Aerobic and Anaerobic Metabolism of 6,10,14-Trimethylpentadecan-2-one by a Denitrifying-bacterium Isolated from Marine Environments

This report describes the metabolism of 6,10,14-trimethylpentadecan-2-one by a denitrifying bacterium (Marinobacter sp. strain CAB) isolated from marine sediments. Under aerobic and denitrifying conditions, this strain efficiently degraded this ubiquitous isoprenoid ketone. Several bacterial metabolites, 4,8,12-trimethyltridecan-1-ol, 4,8,12-trimethyltridecanal, 4,8,12-trimethyltridecanoic acid, Z-3,7-dimethylocten-2-oic acid,Z-3,7, 11-trimethyldodecen-2-oic acid, and 6,10,14-trimethylpentadecan-2-ol, were formally identified, and different pathways were proposed to explain the formation of such isoprenoid compounds

Lipoxygenase-induced autoxidative degradation of terrestrial particulate organic matter in estuaries: A widespread process enhanced at high and low latitude

International audienceThere exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to organic matter (OM) in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate OM (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study, we propose for the first time the involvement of lipoxygenase (LOX) activity in the induction of autoxidation in mixed waters. The observation of unusual profiles of palmitoleic acid oxidation products and the presence of jasmonic acid in suspended particulate matter (SPM) collected close to the Rhône River, as well as in samples from the Mackenzie and Amazon rivers, is attributed to strong LOX activity. We show the role played by salinity in the induction of this LOX activity and provide an explanation for the differences in estuarine autoxidation level. At high latitude, lower temperatures and irradiance favor photooxidative damage to higher plant debris and, consequently, hydroperoxide production. High hydroperoxide content strongly contributes to LOX activation in mixed waters. The high resulting LOX activity enhances alkoxyl radical production and thus autoxidation. On the contrary, at low latitude, photooxidative effects are limited, and riverine autoxidation is favored. The higher hydroperoxide content of TPOM may, as a consequence, thereby also contribute to a high level of LOX activity and autoxidation in estuaries. In temperate zones, land and riverine photooxidative and autoxidative damage is limited, unlike estuaries where we observed significant LOX-induced and autox-idative damage.

Biotic and abiotic degradation of Δ5-sterols in senescent Mediterranean marine and terrestrial angiosperms

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Use of Gas Chromatography-Mass Spectrometry Techniques (GC-MS, GC-MS/MS and GC-QTOF) for the Characterization of Photooxidation and Autoxidation Products of Lipids of Autotrophic Organisms in Environmental Samples

International audienceThis paper reviews applications of gas chromatography-mass spectrometry techniques for the characterization of photooxidation and autoxidation products of lipids of senescent phototrophic organisms. Particular attention is given to: (i) the selection of oxidation products that are sufficiently stable under environmental conditions and specific to each lipid class and degradation route; (ii) the description of electron ionization mass fragmentation of trimethylsilyl derivatives of these compounds; and (iii) the use of specific fragment ions for monitoring the oxidation of the main unsaturated lipid components of phototrophs. The techniques best geared for this task were gas chromatography-quadrupole-time of flight to monitor fragment ions with very high resolution and accuracy, and gas chromatography-tandem mass spectrometry to monitor very selective transitions in multiple reaction monitoring mode. The extent of the degradation processes can only be estimated if the oxidation products are unaffected by fast secondary oxidation reactions, as it is notably the case of ∆5-sterols, monounsaturated fatty acids, chlorophyll phytyl side-chain, and di- and triterpenoids. In contrast, the primary degradation products of highly branched isoprenoid alkenes possessing more than one trisubstituted double bond, alkenones, carotenoids and polyunsaturated fatty acids, appear to be too unstable with respect to secondary oxidation or other reactions to serve for quantification in environmental samples

Unexpected peaks in electron ionisation mass spectra of trimethylsilyl derivatives resulting from the presence of trace amounts of water and oxygen in GC-QTOF systems

International audienceSilylation is one of the most prevalent derivatization method. Replacement of active hydrogen (in-OH,-SH or =NH groups) by a silyl group reduces the polarity of the compound and hydrogen bonding 1. Electron ionization (EI) mass spectra of trimethylsilyl ethers or esters exhibit a significant [M-15] + ion formed by loss of a methyl group bonded to silicon, which is very useful in determining the molecular mass. EI mass spectra of trimethylsilyl (TMS) derivatives may be employed not only for molecular weight determinations, but also for structural deductions. 2 They are generally stable during GC-MS analyses, although contamination of the mass spectrometer source with organic substances has been reported to cause some decomposition. 3 Moreover, it may be noted that if the amount of water is too hig

Caractérisation de la nature des particules transportées lors des étiages du Rhône

Les études menées sur le Rhône soulignent que, dans le contexte actuel de changement climatique, les situations de faible débit et d’étiage seront probablement de plus en plus fréquentes sur l’ensemble de son bassin. Lors de ces périodes de faibles débits, les concentrations de certains contaminants (métaux, mercure et radionucléides) dans les particules en suspension ont tendance à augmenter, dépassant parfois les seuils de toxicité. Les raisons pouvant expliquer ces observations restent inconnues, mais pourraient être liées à la nature des matières en suspension dont la proportion en matière organique autochtone est plus élevée qu’à débit plus fort. De plus, la variation des proportions des principaux stérols démontre un contraste quant à l’origine de cette matière organique entre certains affluents (Ardèche et Durance) et le Rhône

Electron ionization mass fragmentation of monounsaturated long-chain alpha,omega-dicarboxylic acid trimethylsilyl derivatives.

International audienceRATIONALELong-chain monounsaturated -dicarboxylic acids are important components of the cuticle and suberized cell walls of plants.Identification and quantification of these compounds, which are widespread in environmental samples, can be challenging.METHODSThe EI-MS fragmentation pathways of long-chain monounsaturated -dicarboxylic acid TMS derivatives were investigated. Thesepathways were deduced by low-energy CID-GC-EI-MS/MS and accurate mass measurement.RESULTSLow-energy CID-MS/MS analyses and accurate mass measurement enabled us to elucidate EI-MS fragmentations of long-chainmonounsaturated -dicarboxylic acid TMS derivatives. These fragmentations involves successive losses of neutral molecules of TMSOHand CO initiated by transfer of allylic hydrogen atom to the ionized ester groups, which are thus totally lacking in EI mass spectra of saturatedhomologues.CONCLUSIONSEI-MS fragmentations of long-chain monounsaturated -dicarboxylic acids TMS derivatives exhibit specific fragment ions that can be veryuseful for the quantification in MRM mode of trace amounts of these compounds in environmental samples

Electron ionization mass fragmentation of monounsaturated long-chain alpha,omega-dicarboxylic acid trimethylsilyl derivatives.

RATIONALELong-chain monounsaturated -dicarboxylic acids are important components of the cuticle and suberized cell walls of plants.Identification and quantification of these compounds, which are widespread in environmental samples, can be challenging.METHODSThe EI-MS fragmentation pathways of long-chain monounsaturated -dicarboxylic acid TMS derivatives were investigated. Thesepathways were deduced by low-energy CID-GC-EI-MS/MS and accurate mass measurement.RESULTSLow-energy CID-MS/MS analyses and accurate mass measurement enabled us to elucidate EI-MS fragmentations of long-chainmonounsaturated -dicarboxylic acid TMS derivatives. These fragmentations involves successive losses of neutral molecules of TMSOHand CO initiated by transfer of allylic hydrogen atom to the ionized ester groups, which are thus totally lacking in EI mass spectra of saturatedhomologues.CONCLUSIONSEI-MS fragmentations of long-chain monounsaturated -dicarboxylic acids TMS derivatives exhibit specific fragment ions that can be veryuseful for the quantification in MRM mode of trace amounts of these compounds in environmental samples