were obtained with seven other strains (B159, AW106, YT91, LC1, T81, J1, and YZ70). Specific activities of deamination (based on Casamino acids) of the eight strains ranged from 100 (strain JL1) to 325 (strain B159) nmol mg protein(-1) min(-1). None of the strains could utilize branched-chain amino acids as an energy source for growth, but specific activities of branched-chain amino acid deamination ranged from 15 to 65 nmol mg protein(-1) min(-1). All eight of the M. elsdenii strains grew well in the presence of 5 micro M monensin, and only two of the strains were strongly inhibited by 20 micro M monensin. On the basis of these results, it appears that M. elsdenii is deficient in peptidase activity and can utilize only a few amino acids. Some M. elsdenii strains produced ammonia and branched-chain volatile fatty acids nearly as fast as obligate amino acid-fermenting ruminal bacteria, but the extent of this production was at least fourfold lower. Because all of the strains could tolerate 5 micro M monensin, it is unlikely that this feed additive would significantly inhibit M. elsdenii in vivo.