De novo synthesis of amino acids by the ruminal bacteria Prevotella bryantii B14, Selenomonas ruminantium HD4, and Streptococcus bovis ES1

The Human Gut Microbiota: A Dynamic Biologic Factory

The human body constitutes a living environment for trillions of microorganisms, which establish the microbiome and, the largest population among them, reside within the gastrointestinal tract, establishing the gut microbiota. The term "gut microbiota" refers to a set of many microorganisms [mainly bacteria], which live symbiotically within the human host. The term "microbiome" means the collective genomic content of these microorganisms. The number of bacterial cells within the gut microbiota exceeds the host's cells; collectively and their genes quantitatively surpass the host's genes. Immense scientific research into the nature and function of the gut microbiota is unraveling its roles in certain human health activities such as metabolic, physiology, and immune activities and also in pathologic states and diseases. Interestingly, the microbiota, a dynamic ecosystem, inhabits a particular environment such as the human mouth or gut. Human microbiota can evolve and even adapt to the host's unique features such as eating habits, genetic makeup, underlying diseases, and even personalized habits. In the past decade, biologists and bioinformaticians have concentrated their research effort on the potential roles of the gut microbiome in the development of human diseases, particularly immune-mediated diseases and colorectal cancer, and have initiated the assessment of the impact of the gut microbiome on the host genome. In the present chapter, we focus on the biological features of gut microbiota, its physiology as a biological factory, and its impacts on the host's health and disease status.

Essential Amino Acid Metabolites as Chemical Mediators of Host-Microbe Interaction in the Gut

Amino acids are indispensable substrates for protein synthesis in all organisms and incorporated into diverse aspects of metabolic physiology and signaling. However, animals lack the ability to synthesize several of them and must acquire these essential amino acids from their diet or perhaps their associated microbial communities. The essential amino acids therefore occupy a unique position in the health of animals and their relationships with microbes. Here we review recent work connecting microbial production and metabolism of essential amino acids to host biology, and the reciprocal impacts of host metabolism of essential amino acids on their associated microbes. We focus on the roles of the branched-chain amino acids (valine, leucine, and isoleucine) and tryptophan on host-microbe communication in the intestine of humans and other vertebrates. We then conclude by highlighting research questions surrounding the less-understood aspects of microbial essential amino acid synthesis in animal hosts.

Piglet cardiopulmonary bypass induces intestinal dysbiosis and barrier dysfunction associated with systemic inflammation

The intestinal microbiome is essential to human health and homeostasis, and is implicated in the pathophysiology of disease, including congenital heart disease and cardiac surgery. Improving the microbiome and reducing inflammatory metabolites may reduce systemic inflammation following cardiac surgery with cardiopulmonary bypass (CPB) to expedite recovery post-operatively. Limited research exists in this area and identifying animal models that can replicate changes in the human intestinal microbiome after CPB is necessary. We used a piglet model of CPB with two groups, CPB (n=5) and a control group with mechanical ventilation (n=7), to evaluate changes to the microbiome, intestinal barrier dysfunction and intestinal metabolites with inflammation after CPB. We identified significant changes to the microbiome, barrier dysfunction, intestinal short-chain fatty acids and eicosanoids, and elevated cytokines in the CPB/deep hypothermic circulatory arrest group compared to the control group at just 4 h after intervention. This piglet model of CPB replicates known human changes to intestinal flora and metabolite profiles, and can be used to evaluate gut interventions aimed at reducing downstream inflammation after cardiac surgery with CPB.

Measurement of True Indispensable Amino Acid Digestibility by the Dual Isotope Tracer Technique: A Methodological Review

The digestible indispensable amino acid score uses ileal digestibility of each indispensable amino acid (IAA) of a dietary protein to calculate its protein quality. However, true ileal digestibility, which is the exclusive sum of digestion and absorption of a dietary protein up to the terminal ileum, is difficult to measure in humans. It is traditionally measured using invasive oro-ileal balance methods but can be confounded by endogenous secreted protein in the intestinal lumen, although the use of intrinsically labeled protein corrects for this. A recent, minimally invasive dual isotope tracer technique is now available to measure true IAA digestibility of dietary protein sources. This method involves simultaneous ingestion of 2 intrinsically but differently (stable) isotopically labeled proteins, a (²H or ¹⁵N-labeled) test protein and (¹³C-labeled) reference protein whose true IAA digestibility is known. Using a plateau-feeding protocol, the true IAA digestibility is determined by comparing the steady state ratio of blood to meal test protein IAA enrichment to the similar reference protein IAA ratio. The use of intrinsically labeled protein also distinguishes between IAA of endogenous and dietary origin. The collection of blood samples makes this method minimally invasive. As the α-¹⁵N and α-²H atoms of AAs of the intrinsically labeled protein are prone to label loss because of transamination, underestimation of digestibility, appropriate correction factors need to be employed when using ¹⁵N or ²H labeled test protein. The true IAA digestibility values of highly digestible animal protein by the dual isotope tracer technique are comparable to that measured by direct oro-ileal balance measurements, but no data are yet available for proteins with lower digestibility. A major advantage is that the minimally invasive method allows for true IAA digestibility measurement in humans across different age groups and physiological conditions.

In vitro effects of different levels of quebracho and chestnut tannins on rumen methane production, fermentation parameters, and microbiota

Both condensed and hydrolysable tannins (CTs and HTs, respectively) have the ability to reduce enteric CH₄ production in ruminants. However, the precise mechanism of action is not fully understood. Among the proposed hypotheses are the reduction of ruminal digestibility, direct control action on protozoa, reduction of archaea, and a hydrogen sink mechanism. In this in vitro study, which simulated rumen fermentation, two additives, one containing CTs (70% based on DM) from quebracho and one with HTs (75% based on DM) from chestnut, at four levels of inclusion (2, 4, 6, 8% on an as-fed basis) were added to the fermentation substrate and tested against a negative control. Both types of tannins significantly reduced total gas (GP) and CH₄ (ml/g DM) production during the 48 h of incubation. The lower GP and CH₄ production levels were linked to the reduction in dry matter digestibility caused by CTs and HTs. Conversely, no significant differences were observed for the protozoan and archaeal populations, suggesting a low direct effect of tannins on these rumen microorganisms in vitro. However, both types of tannins had negative correlations for the families Bacteroidales_BS11 and F082 and positive correlations for the genera Prevotella and Succinivibrio. Regarding the fermentation parameters, no differences were observed for pH and total volatile fatty acid production, while both CTs and HTs linearly reduced the NH₃ content. CTs from quebracho were more effective in reducing CH₄ production than HTs from chestnut. However, for both types of tannins, the reduction in CH₄ production was always associated with a lower digestibility without any changes in archaea or protozoa. Due to the high variability of tannins, further studies investigating the chemical structure of the compounds and their mechanisms of action are needed to understand the different results reported in the literature.

Prevotella: A Key Player in Ruminal Metabolism

Ruminants are foregut fermenters that have the remarkable ability of converting plant polymers that are indigestible to humans into assimilable comestibles like meat and milk, which are cornerstones of human nutrition. Ruminants establish a symbiotic relationship with their microbiome, and the latter is the workhorse of carbohydrate fermentation. On the other hand, during carbohydrate fermentation, synthesis of propionate sequesters H, thus reducing its availability for the ultimate production of methane (CH4) by methanogenic archaea. Biochemically, methane is the simplest alkane and represents a downturn in energetic efficiency in ruminants; environmentally, it constitutes a potent greenhouse gas that negatively affects climate change. Prevotella is a very versatile microbe capable of processing a wide range of proteins and polysaccharides, and one of its fermentation products is propionate, a trait that appears conspicuous in P. ruminicola strain 23. Since propionate, but not acetate or butyrate, constitutes an H sink, propionate-producing microbes have the potential to reduce methane production. Accordingly, numerous studies suggest that members of the genus Prevotella have the ability to divert the hydrogen flow in glycolysis away from methanogenesis and in favor of propionic acid production. Intended for a broad audience in microbiology, our review summarizes the biochemistry of carbohydrate fermentation and subsequently discusses the evidence supporting the essential role of Prevotella in lignocellulose processing and its association with reduced methane emissions. We hope this article will serve as an introduction to novice Prevotella researchers and as an update to others more conversant with the topic.

Interactions between gut microbiota and Parkinson's disease: The role of microbiota-derived amino acid metabolism

Non-motor symptoms (NMS) of Parkinson's disease (PD), such as constipation, sleep disorders, and olfactory deficits, may emerge up to 20 years earlier than motor symptoms. A series of evidence indicates that the pathology of PD may occur from the gastrointestinal tract to the brain. Numerous studies support that the gut microbiota communicates with the brain through the immune system, special amino acid metabolism, and the nervous system in PD. Recently, there is growing recognition that the gut microbiota plays a vital role in the modulation of multiple neurochemical pathways via the “gut microbiota-brain axis” (GMBA). Many gut microbiota metabolites, such as fatty acids, amino acids, and bile acids, convey signaling functions as they mediate the crosstalk between gut microbiota and host physiology. Amino acids' abundance and species alteration, including glutamate and tryptophan, may disturb the signaling transmission between nerve cells and disrupt the normal basal ganglia function in PD. Specific amino acids and their receptors are considered new potential targets for ameliorating PD. The present study aimed to systematically summarize all available evidence on the gut microbiota-derived amino acid metabolism alterations associated with PD.

Altering Dietary Soluble Protein Levels With Decreasing Crude Protein May Be a Potential Strategy to Improve Nitrogen Efficiency in Hu Sheep Based on Rumen Microbiome and Metabolomics

Ruminants account for a relatively large share of global nitrogen (N) emissions. It has been reported that nutrition control and precise feeding can improve the N efficiency of ruminants. The objective of the study was to determine the effects of soluble protein (SP) levels in low-protein diets on growth performance, nutrient digestibility, rumen microbiota, and metabolites, as well as their associations of N metabolism in fattening Hu sheep. Approximately 6-month-old, 32 healthy fattening male Hu sheep with similar genetic merit and an initial body weight of 40.37 ± 1.18 kg were selected, and divided into four groups (n = 8) using the following completely randomized design: the control diet (CON) with a 16.7% crude protein (CP) content was prepared to meet the nutritional requirements of fattening sheep [body weight (BW): 40 kg, average daily gain (ADG): 200–250 g/d] according to the NRC recommendations; other three include low protein diets (LPA, LPB, and LPC) of CP decreased by ~10%, with SP proportion (%CP) of 21.2, 25.9, and 29.4 respectively. The feeding trial lasted for 5 weeks including the first week of adaptation. The results showed no difference in the growth performance (P > 0.05); DM and CP digestibility were higher in LPB and LPC, with maximum organic matter digestibility in LPB (P < 0.05). Low-protein diets decreased serum urea-N whereas urinary urea-N was lower in LPB and LPC (P < 0.05), while N retention and the biological value of N were higher in LPB and LPC (P < 0.05). Ruminal NH₃-N concentration in LPA and LPB was low than CON (P < 0.05), while total volatile fatty acid (TVFA), acetate, propionate, and butanoate were all lowest in LPA (P < 0.05). In the rumen microbiome, LPB increased the community richness in Prevotellaceae and Prevotella_1 (P < 0.05); Metabolomics analysis revealed low-protein diets downregulated the amino acid metabolism pathways, while the biosynthesis of unsaturated fatty acids along with vitamin B6 metabolism were upregulated with increased SP. These findings could help us understand the role of different SP levels in the regulation of rumen microbial metabolism and N efficiency. Overall, low-protein diets (CP decreased by ~10%) can reduce serum urea-N and ruminal NH₃-N without affecting the growth performance of fattening Hu sheep. Additionally higher N efficiency was obtained with an SP proportion of ~25–30%.

Evaluation of Protein Quality in Humans and Insights on Stable Isotope Approaches to Measure Digestibility - A Review

The recent Food and Agricultural Organization/World Health Organization/United Nations University expert consultations on protein requirements and quality have emphasized the need for the new Digestible Indispensable Amino Acid Score (DIAAS), as a measure of protein quality. This requires human measurements of the true ileal digestibility of individual indispensable amino acids (IAAs) until the end of the small intestine. Digestibility is measured using standard oro-ileal balance methods, which can only be achieved by an invasive naso-ileal intubation in healthy participants or fistulation at the terminal ileum. Significant efforts have been made over the last 2 decades to develop noninvasive or minimally invasive methods to measure IAA digestibility in humans. The application of intrinsically labeled (with stable isotopes like 13C, 15N, and 2H) dietary proteins has helped in circumventing the invasive oro-ileal balance techniques and allowed the differentiation between endogenous and exogenous protein. The noninvasive indicator amino acid oxidation (IAAO) technique, which is routinely employed to measure IAA requirements, has been modified to estimate metabolic availability (a sum of digestibility and utilization) of IAA in foods, but provides an estimate for a single IAA at a time and is burdensome for participants. The recently developed minimally invasive dual isotope tracer method measures small intestinal digestibility of multiple amino acids at once and is suitable for use in vulnerable groups and disease conditions. However, it remains to be validated against standard oro-ileal balance techniques. This review critically evaluates and compares the currently available stable isotope-based protein quality evaluation methods with a focus on the digestibility and metabolic availability measurements in humans. In view of building a reliable DIAAS database of various protein sources and subsequently supporting protein content claims in food labeling, a re-evaluation and harmonization of the available methods are necessary.

Dietary Energy Levels Affect Carbohydrate Metabolism-Related Bacteria and Improve Meat Quality in the Longissimus Thoracis Muscle of Yak (Bos grunniens)

The effects of different dietary energy levels on the ruminal bacterial population, selected meat quality indices, and their relationship in yak longissimus thoracis (LT) muscle were assessed in this study. A total of 15 castrated yaks were randomly assigned to three groups with low- (NEg: 5.5 MJ/Kg, LE), medium- (NEg: 6.2 MJ/Kg, ME), and high- (NEg: 6.9 MJ/Kg, HE) dietary energy levels and occurred in the cold season (March to May). All yaks from each treatment group were humanely slaughtered and sampled on the day of completion of their feeding treatment. The results showed that the water content and crude fat levels of the LT muscle were markedly elevated in the HE group (P < 0.05), while the shear force was drastically reduced (P = 0.001). Methionine, aspartic acid, and glycine levels in the LT muscle were higher in the LE group compared with the ME and HE groups (P < 0.05). The glutamic acid level in the ME group was greater in comparison to the LE and HE groups (P < 0.05), while the histidine level in the ME group was higher than that in the HE group (P < 0.05). Additionally, the HE diet significantly elevated (P < 0.05) the abundance of carbohydrate metabolism-associated bacteria including Prevotella_1, Lachnospiraceae_NK4A136_group, U29_B03, Ruminiclostridium_6, and Ruminococcaceae_UCG_013 in the rumen. The results of the Spearman's rank correlation analysis showed that the abundance of uncultured_bacterium_f_vadinBE97 and uncultured_bacterium_f_Lachnospiraceae showed a significant influence on the indicator of IMF and SF. In conclusion, a high dietary energy level improved the meat quality in the LT muscle of yak mainly by increasing the relative abundance of ruminal amylolytic bacteria to provide substrates for fatty acid synthesis.

Comparative untargeted metabolome analysis of ruminal fluid and feces of Nelore steers (Bos indicus)

We conducted a study to identify the fecal metabolite profile and its proximity to the ruminal metabolism of Nelore steers based on an untargeted metabolomic approach. Twenty-six Nelore were feedlot with same diet during 105 d. Feces and rumen fluid were collected before and at slaughter, respectively. The metabolomics analysis indicated 49 common polar metabolites in the rumen and feces. Acetate, propionate, and butyrate were the most abundant polar metabolites in both bio-samples. The rumen presented significantly higher concentrations of the polar compounds when compared to feces (P < 0.05); even though, fecal metabolites presented an accentuated representability of the ruminal fluid metabolites. All fatty acids present in the ruminal fluid were also observed in the feces, except for C20:2n6 and C20:4n6. The identified metabolites offer information on the main metabolic pathways (higher impact factor and P < 0.05), as synthesis and degradation of ketone bodies; the alanine, aspartate and glutamate metabolisms, the glycine, serine; and threonine metabolism and the pyruvate metabolism. The findings reported herein on the close relationship between the ruminal fluid and feces metabolic profiles may offer new metabolic information, in addition to facilitating the sampling for metabolism investigation in animal production and health routines.

Non-oral Prevotella stepping into the spotlight

Species now affiliated to genus Prevotella have been known for decades as an integral part of human oral cavity microbiota. They were frequently isolated from patients with periodontitis or from dental root canals but also from healthy subjects. With the exception of Prevotella intermedia, they were considered opportunistic pathogens, as they were isolated also from various bacterial abscesses from the head, neck, breast, skin and various other body sites. Consequently, Prevotella were not in the focus of research activities. On the other hand, the four species found in the rumen never caused any disease and seemed early on to be numerous and important part of the rumen ecosystem indicating this genus harbored bacteria with enormously diverse habitats and lifestyles. The purpose of this review is to illustrate the main research themes performed in Prevotella on a path from less noted oral bacteria and from hard to cultivate and study rumen organisms to important mutualistic bacteria in guts of various mammals warranting major research efforts.

Short-Chain Fatty Acids Modulate Metabolic Pathways and Membrane Lipids in Prevotella bryantii B14

Short-chain fatty acids (SCFAs) are bacterial products that are known to be used as energy sources in eukaryotic hosts, whereas their role in the metabolism of intestinal microbes is rarely explored. In the present study, acetic, propionic, butyric, isobutyric, valeric, and isovaleric acid, respectively, were added to a newly defined medium containing Prevotella bryantii B14 cells. After 8 h and 24 h, optical density, pH and SCFA concentrations were measured. Long-chain fatty acid (LCFA) profiles of the bacterial cells were analyzed via gas chromatography-time of flight-mass spectrometry (GC-ToF MS) and proteins were quantified using a mass spectrometry-based, label-free approach. Cultures supplemented with single SCFAs revealed different growth behavior. Structural features of the respective SCFAs were identified in the LCFA profiles, which suggests incorporation into the bacterial membranes. The proteomes of cultures supplemented with acetic and valeric acid differed by an increased abundance of outer membrane proteins. The proteome of the isovaleric acid supplementation showed an increase of proteins in the amino acid metabolism. Our findings indicate a possible interaction between SCFAs, the lipid membrane composition, the abundance of outer membrane proteins, and a modulation of branched chain amino acid biosynthesis by isovaleric acid.

Vitamin Biosynthesis by Human Gut Butyrate-Producing Bacteria and Cross-Feeding in Synthetic Microbial Communities

We investigated the requirement of 15 human butyrate-producing gut bacterial strains for eight B vitamins and the proteinogenic amino acids by a combination of genome sequence analysis and in vitro growth experiments. The Ruminococcaceae species Faecalibacterium prausnitzii and Subdoligranulum variabile were auxotrophic for most of the vitamins and the amino acid tryptophan. Within the Lachnospiraceae, most species were prototrophic for all amino acids and several vitamins, but biotin auxotrophy was widespread. In addition, most of the strains belonging to Eubacterium rectale and Roseburia spp., but few of the other Lachnospiraceae strains, were auxotrophic for thiamine and folate. Synthetic coculture experiments of five thiamine or folate auxotrophic strains with different prototrophic bacteria in the absence and presence of different vitamin concentrations were carried out. This demonstrated that cross-feeding between bacteria does take place and revealed differences in cross-feeding efficiency between prototrophic strains. Vitamin-independent growth stimulation in coculture compared to monococulture was also observed, in particular for F. prausnitzii A2-165, suggesting that it benefits from the provision of other growth factors from community members. The presence of multiple vitamin auxotrophies in the most abundant butyrate-producing Firmicutes species found in the healthy human colon indicates that these bacteria depend upon vitamins supplied from the diet or via cross-feeding from other members of the microbial community.IMPORTANCE Microbes in the intestinal tract have a strong influence on human health. Their fermentation of dietary nondigestible carbohydrates leads to the formation of health-promoting short-chain fatty acids, including butyrate, which is the main fuel for the colonic wall and has anticarcinogenic and anti-inflammatory properties. A good understanding of the growth requirements of butyrate-producing bacteria is important for the development of efficient strategies to promote these microbes in the gut, especially in cases where their abundance is altered. The demonstration of the inability of several dominant butyrate producers to grow in the absence of certain vitamins confirms the results of previous in silico analyses. Furthermore, establishing that strains prototrophic for thiamine or folate (butyrate producers and non-butyrate producers) were able to stimulate growth and affect the composition of auxotrophic synthetic communities suggests that the provision of prototrophic bacteria that are efficient cross feeders may stimulate butyrate-producing bacteria under certain in vivo conditions.

Inhibiting Methanogenesis Stimulated de novo Synthesis of Microbial Amino Acids in Mixed Rumen Batch Cultures Growing on Starch but Not on Cellulose

Ameliorating methane (CH₄) emissions from ruminants would have environmental benefits, but it is necessary to redirect metabolic hydrogen ([H]) toward useful sinks to also benefit animal productivity. We hypothesized that inhibiting rumen methanogenesis would increase de novo synthesis of microbial amino acids (AA) as an alternative [H] sink if sufficient energy and carbon are provided. We examined the effects of inhibiting methanogenesis with 9, 10-anthraquione (AQ) on mixed rumen batch cultures growing on cellulose or starch as sources of energy and carbon contrasting in fermentability, with ammonium (NH₄⁺) or trypticase (Try) as nitrogen (N) sources. Inhibiting methanogenesis with AQ inhibited digestion with cellulose but not with starch, and decreased propionate and increased butyrate molar percentages with both substrates. Inhibiting methanogenesis with 9, 10-anthraquinone increased de novo synthesis of microbial AA with starch but not with cellulose. The decrease in the recovery of [H] caused by the inhibition of methanogenesis was more moderate with starch due to an enhancement of butyrate and AA as [H] sinks. There may be an opportunity to simultaneously decrease the emissions of CH₄ and N with some ruminant diets and replace plant protein supplements with less expensive non-protein nitrogen sources such as urea.

In vitro rumen fermentation of feed substrates added with chestnut tannins or an extract from Stevia rebaudiana Bertoni

Rumen fermentation parameters and microbiota were evaluated in 3 in vitro rumen fermentation experiments after addition of chestnut tannins (CWT) or an extract from Stevia rebaudiana Bertoni (SB) to substrates. A control (CTR) substrate was fermented alone or added with 1.5% of CWT or SB extracts in a batch culture system (Exp. 1, fermentation in 500 mL for 24 h) and in a subsequent continuous culture system (Exp. 2, fermentation in 2 L bottles for 9 d). Experiment 3 used the fermentation system of Exp. 1 and tested 7 doses of each extract added to CTR (additions of 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2% and 1.4% for 48 h). The addition of CWT lowered (P < 0.01) the in vitro rumen ammonia concentration in all experiments and reduced the protozoa counts in Exp. 1 (P < 0.05). In contrast, the SB extract did not modify the ammonia concentrations, but significantly lowered the protozoa counts in all 3 experiments (reduction of 47% and 20% in Exp. 1 and 2, P < 0.05; and a quadratic reduction in Exp. 3, R² = 0.63, P < 0.01). Neither extract affected the fermentation in terms of gas production (Exp. 1 and 3) nor volatile fatty acids (VFA) yield (Exp. 1 and 2), if we exclude a reduction at the highest CWT concentration in Exp. 3. Changes in VFA profile were induced by CWT and were limited to reductions in the iso-valerate (P < 0.01, in Exp. 2) and iso-butyrate levels (P < 0.01, Exp. 2). The CWT increased the abundance of Prevotella ruminicola and Selenomonas ruminantium and decreased that of Ruminobacter amylophilus (P < 0.01, P < 0.05 and P < 0.05, respectively). The SB extract increased the relative abundance of Treponema saccarophylum (P < 0.05). Both of the studied substances had an impact on rumen metabolism, with SB reducing protozoa counts and CWT lowering the rumen ammonia concentration. The effects of both extracts on the rumen were appreciable at low dietary doses, and the negative impacts on fermentation were limited to the reduction in protein degradation with the addition of CWT.

Factors influencing the gut microbiome in children: from infancy to childhood

The human microbiota plays a crucial role in educating the immune system and influencing host health right since birth. Various maternal factors along with the vertical microbial transfer from the mother, as well as the horizontal environmental transmission and internal factors relating to the infant, play a crucial role in modulating the gut microbiota. The early life microflora is highly unstable and undergoes dynamic changes during the first few years, converging towards a more stabilized adult microbiota by co-evolving with the host by the age of 3-4 years. Microbiota studies have underlined the role of dysbiosis in developing several metabolic disorders like obesity, diabetes and immune-related disorders like asthma, to name a few. Thus, understanding early life microbial composition and various factors affecting the microbial community will provide a platform for developing strategies/techniques to maintain host health by restoring gut microbial flora. This review focuses on the factors that affect the microbial composition of the foetus in utero, during birth, infancy through childhood.

Dietary supplementation of black soldier fly (Hermetica illucens) meal modulates gut microbiota, innate immune response and health status of marron (Cherax cainii, Austin 2002) fed poultry-by-product and fishmeal based diets

The present study aimed to evaluate the dietary supplementary effects of black soldier fly (Hermetia illucens) (BSF) meal on the bacterial communities in the distal gut, immune response and growth of freshwater crayfish, marron (Cherax cainii) fed poultry-by-product meal (PBM) as an alternative protein source to fish meal (FM). A total of 64 marron were randomly distributed into 16 different tanks with a density of four marron per tank. After acclimation, a 60-days feeding trial was conducted on marron fed isonitrogenouts and isocalorific diets containing protein source from FM, PBM, and a combination of FM + BSF and PBM + BSF. At the end of the trial, weight gain and growth of marron were found independent of any dietary treatment, however, the two diets supplemented with BSF significantly (P < 0.05) enhanced haemolymph osmolality, lysozyme activity, total haemocyte counts, and protein and energy contents in the tail muscle. In addition, the analysis of microbiota and its predicted metabolic pathways via 16s rRNA revealed a significantly (P < 0.05) higher bacterial activity and gene function correlated to biosynthesis of protein, energy and secondary metabolites in PBM + BSF than other dietary groups. Diets FM + BSF and PBM + BSF were seen to be associated with an up-regulation of cytokine genes in the intestinal tissue of marron. Overall, PBM + BSF diet proved to be a superior diet in terms of improved health status, gut microbiota and up-regulated expression of cytokine genes for marron culture.

Functional adaptations in the cecal and colonic metagenomes associated with the consumption of transglycosylated starch in a pig model

Background

Both phylogeny and functional capabilities within the gut microbiota populations are of great importance for influencing host health. As a novel type of resistant starch, transglycosylated starch (TGS) modifies the microbial community and metabolite profiles along the porcine gut, but little is known about the related functional adaptations in key metabolic pathways and their taxonomic identity.

Results

Metagenomic sequencing was used to characterize the functional alterations in the cecal and colonic microbiomes of growing pigs fed TGS or control starch (CON) diets for 10 days (n = 8/diet). Bacterial communities were clearly distinguishable at taxonomic and functional level based on the dietary starch, with effects being similar at both gut sites. Cecal and colonic samples from TGS-fed pigs were enriched in Prevotella, Bacteroides, Acidaminoccus and Veillonella, whereas Treponema, Ruminococcus, and Aeromonas declined at both gut sites compared to CON-fed pigs (log₂ fold change > ±1; p < 0.001 (q < 0.05)). This was associated with increased enzymatic capacities for amino acid metabolism, galactose, fructose and mannose metabolism, pentose and glucuronate interconversions, citrate cycle and vitamin metabolism for samples from TGS-fed pigs. However, TGS-fed pigs comprised fewer reads for starch and sucrose metabolism and genetic information processing. Changes in key catabolic steps were found to be the result of changes in taxa associated with each type of starch. Functional analysis indicated steps in the breakdown of TGS by the action of α- and β-galactosidases, which mainly belonged to Bacteroides and Prevotella. Reads mapped to alpha-amylase were less frequent in TGS- compared to CON-fed pigs, with the major source of this gene pool being Bacillus, Aeromonas and Streptococcus. Due to the taxonomic shifts, gene abundances of potent stimulants of the mucosal innate immune response were altered by the starches. The cecal and colonic metagenomes of TGS-fed pigs comprised more reads annotated in lipopolysaccharides biosynthesis, whereas they became depleted of genes for flagellar assembly compared to CON-fed pigs.

Conclusions

Metagenomic sequencing revealed distinct cecal and colonic bacterial communities in CON- and TGS-fed pigs, with strong discrimination among samples by functional capacities related to the respective starch in each pig’s diet.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1462-2) contains supplementary material, which is available to authorized users.

Establishment of an ideal gut microbiota to boost healthy growth of neonates

For decades, supporting the optimal growth of low birth weight (LBW) infants has been considered one of the most important paediatric challenges, despite advances in neonatal intensive care technology and nutrition interventions. Since gut microbiota affects such diverse phenotypes in adults, the difference in gut microbiota composition between normal infants and LBW infants raises the possibility of gut microbiota playing an important role in different growth rates of neonates. Based on the concept that probiotics are generally beneficial to the health, numerous studies have been made on probiotics as a supplement to the diet of the LBW infants. However, clinical results on the effects of probiotics on LBW infant growth are either inconsistent or contradictory with each other, and thus the contribution of gut microbiota in neonatal growth has remained inconclusive. In this review, recent researches on neonatal gut microbiota are discussed to develop a new strategy for targeting gut microbiota as a solution to growth retardation in LBW infants. We also discuss how to establish the ideal gut microbiota to support optimal growth of LBW infants.

Whole rumen metagenome sequencing allows classifying and predicting feed efficiency and intake levels in cattle

The current research was carried out to determine the associations between the rumen microbiota and traits related with feed efficiency in a Holstein cattle population (n = 30) using whole metagenome sequencing. Improving feed efficiency (FE) is important for a more sustainable livestock production. The variability for the efficiency of feed utilization in ruminants is partially controlled by the gastrointestinal microbiota. Modulating the microbiota composition can promote a more sustainable and efficient livestock. This study revealed that most efficient cows had larger relative abundance of Bacteroidetes (P = 0.041) and Prevotella (P = 0.003), while lower, but non-significant (P = 0.119), relative abundance of Firmicutes. Methanobacteria (P = 0.004) and Methanobrevibacter (P = 0.003) were also less abundant in the high-efficiency cows. A de novo metagenome assembly was carried out using de Bruijn graphs in MEGAHIT resulting in 496,375 contigs. An agnostic pre-selection of microbial contigs allowed high classification accuracy for FE and intake levels using hierarchical classification. These microbial contigs were also able to predict FE and intake levels with accuracy of 0.19 and 0.39, respectively, in an independent population (n = 31). Nonetheless, a larger potential accuracy up to 0.69 was foreseen in this study for datasets that allowed a larger statistical power. Enrichment analyses showed that genes within these contigs were mainly involved in fatty acids and cellulose degradation pathways. The findings indicated that there are differences between the microbiota compositions of high and low-efficiency animals both at the taxonomical and gene levels. These differences are even more evident in terms of intake levels. Some of these differences remain even between populations under different diets and environments, and can provide information on the feed utilization performance without information on the individual intake level.

Berberine alleviates insulin resistance by reducing peripheral branched-chain amino acids

Increased circulating branched-chain amino acids (BCAAs) have been involved in the pathogenesis of obesity and insulin resistance (IR). However, evidence relating berberine (BBR), gut microbiota, BCAAs, and IR is limited. Here, we showed that BBR could effectively rectify steatohepatitis and glucose intolerance in high-fat diet (HFD)-fed mice. BBR reorganized gut microbiota populations under both the normal chow diet (NCD) and HFD. Particularly, BBR noticeably decreased the relative abundance of BCAA-producing bacteria, including order Clostridiales; families Streptococcaceae, Clostridiaceae, and Prevotellaceae; and genera Streptococcus and Prevotella. Compared with the HFD group, predictive metagenomics indicated a reduction in the proportion of gut microbiota genes involved in BCAA biosynthesis but the enrichment genes for BCAA degradation and transport by BBR treatment. Accordingly, the elevated serum BCAAs of HFD group were significantly decreased by BBR. Furthermore, the Western blotting results implied that BBR could promote the BCAA catabolism in the liver and epididymal white adipose tissues of HFD-fed mice by activation of the multienzyme branched-chain α-ketoacid dehydrogenase complex (BCKDC), whereas by inhibition of the phosphorylation state of BCKDHA (E1α subunit) and branched-chain α-ketoacid dehydrogenase kinase (BCKDK). The ex vivo assay further confirmed that BBR could increase BCAA catabolism in both AML12 hepatocytes and 3T3-L1 adipocytes. Finally, data from healthy subjects and diabetics confirmed that BBR could improve glycemic control and modulate circulating BCAAs. Together, our findings clarified BBR improving IR associated not only with gut microbiota alteration in BCAA biosynthesis but also with BCAA catabolism in liver and adipose tissues.

Short communication: Signs of host genetic regulation in the microbiome composition in 2 dairy breeds: Holstein and Brown Swiss

This study aimed to evaluate whether the host genotype exerts any genetic control on the microbiome composition of the rumen in cattle. Microbial DNA was extracted from 18 samples of ruminal content from 2 breeds (Holstein and Brown Swiss). Reads were processed using mothur (https://www.mothur.org/) in 16S and 18S rRNA gene-based analyses. Then, reads were classified at the genus clade, resulting in 3,579 operational taxonomic units (OTU) aligned against the 16S database and 184 OTU aligned against the 18S database. After filtering on relative abundance (>0.1%) and penetrance (95%), 25 OTU were selected for the analyses (17 bacteria, 1 archaea, and 7 ciliates). Association with the genetic background of the host animal based on the principal components of a genomic relationship matrix based on single nucleotide polymorphism markers was analyzed using Bayesian methods. Fifty percent of the bacteria and archaea genera were associated with the host genetic background, including Butyrivibrio, Prevotella, Paraprevotella, and Methanobrevibacter as main genera. Forty-three percent of the ciliates analyzed were also associated with the genetic background of the host. In total, 48% of microbes were associated with the host genetic background. The results in this study support the hypothesis and provide some evidence that there exists a host genetic component in cattle that can partially regulate the composition of the microbiome.

Effects of infusing milk precursors into the artery on rumen fermentation in lactating cows

This experiment was conducted to investigate the effects of infusing milk precursors into the external pudic artery on rumen fermentation in lactating dairy cows. Eight multiparous Holstein cows were randomly assigned to Group A (experimental group) and Group B (control group) with 4 cows each. A 2 × 4 complex factor crossover design was used. Cows in Group A were fed corn straw as the only roughage, and cows in Group B were fed mixed roughage. The experiment was divided into two periods. In the first period, cows in Group A, received treatments: 1) a basal infusate as a control (CSC); 2) a milk fat precursor infusion including C16:0, C18:0, C18:1c9, C18:2c6, C18:3n3, acetic acid (CSF); 3) a milk protein precursor infusion including 16 amino acids (CSA); 4) the mixed infusion of milk fat and protein precursors (CSFA). And meanwhile, cows in Group B were infused the basal infusate as a control group. In the second period, the cows in both Groups A and B were crossed over, which cows in Group A were named as Group B and the cows originally in Group B were in Group A. The experimental results showed that cows in experimental group had higher ruminal pH compared with the control, and ruminal pH in CSC, CSF, CSA were significantly higher than those in their respective control group (P < 0.05). The concentration of ammonia nitrogen (NH₃–N) was significantly higher in CSA and CSFA compared with Group B (P < 0.05). We also observed that the infusion of mixed amino acids significantly increased the bacterial protein (BCP) content in rumen (P < 0.05) and influenced the rumen acetic acid concentration as well as the acetic to propionic ratio (P < 0.05). Milk fat precursors infusion significantly affected butyric acid concentration (P < 0.05). In addition, the content of lipopolysaccharide (LPS) in CSA was significantly higher than that in the control group (P < 0.05). It is concluded that the milk precursors infused into external pudic artery caused feedback effects on ruminal fermentation under the corn straw roughage conditions. The milk protein precursor increased the ruminal pH, the contents of BCP and acetic acid, which adjust rumen fermentation and improve milk performance.

Amino Acid and Peptide Utilization Profiles of the Fluoroacetate-Degrading Bacterium Synergistetes Strain MFA1 Under Varying Conditions

Synergistetes strain MFA1 is an asaccharolytic ruminal bacterium isolated based on its ability to degrade fluoroacetate, a plant toxin. The amino acid and peptide requirements of the bacterium were investigated under different culturing conditions. The growth of strain MFA1 and its fluoroacetate degradation rate were enhanced by peptide-rich protein hydrolysates (tryptone and yeast extract) compared to casamino acid, an amino acid-rich protein hydrolysate. Complete utilization and preference for arginine, asparagine, glutamate, glycine, and histidine as free amino acids from yeast extract were observed, while the utilization of serine, threonine, and lysine in free form and peptide-bound glutamate was stimulated during growth on fluoroacetate. A predominant peptide in yeast extract preferentially utilized by strain MFA1 was partially characterized by high-liquid performance chromatography-mass spectrometry as a hepta-glutamate oligopeptide. Similar utilization profiles of amino acids were observed between the co-culture of strain MFA1 with Methanobrevibacter smithii without fluoroacetate and pure strain MFA1 culture with fluoroacetate. This suggests that growth of strain MFA1 could be enhanced by a reduction of hydrogen partial pressure as a result of hydrogen removal by a methanogen or reduction of fluoroacetate.

The role of microbial amino acid metabolism in host metabolism

Disruptions in gut microbiota composition and function are increasingly implicated in the pathogenesis of obesity, insulin resistance, and type 2 diabetes mellitus. The functional output of the gut microbiota, including short-chain fatty acids and amino acids, are thought to be important modulators underlying the development of these disorders. Gut bacteria can alter the bioavailability of amino acids by utilization of several amino acids originating from both alimentary and endogenous proteins. In turn, gut bacteria also provide amino acids to the host. This could have significant implications in the context of insulin resistance and type 2 diabetes mellitus, conditions associated with elevated systemic concentrations of certain amino acids, in particular the aromatic and branched-chain amino acids. Moreover, several amino acids released by gut bacteria can serve as precursors for the synthesis of short-chain fatty acids, which also play a role in the development of obesity. In this review, we aim to compile the available evidence on the contribution of microbial amino acids to host amino acid homeostasis, and to assess the role of the gut microbiota as a determinant of amino acid and short-chain fatty acid perturbations in human obesity and type 2 diabetes mellitus.

Bioprocessing of wheat straw into nutritionally rich and digested cattle feed

Wheat straw was fermented by Crinipellis sp. RCK-1, a lignin degrading fungus, under solid state fermentation conditions. The fungus degraded 18.38% lignin at the expense of 10.37% cellulose within 9 days. However, when wheat straw fermented for different duration was evaluated in vitro, the 5 day fungal fermented wheat straw called here "Biotech Feed" was found to possess 36.74% organic matter digestibility (OMD) and 5.38 (MJ/Kg Dry matter) metabolizable energy (ME). The Biotech Feed was also observed to be significantly enriched with essential amino acids and fungal protein by fungal fermentation, eventually increasing its nutritional value. The Biotech Feed upon in vitro analysis showed potential to replace 50% grain from concentrate mixture. Further, the calves fed on Biotech Feed based diets exhibited significantly higher (p<0.05) dry matter intake (DMI: 3.74 Kg/d), dry matter digestibility (DMD: 57.82%), total digestible nutrients (TDN: 54.76%) and comparatively gained 50 g more daily body weight.

Effect of dietary protein supply originating from soybean meal or casein on the intestinal microbiota of piglets

Dietary composition is a major factor influencing the intestinal microbial ecosystem of pigs. To alleviate weaning-associated disorders, variations in dietary protein supply may beneficially affect microbial composition in the gastrointestinal tract of piglets. A total of 48 piglets, fitted with simple ileal T-cannulas, was used to examine the effect of protein supply of either highly digestible casein or less digestible, fiber-rich soybean meal (SBM) on the composition of the intestinal microbiota. Gene copies of 7 bacteria groups were determined by real-time PCR in ileal digesta and feces. Ileal counts of total eubacteria, the Bacteroides-Prevotella-Porphyromonas group, Enterobacteriaceae and Clostridium Cluster XIVa were higher (P < 0.001) in the casein-based diets. Fecal counts of all analyzed bacterial groups were higher for the SBM-based diets (P < 0.001), apart from Enterobacteriaceae (P < 0.05) which were higher in the casein-based diets. Ileal counts of lactobacilli linearly increased as the crude protein level was increased up to 335 g/kg (P < 0.01). The Bacteroides-Prevotella-Porphyromonas group linearly decreased in ileal samples (P < 0.01) and increased in fecal samples (P < 0.05) as the crude protein level in the SBM-based diet was increased. Both, protein level and protein source may affect intestinal microbial balance. Higher dietary protein levels in combination with diets low in fiber contents might stimulate proliferation of protein fermenting bacteria in piglet's large intestine. Further studies are warranted to clarify, whether this would be associated with intestinal disturbances.

Dietary and endogenous amino acids are the main contributors to microbial protein in the upper gut of normally nourished pigs

Although amino acids (AA) synthesized by enteric microbiota in the upper gut of nonruminants can be absorbed, they do not necessarily make a net contribution to the host's AA supply. That depends on whether protein or nonprotein nitrogen sources are used for microbial protein production. We determined the contributions of urea, endogenous protein (EP), and dietary protein (DP) to microbial valine (M.VAL) at the distal ileum of growing pigs, based on isotope dilutions after a 4-d continuous infusion of l-[1-(13)C]valine to label EP and of [(15)N(15)N]urea. Eight barrows were assigned to either a cornstarch and soybean meal-based diet with or without 12% added fermentable fiber from pectin. Dietary pectin did not affect (P > 0.10) the contributions of the endogenous and DP to M.VAL. More than 92% of valine in microbial protein in the upper gut was derived from preformed AA from endogenous and DP, suggesting that de novo synthesis makes only a small contribution to microbial AA.

The effect of carbon and nitrogen sources on bovicin HC5 production by Streptococcus bovis HC5

AIMS

To investigate the effect of media composition and agroindustrial residues on bovicin HC5 production by Streptococcus bovis HC5.

METHODS AND RESULTS

Batch cultures of S. bovis HC5 were grown in basal medium containing different carbon and nitrogen sources. The activity of cell-free and cell-associated bovicin HC5 was determined in culture supernatants and acidic extracts obtained from cell pellets, respectively. Streptococcus bovis HC5 produced bovicin using a variety of carbon and nitrogen sources. The highest specific activity was obtained in media containing 16 g l(-1) of glucose, after 16 h of incubation. The peak in cell-free and cell-associated bovicin HC5 activity was detected when S. bovis HC5 cultures reached stationary phase. The bovicin HC5 specific activity and bacterial cell mass increased approximately 3-fold when yeast extract and trypticase (0.5 and 1.0 g l(-1), respectively) were added together to the basal medium. Streptococcus bovis HC5 cultures produced bovicin HC5 in cheese whey and sugar cane juice and maximal volumetric productivity was obtained after 12 h of incubation.

CONCLUSIONS

Streptococcus bovis HC5 is a versatile lactic acid bacterium that can utilize several carbon and nitrogen sources for bovicin HC5 production. This bacterium could be a useful model to study bacteriocin production in the rumen ecosystem.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of agroindustrial residues as carbon sources could have an economical impact on bovicin HC5 production. To our knowledge, this is the first report to show the use of sugar cane juice for bacteriocin production by lactic acid bacteria.

Use of stable isotopes to measurede novosynthesis and turnover of amino acid-C and -N in mixed micro-organisms from the sheep rumenin vitro

Protein synthesis and turnover in ruminal micro-organisms were assessed by stable-isotope methods in order to follow independently the fate of amino acid (AA)-C and -N in different AA. Rumen fluid taken from sheep receiving a grass hay–concentrate diet were strained and incubatedin vitrowith starch–cellobiose–xylose in the presence of NH3and 5 g algal protein hydrolysate (APH)/l, in incubations where the labels were15NH3, [15N]APH or [13C]APH. Total15N incorporation was calculated from separate incubations with15NH3and [15N]APH, and net N synthesis from the increase in AA in protein-bound material. The large difference between total and net AA synthesis indicated that substantial turnover of microbial protein occurred, averaging 3·5 %/h. Soluble AA-N was incorporated on average more extensively than soluble AA-C (70v.50 % respectively,P=0·001); however, incorporation of individual AA varied. Ninety percent of phenylalanine-C was derived from the C-skeleton of soluble AA, whereas the incorporation of phenylalanine-N was 72 %. In contrast, only 15 % aspartate-C + asparagine-C was incorporated, while 45 % aspartate-N+asparagine-N was incorporated. Deconvolution analysis of mass spectra indicated substantial exchange of carboxyl groups in several AA before incorporation and a condensation of unidentified C2and C4intermediates during isoleucine metabolism. The present results demonstrate that differential labelling with stable isotopes is a way in which fluxes of AA synthesis and degradation, their biosynthetic routes, and separate fates of AA-C and -N can be determined in a mixed microbial population.

Metabolic properties of Eubacterium pyruvativorans, a ruminal 'hyper-ammonia-producing' anaerobe with metabolic properties analogous to those of Clostridium kluyveri

Eubacterium pyruvativorans I-6(T) is a non-saccharolytic, amino-acid-fermenting anaerobe from the rumen, isolated by its ability to grow on pancreatic casein hydrolysate (PCH) as sole C source. This study investigated its metabolic properties and its likely ecological niche. Additional growth was supported by pyruvate, vinyl acetate, and, to a lesser extent, lactate and crotonate, and also by a mixture of amino acids (alanine, glycine, serine and threonine) predicted to be catabolized to pyruvate. No single amino acid supported growth, and peptides were required for growth on amino acids. Alanine, followed by leucine, serine and proline, were used most extensively during growth, but only alanine and asparate were extensively modified before incorporation. Growth on PCH, but not on pyruvate, was increased by the addition of acetate, propionate and butyrate. l-Lactate was fermented incompletely, mainly to acetate, but no lactate-C was incorporated. Propionate and butyrate were utilized during growth, forming valerate and caproate, respectively. Labelling experiments suggested a metabolic pattern where two C atoms of butyrate, valerate and caproate were derived from amino acids, with the others being formed from acetate, propionate and butyrate. The metabolic strategy of E. pyruvativorans therefore resembles that of Clostridium kluyveri, which ferments ethanol only when the reaction is coupled to acetate, propionate or butyrate utilization. The fermentative niche of E. pyruvativorans appears to be to scavenge amino acids, lactate and possibly other metabolites in order to generate ATP via acetate formation, using volatile fatty acid elongation with C(2) units derived from other substrates to dispose of reducing equivalents.

De novo synthesis of amino acids by the ruminal anaerobic fungi, Piromyces communis and Neocallimastix frontalis

Anaerobic fungi are an important component of the cellulolytic ruminal microflora. Ammonia alone as N source supports growth, but amino acid mixtures are stimulatory. In order to evaluate the extent of de novo synthesis of individual amino acids in Piromyces communis and Neocallimastix frontalis, isotope enrichment in amino acids was determined during growth on (15)NH(4)Cl in different media. Most cell N (0.78 and 0.63 for P. communis and N. frontalis, respectively) and amino acid N (0.73 and 0.59) continued to be formed de novo from ammonia when 1 g l(-1) trypticase was added to the medium; this concentration approximates the peak concentration of peptides in the rumen after feeding. Higher peptide/amino acid concentrations decreased de novo synthesis. Lysine was exceptional, in that its synthesis decreased much more than other amino acids when Trypticase or amino acids were added to the medium, suggesting that lysine synthesis might limit fungal growth in the rumen.

Influence of nitrogen source on the fermentation of fibre from barley straw and sugarbeet pulp by ruminal micro-organisms in vitro

Incubations were carried out with a batch culture system to study the effects of different N sources on the fermentation by ruminal micro-organisms from Merino sheep of two fibre substrates derived from feedstuffs that differed in their fermentation rate. The substrates were neutral-detergent fibre (NDF) from barley straw and sugarbeet pulp. N sources were ammonia (NH4Cl) and peptides (Trypticase). Three treatments were made by replacing ammonia-N with peptide-N at levels of 0 (AMMO), 33 (PEPLOW) and 66 % (PEPHIGH) of total N. There were no differences (P>0.05) between treatments in NDF degradation for both the barley straw and the sugarbeet pulp. Peptides increased (P<0.05) total volatile fatty acids daily production for both substrates, with greater values (P<0.001) for PEPHIGH than for PEPLOW for the sugarbeet pulp. The presence of peptides also increased (P<0.05) microbial N synthesis compared with AMMO, with PEPHIGH supporting more growth (P<0.001) than PEPLOW when the sugarbeet pulp NDF was fermented. The presence of peptides increased (P<0.01) the amount of solids-associated micro-organisms (SAM)-N for both the barley straw and the sugarbeet pulp fibres, values in the PEPHIGH treatment being higher (P<0.001) than those in PEPLOW. The proportion of SAM-N in the total microbial N was not affected (P>0.05) by the presence of peptides compared with the AMMO treatment, but values were greater for the PEPHIGH compared with the PEPLOW N source, reaching statistical significance (P<0.05) only for the sugarbeet pulp. For liquid-associated micro-organisms, the AMMO treatment resulted in the greatest (P<0.05) proportion of N derived from ammonia for both substrates, with a further decrease (P<0.01) for the PEPHIGH treatment compared with the PEPLOW for the sugarbeet pulp, indicating preferential uptake of peptides when they were available. Microbial growth efficiency (g microbial N/kg NDF degraded) was not affected (P>0.05) by N source. These results indicate that N forms other than ammonia are needed for maximal growth of fibre-digesting ruminal micro-organisms.

Incorporation of [(15)N] ammonia by the cellulolytic ruminal bacteria Fibrobacter succinogenes BL2, Ruminococcus albus SY3, and Ruminococcus flavefaciens 17

The origin of cell nitrogen and amino acid nitrogen during growth of ruminal cellulolytic bacteria in different growth media was investigated by using (15)NH(3). At high concentrations of peptides (Trypticase, 10 g/liter) and amino acids (15.5 g/liter), significant amounts of cell nitrogen of Fibrobacter succinogenes BL2 (51%), Ruminococcus flavefaciens 17 (43%), and Ruminococcus albus SY3 (46%) were derived from non-NH(3)-N. With peptides at 1 g/liter, a mean of 80% of cell nitrogen was from NH(3). More cell nitrogen was formed from NH(3) during growth on cellobiose compared with growth on cellulose in all media. Phenylalanine was essential for F. succinogenes, and its (15)N enrichment declined more than that of other amino acids in all species when amino acids were added to the medium.

Interactions between carbon and nitrogen metabolism in Fibrobacter succinogenes S85: a 1H and 13C nuclear magnetic resonance and enzymatic study

The effect of the presence of ammonia on [1-13C]glucose metabolism in the rumen fibrolytic bacterium Fibrobacter succinogenes S85 was studied by 13C and 1H nuclear magnetic resonance (NMR). Ammonia halved the level of glycogen storage and increased the rate of glucose conversion into acetate and succinate 2.2-fold and 1.4-fold, respectively, reducing the succinate-to-acetate ratio. The 13C enrichment of succinate and acetate was precisely quantified by 13C-filtered spin-echo difference 1H-NMR spectroscopy. The presence of ammonia did not modify the 13C enrichment of succinate C-2 (without ammonia, 20.8%, and with ammonia, 21.6%), indicating that the isotopic dilution of metabolites due to utilization of endogenous glycogen was not affected. In contrast, the presence of ammonia markedly decreased the 13C enrichment of acetate C-2 (from 40 to 31%), reflecting enhanced reversal of the succinate synthesis pathway. The reversal of glycolysis was unaffected by the presence of ammonia as shown by 13C-NMR analysis. Study of cell extracts showed that the main pathways of ammonia assimilation in F. succinogenes were glutamate dehydrogenase and alanine dehydrogenase. Glutamine synthetase activity was not detected. Glutamate dehydrogenase was active with both NAD and NADP as cofactors and was not repressed under ammonia limitation in the culture. Glutamate-pyruvate and glutamate-oxaloacetate transaminase activities were evidenced by spectrophotometry and 1H NMR. When cells were incubated in vivo with [1-13C]glucose, only 13C-labeled aspartate, glutamate, alanine, and valine were detected. Their labelings were consistent with the proposed amino acid synthesis pathway and with the reversal of the succinate synthesis pathway.