Anaerobic degradation of n-hexane in a denitrifying bacterium: Further degradation of the initial intermediate (1-methylpentyl) succinate via C-skeleton rearrangement

The anaerobic degradation pathway of the saturated hydrocarbon n-hexane in a denitrifying strain (HxN1) was examined by gas chromatography-mass spectrometry of derivatized extracts from cultures grown with unlabeled and deuterated substrate; several authentic standard compounds were included for comparison. The study was focused on possible reaction steps that follow the initial formation of (1-methylpentyl)succinate from n-hexane and fumarate. 4-Methyloctanoic, 4-methyloct-2-enoic, 2-methylhexanoic, 2-methylhex-2-enoic and 3-hydroxy-2-methylhexanoic acids (in addition to a few other methyl-branched acids) were detected in n-hexane-grown but not in n-hexanoate-grown cultures. Labeling indicated preservation of the original carbon chain of n-hexane in these acids. Tracing of the deuterium label of 3- d1-(1-methylpentyl)succinate in tentative subsequent products indicated a deuterium/carboxyl carbon exchange in the succinate moiety. This suggests that the metabolism of (1-methylpentyl)succinate employs reactions analogous to those in the established conversion of succinyl-CoA via methylmalonyl-CoA to propionyl-CoA. Accordingly, a pathway is proposed in which (1-methylpentyl)succinate is converted to the CoA-thioester, rearranged to (2-methylhexyl)malonyl-CoA and decarboxylated (perhaps by a transcarboxylase) to 4-methyloctanoyl-CoA. The other identified fatty acids match with a further degradation of 4-methyloctanoyl-CoA via rounds of conventional beta-oxidation. Such a pathway would also allow regeneration of fumarate (for n-hexane activation) from propionyl-CoA formed as intermediate and hence present a cyclic process

Aromatic hydrocarbon biomarkers in terrestrial organic matter of Devonian to Permian age

This paper presents the results of a detailed study on the occurrence and distribution of alkylnaphthalenes and alkylphenanthrenes in 39 coal and sediment samples from the Late Palaeozoic containing predominantly terrestrial organic matter. Most of the samples represent the Euramerian flora realm and originate from locations beyond the Variscan front in Eastern, Northern and Central Europe, i.e. especially England and the Moscow Basin. The samples are of relatively low maturity (0.32 to 1.80% R-r) and consist mainly of mixtures of type III and II kerogen. Quantification of the C-0- to C-4-naphthalenes and the C-0- to C-4-phenanthrenes showed that these compound classes were highly abundant in all samples. Aromatic hydrocarbon maturity parameters in general are in good agreement with measured vitrinite reflectance values. 1,2,7-Trimethylnaphthalene, an assumed diagenetic product of oleanane type biomarkers was present in all investigated samples. This observation provides evidence that oleanane type lipids were biosynthesised by organisms predating the evolution of angiosperms or that assumed formation pathways for 1,2,7-trimethylnaphthalene are insecure. 1,2,8-Trimethylphenanthrene was significantly enriched in samples from the Permian and the one sample from the Devonian investigated in this study. The precursor(s) of 1,2,8-trimethylphenanthrene therefore may have been produced by organisms which were least abundant in the Carboniferous depositional environments represented by our samples. (c) 2006 Elsevier B.V. All rights reserved

Characterisation of non-extractable macromolecular organic matter in Palaeozoic coals

Comprehensive organic-geochemical investigations were applied to Permian, Carboniferous and Devonian coals. The major goal of the investigation was to quantify differences in organic matter composition of the coals on a molecular level and to associate these differences with either i) primary composition of the precursor plant material, or ii) diagenetic processes related to burial and temperature increase or iii) evolutionary time trends.The pre-extracted samples were analysed by means of pyrolytic and chemical degradation techniques as well as FTIR spectroscopy. Additionally, Rock-Eval pyrolysis and organic petrography were used to obtain information on the bulk of the coal samples.The degradation analysis revealed a wide variety of individual compounds including n-alkanes, isoprenoids, polycylic aromatic compounds, fatty acids, alkylbenzenes, aromatic carboxylic acids and phenols. Relative concentrations of substances or compound groups were correlated with bulk parameters and age of the samples.Significant correlations of the chemical data were found out mainly for maturity parameters and maceral composition. Time depending changes in chemical composition were observed only to a minor extent. Thus, the rapid morphologic evolution of higher land plants in the Late Palaeozoic is not reflected in a significant way by the chemical composition of the non-extractable matter in the coal samples investigated. (c) 2006 Elsevier B.V. All rights reserved