Structural analysis of the carbohydrate components of the outer membrane of the lipopolysaccharide-lacking cellulolytic ruminal bacterium Fibrobacter succinogenes S85

Supplementing branched-chain volatile fatty acids in dual-flow cultures varying in dietary forage and corn oil concentrations. II: Biohydrogenation and incorporation into bacterial lipids

To maintain membrane homeostasis, ruminal bacteria synthesize branched-chain fatty acids (BCFA) or their derivatives (vinyl ethers) that are recovered during methylation procedures as branched-chain aldehydes (BCALD). Many strains of cellulolytic bacteria require 1 or more branched-chain volatile fatty acid (BCVFA). Therefore, the objective of this study was to investigate BCVFA incorporation into bacterial lipids under different dietary conditions. The study was an incomplete block design with 8 continuous culture fermenters used in 4 periods with treatments (n = 4) arranged as a 2 × 2 × 2 factorial. The factors were high (HF) or low forage (LF, 67 or 33% forage, 33:67 alfalfa:orchardgrass), without or with supplemental corn oil (CO; 3% dry matter, 1.5% linoleic fatty acid), and without or with 2.15 mmol/d (5 mg/d 13C each of isovalerate, isobutyrate, and 2-methylbutyrate). After methylation of bacterial pellets collected from each fermenter's effluent, fatty acids and fatty aldehydes were separated before analysis by gas chromatography and isotope ratio mass spectrometry. Supplementation of BCVFA did not influence biohydrogenation extent. Label was only recovered in branched-chain lipids. Lower forage inclusion decreased BCFA in bacterial fatty acid profile from 9.45% with HF to 7.06% with LF and decreased BCALD in bacterial aldehyde profile from 55.4% with HF to 51.4% with LF. Supplemental CO tended to decrease iso even-chain BCFA and decreased iso even-chain BCALD in their bacterial lipid profiles. The main 18:1 isomer was cis-9 18:1, which increased (P < 0.01) by 25% from CO (data not shown). Dose recovery in bacterial lipids was 43.3% lower with LF than HF. Supplemental CO decreased recovery in the HF diet but increased recovery with LF (diet × CO interaction). Recovery from anteiso odd-chain BCFA and BCALD was the greatest; therefore, 2-methylbutyrate was the BCVFA primer most used for branched-chain lipid synthesis. Recovery in iso odd-chain fatty acids (isovalerate as primer) was greater than label recovery in iso even-chain fatty acids (isobutyrate as primer). Fatty aldehydes were less than 6% of total bacterial lipids, but 26.0% of 13C recovered in lipids were recovered in BCALD because greater than 50% of aldehydes were branched-chain. Because BCFA and BCALD are important in the function and growth of bacteria, especially cellulolytics, BCVFA supplementation can support the rumen microbial consortium, increasing fiber degradation and efficiency of microbial protein synthesis.

Phosphoenolpyruvate mutase-catalyzed C-P bond formation: mechanistic ambiguities and opportunities

Phosphonates are produced across all domains of life and used widely in medicine and agriculture. Biosynthesis almost universally originates from the enzyme phosphoenolpyruvate mutase (Ppm), EC 5.4.2.9, which catalyzes O-P bond cleavage in phosphoenolpyruvate (PEP) and forms a high energy C-P bond in phosphonopyruvate (PnPy). Mechanistic scrutiny of this unusual intramolecular O-to-C phosphoryl transfer began with the discovery of Ppm in 1988 and concluded in 2008 with computational evidence supporting a concerted phosphoryl transfer via a dissociative metaphosphatelike transition state. This mechanism deviates from the standard 'in-line attack' paradigm for enzymatic phosphoryl transfer that typically involves a phosphoryl-enzyme intermediate, but definitive evidence is sparse. Here we review the experimental evidence leading to our current mechanistic understanding and highlight the roles of previously underappreciated conserved active site residues. We then identify remaining opportunities to evaluate overlooked residues and unexamined substrates/inhibitors.

2-aminoethylphosphonate utilisation in Pseudomonas putida BIRD-1 is controlled by multiple master regulators

Bacteria possess various regulatory mechanisms to detect and coordinate a response to elemental nutrient limitation. In pseudomonads, the two‐component system regulators CbrAB, NtrBC and PhoBR, are responsible for regulating cellular response to carbon (C), nitrogen (N) and phosphorus (P) respectively. Phosphonates are reduced organophosphorus compounds produced by a broad range of biota and typified by a direct C‐P bond. Numerous pseudomonads can use the environmentally abundant phosphonate species 2‐aminoethylphosphonate (2AEP) as a source of C, N, or P, but only PhoBR has been shown to play a role in 2AEP utilization. On the other hand, utilization of 2AEP as a C and N source is considered substrate inducible. Here, using the plant‐growth‐promoting rhizobacterium Pseudomonas putida BIRD‐1 we present evidence that 2AEP utilization is under dual regulation and only occurs upon depletion of C, N, or P, controlled by CbrAB, NtrBC, or PhoBR respectively. However, the presence of 2AEP was necessary for full gene expression, i.e. expression was substrate inducible. Mutation of a LysR‐type regulator, termed AepR, upstream of the 2AEP transaminase‐phosphonatase system (PhnWX), confirmed this dual regulatory mechanism. To our knowledge, this is the first study identifying coordination between global stress response and substrate‐specific regulators in phosphonate metabolism.

An inventory of early branch points in microbial phosphonate biosynthesis

Microbial phosphonate biosynthetic machinery has been identified in ~5 % of bacterial genomes and encodes natural products like fosfomycin as well as cell surface decorations. Almost all biological phosphonates originate from the rearrangement of phosphoenolpyruvate (PEP) to phosphonopyruvate (PnPy) catalysed by PEP mutase (Ppm), and PnPy is often converted to phosphonoacetaldehyde (PnAA) by PnPy decarboxylase (Ppd). Seven enzymes are known or likely to act on either PnPy or PnAA as early branch points en route to diverse biosynthetic outcomes, and these enzymes may be broadly classified into three reaction types: hydride transfer, aminotransfer, and carbon-carbon bond formation. However, the relative abundance of these branch points in microbial phosphonate biosynthesis is unknown. Also unknown is the proportion of ppm-containing gene neighbourhoods encoding new branch point enzymes and potentially novel phosphonates. In this study we computationally sorted 434 ppm-containing gene neighbourhoods based on these seven branch point enzymes. Unsurprisingly, the majority (56 %) of these pathways encode for production of the common naturally occurring compound 2-aminoethylphosphonate (AEP) or a hydroxylated derivative. The next most abundant genetically encoded intermediates were phosphonoalanine (PnAla, 9.2 %), 2-hydroxyethylphosphonate (HEP, 8.5 %), and phosphonoacetate (PnAc, 6 %). Significantly, about 13 % of the gene neighbourhoods could not be assigned to any of the seven branch points and may encode novel phosphonates. Sequence similarity network analysis revealed families of unusual gene neighbourhoods including possible production of phosphonoacrylate and phosphonofructose, the apparent biosynthetic use of the C-P lyase operon, and a virus-encoded phosphonate. Overall, these results highlight the utility of branch point inventories to identify novel gene neighbourhoods and guide future phosphonate discovery efforts.

Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. III: Relation with solid passage rate and pH on prokaryotic fatty acid profile and community in continuous culture

Our objectives were to evaluate potential interactions in culture conditions that influence how exogenously dosed branched-chain VFA (BCVFA) would be recovered as elongated fatty acids (FA) or would affect bacterial populations. A 2 × 2 × 2 factorial arrangement of treatments evaluated 3 factors: (1) without versus with BCVFA (0 vs. 2 mmol/d each of isobutyrate, isovalerate, and 2-methylbutyrate; each dose was partially substituted with ¹³C-enriched tracers before and during the collection period); (2) high versus low pH (ranging diurnally from 6.3 to 6.8 vs. 5.7 to 6.2); and (3) low versus high particulate-phase passage rate (k_p; 2.5 vs. 5.0%/h) in continuous cultures administered a 50:50 forage:concentrate diet twice daily. Samples of effluent were collected and composited before harvesting bacteria from which FA and DNA were extracted. Profiles and enrichments of FA in bacteria were evaluated by gas chromatography and isotope-ratio mass spectrometry. The ¹³C enrichment in bacterial FA was calculated as percentage recovery of dosed ¹³C-labeled BCVFA. Dosing BCVFA increased the even-chain iso-FA, preventing the reduced concentration at higher k_p and potentially as a physiological response to decreased pH. However, decreasing pH decreased recovery of ¹³C in these even-chain FA, suggesting greater reliance on isobutyrate produced from degradation of dietary valine. The iso-FA were decreased, whereas anteiso-FA and 16:0 increased with decreasing pH. Thus, 2-methylbutyrate still appeared to be important as a precursor for anteiso-FA to counter the increased rigidity of bacterial membranes that had more saturated straight-chain FA when pH decreased. Provision of BCVFA stimulated the relative sequence abundance of Fibrobacter and Treponema, both of which require isobutyrate and 2-methylbutyrate. Numerous bacterial community members were shifted by low pH, including increased Prevotella and genera within the phylum Proteobacteria, at the expense of members within phylum Firmicutes. Because of relatively few interactions with pH and k_p, supplementation of BCVFA can stimulate neutral detergent fiber degradability via key fibrolytic bacteria across a range of conditions. Decreasing pH shifted bacterial populations and their FA composition, suggesting that further research is needed to distinguish pH from dietary changes.

One or two membranes? Diderm Firmicutes challenge the Gram-positive/Gram-negative divide

How, when and why the transition between cell envelopes with one membrane (Gram-positives or monoderms) and two (Gram-negative or diderms) occurred in Bacteria is a key unanswered question in evolutionary biology. Different hypotheses have been put forward, suggesting that either the monoderm or the diderm phenotype is ancestral. The existence of diderm members in the classically monoderm Firmicutes challenges the Gram-positive/Gram-negative divide and provides a great opportunity to tackle the issue. In this review, we present current knowledge on the diversity of bacterial cell envelopes, including these atypical Firmicutes. We discuss how phylogenomic analysis supports the hypothesis that the diderm cell envelope architecture is an ancestral character in the Firmicutes, and that the monoderm phenotype in this phylum arose multiple times independently by loss of the outer membrane. Given the overwhelming distribution of diderm phenotypes with respect to monoderm ones, this scenario likely extends to the ancestor of all bacteria. Finally, we discuss the recent development of genetic tools for Veillonella parvula, a diderm Firmicute member of the human microbiome, which indicates it as an emerging new experimental model to investigate fundamental aspects of the diderm/monoderm transition.

Phosphonate Biochemistry

Organophosphonic acids are unique as natural products in terms of stability and mimicry. The C-P bond that defines these compounds resists hydrolytic cleavage, while the phosphonyl group is a versatile mimic of transition-states, intermediates, and primary metabolites. This versatility may explain why a variety of organisms have extensively explored the use organophosphonic acids as bioactive secondary metabolites. Several of these compounds, such as fosfomycin and bialaphos, figure prominently in human health and agriculture. The enzyme reactions that create these molecules are an interesting mix of chemistry that has been adopted from primary metabolism as well as those with no chemical precedent. Additionally, the phosphonate moiety represents a source of inorganic phosphate to microorganisms that live in environments that lack this nutrient; thus, unusual enzyme reactions have also evolved to cleave the C-P bond. This review is a comprehensive summary of the occurrence and function of organophosphonic acids natural products along with the mechanisms of the enzymes that synthesize and catabolize these molecules.

Host-Associated Genomic Features of the Novel Uncultured Intracellular Pathogen Ca. Ichthyocystis Revealed by Direct Sequencing of Epitheliocysts

Advances in single-cell and mini-metagenome sequencing have enabled important investigations into uncultured bacteria. In this study, we applied the mini-metagenome sequencing method to assemble genome drafts of the uncultured causative agents of epitheliocystis, an emerging infectious disease in the Mediterranean aquaculture species gilthead seabream. We sequenced multiple cyst samples and constructed 11 genome drafts from a novel beta-proteobacterial lineage, Candidatus Ichthyocystis. The draft genomes demonstrate features typical of pathogenic bacteria with an obligate intracellular lifestyle: a reduced genome of up to 2.6 Mb, reduced G + C content, and reduced metabolic capacity. Reconstruction of metabolic pathways reveals that Ca Ichthyocystis genomes lack all amino acid synthesis pathways, compelling them to scavenge from the fish host. All genomes encode type II, III, and IV secretion systems, a large repertoire of predicted effectors, and a type IV pilus. These are all considered to be virulence factors, required for adherence, invasion, and host manipulation. However, no evidence of lipopolysaccharide synthesis could be found. Beyond the core functions shared within the genus, alignments showed distinction into different species, characterized by alternative large gene families. These comprise up to a third of each genome, appear to have arisen through duplication and diversification, encode many effector proteins, and are seemingly critical for virulence. Thus, Ca Ichthyocystis represents a novel obligatory intracellular pathogenic beta-proteobacterial lineage. The methods used: mini-metagenome analysis and manual annotation, have generated important insights into the lifestyle and evolution of the novel, uncultured pathogens, elucidating many putative virulence factors including an unprecedented array of novel gene families.

Magnesium requirement of some of the principal rumen cellulolytic bacteria

Information available on the role of Mg for growth and cellulose degradation by rumen bacteria is both limited and inconsistent. In this study, the Mg requirements for two strains each of the cellulolytic rumen species Fibrobacter succinogenes (A3c and S85), Ruminococcus albus (7 and 8) and Ruminococcus flavefaciens (B34b and C94) were investigated. Maximum growth, rate of growth and lag time were all measured using a complete factorial design, 2(3)×6; factors were: strains (2), within species (3) and Mg concentrations (6). R. flavefaciens was the only species that did not grow when Mg was singly deleted from the media, and both strains exhibited a linear growth response to increasing Mg concentrations (P<0.001). The requirement for R. flavefaciens B34b was estimated as 0.54 mM; whereas the requirement for R. flavefaciens C94 was >0.82 as there was no plateau in growth. Although not an absolute requirement for growth, strains of the two other species of cellulolytic bacteria all responded to increasing Mg concentrations. For F. succinogenes S85, R. albus 7 and R. albus 8, their requirement estimated from maximum growth was 0.56, 0.52 and 0.51, respectively. A requirement for F. succinogenes A3c could not be calculated because there was no solution for contrasts. Whether R. flavefaciens had a Mg requirement for cellulose degradation was determined in NH3-free cellulose media, using a 2×4 factorial design, 2 strains and 4 treatments. Both strains of R. flavefaciens were found to have an absolute Mg requirement for cellulose degradation. Based on reported concentrations of Mg in the rumen, 1.0 to 10.1 mM, it seems unlikely that an in vivo deficiency of this element would occur.

Purification and characterization of phosphonoglycans from Glycomyces sp. strain NRRL B-16210 and Stackebrandtia nassauensis NRRL B-16338

Two related actinomycetes, Glycomyces sp. strain NRRL B-16210 and Stackebrandtia nassauensis NRRL B-16338, were identified as potential phosphonic acid producers by screening for the gene encoding phosphoenolpyruvate (PEP) mutase, which is required for the biosynthesis of most phosphonates. Using a variety of analytical techniques, both strains were subsequently shown to produce phosphonate-containing exopolysaccharides (EPS), also known as phosphonoglycans. The phosphonoglycans were purified by sequential organic solvent extractions, methanol precipitation, and ultrafiltration. The EPS from the Glycomyces strain has a mass of 40 to 50 kDa and is composed of galactose, xylose, and five distinct partially O-methylated galactose residues. Per-deutero-methylation analysis indicated that galactosyl residues in the polysaccharide backbone are 3,4-linked Gal, 2,4-linked 3-MeGal, 2,3-linked Gal, 3,6-linked 2-MeGal, and 4,6-linked 2,3-diMeGal. The EPS from the Stackebrandtia strain is comprised of glucose, galactose, xylose, and four partially O-methylated galactose residues. Isotopic labeling indicated that the O-methyl groups in the Stackebrandtia phosphonoglycan arise from S-adenosylmethionine. The phosphonate moiety in both phosphonoglycans was shown to be 2-hydroxyethylphosphonate (2-HEP) by (31)P nuclear magnetic resonance (NMR) and mass spectrometry following strong acid hydrolysis of the purified molecules. Partial acid hydrolysis of the purified EPS from Glycomyces yielded 2-HEP in ester linkage to the O-5 or O-6 position of a hexose and a 2-HEP mono(2,3-dihydroxypropyl)ester. Partial acid hydrolysis of Stackebrandtia EPS also revealed the presence of 2-HEP mono(2,3-dihydroxypropyl)ester. Examination of the genome sequences of the two strains revealed similar pepM-containing gene clusters that are likely to be required for phosphonoglycan synthesis.

2-Aminoethylphosphonate utilization by the cold-adapted Geomyces pannorum P11 strain

Cold-adapted strain of Geomyces pannorum P11 was found to mineralize of phosphorus–carbon bond-containing compound—2-aminoethylphosphonic acid (2-AEP, ciliatine). The biodegradation process proceeded in the phosphate-independent manner. Ciliatine-metabolizing enzymes' activity was detectable in cell-free extracts prepared from psychrophilic G. pannorum pregrown on 4 mM 2-AEP. Phosphonoacetaldehyde hydrolase (phosphonatase) activity in a partially purified extract was demonstrated at 10 °C.

Effects of tea saponins on rumen microbiota, rumen fermentation, methane production and growth performance--a review

Reducing methane emission from ruminant animals has implications not only for global environmental protection but also for efficient animal production. Tea saponins (TS) extracted from seeds, leaves or roots of tea plant are pentacyclic triterpenes. They have a lasting antiprotozoal effect, but little effect on the methanogen population in sheep. There was no significant correlation between the protozoa counts and methanogens. The TS decreased methanogen activity. It seems that TS influenced the activity of the methanogens indirectly via the depressed ciliate protozoal population. The TS addition decreased fungal population in the medium containing rumen liquor in in vitro fermentation, but no such effect was observed in the rumen liquor of sheep fed TS. Tea saponins had a minor effect on the pattern of rumen fermentation and hence on nutrient digestion. When added at 3 g/day in diets, TS could improve daily weight gain and feed efficiency in goats. No positive associative effect existed between TS and disodium fumarate or soybean oil on methane suppression. Inclusion of TS in diets may be an effective way for improving feed efficiency in ruminants.

The effect and mode of action of saponins on the microbial populations and fermentation in the rumen and ruminant production

The growing public concerns over chemical residues in animal-derived foods and threats of antibiotic-resistant bacteria have renewed interest in exploring safer alternatives to chemical feed additives in ruminant livestock. Various bioactive phytochemicals including saponins appear to be potential 'natural' alternatives to 'chemical' additives in modulating rumen fermentation favourably and animal performance. Saponins are a diverse group of glycosides present in many families of plants. The primary effect of saponins in the rumen appears to be to inhibit the protozoa (defaunation), which might increase the efficiency of microbial protein synthesis and protein flow to the duodenum. Furthermore, saponins may decrease methane production via defaunation and/or directly by decreasing the activities (i.e. rate of methanogenesis or expression of methane-producing genes) and numbers of methanogens. Saponins may also selectively affect specific rumen bacteria and fungi, which may alter the rumen metabolism beneficially or adversely. The ammonia-adsorption and modulation of digesta passage in the rumen by saponins have also been implicated in altering rumen metabolism, but their physiological responses are likely to be negligible compared with microbiological effects. The effects of saponins on rumen fermentation have not been found to be consistent. These discrepancies appear to be related to the chemical structure and dosage of saponins, diet composition, microbial community and adaptation of microbiota to saponins. There is need for systematic research based on chemical structures of saponins, nutrient composition of diets and their effects on rumen microbial ecosystem to obtain consistent results. The present paper reviews and discusses the effects and mode of action of saponins on microbial community and fermentation in the rumen, and ruminant performance.

Changes in microbial community structure, methanogenesis and rumen fermentation in response to saponin-rich fractions from different plant materials

AIMS

Investigation of the effects of saponin-rich fractions on rumen fermentation, methane production and the microbial community.

METHODS AND RESULTS

Saponins were extracted from Carduus, Sesbania and Knautia leaves and fenugreek seeds. Two levels of saponin-rich fractions with a substrate were incubated using the Hohenheim gas method. Methane was measured using an infrared-based methane analyser and microbial communities using quantitative PCR. On addition of saponin-rich fractions, methane and short-chain fatty acid production was not affected. The protozoal counts decreased by 10-39%. Sesbania saponins decreased methanogen population by 78%. Decrease in ruminal fungal population (20-60%) and increase in Fibrobacter succinogenes (21-45%) and Ruminococcus flavefaciens (23-40%) were observed.

CONCLUSIONS

The saponins evaluated possessed anti-protozoal activity; however, this activity did not lead to methane reduction. Fenugreek saponins seemed to have potential for increasing rumen efficiency. The saponins altered the microbial community towards proliferation of fibre-degrading bacteria and inhibition of fungal population.

SIGNIFICANCE AND IMPACT OF THE STUDY

The uni-directional relationship between protozoal numbers and methanogenesis, as affected by saponins, is not obligatory. All saponins might not hold promise for decreasing methane production from ruminants.

Ruminal acidosis in beef cattle: the current microbiological and nutritional outlook

Ruminal acidosis continues to be a common ruminal digestive disorder in beef cattle and can lead to marked reductions in cattle performance. Ruminal acidosis or increased accumulation of organic acids in the rumen reflects imbalance between microbial production, microbial utilization, and ruminal absorption of organic acids. The severity of acidosis, generally related to the amount, frequency, and duration of grain feeding, varies from acute acidosis due to lactic acid accumulation, to subacute acidosis due to accumulation of volatile fatty acids in the rumen. Ruminal microbial changes associated with acidosis are reflective of increased availability of fermentable substrates and subsequent accumulation of organic acids. Microbial changes in the rumen associated with acute acidosis have been well documented. Microbial changes in subacute acidosis resemble those observed during adaptation to grain feeding and have not been well documented. The decrease in ciliated protozoal population is a common feature of both forms of acidosis and may be a good microbial indicator of an acidotic rumen. Other microbial factors, such as endotoxin and histamine, are thought to contribute to the systemic effects of acidosis. Various models have been developed to assess the effects of variation in feed intake, dietary roughage amount and source, dietary grain amount and processing, step-up regimen, dietary addition of fibrous byproducts, and feed additives. Models have been developed to study effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided useful information related to ruminal acidosis, many are inadequate for detecting responses to treatment due to inadequate replication, low feed intakes by the experimental cattle that can limit the expression of acidosis, and the feeding of cattle individually, which reduces experimental variation but limits the ability of researchers to extrapolate the data to cattle performing at industry standards. Optimal model systems for assessing effects of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feed yards. Such data could provide valuable insight into the true extent to which acidosis affects cattle performance.

The structures of glycolipids isolated from the highly thermophilic bacterium Thermus thermophilus Samu-SA1

Thermophiles constitute a class of microorganisms able to grow at extremely elevated temperatures. Some of these species are classified as Gram-negative bacteria, because of the presence of an outer membrane in the cell envelope, which is located on the top of a thick murein layer. Unlike typical Gram-negative bacteria, the outer membranes of Thermus species are not composed of lipopolysaccharides but of peculiar glycolipids (GL), whose structures seem to be strictly involved in the adaptation to high temperatures. In this work, the complete structures of the major GL components from the cell envelope of the thermophilic bacterium Thermus thermophilus Samu-SA1 are presented. Protocols conventionally adopted for Gram-negative bacteria were used, and, for the first time, GL from Thermus were analyzed in their native form. Two GL and one phosphoglycolipid (PGL) were detected and characterized. The two GL, analyzed by nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR) mass spectrometry, possessed the same tetrasaccharide structure linked to a glycerol unit or, alternatively, to a long-chain diol. Moreover, a PGL from Thermus was characterized for the first time, in which N-glyceroyl-heptadecaneamine was present. These molecules are chemically related to other GL from thermophile bacteria, in which they play a crucial role in the adaptation of cell membranes to heat.

The dynamics of major fibrolytic microbes and enzyme activity in the rumen in response to short- and long-term feeding of Sapindus rarak saponins

AIMS

To investigate the short- and long-term effects of an extract of Sapindus rarak saponins (SE) on the rumen fibrolytic enzyme activity and the major fibrolytic micro-organisms.

METHODS AND RESULTS

Two feeding trials were conducted. In the short-term trial, four fistulated goats were fed a basal diet containing sugar cane tops and wheat pollard (65:35, w/w) and were supplemented for 7 days with SE at a level of 0.6 g kg(-1) body weight. Rumen liquor was taken before, during and after SE feeding. In the long-term trial, 28 sheep were fed the same basal diet as the goats and were supplemented for 105 days with 0.24, 0.48 and 0.72 g kg(-1) body mass of the extract. Rumen liquor was taken on days 98 and 100. Protozoal numbers were counted under the microscope. Cell wall degradation was determined by enzyme assays and the major fibrolytic micro-organisms were quantified by dot blot hybridization. Sapindus extract significantly depressed rumen xylanase activity in both trials and carboxymethylcellulase activity in the long-term trial (P < 0.01). Fibrobacter sp. were not affected by the SE in both trials, while ruminococci and the anaerobic fungi showed a short-term response to the application of saponins. Protozoal counts were decreased only in the long-term trial with sheep.

CONCLUSION

These data suggest that there is an adaptation of Ruminococcus albus, Ruminococcus flavefaciens and Chytridiomycetes (fungi) to saponin when fed over a long period. The fact that no correlation between the cell wall degrading enzyme activities and the cell wall degrading micro-organisms was observed suggests that the organisms tracked in this experiment are not the only key players in ruminal cell wall degradation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Sapindus rarak saponins partially defaunate the rumen flora. Their negative effect on cell wall degradation, however, is not related to rumen organisms currently recognized as the major cell wall degrading species. The adaptation of microbes in the long-term feeding experiment suggests that the results from short-term trial on the ruminal microbial community have to be interpreted carefully.

The structure and biological characteristics of the Spirochaeta aurantia outer membrane glycolipid LGLB

In an attempt to isolate lipopolysaccharide from Spirochaeta aurantia, Darveau-Hancock extraction of the cell mass was performed. While no lipopolysaccharide was found, two carbohydrate-containing compounds were detected. They were resolved by size-exclusion chromatography into high molecular mass (LGLA) and low molecular mass (LGLB) fractions. Here we present the results of the analysis of the glycolipid LGLB. Deacylation of LGLB with hydrazine and separation of the products by using anion-exchange chromatography gave two major products. Their structure was determined by using chemical methods, NMR and mass spectrometry. All monosaccharides had the D-configuration, and aspartic acid had the L-configuration. Intact LGLB contained two fatty groups at O-2 and O-3 of the glycerol residue. Nonhydroxylated C14 to C18 fatty acids were identified, which were predominantly unsaturated or branched. LGLB was able to gel Limulus amebocyte lysate, albeit at a lower level than that observed for Escherichia coli O113 lipopolysaccharide. However, even large amounts of LGLB were unable to stimulate any Toll-like receptor (TLR) examined, including TLR4 and TLR2, previously shown to be sensitive to lipopolysaccharide and glycolipids from diverse bacterial origins, including other spirochetes.

Lipopolysaccharide endotoxins

Bacterial lipopolysaccharides (LPS) typically consist of a hydrophobic domain known as lipid A (or endotoxin), a nonrepeating "core" oligosaccharide, and a distal polysaccharide (or O-antigen). Recent genomic data have facilitated study of LPS assembly in diverse Gram-negative bacteria, many of which are human or plant pathogens, and have established the importance of lateral gene transfer in generating structural diversity of O-antigens. Many enzymes of lipid A biosynthesis like LpxC have been validated as targets for development of new antibiotics. Key genes for lipid A biosynthesis have unexpectedly also been found in higher plants, indicating that eukaryotic lipid A-like molecules may exist. Most significant has been the identification of the plasma membrane protein TLR4 as the lipid A signaling receptor of animal cells. TLR4 belongs to a family of innate immunity receptors that possess a large extracellular domain of leucine-rich repeats, a single trans-membrane segment, and a smaller cytoplasmic signaling region that engages the adaptor protein MyD88. The expanding knowledge of TLR4 specificity and its downstream signaling pathways should provide new opportunities for blocking inflammation associated with infection.