Incorporation of carbon originating from CO2 into different compounds of soil microbial biomass and soil organic matter

In general, soils without the vegetation growing on them are regarded as sources of CO2. However, there are indications that CO2 is also fixed by soil microorganisms. Although this process is not significant from a quantitative point of view, it may change the isotopic composition of soil organic matter. Therefore, we conducted an incubation study with soil and 13C-labeled CO2 to investigate this process. We found that the label was transferred from CO2 into organic compounds in soil. At the end of a 61-day incubation period, 1.3 micromol C g(-1) soil, corresponding to approximately 0.08% of the soil organic carbon, had been fixed. CO2 may, therefore, be an additional source of soil organic carbon. Compound-specific analysis of amino sugars, amino acids, and fatty acids indicated that the label is incorporated into microbial, mainly bacterial, biomass. All groups of microorganisms were involved in the assimilation of CO2, but the relatively high enrichment of mono-unsaturated and mid-chain branched fatty acids indicates that gram negative bacteria and actinomycetes may be slightly more important in this process than other groups of microorganisms.     

Electronic coupling in the excited electronic state of stacked DNA base homodimers

The nature of the electronic coupling of stacked nucleic acid bases adenine (A), thymine (T), and cytosine (C), in A-A, T-T, and C-C complexes in their excited states was investigated; a different character of the electronic coupling for the T-T complex was shown.     

Evaluation of the performance of high temperature conversion reactors for compound-specific oxygen stable isotope analysis

In this study conversion conditions for oxygen gas chromatography high temperature conversion (HTC) isotope ratio mass spectrometry (IRMS) are characterised using qualitative mass spectrometry (IonTrap). It is shown that physical and chemical properties of a given reactor design impact HTC and thus the ability to accurately measure oxygen isotope ratios. Commercially available and custom-built tube-in-tube reactors were used to elucidate (i) by-product formation (carbon dioxide, water, small organic molecules), (ii) 2nd sources of oxygen (leakage, metal oxides, ceramic material), and (iii) required reactor conditions (conditioning, reduction, stability). The suitability of the available HTC approach for compound-specific isotope analysis of oxygen in volatile organic molecules like methyl tert-butyl ether is assessed. Main problems impeding accurate analysis are non-quantitative HTC and significant carbon dioxide by-product formation. An evaluation strategy combining mass spectrometric analysis of HTC products and IRMS ¹⁸O/¹⁶O monitoring for future method development is proposed.     

Production of highly aligned microfiber bundles from polymethyl methacrylate via stable jet electrospinning for organic solid-state lasers

The fabrication of micron-sized poly(methyl methacrylate) (PMMA) polymer optical fibers doped with rhodamine B as an organic dye is demonstrated. Highly aligned and defect-free fibers are fabricated by using the stable jet electrospinning (SJES) method and systematically varying critical parameters such as solvent type and polymer concentration. At optimal conditions, for example, a polymer concentration of 35 wt% of PMMA in butanone, ribbon-shaped fibers with a smooth surface and diameter of about 20 μm could be spun using SJES mode and deposited on a rotating drum as target in a highly aligned manner. Photoluminescence spectra of the doped fibers excited longitudinally and transversely with a laser show an excitation peak with full-width-at-half-maximum of only 5.05 nm and a low lasing threshold at a pump energy of 0.55 μJ, indicating that SJES could become a new source of amplified optics components or organic solid-state fiber lasers.     

Comparison of methods for simultaneous identification of bacterial species and determination of metabolic activity by protein‐based stable isotope probing (Protein‐SIP) experiments

We developed a concept for analysing carbon and nitrogen fluxes in microbial communities by employing protein‐based stable isotope probing (Protein‐SIP) in metabolic labelling experiments with stable isotope labelled substrates. For identification of microbial species intact protein profiling (IPP) can be used, whereas the assessment of their metabolic activity is achieved by shotgun mass mapping (SMM). Microbial cultures were grown on substrates containing ¹³C or ¹⁵N. For identification of species we tested both the IPP and the SMM approaches. Mass spectra (MALDI‐MS) were taken from mixtures of either intact proteins or peptides from tryptic digestion for generating species‐specific peak patterns. In the case of SMM, the fragmentation of peptides was additionally used to obtain sequence information for species identification. Mass spectra of peptide sequences allow calculation of the amount of ¹³C or ¹⁵N incorporation within peptides for determining metabolic activity of the specific species. The comparison of IPP and SMM revealed a higher robustness of species identification by SMM. In addition, the assessment of incorporation levels of ¹³C and ¹⁵N into peptides by SMM revealed a lower uncertainty (0.5–0.8 atom %) compared to IPP (6.4–8.9 atom %). The determination of metabolic activity and function of individual species by Protein‐SIP can help to analyse carbon and nitrogen fluxes within microbial communities. Copyright © 2009 John Wiley & Sons, Ltd.