Carbon isotope composition in relation to leaf gas exchange and environmental conditions in Hawaiian Metrosideros polymorpha populations

Summary Carbon isotope composition, photosynthetic gas exchange, and nitrogen content were measured in leaves of three varieties of Metrosideros polymorpha growing in sites presenting a variety of precipitation, temperature and edaphic regimes. The eight populations studied could be divided into two groups on the basis of their mean foliar ¹³C values, one group consisting of three populations with mean ¹³C values ca.-26 and another group with ¹³C values ca.-28. Less negative ¹³C values appeared to be associated with reduced physiological availability of soil moisture resulting from hypoxic conditions at a poorly drained high elevation bog site and from low precipitation at a welldrained, low elevation leeward site. Gas exchange measurements indicated that foliar ¹³C and intrinsic wateruse efficiency were positively correlated. Maximum photosynthetic rates were nearly constant while maximum stomatal conductance varied substantially in individuals with foliar ¹³C ranging from-29 to-24. In contrast with the patterns of ¹³C observed, leaf nitrogen content appeared to be genetically determined and independent of site characteristics. Photosynthetic nitrogenuse efficiency was nearly constant over the range of ¹³C observed, suggesting that a compromise between intrinsic water- and N-use efficiency did not occur. In one population variations in foliar ¹³C and gas exchange with leaf cohort age, caused the ratio of intercellular to atmospheric partial pressure of CO₂ predicted from gas exchange and that calculated from ¹³C to be in close agreement only in the two youngest cohorts of fully expanded leaves. The results indicated that with suitable precautions concerning measurement protocol, foliar ¹³C and gas exchange measurements were reliable indicators of potential resource use efficiency by M. polymorpha along environmental gradients.     

Effect of size on the energy acquired in species of the fish from a neotropical reservoir,Brazil

In this paper we analysed autotrophic sources of the carbon ( ¹³C) and the trophic position ( ¹⁵N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C₄ grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of ¹³C recorded for middle sized individuals is attributed to the large contribution of C₄ plants in their diet. Small individuals sampled upstream also receive similar contribution from C₄ plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C₄ plants. The ¹³C negative character of small individuals from downstream is due to the larger contribution of C₃ plants (except periphyton). At larger sizes we found intermediate ¹³C values. The ¹⁵N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the ¹³C concentration in the muscle, except for small individuals, when the values were equal.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

New organisms—novel genetics

This report describes a method for quantifying -endotoxin contents in spray-dried preparations ofBacillus thuringiensis strain GC-91. -Endotoxin is solubilized in the pro-toxin form and separated from other soluble compounds by ion exchange chromatography. The method does not discriminate between the different -endotoxins produced by strain GC-91. It is suitable for quality control, since -endotoxin concentrations found in different preparations correlate inversely with the LC 50 in bioassays on artificial diet against freshly hatched larvae ofSpodoptera littoralis. A typical batch of spray-dried material contains 1.22%±0.08% -endotoxin. The method is most accurate with preparations containing 0.5 to 2.0% toxin, for which triplicate estimations give standard errors close to±0.2%.     

Comparisons of δ13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants

Summary The ¹³C values of submerged aquatic plants from contrasting but relatively defined habitats, and the ¹³C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the ¹³C values of dissolved inorganic carbon in the water were also measured. Plant ¹³C values in the vicinity of-40 to-50 were found in rapidly flowing spring waters with carbonate ¹³C values of-16 to-21, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO₂ via RuP₂ carboxylase. Plant ¹³C values in the vicinity of-10 to-15 in sluggish water with carbonate ¹³C values of about-5 were observed, consistent with the notion that boundary layer diffusion and/or HCO₃ ^- uptake may determine the ¹³C value of submerged aquatic plants in these circumstances. Comparisons of ¹³C values of the same or related species growing in waters of similar carbonate ¹³C value but different flow rates confirmed this view; more negative ¹³C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the ¹³C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The ¹³C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO₂, as opposed to atmospheric carbon. The contributions of these variations in ¹³C of the carbon source, and of isotope fractionation in diffusion, to the ¹³C value of submerged parts of dimorphic plants is discussed.     

The use of BRM-activated killer cells in adoptive immunotherapy: A pilot study with nine advanced cancer patients

Adoptive immunotherapy using MHC-nonrestricted-lymphocytes, peripheral blood T cells and NK cells was devised. Peripheral blood mononuclear cells (3 x 107) were selected by immobilization to anti-CD3 monoclonal antibody for 4 days and cultured for 2 weeks in the presence of IL-2. Thereafter they were reactivated by 500 U/ml of IFN- and 1000 U/ml of IL-2 for 1 hour. Enhancement of NK and LAK activities was confirmed. Peripheral blood T cells proliferated in response to immobilized anti-CD3 antibody (3% to 30%). Approximately 6 x 109 BRM-activated killer (BAK) cells composed of CD56+ T cells and CD56+ NK cells, were dispensed to cancer patients via intravenous drip infusion. Nine patients were treated with BAK cells every 2 weeks or every month on an outpatient basis. During the course of adoptive immunotherapy, the crossed affinity immunoelectrophoresis (CAIE) pattern of serum immunosuppressive acidic protein (IAP) was analysed. Both the production and glycosylation pattern of IAP is changed in response to tumor enlargement and may therefore act as a marker of the disease progression. During the course of BAK therapy, the glycosylation IAP pattern of 6 patients changed from tumor (T) to normal (N). In addition, the performance status of all patients was maintained at 90–100% of the Karnofsky scale and any side effects including fever were not observed during treatments with BAK cells. Moreover, the overall quality of life (QOL) of the patients, scored at the Face scale was favorable. In addition, blood levels of activated T cells producing IFN- were assayed as an indication marker of BAK therapy. The normal range of IFN- producing T cells comprised 6.9 ± 0.9% of peripheral blood mononuclear cells (PBMC), according to a single cell FACScan analyses of PBMCs derived from normal individuals. IFN- producing T cells of Patients No. 8 and 9, who received extensive chemotherapy before initiation of BAK therapy, comprised only 0.2% and 2% of PBMC, respectively. These patients died 3 and 6 months after beginning BAK therapy. Peripheral blood T cells of Patients Nos. 1–7 proliferated in response to immobilized anti-CD3 antibody and the frequency of IFN- producing T cells in PBMC preparation of these patients were over 3% before initiation of BAK therapy. Since our data show a positive correlation between survival time and initial T cell counts, a low frequency of these cells may contraindicate BAK therapy.     

15N natural abundance studies in Australian commercial sugarcane

The measurement of natural ¹⁵N abundance is a well-established technique for the identification and quantification of biological N₂ fixation in plants. Associative N₂ fixing bacteria have been isolated from sugarcane and reported to contribute potentially significant amounts of N to plant growth and development. It has not been established whether Australian commercial sugarcane receives significant input from biological N₂ fixation, even though high populations of N₂ fixing bacteria have been isolated from Australian commercial sugarcane fields and plants. In this study, ¹⁵N measurements were used as a primary measure to identify whether Australian commercial sugarcane was obtaining significant inputs of N via biological N₂ fixation. Quantification of N input, via biological N₂ fixation, was not possible since suitable non-N₂ fixing reference plants were not present in commercial cane fields. The survey of Australian commercially grown sugarcane crops showed the majority had positive leaf ¹⁵N values (73% >3.00, 63% of which were >5.00), which was not indicative of biological N₂ fixation being the major source of N for these crops. However, a small number of sites had low or negative leaf ¹⁵N values. These crops had received high N fertiliser applications in the weeks prior to sampling. Two possible pathways that could result in low ¹⁵N values for sugarcane leaves (other than N₂ fixation) are proposed; high external N concentrations and foliar uptake of volatilised NH₃. The leaf ¹⁵N value of sugarcane grown in aerated solution culture was shown to decrease by approximately 5 with increasing external N concentration (0.5–8.0 mM), with both NO₃ ^– and NH₄ ⁺ nitrogen forms. Foliar uptake of atmospheric NH₃ has been shown to result in depleted leaf ¹⁵N values in many plant species. Acid traps collected atmospheric N with negative ¹⁵N value (–24.45±0.90) from above a field recently surface fertilised with urea. The ¹⁵N of leaves of sugarcane plants either growing directly in the soil or isolated from soil in pots dropped by 3.00 in the same field after the fertiliser application. Both the high concentration of external N in the root zone (following the application of N-fertilisers) and/or subsequent foliar uptake of volatilised NH₃ could have caused the depleted leaf ¹⁵N values measured in the sugarcane crops at these sites.     

γδ T-cell receptor repertoire in human peripheral blood and thymus

T-cell clones expressing the T-cell receptor (Tcr) were generated from peripheral blood lymphocytes (PBLs) and from a thymus sample. In the panel of ten thymus-derived clones, four Tcr phenotypes [as defined by the reaction of monoclonal antibodies (mAbs) directed against known V and V regions] were identified. All the clones lacked expression of the V3 V region, while seven clones were V1+ . V1 was found in combination with V9 or with undefined VVregions. In addition, two other Tcr phenotypes were identified on these clones: V9⁺ V1^– V3^– and V9^– V1^– V3^– One of the clones expressed CD4 and another was CD8positive. The remaining clones were CD4^– CD8^–. In the panel of 76 PBL-derived, Tcr-bearing clones, five Tcr phenotypes could be identified. In contrast to the thymus-derived clones, 30% of the clones were V3⁺ whereas V1 was expressed by a minority of the clones only. One clone was CD4-positive and approximately 30% of the clones were CD8-positive. Four of the five mAb-defined Tcr phenotypes could be identified on both thymus and PBL-derived T-cell clones. However, biochemical analysis of the Tcrs demonstrates differences in the usage of Ct- and C2-encoded y chains by T cells derived from the thymus and PBLs. The results therefore indicate that, at the clonal level, similarities and differences exist between the Tcr repertoires expressed in the thymus and by PBLs. Furthermore, they indicate that combinatorial Tcr heterogeneity is larger than has so far been described. The receptor diversity, combined with the potential of Tcr+ cells to express CD4 or CD8, indicates that these cells are a heterogeneous population that might mediate a number of immune functions.     

Heterogeneous binding and killing behaviour of human γ/δ-TCR+ lymphokine-activated killer cells against K562 and Daudi cells

Effector-target conjugates, formed by coincubation of lymphokine-activated killer (LAK) cells with either K562 or Daudi cells, were separated from single cells by Percoll sedimentation. The occurrence of various CD molecules (CD3, CD56, CD57, CD16, /-TCR) was compared in both fractions. Only LAK cells expressing the / T cell receptor (TCR) were found in a significantly increased percentage in fractions containing conjugates indicating that /-TCR⁺ LAK cells were preferably bound to target cells at the time of separation. In order to determine whether /-TCR⁺ LAK cells also show a preferred killing activity against the targets, cultures enriched with or depleted of /-TCR⁺ cells were established. Against K562 cells, /-TCR⁺-enriched cultures showed a greatly reduced killing activity compared to LAK bulk cultures or cultures depleted of /-TCR⁺ cells. Using Daudi cells as targets the enriched fraction revealed a slightly increased killing activity compared to bulk cultures or depleted fractions. Preincubation of /-TCR⁺ LAK cells with anti-/ or anti-CD3 mAb resulted in a distinct increase of the killing activity against K562 cells, but in only a slightly enhanced activity against Daudi cells. It is postulated that /-TCR⁺ LAK cells use the same adhesion mechanism for both targets but that only Daudi cells express a specific ligand for the /-TCR. Occupation of the /-TCR/CD3 complex by mAb, however, seems to substitute for the absent epitope on K562 cells by eliciting stimulatory signals in /-TCR⁺ LAK cells which, in combination with the binding stimulus, trigger cytolytic activity.This work was supported by the Hartmann-Müller Foundation, Zürich     

The skeletal isotopic composition as an indicator of ecological and physiological plasticity in the coral genus<Emphasis Type="Italic"> Madracis</Emphasis>

Three species of the reef coral genus Madracis display skeletal isotopic characteristics that relate to depth, colony topography, and consequently to coral physiology. The joint interpretation of skeletal ¹³C and ¹⁸O provides information on the ecological plasticity and adaptation to depth of a coral species. Isotopic results are most easily understood in terms of kinetic effects, which reduce both ¹⁸O and ¹³C below isotopic equilibrium values, and metabolic effects, which only influence the skeletal ¹³C. Madracis mirabilis is adapted to depths shallower than 20 m, and shows the greatest range in kinetic effects and the strongest metabolic ¹³C enrichments caused by symbiont photosynthesis. Madracis formosa lives deeper than 40 m, and shows a reduced range of kinetic effects and relatively weak metabolic ¹³C enrichments. Madracis pharensis inhabits depths from 5 to >60 m, and does not attain the strength of kinetic effects of either of the other two species, apparently because it is not quite as well adapted to rapid growth at either extreme.     

Mean oxygen-isotope signatures in Porites spp. corals: inter-colony variability and correction for extension-rate effects

The assessment of inter-colony variability in the mean skeletal ¹⁸O signatures of modern Porites spp. corals is a prerequisite for the estimation of past mean climate conditions based on fossil colonies. Here we show that the mean ¹⁸O signatures of Porites spp. corals from the northern end of the Gulf of Aqaba (Red Sea) with mean extension rates between 0.2 and 1.5 cm/year can have an inter-colony variability as large as 1.28. At extension rates of less than 0.6 cm/year the mean coral ¹⁸O values of the individual colonies are strongly dependent on the mean extension rate, with increasingly higher ¹⁸O values corresponding to decreasing extension rate. This suggests that extension-rate-related kinetic isotope disequilibrium effects are responsible for a large proportion of the inter-colony differences in the mean coral ¹⁸O signatures. A correction procedure for these effects based on the relationship between mean ¹⁸O values and mean extension rate reduces the variability of mean coral ¹⁸O values among the individual colonies to 0.43. Although certainly not perfect, the correction procedure enables a better assessment of mid-Holocene climate conditions at this location based on Porites spp. with mean extension rates of less than 0.6 cm/year.     

Stable oxygen isotopes in<Emphasis Type="Italic"> Porites</Emphasis> corals monitor weekly temperature variations in the northern Gulf of Aqaba,Red Sea

In order to assess the ability of Porites corals to accurately record environmental variations, high-resolution (weekly/biweekly) coral ¹⁸O records were obtained from four coral colonies from the northern Gulf of Aqaba, which grew at depths of 7, 19, 29, and 42 m along one transect. Adjacent to each colony, hourly temperatures, biweekly salinities, and monthly ¹⁸O of seawater were continuously recorded over a period of 14 months (April 1999 to June 2000). Contrary to water temperature, which shows a regular and strong seasonal variation and change with depth, seawater ¹⁸O exhibits a weak seasonality and little change with depth. Positive correlations between seawater ¹⁸O and salinity were observed. The two parameters were related to each other by the equation ¹⁸O _Seawater (, VSMOW) = 0.281 × Salinity – 9.14. The high-resolution coral ¹⁸O records from this study show a regular pattern of seasonality and are able to capture fine details of the weekly average temperature records. They resolve more than 95% of the weekly average temperature range. On the other hand, attenuation and amplification of coral seasonal amplitudes were recorded in deep, slow-growing corals, which were not related to environmental effects (temperature and/or seawater ¹⁸O) or sampling resolution. We propose that these result from a combined effect of subannual variations in extension rate and variable rates of spine thickening of skeletal structures within the tissue layer. However, no smoothing or distortion of the isotopic signals was observed due to calcification within the tissue layer in shallow-water, fast-growing corals. The calculations from coral ¹⁸O calibrations against the in situ measurements show that temperature (T) is related to coral ¹⁸O ( _c ) and seawater ¹⁸O ( _w ) by the equation T (°C) = –5.38 ( _c – _w ) –1.08. Our results demonstrate that coral ¹⁸O from the northern Gulf of Aqaba is a reliable recorder of temperature variations, and that there is a minor contribution of seawater ¹⁸O to this proxy, which could be ignored.     

Subdomain organization ofBacillus thuringiensis entomocidal proteins'' N-terminal domains

N-Terminal domain (65 kD) of -endotoxin produced byBacillus thuringiensis ssp.alesti, as shown by limited proteolysis, consists of two subdomains of molecular mass 30 and 33 kD that correspond, respectively, to conservative and variable regions of the -endotoxin primary structure. Furthermore, proteolysis of these subdomains leads to their conversion into at least two fragments of molecular mass 10 kD stable to proteinase action. Such a pattern of molecular organization appears to be common for several structurally related -endotoxins that belong to thekurstaki group. Entomicidal protein produced by ssp.israelensis (70 kD), which differs strongly fromalesti and otherkurstaki group -endotoxins, retains a similar type of molecular organization and consists of two subdomains with molecular mass of 35 kD. Apparently, the characteristic pattern of the -endotoxins' molecular structure reflects separation of functions (e.g., host recognition and toxicityper se) between domains and subdomains of these proteins.     

Solution conformations of proline rings in proteins studied by NMR spectroscopy

Summary Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine -, - and -hydrogens have been made on the basis of ¹H-¹H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs -³, ³-³, ²-², ²-², and ³-³ (2.3 Å) are shorter than those in the pairs -², ²-³, ³-², ²-³, and ³-² (2.7–3.0 Å), resulting in stronger NOESY cross peaks. For the Up conformation, the ³-² and ²-³ spin-spin coupling constants are small (<3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the -², ²-³, and ³-² vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined.     

Partial mispairing and crossing-over between β0 and δ genes as the origin of the δ β0 thalassemia gene

Summary Two double heterozygous ⁰/⁰ thalassemic sibs of Mexican descent were studied. The father had a ⁰/⁰ genotype, while the mother, one sib and several maternal relatives were ⁰/⁰ heterozygotes. Parental consanguinity and an apparently low frequency of thalassemia among Mexicans suggested a possible common origin of both ⁰ and ⁰ genes. A hypothesis to explain such a possibility is proposed on the basis of a partial mispairing between ⁰ and genes followed by a crossing-over which would results in a ⁰ recombinant gene. This hypothesis could also be extended to explain the 22 gluala, 22 alaglu and 116 arghis Hb variants as recombinants from double crossing-over between and mispaired genes for which the name interstitial-Lepore is proposed.     

Involvement of polyamines in cytoplasmic male sterility of stem mustard (Brassica juncea var. tsatsai)

Changes in carbon isotope composition(¹³C) and leaf morphology associated withvegetative phase change were monitored in Metrosiderosexcelsa Sol. ex Gaertn. (family Myrtaceae). Plants of threeontogenetic states were used: juvenile seedlings, micropropagated plants in arejuvenated state, and reproductively mature plants bearing leaves with adultcharacteristics. The effects of temperature regime (32/24 °C,24/16 °C, and 16/8 °C day/night) and plantarchitecture (branched and single-stemmed plants) were studied in two separateexperiments. Although both juvenile and rejuvenated plants exhibited juvenileleaf morphology at the start of the experiments, there was no differencebetweenleaf ¹³C in these plants and that in adultplantsat this time (mean ca. –27%). Vegetative phase change occurred injuvenileand rejuvenated plants grown at 24/16 °C, and there was acorresponding increase in leaf ¹³C (from ca.–27% to –23%) in these two groups of plants. Leaf¹³C in adult plants remained relatively constant(ca. –26%) at 24/16 °C. There was little change in leaf¹³C in all plant states maintained at 32/24°C or 16/8 °C, and vegetative phase change didnot occur in juvenile and rejuvenated plants grown under these two temperatureregimes. Rejuvenated plants grown in a greenhouse also exhibited a progressivedevelopment of adult leaf morphology, accompanied by an increase in leaf¹³C, an effect that was more pronounced insingle-stemmed (from –26.4% to ca. –24%) than in branched plants. Itis suggested that increasing ¹³C in juvenile andrejuvenated plants undergoing phase change is a result of reduced sink strengthin single-stemmed plants, and to a lesser extent within each branch of branchedplants, causing reduced stomatal conductance and photosynthesis.     

Microanalysis of C and O isotopes of azooxanthellate and zooxanthellate corals by ion microprobe

We have determined the ¹⁸O and ¹³C values of azooxanthellate (Lophelia pertusa) and zooxanthellate (Porites lutea) corals at a micrometer scale using an ion microprobe (SIMS—secondary ion mass spectrometry). In P. lutea, centers of calcification are small (10 to 15 m) and difficult to locate during measurements. In L. pertusa, they are large (50 m) and arranged in lines of centers of calcification. Our results show that centers of calcification in L. pertusa have a restricted range of variation in ¹⁸O [-2.8±0.3 (PDB)], and a larger range in ¹³C [14.3 to 10.9 (PDB)]. Surrounding skeletal fibers exhibit large isotopic variation both for C and O (up to 12), and ¹³C and ¹⁸O are positively correlated. The C and O isotopic compositions of the center of calcification deviate from this linear trend at the lightest ¹⁸O values of the surrounding fibers. Ion microprobe results on P. lutea demonstrate also a large range of variation for the ¹⁸O values (up to 10). No correlation is found with C isotopes that exhibit, in comparison with L. pertusa, a small range of variation (2). This variation of ¹⁸O at a micrometer scale is probably the result of two processes: (1) an isotopic equilibrium calcification with 1 pH unit variation in the calcification fluid as indicated by direct measurements of coelenteron pH in the coral Galaxea fascicularis (Al-Horani et al. 2003) and (2) a kinetic fractionation. The ¹³C apparent disequilibrium in P. lutea may be the result of mixing between metabolic CO₂ (respiration) and dissolved inorganic carbon (DIC) coming directly from seawater.     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Feeding level and individual metabolic rate affect δ13C and δ15N values in carp: implications for food web studies

Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animals diet. One prerequisite for a precise calculation is the determination of the diet-tissue fractionation factor. Isotopic ratios in animals are not only affected by the composition of the diet, but also by the amount of food consumed. Previous findings regarding the latter point are controversial. As stable isotope analyses have often been used to investigate aquatic food webs, an experiment with carp (Cyprinus carpio L.) was carried out to test the influence of the feeding level and individual metabolic rate on ¹³C and ¹⁵N values of the whole body. After an initial phase, 49 carp were assigned randomly to four groups and fed the same diet at different levels for 8 weeks. For 15 fish, the energy budget was determined by indirect calorimetry. Feed and individual fish were analysed for their proximate composition, gross energy content and ¹³C and ¹⁵N values. ¹³C and ¹⁵N values differed significantly at different feeding levels. While ¹³C values of the lipids and ¹⁵N values decreased with increasing feeding rate, ¹³C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between ¹³C values and the percentage retention of metabolizable energy. Our results show that reconstructing the diets of fish from the isotopic ratios when the feeding level and individual metabolic rates are unknown would introduce an error into the data used for back-calculation of up to 1 for both ¹³C and ¹⁵N values and may have substantial effects on the results of calculated diets. As other workers have pointed out, the development and application of stable isotopes to nutritional ecology studies is a field in its infancy and gives rise to erroneous, misleading results without nutritional, physiological and ecological knowledge.     

Stacking Interactions of nucleobases: NMR-Investigations I. Selfassociation of N6,N9-Dimethyladenine and N6-Dimethyl-N9-Ethyladenine

The selfassociation of N⁶,N⁹-dimethyladenine and N⁶-dimethyl-N⁹-ethyladenine has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model with three NMR parameters (the monomer shift _M and two complex shifts ₂ and ₃).The dependence of the thermodynamic quantities on the NMR parameters is discussed. Special attention is given to the determination of _M and its temperature dependence.Calculations with ₃=2· ₂ and _M taken independently of temperature result in an average entropy _S =–17.9±1.8 e.u. for N⁶,N⁹-dimethyladenine and _S =–16.7±1.7 e.u. for N⁶-dimethyl-N⁹-ethyladenine and in an average enthalpy _H=–7.2±0.6 kcal· mol^–1 for both substances investigated.Part of the Ph.D. Theses of W. Schimmack and H. Sapper.Dedicated to Professor Dr. A. Schraub on the occasion of his 65th birthday.