Metabolites from intestinal microbes shape Treg

Intestinal bacterial metabolites are an important communication tool between the host immune system and the commensal microbiota to establish mutualism. In a recent paper published in Science, Wendy Garrett and her colleagues report an exciting role of the three most abundant microbial-derived short-chain fatty acids (SCFA), acetic acid, propionic acid and butyric acid, in colonic regulatory T cell (cTreg) homeostasis.

Oviposition by a moth suppresses constitutive and herbivore-induced plant volatiles in maize

Plant volatiles function as important signals for herbivores, parasitoids, predators, and neighboring plants. Herbivore attack can dramatically increase plant volatile emissions in many species. However, plants do not only react to herbivore-inflicted damage, but also already start adjusting their metabolism upon egg deposition by insects. Several studies have found evidence that egg deposition itself can induce the release of volatiles, but little is known about the effects of oviposition on the volatiles released in response to subsequent herbivory. To study this we measured the effect of oviposition by Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) moths on constitutive and herbivore-induced volatiles in maize (Zea mays L.). Results demonstrate that egg deposition reduces the constitutive emission of volatiles and suppresses the typical burst of inducible volatiles following mechanical damage and application of caterpillar regurgitant, a treatment that mimics herbivory. We discuss the possible mechanisms responsible for reducing the plant's signaling capacity triggered by S. frugiperda oviposition and how suppression of volatile organic compounds can influence the interaction between the plant, the herbivore, and other organisms in its environment. Future studies should consider oviposition as a potential modulator of plant responses to insect herbivores. © 2011 Springer-Verlag.

Dietary inclusion of feathers affects intestinal microbiota and microbial metabolites in growing Leghorn-type chickens.

Feather pecking in laying hens is a serious behavioral problem that is often associated with feather eating. The intake of feathers may influence the gut microbiota and its metabolism. The aim of this study was to determine the effect of 2 different diets, with or without 5% ground feathers, on the gut microbiota and the resulting microbial fermentation products and to identify keratin-degrading bacteria in chicken digesta. One-day-old Lohmann-Selected Leghorn chicks were divided into 3 feeding groups: group A (control), B (5% ground feathers in the diet), and C, in which the control diet was fed until wk 12 and then switched to the 5% feather diet to study the effect of time of first feather ingestion. The gut microbiota was analyzed by cultivation and denaturing gradient gel electrophoresis of ileum and cecum digesta. Short-chain fatty acids, ammonia, and lactate concentrations were measured as microbial metabolites. The concentration of keratinolytic bacteria increased after feather ingestion in the ileum (P < 0.001) and cecum (P = 0.033). Bacterial species that hydrolyzed keratin were identified as Enterococcus faecium, Lactobacillus crispatus, Lactobacillus reuteri-like species (97% sequence homology), and Lactobacillus salivarius-like species (97% sequence homology). Molecular analysis of cecal DNA extracts showed that the feather diet lowered the bacterial diversity indicated by a reduced richness (P < 0.001) and shannon (P = 0.012) index. The pattern of microbial metabolites indicated some changes, especially in the cecum. This study showed that feather intake induced an adaptation of the intestinal microbiota in chickens. It remains unclear to what extent the changed metabolism of the microbiota reflects the feather intake and could have an effect on the behavior of the hens.

Relationship between cobalamin-dependent metabolites and both serum albumin and alpha1 -proteinase inhibitor concentrations in hypocobalaminemic dogs of 7 different breeds.

BACKGROUND Increased serum concentrations of homocysteine (HCY) and methylmalonic acid (MMA), the 2 main cobalamin-dependent metabolites, as well as decreased serum albumin and canine alpha1 -proteinase inhibitor (cα1 -PI) concentrations have previously been described in hypocobalaminemic dogs with gastrointestinal disease. However, no studies have been conducted to evaluate potential relationships between these serum biomarkers. OBJECTIVE The aim of this study was to evaluate the relationship between HCY and MMA, 2 cobalamin-dependent metabolites, and both serum albumin and cα1 -PI concentrations in hypocobalaminemic dogs. METHODS Serum samples from 285 dogs including 7 different breeds (Beagle, Boxer, Cocker Spaniel, German Shepherd, Labrador Retriever, Chinese Shar-Pei, and Yorkshire Terrier) with hypocobalaminemia were used. Serum HCY, MMA, albumin, and cα1 -PI concentrations were determined. RESULTS There was a significant correlation between serum HCY and albumin concentrations, as well as serum HCY and cα1 -PI concentrations (ρ = 0.62 and ρ = 0.37, respectively; P < .0001). No correlations were observed between serum MMA and albumin concentrations, or cα1 -PI concentrations (ρ = 0.01 and ρ = 0.08, respectively; P > .05). In addition, significant breed-specific correlations were observed between serum MMA and albumin concentrations in German Shepherds, and serum HCY and MMA concentrations in Chinese Shar-Peis with hypocobalaminemia. CONCLUSIONS This study shows a correlation between serum albumin and cα1 -PI and HCY concentrations, but not with serum MMA concentration in dogs with hypocobalaminemia. In addition, significant breed-specific correlations were observed between serum MMA and albumin concentrations in German Shepherds, as well as serum HCY and MMA concentrations in Chinese Shar-Peis, emphasizing the unique metabolic interactions in those dog breeds affected by hypocobalaminemia.

Fibrinogen association with human monocytes: evidence for constitutive expression of fibrinogen receptors and for involvement of Mac-1 (CD18, CR3) in the binding

Radiolabeled fibrinogen (Fg) specifically binds to mononuclear leukocytes (MNL) and to purified monocytes, but not to nylon-nonadherent lymphocytes. The association is rapid, Ca++-dependent and reversible. MNL containing Fg-binding monocytes had not been exposed to endotoxin (less than 4 pg/mL) during the isolation and the binding test, and Fg binding was not altered by preincubation of MNL with lipopolysaccharide. The binding of Fg was inhibited by anti-Mac-1 antibodies (OKM1). Antibodies to surface-bound Fg were able to induce luminol-dependent chemiluminescence, indicating that Fg binding sites have receptor function. Emission of a signal depended on MNL exposure to Fg, on specific, divalent antibodies, but not on the antibody Fc portion. These data show that human monocytes constitutively express specific Fg receptors and suggest that Mac-1, a member of the integrin superfamily, is involved in Fg recognition.

Defensive weapons and defense signals in plants: Some metabolites serve both roles

The defense of plants against herbivores and pathogens involves the participation of an enormous range of different metabolites, some of which act directly as defensive weapons against enemies (toxins or deterrents) and some of which act as components of the complex internal signaling network that insures that defense is timed to enemy attack. Recent work reveals a surprising trend: The same compounds may act as both weapons and signals of defense. For example, two groups of well-studied defensive weapons, glucosinolates and benzoxazinoids, trigger the accumulation of the protective polysaccharide callose as a barrier against aphids and pathogens. In the other direction, several hormones acting in defense signaling (and their precursors and products) exhibit activity as weapons against pathogens. Knowing which compounds are defensive weapons, which are defensive signals and which are both is vital for understanding the functioning of plant defense systems.

Constitutive notch signaling in adult transgenic mice inhibits bFGF-induced angiogenesis and blocks ovarian follicle development

Notch signaling is important in angiogenesis during embryonic development. However, the embryonic lethal phenotypes of knock-out and transgenic mice have precluded studies of the role of Notch post-natally. To develop a mouse model that would bypass the embryonic lethal phenotype and investigate the possible role of Notch signaling in adult vessel growth, we developed transgenic mice with Cre-conditional expression of the constitutively active intracellular domain of Notch1 (IC-Notch1). Double transgenic IC-Notch1/Tie2-Cre embryos with endothelial specific IC-Notch1 expression died at embryonic day 9.5. They displayed collapsed and leaky blood vessels and defects in angiogenesis development. A tetracycline-inducible system was used to express Cre recombinase postnatally in endothelial cells. In adult mice, IC-Notch1 expression inhibited bFGF-induced neovascularization and female mice lacked mature ovarian follicles, which may reflect the block in bFGF-induced angiogenesis required for follicle growth. Our results demonstrate that Notch signaling is important for both embryonic and adult angiogenesis and indicate that the Notch signaling pathway may be a useful target for angiogenic therapies.

Separation of small metabolites and lipids in spectra from biopsies by diffusion-weighted HR-MAS NMR: a feasibility study.

High Resolution Magic Angle Spinning (HR-MAS) NMR allows metabolic characterization of biopsies. HR-MAS spectra from tissues of most organs show strong lipid contributions that are overlapping metabolite regions, which hamper metabolite estimation. Metabolite quantification and analysis would benefit from a separation of lipids and small metabolites. Generally, a relaxation filter is used to reduce lipid contributions. However, the strong relaxation filter required to eliminate most of the lipids also reduces the signals for small metabolites. The aim of our study was therefore to investigate different diffusion editing techniques in order to employ diffusion differences for separating lipid and small metabolite contributions in the spectra from different organs for unbiased metabonomic analysis. Thus, 1D and 2D diffusion measurements were performed, and pure lipid spectra that were obtained at strong diffusion weighting (DW) were subtracted from those obtained at low DW, which include both small metabolites and lipids. This subtraction yielded almost lipid free small metabolite spectra from muscle tissue. Further improved separation was obtained by combining a 1D diffusion sequence with a T2-filter, with the subtraction method eliminating residual lipids from the spectra. Similar results obtained for biopsies of different organs suggest that this method is applicable in various tissue types. The elimination of lipids from HR-MAS spectra and the resulting less biased assessment of small metabolites have potential to remove ambiguities in the interpretation of metabonomic results. This is demonstrated in a reproducibility study on biopsies from human muscle.

Within-plant distribution of 1,4-benzoxazin-3-ones contributes to herbivore niche differentiation in maize

Plant defences vary in space and time, which may translate into specific herbivore-foraging patterns and feeding niche differentiation. To date, little is known about the effect of secondary metabolite patterning on within-plant herbivore foraging. We investigated how variation in the major maize secondary metabolites, 1,4-benzoxazin-3-one derivatives (BXDs), affects the foraging behaviour of two leaf-chewing herbivores. BXD levels varied substantially within plants. Older leaves had higher levels of constitutive BXDs while younger leaves were consistently more inducible. These differences were observed independently of plant age, even though the concentrations of most BXDs declined markedly in older plants. Larvae of the well-adapted maize pest Spodoptera frugiperda preferred and grew better on young inducible leaves irrespective of plant age, while larvae of the generalist Spodoptera littoralis preferred and tended to grow better on old leaves. In BXD-free mutants, the differences in herbivore weight gain between old and young leaves were absent for both species, and leaf preferences of S. frugiperda were attenuated. In contrast, S. littoralis foraging patterns were not affected. In summary, our study shows that plant secondary metabolites differentially affect performance and foraging of adapted and non-adapted herbivores and thereby likely contribute to feeding niche differentiation

Jasmonate-dependent depletion of soluble sugars compromises plant resistance to Manduca sexta

Jasmonates regulate plant secondary metabolism and herbivore resistance. How they influence primary metabolites and how this may affect herbivore growth and performance are not well understood. We profiled sugars and starch of jasmonate biosynthesis-deficient and jasmonate-insensitive Nicotiana attenuata plants and manipulated leaf carbohydrates through genetic engineering and in vitro complementation to assess how jasmonate-dependent sugar accumulation affects the growth of Manduca sexta caterpillars. We found that jasmonates reduce the constitutive and herbivore-induced concentration of glucose and fructose in the leaves across different developmental stages. Diurnal, jasmonate-dependent inhibition of invertase activity was identified as a likely mechanism for this phenomenon. Contrary to our expectation, both in planta and in vitro approaches showed that the lower sugar concentrations led to increased M. sexta growth. As a consequence, jasmonate-dependent depletion of sugars rendered N. attenuata plants more susceptible to M. sexta attack. In conclusion, jasmonates are important regulators of leaf carbohydrate accumulation and this determines herbivore growth. Jasmonate-dependent resistance is reduced rather than enhanced through the suppression of glucose and fructose concentrations, which may contribute to the evolution of divergent resistance strategies of plants in nature.

Identification, quantification, spatiotemporal distribution and genetic variation of major latex secondary metabolites in the common dandelion (Taraxacum officinale agg.)

The secondary metabolites in the roots, leaves and flowers of the common dandelion (Taraxacum officinale agg.) have been studied in detail. However, little is known about the specific constituents of the plant’s highly specialized laticifer cells. Using a combination of liquid and gas chromatography, mass spectrometry and nuclear magnetic resonance spectrometry, we identified and quantified the major secondary metabolites in the latex of different organs across different growth stages in three genotypes, and tested the activity of the metabolites against the generalist root herbivore Diabrotica balteata. We found that common dandelion latex is dominated by three classes of secondary metabolites: phenolic inositol esters (PIEs), triterpene acetates (TritAc) and the sesquiterpene lactone taraxinic acid β-d-glucopyranosyl ester (TA-G). Purification and absolute quantification revealed concentrations in the upper mg g−1 range for all compound classes with up to 6% PIEs, 5% TritAc and 7% TA-G per gram latex fresh weight. Contrary to typical secondary metabolite patterns, concentrations of all three classes increased with plant age. The highest concentrations were measured in the main root. PIE profiles differed both quantitatively and qualitatively between plant genotypes, whereas TritAc and TA-G differed only quantitatively. Metabolite concentrations were positively correlated within and between the different compound classes, indicating tight biosynthetic co-regulation. Latex metabolite extracts strongly repelled D. balteata larvae, suggesting that the latex constituents are biologically active.

The Role of Plant Primary and Secondary Metabolites in Root-Herbivore Behaviour, Nutrition and Physiology

Many insect herbivores feed on belowground plant tissues. In this chapter, we discuss how they have adapted to deal with root primary and secondary metabolites. It is becoming evident that root herbivores can use root volatiles and exudates for host location and foraging. Their complex sensory apparatus suggests a sophisticated recognition and signal transduction system. Furthermore, endogenous metabolites trigger attractive or repellent responses in root feeders, indicating that they may specifically fine-tune food uptake to meet their dietary needs. Little evidence for direct toxic effects of root secondary metabolites has accumulated so far, indicating high prevalence of tolerance mechanisms. Root herbivores furthermore facilitate the entry of soil microbes into the roots, which may influence root nutritional quality. Investigating the role of plant metabolites in an ecologically and physiologically relevant context will be crucial to refine our current models on root-herbivore physiology and behaviour in the future.

Metabolomics reveals herbivore-induced metabolites of resistance and susceptibility in maize leaves and roots

Plants respond to herbivory by reprogramming their metabolism. Most research in this context has focused on locally induced compounds that function as toxins or feeding deterrents. We developed an ultra-high-pressure liquid chromatography time-of-flight mass spectrometry (UHPLC-TOF-MS)-based metabolomics approach to evaluate local and systemic herbivore-induced changes in maize leaves, sap, roots and root exudates without any prior assumptions about their function. Thirty-two differentially regulated compounds were identified from Spodoptera littoralis-infested maize seedlings and isolated for structure assignment by microflow nuclear magnetic resonance (CapNMR). Nine compounds were quantified by a high throughput direct nano-infusion tandem mass spectrometry/mass spectrometry (MS/MS) method. Leaf infestation led to a marked local increase of 1,3-benzoxazin-4-ones, phospholipids, N-hydroxycinnamoyltyramines, azealic acid and tryptophan. Only few changes were found in the root metabolome, but 1,3-benzoxazin-4-ones increased in the vascular sap and root exudates. The role of N-hydroxycinnamoyltyramines in plant–herbivore interactions is unknown, and we therefore tested the effect of the dominating p-coumaroyltyramine on S. littoralis. Unexpectedly, p-coumaroyltyramine was metabolized by the larvae and increased larval growth, possibly by providing additional nitrogen to the insect. Taken together, this study illustrates that herbivore attack leads to the induction of metabolites that can have contrasting effects on herbivore resistance in the leaves and roots.