Abstract-We propose that organic compounds found in a Miocene limestone from Marmorito (Northem Italy) are source markers for organic matter present in aneient methane vent systems (cold seeps). The limestone contains high concentrations of the tail-to-taillinked, acyclic C 20 isoprenoid 2,6,11,15-tetramethylhexadecane (crocetane), a C 25 homolog 2,6,10,15,19-pentamethylicosane (PME), and a distinctive glycerol ether lipid containing 3,7,1l,15-tetramethylhexadecyl (phytanyl-) moieties. The chemical structures of these biomarkers indicate a common origin from archaea. Their extreme1y l3C-depleted isotope compositions (8 13 C "'" -108 to -115.6%0 PDB) suggest that the respective archaea have directly or indirectly introduced isotopically depleted, methane-derived carbon into their biomass. We postulate that a second major cluster of biomarkers showing heavier isotope values (8 l3 C "'" -88%0) is derived from sulfate-redueing bacteria (SRB). The observed biomarkers sustain the idea that methanogenic bacteria, in a syntrophic community with SRB, are responsible for the anaerobic oxidation of methane in marine sediments. Marmorito may thus represent a conceivable aneient scenario for methane consumption performed by a defined, two-membered bacterial consortium: (1) archaea that perform reversed methanogenesis by oxidizing methane and produeing CO 2 and H 2 ; and (2) SRB that consume the resulting H 2 . Furthermore, the respective organic molecules are, unlike other compounds, tightly bound to the crystalline carbonate phase. The Marmorito carbonates can thus be regarded as "cold seep microbialites" rather than mere "authigenic" carbonates.

A resistant soil organic residue, 'humin', has been analysed by solid-state 13 C-NMR and pyrolysis followed by molecular and 13 C determination of the pyrolysate alkane-alkene fraction. The results show the occurrence of highly aliphatic, straight-chain biopolymer material as a substantial part of soil organic matter. They confirm the hypothesis by which a part of soil organic matter can be formed by selective preservation of resistant highly aliphatic microbial polymers. This pathway comes in addition to the longstanding neogenesis hypothesis involving recondensation of small polar molecules such as amino acids, carbohydrates and phenols.

a b s t r a c tPyoverdine I (PVDI) is the major siderophore produced by Pseudomonas aeruginosa to import iron. Biosynthesis of this chelator involves non-ribosomal peptide synthetases and other enzymes. PvdQ is a periplasmic enzyme from the NTN hydrolase family and is involved in the final steps of PVDI biosynthesis. A pvdQ mutant produces two non-fluorescent PVDI precursors with a higher molecular mass than PVDI. In the present study, we describe the use of mass spectrometry to determine the structure of these PVDI precursors and show that they both contain a unformed chromophore like ferribactin, and either a myristic or myristoleic chain that must be removed before PVDI is secreted into the extracellular medium.

No abstract

No abstract