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.     

Possible ideas on carbon and nitrogen trophic fractionation of food chains: a new aspect of food-chain stable isotope analysis in Lake Biwa, Lake Baikal, and the Mongolian grasslands

Trophic fractionation of carbon and nitrogen isotopes (Δδ¹³C, Δδ¹⁵N) was examined using previously complied databases for food chains in Lake Biwa, Lake Baikal, and Mongolian grassland. The following two features were clarified: (1) For each ecosystem, the ratios of trophic fractionation of carbon and nitrogen isotopes (Δδ¹⁵N/Δδ¹³C) throughout food chain could be obtained as the slope of linear regression line on the δ¹⁵N–δ¹³C plot. (2) Further, analysis of covariance (ANCOVA) revealed the slopes on δ¹⁵N–δ¹³C were not significantly different among these various ecosystems and allowed us to have the regression by setting δ¹⁵N as the response variable: δ¹⁵N = 1.61 δ¹³C + [ecosystem specific constant] with standard errors of [±0.41] and [±9.7] for the slope and the intercept, respectively. It was suggested that the slope of the regression (or the ratio Δδ¹⁵N/Δδ¹³C) could be applicable to more complicated food webs in case nitrogen and carbon isotope ratios of primary producers can be assumed constant in space and time within the ecosystems. The results from simple linear regression analyses coincided well with the ANCOVA results for these ecosystems, although there was some discrepancy between the results of the two statistical analyses. Possible factors that govern the linear relationship between δ¹⁵N and δ¹³C along a food chain are discussed together with a new scope for the stable isotope food chain analyses.     

Stable‐isotope comparisons between embryos and mothers of a placentatrophic shark species

Stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotopes of Atlantic sharpnose shark Rhizoprionodon terraenovae embryos and mothers were analysed. Embryos were generally enriched in ¹⁵N in all studied tissue relative to their mothers' tissue, with mean differences between mother and embryo δ¹⁵N (i.e. Δδ¹⁵N) being 1·4‰ for muscle, 1·7‰ for liver and 1·1‰ for cartilage. Embryo muscle and liver were enriched in ¹³C (both Δδ¹³C means = 1·5‰) and embryo cartilage was depleted (Δδ¹³C mean = ?1·01‰) relative to corresponding maternal tissues. While differences in δ¹⁵N and δ¹³C between mothers and their embryos were significant, muscle δ¹⁵N values indicated embryos to be within the range of values expected if they occupied a similar trophic position as their respective mothers. Positive linear relationships existed between embryo total length (L_T) and Δδ¹⁵N for muscle and liver and embryo L_T and Δδ¹³C for muscle, with those associations possibly resulting from physiological differences between smaller and larger embryos or differences associated with the known embryonic nutrition shift (yolk feeding to placental feeding) that occurs during the gestation of this placentatrophic species. Together these results suggest that at birth, the δ¹⁵N and δ¹³C values of R. terraenovae are likely higher than somewhat older neonates whose postpartum feeding habits have restructured their isotope profiles to reflect their postembryonic diet.     

Improving estimates of trophic shift (Δδtrophic) for diet reconstruction studies using enzyme activities

For diet reconstruction studies using stable isotopes, accurate estimates of trophic shift (Δδ_trophic) are necessary to get reliable results. Several factors have been identified which affect the trophic shift. The goal of the present experiment was to test whether measurements of the activities of enzymes could improve the accuracy of estimation of trophic shift in fish. Forty-eight Nile tilapia (Oreochromis niloticus) were fed under controlled conditions with two diets differing in their protein content (21 and 41%) each at four different levels (4, 8, 12 and 16 g kg^? 0.8 d^? 1). At the end of the feeding experiment, proximate composition, whole body δ¹³C and δ¹⁵N as well as the activities of enzymes involved in anabolism and catabolism were measured. Step-wise regression specified contributing variables for Δδ¹⁵N (malic enzyme, aspartate aminotransferase and protein content) and Δδ¹³C_{lipid-free material} (aspartate aminotransferase and protein content). Explained variation by using the significant main effects was about 70% for Δδ¹⁵N and Δδ¹³C_{lipid-free material}, respectively. The results of the present study indicate that enzyme activities are suitable indicators to improve estimates of trophic shift.     

Stable isotope fractionation between maternal and embryo tissues in the Bonnethead shark (<Emphasis Type="Italic">Sphyrna tiburo</Emphasis>)

Evaluating tissue fractionation between mothers and their offspring is fundamental for informing our interpretation of stable isotope values in young individuals and can provide insight into the dynamics of maternal provisioning. The objectives of this study were to investigate the isotopic relationships between maternal reproductive (i.e., yolk, yolk-sac placenta) and somatic tissues (i.e., muscle and liver) relative to embryos in the Bonnethead Shark Sphyrna tiburo, to evaluate the fractionation of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes between these tissues. Additionally, we examined intra-uterine variability in the isotopic relationships to ascertain whether this species may exhibit variable nutrient allocation. Embryos showed similar magnitudes of enrichment in ¹³C (i.e., Δδ¹³C, difference between adult and embryo) relative to adult tissues (Δδ¹³C?=?~1.0‰). However, embryos were depleted in ¹⁵N relative to adult muscle tissues (Δδ¹⁵N?=??1.0‰), a finding that contrasts Δδ¹⁵N values reported for other placentotrophic sharks. Embryo-muscle Δδ¹⁵N was correlated with length, supporting the contention that the magnitude of enrichment between embryonic and maternal tissues results from the shift from yolk to placental feeding. Embryo δ¹⁵N and Δδ¹⁵N values showed significant intra-uterine variability; a result not observed for δ¹³C and Δδ¹³C values. The contrasting patterns in fractionation among placentotrophic sharks highlight the importance of evaluating these relationships across elasmobranch taxa with consideration for different tissues, reproductive strategies and stages of gestation. The divergent findings support future evaluation of stable isotope relationships between mothers and offspring for purposes of estimating inherent isotopic variability and how this variability may inform physiological and dietary mechanisms.     

Stable Isotope Trophic Shifts in White-Tailed Deer

Abstract Differences between diet and tissue isotope values known as trophic shifts (Δδ¹³C and Δδ¹⁵N) occur during digestion and assimilation of consumed food. Consideration of trophic shifts is essential when using stable isotopes for dietary reconstruction but has received little attention for cervids. Therefore, our purpose was to determine C and N trophic shifts in tissues of captive white-tailed deer (Odocoileus virginianus) fed corn and alfalfa in known amounts over a 4-month period. Antler has also received limited consideration for use in dietary reconstruction, thus, we analyzed tissue to expose variation among locations along the main beam and between antler components. We collected antler, hair, red blood cells (RBCs), and serum at the end of the feeding trial and analyzed them to determine C (δ¹³C) and N (δ¹⁵N) isotope values. Trophic shifts occurred between diet and all tissues for both isotopes with mean Δδ¹³C = 1.19 ± 2.23% and Δδ¹⁵N = 4.93 ± 0.74%. Antler trophic shifts were greater than those in all other tissues for δ¹³C, whereas antler and RBCs shared similar trophic enrichment over diet but differed from hair and serum for Δδ¹⁵N. Trophic shift values were significantly related to diet in hair and serum for δ¹³C and antler and RBCs for Δδ¹⁵N. Isotope values for antler core and periphery plus antler locations along the main beam did not vary. Antler collagen significantly varied from whole antler for δ¹³C but not δ¹⁵N. Our findings provide mean trophic shift values by tissue that can be used for dietary reconstruction in the study and management of cervids.     

A Method for the Determination of Furanose Ring Coordinates in its Pseudorotation Circuit for Different Amplitudes of Pucker

Abstract

Interconversion between energetically favored molecular conformations must proceed through less favored intermediate states. Thus, a knowledge of the nucleotide furanose ring conformations, other than the crystallographically well-determined ones, are of interest in investigating nucleotide conformational energies and dynamics. The sugar ring flexibility affects the conformation and dynamics of the monomer and determines the range of feasible nucleic acid secondary and tertiary structures. We have generated furanose geometries for varying amplitudes of pucker over its entire range of pseudorotation by making use of a ring closure procedure and the empirical dependence of endocyclic bond lengths and bond angles on sugar pucker. Atomic coordinates are tabulated here for the furanose ring at pseudorotation phase angle intervals of 9° for the average amplitude (τ_m) of pucker of 39° as well as for decreased (20° and 30°) and increased (44°) values of τ_m. However, the coordinates for any values of P and τ_m can be readily calculated.     

Production of S-adenosyl- L-methionine by a mutant strain of Kluyveromyces lactis

S-Adenosyl-l-methionine (AdoMet) was produced by a mutant strain Kluyveromyces lactis AM-65 grown on whey. A full factorial design method of three factors – (NH₄)₂SO₄ (factor x ₁), corn steep liquor (factor x ₂) and l-methionine (factor x ₃) on three levels – was used to determine the optimal medium conditions for the production of AdoMet. A time course shake-flask experiment in optimal whey medium (x ₁=3.1 g l^–1, x ₂=12.7 g l^–1, x ₃=4.6 g l^–1) was also carried out and the results confirmed the results of the factorial design and subsequent quadratic modelling and optimization of AdoMet production which reached 90 mg g^–1 cell dry wt.     

Determination of the Complete Correlation Between the Sugar Ring Puckers and 5′-Exocyclic Group Rotamers in Conformationally-Flexible Nucleic Acid Components from NMR Study

Abstract

Inspection of stereochemical models suggests a possible correlation between the proportion (Y_g-/Y_t) of the g^? and t rotamers and the S pucker populations irrespective of the anti-syn conformational composition of the base. Interpretation of the NMR vicinal coupling constants in terms of conformational populations shows a decline of Y_g-/Y_t with X_s approaching zero, consistent with high unfavorability of the Ng^? conformational combination in solution, a result supported by a X-ray crystallographic data survey. Hence, the underlying assumption introduced into the present study is that the g^? rotamer and the N pucker do not coexist together in solution. Therefore, the limiting value of Y_g-/Y_t corresponding to the S pucker could be determined for each compound individually. Finally, populations and relative free energies of all conformational combinations of Ng⁺, Nt, Sg⁺, St and Sg^? (except Ng^? which is not important) have been estimated.

Results of the present study suggest several interesting regularities concerning the syn-anti effect on populations and energies of the conformational combinations in ribo- and deoxyribo-nucleosides. (a) In the anti-type nucleosides, the Ng⁺ conformation is about 2 kJ/mol more stable than Nt, but in the syn-type, the Ng⁺ and Nt have comparable energy, (b) No important changes are observed in the Ng⁺ population comparing the anti-type and syn-type of ribo- and deoxyribo-nucleosides separately, (c) The Nt is considerable stabilized and simultaneously the Sg⁺ is strongly destabilized in the syn-type nucleosides relative to the anti-type, (d) Irrespective of the syn-anti composition the St is always more stable (1–2 kJ/mol) than the Sg^? conformational combination.     

A life table study on three genetic strains of Ophryotrocha diadema (Polychaeta,Dorvilleidae)

A life-table study was performed on three strains of Ophryotrocha diadema. The wild type strain, YY (yellow eggs), was compared with a recessive mutant strain, ww (white eggs), and the F₁, hybrid, Yw.

The viability of the YY strain was greater than that of the ww strain. The hybrids were intermediate. Expectation of life. e., of zygotes were: YY 27.9, Yw 19.1, and ww 15.1 wk, respectively. The total outcome of reproduction followed the same pattern; the net reproductive rates, R ₀, were related as 1:0.62:0.47 for YY: Yw: ww.

Reproduction began in the fourth week. A maximum reproductive output during the next 4 wk was followed by a fast decline. The intrinsic rate of natural increase, r, was 0.880 per week for the YY strain, 0.903 for the Yw strain and 0.872 for the ww strain. For all strains, the first 7 wk of reproduction contributed more than 99% of the Lotka equation σ e ^?rx l _x m _x = l, i.e., l _x m _x values at older ages would not substantially affect population growth. In this 7–wk period (and the previous nonreproductive weeks), mortality differences were small among strains. During the period of maximum reproduction the average size of egg masses was approximately the same in all strains. The heterozygote superiority was due to shorter intervals between successive spawnings.

It is suggested that in the opportunistic species O. diadema deviations from an r–selected reproductive pattern are due to small adult size and to its ancestry from a mainly K–selected, very old polychaete group.

O. diadema has proven to be a useful test animal for marine pollution research. Observed effects on survival and reproduction have been summarized in a model to demonstrate population consequences of sublethal pollutant levels.     

Miocene equatorial and southwest Pacific paleoceanography from stable isotope evidence

Stable isotope results from seven Miocene Deep Sea Drilling Projects in the equatorial and southwest Pacific Ocean, previously correlated using carbon isotope stratigraphy, have been examined, discussed, and interpreted in terms of the development of the Miocene Pacific Ocean. The most obvious features of the benthonic foraminiferal stable isotopic records are a major increase inδ¹⁸O(～1.0‰) during the Middle Miocene, a series of long-term oscillations (2–3 My) of amplitude 0.5–0.75‰ and a decrease inδ¹³C values (0.5–;1.0‰) during the latest Miocene. Planktonic foraminiferalδ¹⁸O records show different trends for high and low latitude regions. In the equatorial Pacific, planktonicδ¹⁸O values actually decrease during the Miocene whereas in the higher southern latitudes planktonicδ¹⁸O values become more positive in response to cooling surface waters.Planktonicδ¹³C records show opposite trends toδ¹⁸O with the high latitude values becoming more negative relative to the tropical regions. The development of the Miocene Pacific Ocean in terms of its vertical and horizontal thermal structure and isotopic composition is well illustrated by examining changes in the isotopic difference between planktonic and benthonic foraminifera.Δδ¹⁸O_B-P (Benthonic-Planktonic) is a measure of the thermal structure of the water column.Δδ¹⁸O_PH-PL (high latitude-low latitude) planktonic values is a measure of the latitudinal temperature gradient.Δδ¹³C_B-P is an indirect measure of nutrient concentrations in the water column, andΔδ¹³C_PH-PL measures differences in surface-water nutrient concentrations between high and low latitude.Δδ¹⁸O_B-P increases during the Miocene with the greatest increase occurring in the Middel Miocene at about 14 Ma. By the latest Miocene the isotopic gradient at Site 289 in the equatorial Pacific approaches the present-day isotopic gradient (about 4–5‰). An increase inΔδ¹⁸O_PH-PL during the Miocene suggests that the latitudinal temperature gradient increased by about 6°C to a value of 12°C in the latest Miocene between Sites 289 (Equator) and 281 (subantarctic).Δδ¹³C_B-P and Δδ¹³C_PH-PL values are relatively constant through the Early Miocene but begin to increase during the Middle Miocene. Bottom-waterδ¹³C values respond similarly at all sites, but surface-waterδ¹³C values exhibit different trends because higher latitude values begin to decrease. This decrease perhaps suggests that phosphate concentrations may have increased due to increased upwelling as the circum-Antarctic circulation system evolved its present day characteristics.The isotopic data compiled in this paper suggest that the southwest Pacific was responding uniformly to some global or at least Pacific-wide control during the Early Miocene. In the Middle Miocene the response became more complex as the low and high latitudes began to show independent trends. The changes in the thermal (vertical and latitudinal) structure probably occurred in respons to the build-up of the East Antarctic ice-sheet, intensification of bottom-water circulation and an increase in zonal circulation in surface waters in the southern hemisphere.The changes inδ¹³C (vertical and latitudinal) gradients are due to some complex interaction of sea-level, continental hypsometry, climate, and biological processes coupled with oceanic circulation changes. A strong correlation between estimated sea-level changes andδ¹³C values suggests that transgressions and regressions play a critical role in controlling the flux of oxidized organic carbon enriched in¹²C, from the continental shelves and epicontinental seas to the open ocean.     

Patterns of soil and plant nitrogen isotope composition and their relationships with climate factors in Xilingol League,Inner Mongolia,China

Background: Plant and soil nitrogen stable isotope (δ¹⁵N) can integrate several fundamental biogeochemical processes in ecosystem nitrogen dynamics, and reflect characteristics of ecosystem nitrogen cycling.

Aims: We investigated how climate change influenced plant-soil nitrogen cycling by relating soil δ¹⁵N, plant δ¹⁵N and Δδ¹⁵N (difference between soil and plant δ¹⁵N) with climatic factors.

Methods: Field investigation was conducted in temperate grasslands in Inner Mongolia during August 2015. Plant δ¹⁵N, soil δ¹⁵N and Δδ¹⁵N were determined, and their relationships with climatic factors were examined by simple regression analyses and general linear models.

Results: Soil δ¹⁵N was significantly higher than plant δ¹⁵N, and there was a positive linear correlation between them. Soil and plant δ¹⁵N were negatively related with mean annual precipitation (MAP) and positively with mean annual temperature (MAT); conversely, Δδ¹⁵N was positively related with MAP and negatively with MAT.

Conclusion: Soil δ¹⁵N was dominantly controlled by MAT, while it was MAP for plant δ¹⁵N. Climate factors influenced plant δ¹⁵N not only through their effects on soil nitrogen dynamics but also strategies of plant nitrogen acquisition. Thus, compared with plant δ¹⁵N, soil δ¹⁵N can more accurately reflect soil nitrogen dynamics, while plant δ¹⁵N may integrate soil nitrogen dynamics and plant nitrogen acquisition.     

N5-(l-1-Carboxyethyl)-l-ornithine: NADP+ oxidoreductase inStreptococcus lactis: Distribution,constitutivity, and regulation

N⁵-(l-1-Carboxyethyl)-l-ornithine: NADP⁺ oxidoreductase [N⁵-(CE)ornithine synthase] catalyzes the NADPH-dependent reductive condensation between pyruvic acid and the terminal amino group ofl-ornithine andl-lysine to yield N⁵-(l-1-carboxyethyl)-l-ornithine and N⁶-(l-1-carboxyethyl)-l-lysine respectively. Polyclonal antibodies against N⁵-(CE)ornithine synthase purified fromStreptococcus lactis K1 have been used for the immunochemical (Western blot) detection and sizing of this enzyme in various lactic acid bacteria. The enzyme was confined to about one-half of the strains ofS. lactis examined. N⁵-(CE)ornithine synthase is constitutive, and in strains K1, 6F3, and (plasmid-free)H₁-4125 the native enzyme is a tetramer composed of identical subunits of M_r=38,000. However, in other strains, including 133 (ATCC 11454), C₁₀, and ML₈, the molecular weight of the native enzyme is approximately 130,000 and the corresponding subunit M_r=35,000. Analyses of the amino acid pool components maintained byS. lactis K1 during growth in medium containing [¹⁴C] labeled and unlabeled arginine have revealed that (i) exogenous arginine is the precursor of intracellular ornithine, citrulline, and N⁵-(CE)ornithine, and (ii) the rates of turnover of ornithine and citrulline were considerably faster than that of N⁵-(CE)ornithine. These data account for the biosynthesis and accumulation of N⁵-(CE)ornithine byS. lactis.     

Simplified formulas for three-way chi-square testing

In order to test against contingency in a 3-way table, simplified X²-formulas are given for (1) the general r xcxl-table, (2) for the rxcx2-table, (3) for the 2x2xl-table, and (4) for the 2×2×2-table. The tests are valid only if a sample of N individuals is observed as to 3 discrete or discretisized (dichotomized) variables which are, under H₀, assumed to be totally independent.     

Configurational effects on conformational properties of cyclic nucleotides. I. Theoretical calculations of conformer preferences in α-nucleoside 3′,5′ cyclic monophosphates

A comparative study has been made of the configurational effects on the conformational properties of α- and β-anomers of purine and pyrimidine nucleoside 3′,5′,-cyclic monophosphates and their 2′-arabino epimers. Correlation between orientation of the base and the 2′-hydroxyl group have been studied theoretically using the PCILO (Perturbative Configuration Interaction using Localized Orbitals) method. The effect of change in ribose puckering on the base-hydroxyl interaction has also been studied. The result show that steric repulsions and stabilizing effects of intramolecular hydrogen bonding between the base and the 2′-hydroxyl (OH) group are of major importance in determining configurations of α-anomers and 2′-arabino-β-epimers. For example, hydrogen bonding between the 2′-hydroxyl group and polar centers on the base ring is clearly implicated as a determinant of syn-anti preferences of the purine (adenine) or pyrimidine (uracil) bases in α-nucleoside 3′,5′-cyclic monophosphates. Moreover, barrier heights for interconversion between conformers are sensitive to ribose pucker and 2′-OH orientations. The result clearly show that a change in ribose-ring pucker plays an essential role in relieving repulsive interaction between the base and the 2′-hydroxyl group. Thus a C2′-exo-C3′-endo (₂T³) pucker is favored for α-anomers in contrast with the C4′-exo-C3′-endo (₄T³) from found in β-compounds.     

An evaluation of lipid extraction techniques for interpretation of carbon and nitrogen isotope values in bottlenose dolphin (Tursiops truncatus) skin tissue

We studied the effects of two common chemical extraction techniques on bottlenose dolphin (Tursiops truncatus) skin tissues with the intent to develop a mathematical lipid correction for dolphin skin δ¹³C. One method employs a hot solvent mixture (chloroform and methanol) while the other method requires washing the samples with cold solvent followed by water. The water wash method resulted in significant alteration of tissue δ¹⁵N. We found no correlation between change in sample mass and C/N or between change in sample mass and the change in δ¹³C (Δδ¹³C) following lipid extraction. Although Δδ¹³C was positive following lipid extraction (mean = 1.6‰ and 1.2‰, for the two methods), there was no correlation between C/N and Δδ¹³C for either method. Cumulatively, these results prevented us from applying a mathematical lipid normalization. Based on our findings and consideration of previously reported results, we suggest that applying these extraction techniques to dolphin skin with C/N < 4.5 introduces greater uncertainty than is warranted. We recommend against lipid correction for dolphin skins with C/N < 4.5, but stress that the resulting uncertainty in δ¹³C needs to be accounted for when implementing isotope mixing models to assess diet or organic matter sources.     

A quantitative study of organic phosphate-amine interaction by 31P nuclear magnetic resonance

Interactions between the phosphate group of 4-deoxypyridoxine 5′-phosphate and different protonated amines were quantitatively measured by means of {³¹P}-¹H nuclear magnetic double resonance technique combined with pD titration. An interaction of the phosphate group with added amine resulted in a measurable difference in the ³¹P chemical shift of these phosphate-containing samples with and without amine [Δδ(³¹P)]. Basic amino acids and biogenic amines had significant measurable Δδ(³¹P) values. No interactions were observed for acidic or neutral α, β and γ-amino acids.     

Getting to the fat of the matter: models,methods and assumptions for dealing with lipids in stable isotope analyses

Within an organism, lipids are depleted in ¹³C relative to proteins and carbohydrates (more negative δ¹³C), and variation in lipid content among organisms or among tissue types has the potential to introduce considerable bias into stable isotope analyses that use δ¹³C. Despite the potential for introduced error, there is no consensus on the need to account for lipids in stable isotope analyses. Here we address two questions: (1) If and when is it important to account for the effects of variation in lipid content on δ¹³C? (2) If it is important, which method(s) are reliable and robust for dealing with lipid variation? We evaluated the reliability of direct chemical extraction, which physically removes lipids from samples, and mathematical normalization, which uses the carbon-to-nitrogen (C:N) ratio of a sample to normalize δ¹³C after analysis by measuring the lipid content, the C:N ratio, and the effect of lipid content on δ¹³C (Δδ¹³C) of plants and animals with a wide range of lipid contents. For animals, we found strong relationships between C:N and lipid content, between lipid content and Δδ¹³C, and between C:N and Δδ¹³C. For plants, C:N was not a good predictor of lipid content or Δδ¹³C, but we found a strong relationship between carbon content and lipid content, lipid content and Δδ¹³C, and between and carbon content and Δδ¹³C. Our results indicate that lipid extraction or normalization is most important when lipid content is variable among consumers of interest or between consumers and end members, and when differences in δ¹³C between end members is <10–12‰. The vast majority of studies using natural variation in δ¹³C fall within these criteria. Both direct lipid extraction and mathematical normalization reduce biases in δ¹³C, but mathematical normalization simplifies sample preparation and better preserves the integrity of samples for δ¹⁵N analysis.     

Flexibility of DNA and RNA upon Binding to Different Metal Cations. An Investigation of the B to A to Z Conformational Transition by Fourier Transform Infrared Spectroscopy

Abstract

The interaction of DNA and RNA with Cu(II), Mg(II), [Co(NH₃)₆]³⁺ [Co(NH₃)₅Cl]²⁺ chlorides and, cis- and trans-Pt(NH₃)₂Cl₂ (CIS-DDP, trans-DDP) has been studied by Fourier Transform Infrared (FT-IR) spectroscopy and a correlation between metal-base binding and conformational transitions in the sugar pucker has been established. It has been found that RNA did not change from A-form on complexation with metals, whereas DNA exhibited a B to Z transition. The marker bands for the A-form (C′₃-endo-anti conformation) were found to be near 810–816 cm^?1, while the bands at 825 and 690 cm^?1 are marker bands for the B- conformation (C′₂-endo, anti), The B to Z (C₃′-endo, syn conformation) transition is characterized by the shift of the band at 825 cm^?1 to 810–816 cm^?1 and the shift of the guanine band at 690 cm^?1 to about 600–624 cm^?1.     

Production of acetone and butanol by Clostridium acetobutylicum in continuous culture with cell recycle

Summary To increase the solvent productivity of the acetone-butanol fermentation, a continuous culture of Clostridium acetobytylicum with cell recycling was used. At a dry cell mass concentration of 8 g l^-1 and a dilution rate of D=0.64 h^-1, a solvent productivity of 5.4 g l^-1 h^-1 was attained. To prevent degeneration of the culture, which occurs with high concentrations of solvents (acetone, butanol and ethanol), different reactor cascades were used. A two-stage cascade with cell recycling and turbidostatic cell concentration control turned out to be the best solution, the first stage of which was kept at relatively low cell and product concentrations. A solvent productivity of 3 and 2.3 g l^-1 h^-1, respectively, was achieved at solvent concentrations of 12 and 15 g l^-1.Symbols D Dilution rate (h^-1) - r _p solvent productivity (g l^-1 h^-1) - s residual glucose concentration (g l^-1) - V _R reactor volume (l) - V _O overall volume (l) - x (dry) cell mass concentration (g l^-1) - Y _P/S solvent yield (g g^-1)