Factors that alter rumen microbial ecology

Exposure of sheep scrapie brain homogenate to rumen-simulating conditions does not result in a reduction of PrPSclevels

AIMS

Experiments were designed to evaluate the potential of rumen-simulating conditions to reduce PrP(Sc) levels.

METHODS AND RESULTS

Scrapie-positive brain material was incubated under rumen-simulating conditions. Time points were taken over a 24-h period and PrP(Sc) levels were analysed by Western blot. No loss of PrP(Sc) was observed over a 24-h time period.

CONCLUSIONS

Our results indicate that a fully developed rumen fermentation does not provide significant protection against prion infection via the oral route. Developmental changes including senescence of immune system function or other developmental changes in the gastrointestinal tract are potential mechanisms by which relative bovine spongiform encephalopathy (BSE) susceptibility might vary with age.

SIGNIFICANCE AND IMPACT OF THE STUDY

Epidemiology of the BSE outbreak in the United Kingdom indicates that younger animals were at higher risk of infection. The rumen undergoes pronounced developmental changes early in life, coinciding with the introduction of fibre into the diet. The timeframe of highest risk of infection overlaps the time in life prior to full rumen development. This work indicates that a fully developed rumen does not provide significant protection against prion infection via the oral route of infection. This result implicates other developmental changes that are responsible for the age-dependent susceptibility of cattle to BSE.

Wolinella succinogenes response to ox-bile stress

The bacterium Wolinella succinogenes is the only known species of its genus. It was first isolated from cow ruminal fluid, and in cattle, it dwells in the reticulum and rumen compartments of the stomach. The global protein response of W. succinogenes to ox-bile was investigated with the aim to understand bile-tolerance mechanisms of the bacterium. Bacteria were grown in liquid media supplemented with different bile concentrations to determine its effects on growth and morphology. Proteomic analyses served to identify 14 proteins whose expression was modulated by the presence of 0.2% bile. Quantitative real-time PCR analyses of the expression of selected genes were employed to obtain independent confirmation of the proteomics data. Proteins differentially expressed revealed metabolic pathways involved in the adaptation of W. succinogenes to bile. The data suggested that bile stress elicited complex physiological responses rather than just specific pathways, and identified proteins previously unknown to be involved in the adaptation of bacteria to bile.

Changes in plasma metabolites and muscle glycogen are correlated to bovine spongiform encephalopathy in infected dairy cattle

During the clinical phase of bovine spongiform encephalopathy (BSE), a significant decrease was observed in the ratio of muscle glycogen to plasma L-lactic acid concentrations in BSE infected field case and experimentally infected dairy cattle compared with healthy control cattle (P<0.001), this being due to changes in the concentration of both metabolites in the BSE infected cattle compared with the control group. Furthermore, the concentration of plasma alanine was significantly increased (P<0.05) in the infected animals. No significant difference was detected between these two groups in the ratio of hepatic glycogen to plasma lactate. We infer that BSE infected cattle exhibit signs of altered energy metabolism and when applied in conjunction with changes in other metabolite biomarkers these changes may be useful for discriminating BSE infected cattle from healthy cattle or those suffering with other disorders or diseases.

Regulation of rumen fermentation during seasonal fluctuations in food intake of muskoxen

We studied rumen fermentation of castrated adult muskoxen (Ovibos moschatus; n=4) during periods of low (May) and high (August) food intake. Turnover time (17+/-1.8 h) and volume (26+/-3.9 L) of rumen fluid were consistent between May and August and among days within each season. Rumen temperature did not vary significantly during the day (38.8+/-0.29 degrees C) in either season. Rumen osmolality (271.9+/-16.4 vs. 245.9+/-11.4 mOsm kg(-1)) and pH (6.81+/-0.31 vs. 6.39+/-0.15) were higher in May than in August indicating a shift in the allostatic set point. Rumen fluid pH was more variable in May than in August both before and after a single meal of fermentable substrate even though fermentation acids were lower in May than in August (101.0+/-11.0 vs. 126.0+/-8.74 mM). Changing proportions of minor fermentation acids indicated a shift in metabolic pathways even though bacterial numbers were similar between seasons (6.4+/-5.8x10(9) mL(-1)). Allostatic set points probably alter the homeostatic range of conditions and the microbial diversity of fermentations in herbivores from highly seasonal environments.

Ruminal fermentation and fill change with season in an arctic grazer: responses to hyperphagia and hypophagia in muskoxen (Ovibos moschatus)

We studied castrated adult muskoxen fed a standard diet of grass hay and supplement throughout the year to determine seasonal changes in digesta passage, fill, and fermentation without the confounding effects of reproductive demands or changes in food quality. Although food intake increased by 74% between spring and autumn, mean retention times of fluid and particulate digesta markers were maintained between seasons in both the rumen (9-13 h) and the intestines (27-37 h). The rumen contained 84.5% of digesta and accounted for 79% of dry matter digestion in the whole digestive tract. Ruminal fluid space and whole-gut digesta fill increased by 31%-34%, while ruminal rates of in situ degradation increased by more than 100% between spring and autumn for cellulose and hemicellulose. Hyperphagia in autumn was accompanied by increased bacterial counts in ruminal fluid (30%), declines in ruminal pH, and increases in the concentration of fermentation acids (16%) when compared with spring hypophagia. Consumption of fresh hay and supplement increased the concentrations of acids most markedly during winter and spring when bacterial counts were low. Low food intakes in winter and spring may limit the microbial population, whereas hyperphagia in autumn may foster a much more active microflora that requires consistent supplies of substrate. Plasticity of fill and fermentation in muskoxen minimizes winter costs and maximizes nutrients and energy gained from coarse forages in small home ranges throughout the year.

Outlook for cellulase improvement: screening and selection strategies

Cellulose is the most abundant renewable natural biological resource, and the production of biobased products and bioenergy from less costly renewable lignocellulosic materials is important for the sustainable development of human beings. A reduction in cellulase production cost, an improvement in cellulase performance, and an increase in sugar yields are all vital to reduce the processing costs of biorefineries. Improvements in specific cellulase activities for non-complexed cellulase mixtures can be implemented through cellulase engineering based on rational design or directed evolution for each cellulase component enzyme, as well as on the reconstitution of cellulase components. Here, we review quantitative cellulase activity assays using soluble and insoluble substrates, and focus on their advantages and limitations. Because there are no clear relationships between cellulase activities on soluble substrates and those on insoluble substrates, soluble substrates should not be used to screen or select improved cellulases for processing relevant solid substrates, such as plant cell walls. Cellulase improvement strategies based on directed evolution using screening on soluble substrates have been only moderately successful, and have primarily targeted improvement in thermal tolerance. Heterogeneity of insoluble cellulose, unclear dynamic interactions between insoluble substrate and cellulase components, and the complex competitive and/or synergic relationship among cellulase components limit rational design and/or strategies, depending on activity screening approaches. Herein, we hypothesize that continuous culture using insoluble cellulosic substrates could be a powerful selection tool for enriching beneficial cellulase mutants from the large library displayed on the cell surface.

Nitrogen metabolism in the rumen

Protein metabolism in the rumen is the result of metabolic activity of ruminal microorganisms. The structure of the protein is a key factor in determining its susceptibility to microbial proteases and, thus, its degradability. Ruminal protein degradation is affected by pH and the predominant species of microbial population. Ruminal proteolytic activity decreases as pH decreases with high-forage dairy cattle-type rations, but not in high-concentrate beef-type rations. Accumulation of amino acid (AA) N after feeding suggests that AA uptake by rumen microorganisms could be the limiting factor of protein degradation in the rumen. In addition, there are several AA, such as Phe, Leu, and Ile, that are synthesized by rumen microorganisms with greater difficulty than other AA. The most common assessment of efficiency of microbial protein synthesis (EMPS) is determination of grams of microbial N per unit of rumen available energy, typically expressed as true organic matter or carbohydrates fermented. However, EMPS is unable to estimate the efficiency at which bacteria capture available N in the rumen. An alternative and complementary measure of microbial protein synthesis is the efficiency of N use (ENU). In contrast to EMPS, ENU is a good measurement for describing efficiency of N capture by ruminal microbes. Using EMPS and ENU, it was concluded that optimum bacterial growth in the rumen occurs when EMPS is 29 g of bacterial N/kg of fermented organic matter, and ENU is 69%, implying that bacteria would require about 1.31 x rumen-available N per unit of bacterial N. Because the distribution of N within bacterial cells changes with rate of fermentation, AA N, rather than total bacterial N should be used to express microbial protein synthesis.

Horizontal gene transfer from Bacteria to rumen Ciliates indicates adaptation to their anaerobic, carbohydrates-rich environment

Background

The horizontal transfer of expressed genes from Bacteria into Ciliates which live in close contact with each other in the rumen (the foregut of ruminants) was studied using ciliate Expressed Sequence Tags (ESTs). More than 4000 ESTs were sequenced from representatives of the two major groups of rumen Cilates: the order Entodiniomorphida (Entodinium simplex, Entodinium caudatum, Eudiplodinium maggii, Metadinium medium, Diploplastron affine, Polyplastron multivesiculatum and Epidinium ecaudatum) and the order Vestibuliferida, previously called Holotricha (Isotricha prostoma, Isotricha intestinalis and Dasytricha ruminantium).

Results

A comparison of the sequences with the completely sequenced genomes of Eukaryotes and Prokaryotes, followed by large-scale construction and analysis of phylogenies, identified 148 ciliate genes that specifically cluster with genes from the Bacteria and Archaea. The phylogenetic clustering with bacterial genes, coupled with the absence of close relatives of these genes in the Ciliate Tetrahymena thermophila, indicates that they have been acquired via Horizontal Gene Transfer (HGT) after the colonization of the gut by the rumen Ciliates.

Conclusion

Among the HGT candidates, we found an over-representation (>75%) of genes involved in metabolism, specifically in the catabolism of complex carbohydrates, a rich food source in the rumen. We propose that the acquisition of these genes has greatly facilitated the Ciliates' colonization of the rumen providing evidence for the role of HGT in the adaptation to new niches.

Effects of cattle feeding regimen and soil management type on the fate of Escherichia coli O157:H7 and salmonella enterica serovar typhimurium in manure, manure-amended soil, and lettuce

Survival of the green fluorescent protein-transformed human pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium was studied in a laboratory-simulated lettuce production chain. Dairy cows were fed three different roughage types: high-digestible grass silage plus maize silage (6:4), low-digestible grass silage, and straw. Each was adjusted with supplemental concentrates to high and low crude protein levels. The pathogens were added to manure, which was subsequently mixed (after 56 and 28 days for E. coli O157:H7 and Salmonella serovar Typhimurium, respectively) with two pairs of organically and conventionally managed loamy and sandy soil. After another 14 days, iceberg lettuce seedlings were planted and then checked for pathogens after 21 days of growth. Survival data were fitted to a logistic decline function (exponential for E. coli O157:H7 in soil). Roughage type significantly influenced the rate of decline of E. coli O157:H7 in manure, with the fastest decline in manure from the pure straw diet and the slowest in manure from the diet of grass silage plus maize silage. Roughage type showed no effect on the rate of decline of Salmonella serovar Typhimurium, although decline was significantly faster in the manure derived from straw than in the manure from the diet of grass silage plus maize silage. The pH and fiber content of the manure were significant explanatory factors and were positively correlated with the rate of decline. With E. coli O157:H7 there was a trend of faster decline in organic than in conventional soils. No pathogens were detected in the edible lettuce parts. The results indicate that cattle diet and soil management are important factors with respect to the survival of human pathogens in the environment.

Cellulose utilization by Clostridium thermocellum: bioenergetics and hydrolysis product assimilation

The bioenergetics of cellulose utilization by Clostridium thermocellum was investigated. Cell yield and maintenance parameters, Y(X/ATP)True = 16.44 g cell/mol ATP and m = 3.27 mmol ATP/g cell per hour, were obtained from cellobiose-grown chemostats, and it was shown that one ATP is required per glucan transported. Experimentally determined values for G(ATP)P-T (ATP from phosphorolytic beta-glucan cleavage minus ATP for substrate transport, mol ATP/mol hexose) from chemostats fed beta-glucans with degree of polymerization (DP) 2-6 agreed well with the predicted value of (n-2)/n [corrected] (n = mean cellodextrin DP assimilated). A mean G(ATP)(P-T) value of 0.52 +/- 0.06 was calculated for cellulose-grown chemostat cultures, corresponding to n = 4.20 +/- 0.46. Determination of intracellular beta-glucan radioactivity resulting from 14C-labeled substrates showed that uptake is different for cellulose and cellobiose (G2). For 14C-cellobiose, radioactivity was greatest for G2; substantially smaller but measurable for G1, G3, and G4; undetectable for G5 and G6; and n was approximately 2. For 14C-cellulose, radioactivity was greatest for G5; lower but substantial for G6, G2, and G1; very low for G3 and G4; and n was approximately 4. These results indicate that: (i) C. thermocellum hydrolyzes cellulose by a different mode of action from the classical mechanism involving solubilization by cellobiohydrolase; (ii) bioenergetic benefits specific to growth on cellulose are realized, resulting from the efficiency of oligosaccharide uptake combined with intracellular phosphorolytic cleavage of beta-glucosidic bonds; and (iii) these benefits exceed the bioenergetic cost of cellulase synthesis, supporting the feasibility of anaerobic biotechnological processing of cellulosic biomass without added saccharolytic enzymes.

Ontogenetic development of the gastrointestinal microbiota in the marine herbivorous fish Kyphosus sydneyanus

Molecular techniques were used to investigate the composition and ontogenetic development of the intestinal bacterial community in the marine herbivorous fish Kyphosus sydneyanus from the north eastern coast of New Zealand. Previous work showed that K. sydneyanus maintains an exclusively algivorous diet throughout post-settlement life and passes through an ontogenetic diet shift from a juvenile diet which is readily digestible to an adult diet high in refractory algal metabolites. Terminal restriction fragment length polymorphism (T-RFLP) analysis was used to investigate the relationship between bacterial community structure and fish size. Bacterial diversity was higher in posterior gut sections than anterior gut sections, and in larger fish than in smaller fish. Partial sequencing of bacterial 16S rDNA genes PCR amplified and cloned from intestine content samples was used to identify the phylogenetic affiliation of dominant gastrointestinal bacteria. Phylogenetic analysis of clones showed that most formed a clade within the genus Clostridium, with one clone associated with the parasitic mycoplasmas. No bacteria were specific to a particular intestinal section or size class of host, though some appeared more dominant than others and were established in smaller fishes. Clones closely related to C. lituseburense were particularly dominant in most intestine content samples. All bacteria identified in the intestinal samples were phylogenetically related to those possessing fermentative type metabolism. Short-chain fatty acids in intestinal fluid samples increased from 15.6 +/- 2.1 mM in fish <100 mm to 51.6 +/- 5.5 mM in fish >300 mm. The findings of this study support the hypothesis that the ontogenetic diet shift of K. sydneyanus is accompanied by an increase in the diversity of intestinal microbial symbionts capable of degrading refractory algal metabolites into short-chain fatty acids, which can then be assimilated by the host.

Clostridium cellulolyticum: model organism of mesophilic cellulolytic clostridia

Clostridium cellulolyticum ATCC 35319 is a non-ruminal mesophilic cellulolytic bacterium originally isolated from decayed grass. As with most truly cellulolytic clostridia, C. cellulolyticum possesses an extracellular multi-enzymatic complex, the cellulosome. The catalytic components of the cellulosome release soluble cello-oligosaccharides from cellulose providing the primary carbon substrates to support bacterial growth. As most cellulolytic bacteria, C. cellulolyticum was initially characterised by limited carbon consumption and subsequent limited growth in comparison to other saccharolytic clostridia. The first metabolic studies performed in batch cultures suggested nutrient(s) limitation and/or by-product(s) inhibition as the reasons for this limited growth. In most recent investigations using chemostat cultures, metabolic flux analysis suggests a self-intoxication of bacterial metabolism resulting from an inefficiently regulated carbon flow. The investigation of C. cellulolyticum physiology with cellobiose, as a model of soluble cellodextrin, and with pure cellulose, as a carbon source more closely related to lignocellulosic compounds, strengthen the idea of a bacterium particularly well adapted, and even restricted, to a cellulolytic lifestyle. The metabolic flux analysis from continuous cultures revealed that (i) in comparison to cellobiose, the cellulose hydrolysis by the cellulosome introduces an extra regulation of entering carbon flow resulting in globally lower metabolic fluxes on cellulose than on cellobiose, (ii) the glucose 1-phosphate/glucose 6-phosphate branch point controls the carbon flow directed towards glycolysis and dissipates carbon excess towards the formation of cellodextrins, glycogen and exopolysaccharides, (iii) the pyruvate/acetyl-CoA metabolic node is essential to the regulation of electronic and energetic fluxes. This in-depth analysis of C. cellulolyticum metabolism has permitted the first attempt to engineer metabolically a cellulolytic microorganism.

Effects of esculin and esculetin on the survival of Escherichia coli O157 in human faecal slurries, continuous-flow simulations of the rumen and colon and in calves

The human pathogen Escherichia coli O157:H7 is thought to be spread by direct or indirect contact with infected animal or human faeces. The present study investigated the effects of the plant coumarin esculin and its aglycone esculetin on the survival of a strain of E. coli O157 under gut conditions. The addition of these compounds to human faecal slurries and in vitro continuous-flow fermenter models simulating conditions in the human colon and rumen caused marked decreases in the survival of an introduced strain of E. coli O157. When four calves were experimentally infected with E. coli O157 and fed esculin, the pathogen was detected in five of twenty-eight (18 %) of faecal samples examined post-inoculation, compared with thirteen of thirty-five (37 %) of faecal samples examined from five control calves not fed esculin. Coumarin compounds that occur naturally in dietary plants or when supplemented in the diet probably inhibit the survival of E. coli O157 in the gut.

Inhibition of ruminal microbial methane production by beta-cyclodextrin iodopropane, malate and their combination in vitro

The objective of this study was to evaluate the effects of different concentrations of l-malate (0, 5, 10 and 20 mm), 2-iodopropane-beta-cyclodextrin complex (CD-IP) (0, 0.1, 0.2 and 0.4 mm) and a combination of malate (10 and 20 mm) plus CD-IP (0.2 and 0.4 mm) on methane production from corn starch. Ruminal fluid was collected from dairy cows, mixed with phosphate buffer (1 : 2) and incubated (30 ml) anaerobically at 38 degrees C for 6 h with or without additives. Fermentation of corn starch in the presence of malate resulted in an increase (p < 0.05) in pH of the medium, total volatile fatty acid (VFA), total gas production and molar proportion of propionate. Acetate and ammonia-N concentration were unchanged. Methane production was decreased (p < 0.05) (15.5 to 20.4%). Addition of CD-IP in corn starch resulted in an increase (p < 0.05) in total VFA and molar proportion of propionate. Acetate, pH and ammonia-N concentration of the medium were decreased (p < 0.05). Total gas production was unchanged. Methane production was decreased (p < 0.05) (25.2 to 97.1%) and hydrogen production was increased (p < 0.05). Addition of l-malate to CD-IP resulted in an increase (p < 0.05) in total VFA, total gas production and molar proportion of propionate. Acetate and ammonia-N concentration were decreased (p < 0.05). No effects were observed on medium pH. Methane production was decreased (p < 0.05) (49.5 to 97.1%). Hydrogen production was also decreased (p < 0.05) (54.5 to 64.1%) compared with those of CD-IP alone. Therefore, these additives may be used as supplements to inhibit methane production as well as to improve rumen fermentation and animal performance.

Oral rehydration therapy: new explanations for an old remedy

Diarrheal diseases are among the most devastating illnesses globally, but the introduction of oral rehydration therapy has reduced mortality due to diarrhea from >5 million children, under the age of 5, in 1978 to 1.3 million in 2002. Variations of this simple therapy of salts and sugars are prevalent in traditional remedies in cultures world-wide, but only in the past four decades have the scientific bases for these remedies begun to be elucidated. This review aims to provide a broad understanding of the cellular basis of oral rehydration therapy. The features integral to the success of oral rehydration therapy are active glucose transport in the small intestine, commensal bacteria, and short-chain fatty acid transport in the colon. The review examines these processes and their regulation and considers new approaches that might supplement oral rehydration therapy in controlling diarrheal diseases.

Effect of the ionophore antibiotic monensin on the ruminal biotransformation of benzimidazole anthelmintics

The benzimidazole (BZD) anthelmintics, netobimin (NTB) pro-drug and albendazole sulphoxide (ABZSO) are reduced to albendazole (ABZ) by ruminal microflora. The aim of the current work was to evaluate the influence of the ionophore monensin (MON) on the in vitro biotransformation of NTB and ABZSO by sheep ruminal fluid. Ruminal fluid, collected from Corriedale sheep, was preincubated (24 h) either without (control) or with known MON concentrations (0.5, 1.5 and 3.0 microg/mL) at 38 degrees C under a CO2 atmosphere. Afterwards, aliquots from both MON-pretreated and control ruminal fluid samples were incubated (30 and 60 min) with 2 microg/mL of either NTB or ABZSO. Incubated samples were chemically extracted and analysed by High Performance Liquid Chromatography to quantify the metabolites formed. The rate of ABZ production after 30 min of NTB incubation with control ruminal fluid was 0.023 microg/min. Conversely, the rates of ABZ formation were significantly (P<0.05) lower (0.009, 0.011 and 0.013 microg/min) when NTB was incubated with ruminal fluid pretreated with MON (at 0.5, 1.5 and 3.0 microg/mL, respectively). After both incubation periods, the reduction of ABZSO to ABZ was 22 to 70% lower when the ruminal fluid was preincubated with the different MON concentrations. The lower ABZ production observed in the presence of MON may result in a modified availability of this molecule in the gastrointestinal (GI) tract and hence, on its anthelmintic efficacy against GI nematodes.

Ionophore resistance of ruminal bacteria and its potential impact on human health

In recent years, there has been a debate concerning the causes of antibiotic resistance and the steps that should be taken. Beef cattle in feedlots are routinely fed a class of antibiotics known as ionophores, and these compounds increase feed efficiency by as much as 10%. Some groups have argued that ionophore resistance poses the same public health threat as conventional antibiotics, but humans are not given ionophores to combat bacterial infection. Many ruminal bacteria are ionophore-resistant, but until recently the mechanism of this resistance was not well defined. Ionophores are highly lipophilic polyethers that accumulate in cell membranes and catalyze rapid ion movement. When sensitive bacteria counteract futile ion flux with membrane ATPases and transporters, they are eventually de-energized. Aerobic bacteria and mammalian enzymes can degrade ionophores, but these pathways are oxygen-dependent and not functional in anaerobic environments like the rumen or lower GI tract. Gram-positive ruminal bacteria are in many cases more sensitive to ionophores than Gram-negative species, but this model of resistance is not always clear-cut. Some Gram-negative ruminal bacteria are initially ionophore-sensitive, and even Gram-positive bacteria can adapt. Ionophore resistance appears to be mediated by extracellular polysaccharides (glycocalyx) that exclude ionophores from the cell membrane. Because cattle not receiving ionophores have large populations of resistant bacteria, it appears that this trait is due to a physiological selection rather than a mutation per se. Genes responsible for ionophore resistance in ruminal bacteria have not been identified, but there is little evidence that ionophore resistance can be spread from one bacterium to another. Given these observations, use of ionophores in animal feed is not likely to have a significant impact on the transfer of antibiotic resistance from animals to man.

Commensal bacteria make a difference

Nowhere is the relationship between microorganisms and eukaryotes as diverse, intimate and clinically relevant as in the gastrointestinal tract. An estimated 500-1000 mostly anaerobic species reside in the intestine, approaching enormous densities of 10(11)-10(12) organisms per gram colon content. The commensal interactions between intestinal microorganisms and animal hosts have been difficult to study in the past because of the diversity of microorganisms involved and because of the lack of culturability that accompanies many microbial consortia. However, recent work has provided new insights into these interactions.

Forage feeding to reduce preharvest Escherichia coli populations in cattle, a review

Although Escherichia coli are commensal organisms that reside within the host gut, some pathogenic strains of E. coli can cause hemorrhagic colitis in humans. The most notable enterohemorrhagic E. coli (EHEC) strain is O157:H7. Cattle are asymptomatic natural reservoirs of E. coli O157:H7, and it has been reported that as many as 30% of all cattle are carriers of this pathogen, and in some circumstances this can be as high as 80%. Feedlot and high-producing dairy cattle are fed large grain rations in order to increase feed efficiency. When cattle are fed large grain rations, some starch escapes ruminal microbial degradation and passes to the hind-gut where it is fermented. EHEC are capable of fermenting sugars released from starch breakdown in the colon, and populations of E. coli have been shown to be higher in grain fed cattle, and this has been correlated with E. coli O157:H7 shedding in barley fed cattle. When cattle were abruptly switched from a high grain (corn) diet to a forage diet, generic E. coli populations declined 1000-fold within 5 d, and the ability of the fecal generic E. coli population to survive an acid shock similar to the human gastric stomach decreased. Other researchers have shown that a switch from grain to hay caused a smaller decrease in E. coli populations, but did not observe the same effect on gastric shock survivability. In a study that used cattle naturally infected with E. coli O157:H7, fewer cattle shed E. coli O157:H7 when switched from a feedlot ration to a forage-based diet compared with cattle continuously fed a feedlot ration. Results indicate that switching cattle from grain to forage could potentially reduce EHEC populations in cattle prior to slaughter; however the economic impact of this needs to be examined.

Effects of Moringa oleifera seed extract on rumen fermentation in vitro

Moringa oleifera is a pantropical tree of the family Moringaceae. A previously undescribed property of an aqueous extract from the seeds of this plant is the modulation of ruminal fermentation patterns, especially protein degradation, as demonstrated in a short-term batch incubation system. Gas, short chain fatty acids (SCFA) and cellulolytic enzyme activities were determined as general fermentation parameters. A dot blot assay able to directly detect true protein in rumen fluid samples was used to quantify protein degradation. For complex substrates the interpretation of protein degradation profiles was amended by polyacrylamide gel electrophoresis (PAGE) of the samples. When incubated with pure carbohydrates at a concentration of 1 mg ml(-1), the extract reduced microbial degradation of the model protein, bovine serum albumin (BSA), such that its concentration was at least 40% above the control after 12 h of incubation. Total protein degradation was thus delayed by approximately 9 h. When fermented along with wheat straw, leaf protein (Rubisco) was almost entirely protected during 12 h of fermentation. The degradation of soy proteins was retarded by at least 4-6 h, depending on the protein band. There were strong side effects on the fermentation of pure cellulose (SCFA yield-60% after 12 h), whereas cellobiose and starch fermentation were less affected (-18 and -8%, respectively). When the complex substrates were fermented, SCFA yield was reduced by approximately 30% after 12 h. In our work we clearly demonstrate the efficacy of the new substance, which is neither a tannin nor a saponin, in an in vitro system, using pure as well as complex substrates. The properties shown in vitro for the crude extract suggest that it could have a positive effect on the protein metabolism of ruminants under intensive management and that negative side effects can be overcome by an optimized dosage. If the chemical nature of the active substance and its mechanism of action can be clarified, it may provide an alternative to replace critical synthetic feed additives (such as antibiotics) for high yielding dairy cows.

The binding and degradation of nisin by mixed ruminal bacteria

We found that nisin catalyzed potassium efflux from glycolyzing Streptococcus bovis JB1 cell suspensions and that the steady state concentration of residual potassium was dependent upon the amount of nisin added. The relationship between nisin concentration and potassium depletion was a saturation function that had considerable cooperativity. By pre-incubating mixed ruminal bacteria with nisin and removing them prior to S. bovis JB1 addition, it was possible to estimate the ability of mixed ruminal bacteria to bind or degrade nisin. Low concentrations of mixed ruminal bacteria did not bind or degrade all of the nisin in 6 h, but little nisin remained if the mixed ruminal bacteria were present at more than 50 microg protein ml(-1). Because cell-free ruminal fluid (10% v/v) inactivated the nisin in less than 2 h, and this inactivation could be counteracted by autoclaving, ultra-filtration or proteinase inhibitor, it appeared that there was an enzymatic degradation of nisin. Mixed ruminal bacteria degraded nisin rapidly, but this degradation did not prevent potassium depletion from mixed ruminal bacteria. These latter results indicated that nisin binding was faster than nisin degradation. The idea that nisin binding could protect nisin from degradation was supported by the observation that intact nisin could be extracted from mixed ruminal bacteria. These observations support the hypothesis that bacteriocins can be used to modify ruminal fermentation, but further work will be needed to see if these peptides can be produced economically.

Allisonella histaminiformans gen. nov., sp. nov. A novel bacterium that produces histamine, utilizes histidine as its sole energy source, and could play a role in bovine and equine laminitis

When cattle and horses are fed large amounts of grain, histamine can accumulate in the gastrointestinal tract, and this accumulation can cause an acute inflammation of the hooves (laminitis). When ruminal fluid from dairy cattle fed grain supplements was serially diluted in anaerobic MRS medium containing histidine (50 mM), histamine was detected at dilutions as high as 10(-7). The histidine enrichments were then transferred successively in an anaerobic, carbonate-based medium (50 mM histidine) without glucose. The histamine producing bacteria could not be isolated from the rumens of cattle fed hay; however, histamine producing bacteria could be isolated the feces of cattle fed grain and the cecum of a horse. All of the histamine producing isolates had the same ovoid morphology. The cells stained Gram-negative and were resistant to the ionophore, monensin (25 microM). The doubling time was 110 min, and the yield was 1.5 mg cell protein per mmol histidine. The G+C content was 46.8%. Lysine was the only other amino acid used, but lysine did not allow growth if histidine was absent. Because carbohydrate and organic acid utilization was not detected, it appeared that the isolates used histidine decarboxylation as their sole mechanism of energy derivation. 16s rRNA gene sequencing indicated that the isolates were most closely related to low G+C Gram-positive bacteria (firmicutes), but similarities were < or = 94%. Because the most closely related bacteria (Dialister pneumonsintes, Megasphaera elsdenii and Selenomonas ruminantium) did not produce histamine from histidine, we propose that these histamine producing bacteria be assigned to a new genus, Allisonella, as Allisonella histaminiformans gen. nov., sp. nov. The type strain is MR2 (ATCC BAA610, DSM 15230).

How host-microbial interactions shape the nutrient environment of the mammalian intestine

Humans and other mammals are colonized by a vast, complex, and dynamic consortium of microorganisms. One evolutionary driving force for maintaining this metabolically active microbial society is to salvage energy from nutrients, particularly carbohydrates, that are otherwise nondigestible by the host. Much of our understanding of the molecular mechanisms by which members of the intestinal microbiota degrade complex polysaccharides comes from studies of Bacteroides thetaiotaomicron, a prominent and genetically manipulatable component of the normal human and mouse gut. Colonization of germ-free mice with B. thetaiotaomicron has shown how this anaerobe modifies many aspects of intestinal cellular differentiation/gene expression to benefit both host and microbe. These and other studies underscore the importance of understanding precisely how nutrient metabolism serves to establish and sustain symbiotic relationships between mammals and their bacterial partners.

The effect of bovicin HC5, a bacteriocin from Streptococcus bovis HC5, on ruminal methane production in vitro

Methane represents a loss of feed energy to ruminant animals, and nutritionists have sought methods of inhibiting ruminal methane production. When mixed ruminal bacteria (approximately 400 mg protein ml(-1)) from a cow fed timothy hay were incubated in vitro with carbon dioxide and hydrogen (0.5 atm) for less than 8 h, the first-order rate of methane production was 17 micromol ml(-1). Semi-purified bacteriocin from Streptococcus bovis HC5 (bovicin HC5) inhibited methane production, by as much as 50%, and even a low concentration of bovicin HC5 (128 activity units (AU) ml(-1)) caused a significant decrease. Mixed ruminal bacteria that were transferred successively retained their ability to produce methane from carbon dioxide and hydrogen, and the first-order rate of methane production did not decrease. Cultures that were treated with bovicin HC5 (128 AU ml(-1)) gradually lost their ability to produce methane, and methane was not detected after four transfers. These latter results indicated that ruminal methanogens could not adapt and become resistant to bovicin HC5. When the chromosomal DNA was amplified with 16S rDNA primers specific to archaea, digested with restriction enzymes (HhaI and HaeIII) and separated on agarose gels, approximately 12 fragments were observed. DNA from control and treated cultures (third transfer) had the same fragment pattern indicating bovicin HC5 was not selective. Given the perception that the routine use of antibiotics in animal feeds should be avoided, bacteriocins may provide an alternative strategy for decreasing ruminal methane production.

Bovicin HC5, a bacteriocin from Streptococcus bovis HC5

Previous work indicated that Streptococcus bovis HC5 had significant antibacterial activity, and even nisin-resistant S. bovis JB1 cells could be strongly inhibited. S. bovis HC5 inhibited a variety of Gram-positive bacteria and the spectrum of activity was similar to monensin, a commonly used feed additive. The crude extracts (ammonium sulfate precipitation) were inactivated by Pronase E and trypsin, but the activity was resistant to heat, proteinase K and alpha-chymotrypsin. Most of the antibacterial activity was cell associated, but it could be liberated by acidic NaCl (100 mM, pH 2.0) without significant cell lysis. When glycolysing S. bovis JB1 cells were treated with either crude or acidic NaCl extracts, intracellular potassium declined and this result indicated the antibacterial activity was mediated by a pore-forming peptide. The peptide could be purified by HPLC and matrix-assisted laser desorption ionization time-of-flight analysis indicated that it had a molecular mass of approximately 2440 Da. The terminal amino acid sequence was VGXRYASXPGXSWKYVXF. The unnamed amino acid residues (designated by X) had approximately the same position as dehydroalanines found in some lantibiotics, but samples that were reduced and alkylated prior to Edman degradation did not have cysteine residues. The only other bacteriocin that had significant similarity was the lantibiotic precursor of Streptococcus pyogenes SF370, but the identity was only 55%. Based on these results, the bacteriocin of S. bovis HC5 appears to be novel and the authors now designate it as bovicin HC5.

Fluorescent amplified fragment length polymorphism and repetitive extragenic palindrome-PCR fingerprinting reveal host-specific genetic diversity of Vibrio halioticoli-like strains isolated from the gut of Japanese abalone

When analyzed by fluorescent amplified fragment length polymorphism and repetitive extragenic palindrome-PCR fingerprinting, a total of 47 Vibrio halioticoli strains isolated from four Japanese abalone species and one turban shell species formed three clusters that roughly reflect the different species of host abalone from which they were isolated. The V. halioticoli isolates from turban shells were distributed evenly among the clusters. Representative isolates from two clusters were deemed separate species or subspecies by DNA-DNA hybridization.

Unseen forces: the influence of bacteria on animal development

The diversity of developmental programs present in animal phyla first evolved within the world's oceans, an aquatic environment teeming with an abundance of microbial life. All stages in the life histories of these early animals became adapted to microorganisms bathing their tissues, and countless examples of animal-bacterial associations have arisen as a result. Thus far, it has been difficult for biologists to design ways of determining the extent to which these associations have influenced the biology of animals, including their developmental patterns. The following review focuses on an emerging field, the goal of which is to understand the influence of bacteria on animal developmental programs. This integrative area of research is undergoing a revolution that has resulted from advances in technology and the development of suitable animal-bacterial systems for the study of these complex associations. In this contribution, the current status of the field is reviewed and the emerging research horizons are examined.

Displacement of Escherichia coli O157:H7 from rumen medium containing prebiotic sugars

A fed-batch, anaerobic culture system was developed to assess the behavior of Escherichia coli O157:H7 in a rumen-like environment. Fermentation medium consisted of either 50% (vol/vol) raw or sterile rumen fluid and 50% phosphate buffer. Additional rumen fluid was added twice per day, and samples were removed three times per day to simulate the exiting of digesta and microbes from the rumen environment under typical feeding regimens. With both types of medium, anaerobic and enteric bacteria reached 10(10) and 10(4) cells/ml, respectively, and were maintained at these levels for at least 5 days. When a rifampin-resistant strain of E. coli O157:H7 was inoculated into medium containing raw rumen fluid, growth did not occur. In contrast, when this strain was added to sterile rumen fluid medium, cell densities increased from 10(6) to 10(9) CFU/ml within 24 h. Most strains of E. coli O157:H7 are unable to ferment sorbitol; therefore, we assessed whether the addition of sorbitol as the only added carbohydrate could be used to competitively exclude E. coli O157:H7 from the culture system. When inoculated into raw rumen broth containing 3 g of sorbitol per liter, E. coli O157:H7 was displaced within 72 h. The addition of other competitive sugars, such as L-arabinose, trehalose, and rhamnose, to rumen medium gave similar results. However, whenever E. coli O157:H7 was grown in sterile rumen broth containing sorbitol, sorbitol-positive mutants appeared. These results suggest that a robust population of commensal ruminal microflora is required to invoke competitive exclusion of E. coli O157:H7 by the addition of "nonfermentable" sugars and that this approach may be effective as a preharvest strategy for reducing carriage of E. coli O157:H7 in the rumen.