Spatial and Temporal Variations in Stable Carbon (δ13C) and Nitrogen (δ15N) Isotopic Composition of Symbiotic Scleractinian Corals

Tropical scleractinian corals are considered autotrophic as they rely mainly on photosynthesis-derived nutrients transferred from their photosymbionts. Corals are also able to capture and ingest suspended particulate organic matter, so heterotrophy can be an important supplementary trophic pathway to optimize coral fitness. The aim of this in situ study was to elucidate the trophic status of 10 coral species under contrasted environmental conditions in a French Polynesian lagoon. Carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopic compositions of coral host tissues and photosymbionts were determined at 3 different fringing reefs during wet and dry seasons. Our results highlighted spatial variability in stable isotopic compositions of both coral host tissues and photosymbionts. Samples from the site with higher level of suspended particulate matter were ¹³C-depleted and ¹⁵N-enriched relative to corals and photosymbionts from less turbid sites. However, differences in both δ¹³C and δ¹⁵N between coral host tissues and their photosymbionts (Δ^{host-photosymbionts 13}C and Δ^{host-photosymbionts 15}N) were small (0.27 ± 0.76‰ and 1.40 ± 0.90‰, respectively) and similar at all sites, thus indicating no general increases in the heterotrophic pathway. Depleted δ¹³C and enriched δ¹⁵N values of coral host tissues measured at the most turbid site were explained by changes in isotopic composition of the inorganic nutrients taken up by photosymbionts and also by changes in rate of isotopic fractionation with environmental conditions. Our results also highlighted a lack of significant temporal variations in δ¹³C and δ¹⁵N values of coral host and photosymbiont tissues and in Δ^{host-photosymbionts 13}C and Δ^{host-photosymbionts 15}N values. This temporal stability indicated that corals remained principally autotrophic even during the wet season when photosymbiont densities were lower and the concentrations of phytoplankton were higher. Increased coral heterotrophy with higher food availability thus appears to be species-specific.     

Evaluation of n-alkanes and their carbon isotope enrichments (δ(13)C) as diet composition markers

Plant cuticular n-alkanes have been successfully used as markers to estimate diet composition and intake of grazing herbivores. However, additional markers may be required under grazing conditions in botanically diverse vegetation. This study was conducted to describe the n-alkane profiles and the carbon isotope enrichment of n-alkanes of common plant species from the Mid Rift Valley rangelands of Ethiopia, and evaluate their potential use as nutritional markers. A total of 23 plant species were collected and analysed for long-chain n-alkanes ranging from heptacosane to hexatriacontane (C(27) to C(36)), as well as their carbon isotopic ratio ((13)C/(12)C). The analysis was conducted by gas chromatography/combustion isotope ratio mass spectrometry following saponification, extraction and purification. The isotopic composition of the n-alkanes is reported in the delta notation (δ(13)C) relative to the Vienna Pee Dee Belemnite standard. The dominant n-alkanes in the species were C(31) (mean ± s.d., 283 ± 246 mg/kg dry matter) and C(33) (149 ± 98 mg/kg dry matter). The carbon isotopic enrichment of the n-alkanes ranged from -19.37‰ to -37.40‰. Principal component analysis was used to examine interspecies differences based on n-alkane profiles and the carbon isotopic enrichments of individual n-alkanes. Large variability among the pasture species was observed. The first three principal components explained most of the interspecies variances. Comparison of the principal component scores using orthogonal procrustes rotation indicated that about 0.84 of the interspecies variances explained by the two types of data sets were independent of each other, suggesting that the use of a combination of the two markers can improve diet composition estimations. It was concluded that, while the n-alkane profile of the pasture species remains a useful marker for use in the study region, the δ(13)C values of n-alkanes can provide additional information in discriminating diet components of grazing animals.     

Flanking V and J sequences of complementary determining region 3 of T cell receptor (TCR) δ1 (CDR3δ1) determine the structure and function of TCRγ4δ1

The γδ T cell receptor (TCR) differs from immunoglobulin and αβ TCR in its overall binding mode. In human, genes δ1, δ2, and δ3 are used for TCRδ chains. Previously, we have studied antigen binding determinants of TCRδ2 derived from dominant γδ T cells residing in peripheral blood. In this study we have investigated the critical determinants for antigen recognition and TCR function in TCRδ1 originated from gastric tumor-infiltrating γδ T lymphocytes using three independent experimental strategies including complementary determining region 3 (CDR3) of TCRδ1 (CDR3δ1)-peptide mediated binding, CDR3δ1-grafted TCR fusion protein-mediated binding, and TCRγ4δ1- and mutant-expressing cell-mediated binding. All three approaches consistently showed that the conserved flanking V and J sequences but not the diverse D segment in CDR3δ1 determine the antigen binding. Most importantly, we found that mutations in the V and J regions of CDR3δ1 also abolish the assembly of TCR and TCR-CD3 complexes in TCRγ4δ1-transduced J.RT3-T3.5 cells. Together with our previous studies on CDR3δ2 binding, our finding suggests that both human TCRδ1 and TCRδ2 recognize antigen predominately via flanking V and J regions. These results indicate that TCRγδ recognizes antigens using conserved parts in their CDR3, which provides an explanation for a diverse repertoire of γδTCRs only recognizing a limited number of antigens.     

Isotopic signatures (δO and δC) of bivalve shells from cold seeps and hydrothermal vents

The oxygen and carbon isotopic compositions of 108 modern shells of various bivalve species collected from cold seeps and hydrothermal vents were investigated in order to evaluate whether these parameters can provide information on environmental geochemical variability as well as on bivalve species and on the type of symbiotic bacteria present in their gills. The results show that the carbonate of bivalve shells from hydrothermal vents is characterized by abnormal positive δ¹³C values due to kinetic isotope effects, whereas the carbonate of bivalve shells from cold seeps exhibits positive as well as negative δ¹³C values suggesting that oxidized methane emitted by the seeping fluids may be incorporated in the shell. Comparison of the δ¹⁸O and δ¹³C values of bivalve shells hosting different chemosymbiotic bacteria suggests that each type of symbiosis is associated with a specific environment and bivalve species, indicating that there is a strong physiological/metabolic control on the incorporation of stable isotopes during the biomineralization process.     

Anhydrous and hydrated lanthanide(III) β,δ-triketonates

Complexes of the β,δ-triketones benzoylacetone and diacetylacetone with lanthanide(III) ions are reported. The compounds with the first ligand (formulated Ln(Hbaa)₃) are anhydrous while those with the last one (formulated Ln(Hdaa)₃·H₂O) are hydrated. IR and TGA analyses were carried out to confirm the anhydrous or hydrated character of the complexes. The anhydrous character of the lanthanide complexes with benzoylacetone is discussed in terms of the larger steric requirements in the terminal groups of the ligand with respect to those in the compounds with diacetylacetone.     

Detection and quantification of α-keto-δ-(N(G),N(G)-dimethylguanidino)valeric acid: a metabolite of asymmetric dimethylarginine

Nitric oxide is an ubiquitary cell signaling substance. Its enzymatic production rate by nitric oxide synthase is regulated by the concentrations of the substrate L-arginine and the competitive inhibitor asymmetric dimethylarginine (ADMA). A newly recognized elimination pathway for ADMA is the transamination to α-keto-δ-(N(G),N(G)-dimethylguanidino)valeric acid (DMGV) by the enzyme alanine-glyoxylate aminotransferase 2 (AGXT2). This pathway has been proven to be relevant for nitric oxide regulation, but up to now no method exists for the determination of DMGV in biological fluids. We have developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of DMGV. D(6)-DMGV was used as internal standard. Samples were purified online by column switching, and separation was achieved on a porous graphitic carbon column. The calibration was linear over ranges of 10 to 200 nmol/L for plasma and 0.1 to 20 μmol/L for urine. The intra- and interday accuracies and precisions in plasma and urine were better than 10%. In plasma samples, DMGV was present in concentrations between 19.1 and 77.5 nmol/L. In urine samples, concentrations between 0.0114 and 1.03 μmol/mmol creatinine were found. This method can be used as a tool for the scientific investigation of the ADMA conversion to DMGV via the enzyme AGXT2.     

Isotopic (δ15N) relationship of pregnant females and their embryos: Comparing placental and yolk-sac viviparous elasmobranchs

Nitrogen stable isotopes ratios (δ¹⁵N) were determined for selected tissues (muscle, liver, blood and yolk) of pregnant females and their embryos of a placental viviparous species, the Pacific sharpnose shark (Rhizoprionodon longurio), and a yolk-sac viviparous species, the speckled guitarfish (Pseudobatos glaucostigmus). The R. longurio embryo tissues were ¹⁵N enriched compared to the same tissues in the pregnant female, using the difference in δ¹⁵N (Δδ¹⁵N) between embryo and adult. Mean Δδ¹⁵N was 2.17‰ in muscle, 4.39‰ in liver and 0.80‰ in blood. For P. glaucostigmus, embryo liver tissue was significantly ¹⁵N enriched in comparison with liver of the pregnant female (Δδ¹⁵N mean = 1.22‰), whereas embryo muscle was ¹⁵N depleted relative to the muscle of the pregnant female (Δδ¹⁵N mean = −1.22‰). Both species presented a significant positive linear relationship between Δδ¹⁵N and embryo total length (L_T). The results indicated that embryos have different Δδ¹⁵N depending on their reproductive strategy, tissue type analysed and embryo L_T.     

Production of cyclomaltononaose (δ-cyclodextrin) by cyclodextrin glycosyltransferases from Bacillus spp. and bacterial isolates

The conversion of soluble starch to cyclomaltohexaose (α-CD), cyclomaltoheptaose (β-CD), cyclomaltooctaose (γ-CD) and cyclomaltononaose (δ-CD) by cyclodextrin glycosyltransferases (E.C. 2.4.1.19) from Bacillus spp. and bacterial isolates was studied. The results show that δ-CD was formed by all the enzymes investigated in the range of 5%–11.5% of the total amount of α-, β-, γ-, and δ-CD produced. Received: 17 February 1998 / Received revision: 18 May 1998 / Accepted: 21 May 1998     

Synthesis of (±)-Homosarkomycin and (±)-Rosaprostol

(±)-Homosarkomycin (2) and (±)-rosaprostol (3) were synthesized from (±)-methyl 2-oxo-bicyclo[3.1.0]hexane-1-carboxylate (1) by using the nucleophilic ring opening reaction on the double-activated cyclopropane ring as the key step.     

Synthesis of (±)-Lamprolobine and (±)-Epilamprolobine

(±)-Lamprolobine, the (+)-enatiomer of which was isolated from the leaves of Lamprolobium fruticosum, and (±)-epilamprolobine were synthesized from δ-valerolactam.     

δ-(D-α-Aminoadipoyl)-Cleaving Amidase of Ochrobactrum anthropi

Ochrobactrum anthropi cleaved the delta-(D-alpha-aminoadipoyl)-side chain from delta-(D-alpha-aminoadipoyl)-7-amino-4-methylcoumarin, a beta-lactamase-resistant cephalosporin C analogue. In whole cell conversions up to 1 nkat g(-1) dry cell wt were achieved. O. anthropi possesses also gamma-D-glutamyltranspeptidase activity, 8 nkat g(-1) dry cell wt, the likely cause of delta-(D-alpha-aminoadipoyl)-cleavage.     

Synthesis and application of an Nδ-acetyl-Nδ-hydroxyornithine analog: identification of novel metal complexes of deferriferrichrysin

Synthesis of Fmoc-protected N(δ)-acetyl-N(δ)-(tert-butoxy)-l-ornithine has revealed it to be a metal-chelating amino-acid precursor. This protected amino acid was compatible with the preparation of ferrichrome peptides by standard Fmoc-based solid-phase peptide synthesis. Evaluation of deferriferrichrysin for metal ion chelation revealed that zirconium(IV) and titanium(IV) formed complexes with deferriferrichrysin.     

Syntheses of (±)-Epoformin (Desoxyepoxydon) and (±)-Epiepoformin (Desoxyepiepoxydon)

Boron is an essential nutrient for plants, but it is toxic in excess. Transgenic rice plants expressing an Arabidopsis thaliana borate efflux transporter gene, AtBOR4, at a low level exhibited increased tolerance to excess boron. Those lines with high levels of expression exhibited reduced growth. These findings suggest a potential of the borate transporter BOR4 for the generation of high-boron tolerant rice.     

Synthesis and characterization of tris(β-diketonato)technetium(III) and -(IV) complexes

The preparations and properties of tris(dipivaloylmethanato)technetium(III), tris(trifluoroacetylacetonato)technetium(III), and tris(hexafluoroacetonato)technetium(III) are described. The oxidation of the dipivaloyl derivative to tris(dipivaloyl)technetium(IV) hexafluorophosphate was shown to take place readily. Voltammetric studies and magnetic resonance results on the new complexes are reported. The large shifts observed for the complexes seem to be due to a contact interaction.     

δ(13) C of leaf-respired CO(2) reflects intrinsic water-use efficiency in barley

Leaf intrinsic water-use efficiency (WUE), the ratio of photosynthetic rate to stomatal conductance (A/g(s) ), is a key plant trait linking terrestrial carbon and water cycles. A rapid, integrative proxy for A/g(s) is of benefit to crop breeding programmes aiming to improve WUE, but also for ecologists interested in plant carbon-water balance in natural systems. We hypothesize that the carbon isotope composition of leaf-respired CO(2) (δ(13) C(Rl) ), two hours after leaves are transferred to the dark, records photosynthetic carbon isotope discrimination and so provides a proxy for A/g(s) . To test this hypothesis, δ(13) C(Rl) was measured in four barley cultivars grown in the field at two levels of water availability and compared to leaf-level gas exchange (the ratio of leaf intercellular to ambient CO(2) partial pressure, C(i) /C(a) , and A/g(s) ). Leaf-respired CO(2) was more (13) C-depleted in plants grown at higher water availability, varied between days as environmental conditions changed, and was significantly different between cultivars. A strong relationship between δ(13) C(Rl) and δ(13) C of sucrose was observed. δ(13) C(Rl) was converted into apparent photosynthetic discrimination (Δ(13) C(Rl) ) revealing strong relationships between Δ(13) C(Rl) and C(i) /C(a) and A/g(s) during the vegetative stage of growth. We therefore conclude that δ(13) C(Rl) may provide a rapid, integrative proxy for A/g(s) in barley.     

Linking hydrogen (δ2H) isotopes in feathers and precipitation: sources of variance and consequences for assignment to isoscapes

Background

Tracking small migrant organisms worldwide has been hampered by technological and recovery limitations and sampling bias inherent in exogenous markers. Naturally occurring stable isotopes of H (δ²H) in feathers provide an alternative intrinsic marker of animal origin due to the predictable spatial linkage to underlying hydrologically driven flow of H isotopes into foodwebs. This approach can assess the likelihood that a migrant animal originated from a given location(s) within a continent but requires a robust algorithm linking H isotopes in tissues of interest to an appropriate hydrological isotopic spatio-temporal pattern, such as weighted-annual rainfall. However, a number of factors contribute to or alter expected isotopic patterns in animals. We present results of an extensive investigation into taxonomic and environmental factors influencing feather δ ²H patterns across North America.

Principal Findings

Stable isotope data were measured from 544 feathers from 40 species and 140 known locations. For δ ²H, the most parsimonious model explaining 83% of the isotopic variance was found with amount-weighted growing-season precipitation δ ²H, foraging substrate and migratory strategy.

Conclusions/Significance

This extensive H isotopic analysis of known-origin feathers of songbirds in North America and elsewhere reconfirmed the strong coupling between tissue δ ²H and global hydrologic δ ²H patterns, and accounting for variance associated with foraging substrate and migratory strategy, can be used in conservation and research for the purpose of assigning birds and other species to their approximate origin.     

Variability of stable isotope signatures (δC and δN) in two spider crab populations (Maja brachydactyla) in Western Europe

The ontogenic variations of nitrogen and carbon stable isotopic signatures (δ¹⁵N and δ¹³C) were investigated in two spider crab (Maja brachydactyla) populations inhabiting in different biotopes of Western Europe. The Iroise Sea population is localized in Western Brittany and characterized by a seasonal migration occurring on a large bathymetric and habitat gradient while the Seine Bay population, in the Eastern English Channel, remains in a more homogeneous environment during its migration. In the Iroise Sea population, δ¹³C values increased significantly both with body size and age, revealing a shift towards “benthic-component” prey with spider crab growth. On the contrary, neither body size nor ageing gave rise to a significant trophic level change (derived from the δ¹⁵N). In this M. brachydactyla population, the seasonal migrations from coastal waters in summer to offshore habitats in winter involved significant but slight differences in both δ¹³C and δ¹⁵N. In the Seine Bay population, low variations for both carbon and nitrogen were recorded related to either sex or size or seasonal migration. Thus, the δ¹³C and δ¹⁵N variability in the spider crab depends on the availability and diversity of prey in its different living habitats, as well as on the morphological aptitudes of individuals to feed on prey (individual's size).     

Synthesis and characterization of β-diketiminate germanium(II) and tin(II) bromides

The equimolar reaction of a β-diketiminate lithium salt LLi(OEt₂) [L = HC(CMeNAr)₂; Ar = 2,6-iPr₂C₆H₃] with either GeBr₂ or SnBr₂ in diethyl ether affords the synthetically useful monomeric β-diketiminate-element halides LGeBr (1) and LSnBr (2), respectively. Both are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction analysis.     

Community structure and food web based on stable isotopes (δN and δC) analysis of a North Eastern Atlantic maerl bed

Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources.