Thiomolybdates in rumen contents and rumen cultures

Examination of direct and (Cu)-difference spectra of i) the aqueous supernatants of in vitro cultures of bovine rumen contents incubated with MoO42- and potential sources of S2- and ii) samples drawn directly from the rumen of animals receiving high Mo diets yielded evidence of the presence of thiomolybdates. Only MoS42- was detected in the soluble phase of in vitro cultures. Although intense and variable background absorbance precluded full characterization of thiomolybdate species in samples drawn directly from the rumen, both spectral data and the biochemical and clinical responses of animals given high Mo diets were consistent with the conclusion that MoS42- rather than MoOS32- was the predominant thiomolybdate species present in the aqueous phase. Addition of Ca2+ either to rumen cultures before incubation or as a supplement to diets high in MoO42- content inhibited the appearance of MoS42- in the aqueous phase. Evidence of the sequestration of MoS42- and MoOS32- by particulate or microbial fractions of rumen contents is considered in relation to the inhibitory action of Mo upon Cu absorption by ruminants.     

Modelling the implications of feeding strategy on rumen fermentation and functioning of the rumen wall

The present study gives a critique of the mechanisms involved with the formation of volatile fatty acid (VFA) formed in the lumen of the reticulo-rumen, the absorption of VFA across the reticulo-rumen wall, and the intra-epithelial metabolism of VFA by reticulo-rumen epithelium. In contrast to the empirical treatment of these aspects in previous rumen modelling studies, a mechanistic model was developed which represents each of these aspects separately. Because tissues of the reticulo-rumen may strongly adapt to changing nutritional conditions, this adaptive response was included in the model. The model enabled an evaluation of the implications of VFA yield on the development of the rumen wall, on the transport of VFA, on the extent of intra-epithelial metabolism of VFA, and on the consequences for the supply of VFA to the ruminant. The current modelling effort allowed the integration of existing knowledge on each of these aspects and the model reproduced some essential characteristics of experimental observations on VFA absorption and metabolism. Although further development is still needed, the model appears helpful to distinguish elements that require specific consideration when evaluating rates of net portal appearance of VFA, or when testing hypothesis on the interaction between formation, absorption and intra-epithelial metabolism of VFA under various experimental conditions.     

Taxon-specific associations between protozoal and methanogen populations in the rumen and a model rumen system

Methanogen populations in the rumen and in model rumen systems (operated over a 240-h period) were studied using the small subunit (SSU) rRNA phylogenetic framework for group-specific enumerations. Representatives of the family Methanobacteriaceae were the most abundant methanogen population in the rumen, accounting for 89.3% (± 1.02%) of total archaea in the rumen fluid and 99.2% (± 1.8%) in a protozoal fraction of rumen fluid. Their percentage of archaea in the model rumen systems declined from 84% (± 8.5%) to 54% (± 7.8%) after 48 h of operation, correlated with loss of protozoa from these systems. The Methanomicrobiales, encompassed by the families Methanomicrobiaceae, Methanocorpusculaceae, and Methanospirillaceae were the second most abundant population and accounted for 12.1% (± 2.15%) of total SSU rRNA in rumen fluid. Additionally this group was shown to be essentially free living, since only a negligible hybridization signal was detected with the ruminal protozoal fraction. This group constituted a more significant proportion of total archaea in whole rumen fluid, 12.1% (± 2.1%) and model rumen fluid containing no protozoa (26.3 ± 7.7%). In contrast, the Methanosarcinales, generally considered the second most abundant population of rumen methanogens, accounted for only 2.8% (± 0.3%) of total archaeal SSU rRNA in rumen fluid.     

Desulfovibrio of the sheep rumen.

A sulfate-reducing bacterium has been isolated in pure culture from sheep rumen contents. Its properties agree in all respects tested with those ascribed to Desulfovibrio desulfuricans. The populations observed (about 10(8)/ml) are sufficient to account for published rates of ruminal sulfide production.     

The rumen flagellate Piromonas communis: its life-history and invasion of plant material in the rumen.

The rumen flagellat Piromonas communis is the zoospore of a phycomycete fungus inhabiting the rumen. Zoosporogenesis was stimulated by a dietary component (the inducer), and inhibited by compounds affecting membrane structure and function, but not by inhibitors of protein synthesis. The zoospores showed taxis towards the tissues surrounding the inflorescence of Lolium perenne L. in the rumen, invading principally the stomata and damaged tissues. The zoospores germinated on this substratum and the rhizoids of the developing vegetative stage penetrated the tissue, taking up C14 from labelled plant material, which was incorporated into the fungal cells. The conditions for maximum flagellate production (39 degrees C, pH 6-0 to 7-0, high concentration of CO2, absence of O2) resembled those found in the rumen. The organism was cultured in an undefined medium in vitro in the absence of other flagellates.     

Influence of intoxication with organophosphates on rumen bacteria and rumen protozoa and protective effect of clinoptilolite-rich zeolite on bacterial and protozoan concentration in rumen

The effect ofO-ethyl-S-(2-diisopropylaminoethyl) methylthiophosphonate on rumen bacteria and rumen protozoa was investigated in sheep (after premedication with clinoptilolite-rich zeolite and without that premedication). In control animals a decrease in the total concentration of rumen protozoa was observed 3–7 d after intoxication (particularly in small and large ones). In clinoptilolite-rich-zeolite-treated animals only a slight decrease in protozoan numbers occurred during the first hours after the intoxication. Similarly, in every category of rumen bacteria marked differences between the groups were recorded, particularly in concentration of lipolytic bacteria. The results suggest some protective effect of clinoptilolite-rich zeolite for rumen microbiota against the organophosphate poison.     

Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria

The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed.     

Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria.

The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed.     

Characterization of rumen bacterial strains isolated from enrichments of rumen content in the presence of propolis

Propolis presents many biological properties, including antibacterial activities, and has been proposed as an additive in ruminant nutrition. Twenty bacterial strains, previously isolated from enrichments of Brazilian cow rumen contents in the presence of different propolis extracts (LLOS), were characterized using phenotyping and 16S rRNA identification. Seven strains were assigned to Streptococcus sp., most likely S. bovis, and were all degrading starch. One amylolytic lactate-utilizing strain of Selenomonas ruminantium was also found. Two strains of Clostridium bifermentans were identified and showed proteolytic activity. Two strains were assigned to Mitsuokella jalaludinii and were saccharolytic. One strain belonged to a Bacillus species and seven strains were affiliated with Escherichia coli. All of the 20 strains were able to use many sugars, but none of them were able to degrade the polysaccharides carboxymethylcellulose and xylans. The effect of three propolis extracts (LLOS B1, C1 and C3) was tested on the in vitro growth of four representative isolates of S. bovis, E. coli, M. jalaludinii and C. bifermentans. The growth of S. bovis, E. coli and M. jalaludinii was not affected by the three propolis extracts at 1 mg ml^?1. C. bifermentans growth was completely inhibited at this LLOS concentration, but this bacterium was partially resistant at lower concentrations. LLOS C3, with the lower concentration of phenolic compounds, was a little less inhibitory than B1 and C1 on this strain.     

瘤胃甲烷菌及甲烷生成的调控

甲烷菌属于古细菌 ,参与有机物的厌氧降解 ,生成甲烷。反刍动物瘤胃内甲烷的生成损耗 2 %～ 12 %的饲料能量 ,并且通过嗳气排入大气。甲烷不仅是温室气体之一 ,而且还会破坏大气臭氧层。每年全球反刍动物排放大量的甲烷 ,减少瘤胃内甲烷的生成对提高饲料能量利用率和改善环境具有重要意义。近年来 ,有关瘤胃甲烷菌及甲烷生成调控的报道日益增多。概述甲烷菌的特性以及瘤胃内甲烷生成的途径 ,综述甲烷生成的调控手段 ,主要包括去原虫、日粮配合、添加电子受体、增加乙酸生成菌等方法     

Growth and survival of rumen fungi

The life cycle and growth kinetics of an anaerobic rumen fungus (Neocallimastix R1) in liquid and solid media are described, together with its response to light, temperature and oxygen. These results are discussed in relation to the survival of rumen fungi in saliva and faeces of sheep, and the possible routes for the transfer of anaerobic fungi between ruminants. The thallus and life cycle of Neocallimastix R1 are compared with those of aerobic chytrids.     

Biohydrogenation of linoleic acid by rumen fungi compared with rumen bacteria

AIMS: To investigate biohydrogenation of linoleic acid by rumen fungi compared with rumen bacteria, and to identify the fungus with the fastest biohydrogenation rate. METHODS AND RESULTS: Biohydrogenation of linoleic acid by mixed rumen fungi and mixed rumen bacteria were compared in vitro. With mixed rumen bacteria, all biohydrogenation reactions were finished within 100 min of incubation and the end product of biohydrogenation was stearic acid. With mixed rumen fungi, biohydrogenation proceeded more slowly over a 24-h period. Conjugated linoleic acid (CLA; cis-9, trans-11 C18 : 2) was an intermediate product, and vaccenic acid (VA; trans-11 C18 : 1) was the end product of biohydrogenation. Fourteen pure fungal isolates were tested for biohydrogenation rate. DNA sequencing showed that the isolate with the fastest rate belonged to the Orpinomyces genus. CONCLUSIONS: It is concluded that rumen fungi have the ability to biohydrogenate linoleic acid, but biohydrogenation is slower in rumen fungi than in rumen bacteria. The end product of fungal biohydrogenation is VA, as for group A rumen bacteria. Orpinomyces is the most active biohydrogenating fungus. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to demonstrate that rumen fungi can biohydrogenate fatty acids. Fungi could influence CLA content of ruminant products.