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Ladderane fatty acids are commonly used as biomarkers for bacteria involved in anaerobic ammonium oxidation (anammox). These lipids have been experimentally shown to undergo aerobic microbial degradation to form short chain ladderane fatty acids. However, nothing is known of the production or the distribution of these oxic biodegradation products in the natural environment. In this study, we analysed marine water column particulate matter and sediment from three different oceanic regimes for the presence of ladderane oxidation products (C14 ladderane fatty acids) and of original ladderane fatty acids (C18 and C20 ladderane fatty acids). We found that ladderane oxidation products, i.e. C14 ladderane fatty acids, are already produced within the water column of the Arabian Sea oxygen minimum zone (OMZ) and thus only low amounts of oxygen (< 3 µM) are needed for the β-oxidation of original ladderane fatty acids to proceed. However, no short chain ladderane fatty acids were detected in the Cariaco Basin water column, where oxygen concentrations were below detection limit, suggesting that the β-oxidation pathway is inhibited by the absence of molecular oxygen, or that the microbes performing the degradation are not proliferating under these conditions. Comparison of distributions of ladderane fatty acids indicates that short chain ladderane fatty acids are mostly produced in the water column and at the sediment surface, before being preserved deeper in the sediments. Short chain ladderane fatty acids were abundant in Arabian Sea and Peru Margin sediments (ODP Leg 201), often in higher concentrations than the original ladderane fatty acids. In a sediment core taken from within the Arabian Sea OMZ, short chain ladderanes made up more than 90% of the total ladderanes at depths greater than 5 cm below sea floor. We also found short chain ladderanes in higher concentrations in hydrolysed sediment residues compared to those freely occurring in lipid extracts, suggesting that they had become bound to the sediment matrix. Furthermore, these matrix-bound short chain ladderanes were found at greater sediment depths than short chain ladderanes in the lipid extract, suggesting that binding to the sediment matrix aids the preservation of these lipids. Though sedimentary degradation of short chain ladderane fatty acids did occur, it appeared to be at a slower rate than that of the original ladderane fatty acids, and short chain ladderane fatty acids were found in sediments from the Late Pleistocene (-100 kyr). Together these results suggest that the oxic degradation products of ladderane fatty acids may be suitable biomarkers for past anammox activity in OMZs. [ABSTRACT FROM AUTHOR]

Temporal variations in the abundance and composition of intact polar lipids (IPLs) in North Sea coastal marine water were assessed over a one-year seasonal cycle, and compared with environmental parameters and the microbial community composition. Sulfoquinovosyldiacylglycerol (SQDG) was the most abundant IPL class, followed by phosphatidylcholine (PC), phosphatidylglycerol (PG) and diacylglyceryl-(N,N,N)-trimethylhomoserine (DGTS) in roughly equal concentrations, and smaller amounts of phosphatidylethanolamine (PE). Although the total concentrations of these IPL classes varied substantially throughout the year, the composition of the IPL pool remained remarkably constant. Statistical analysis yielded negative correlations between IPL concentrations and dissolved inorganic nutrient concentrations, but possible phosphorous limitation during the spring bloom did not result in changes in the overall planktonic IPL composition. Significant correlations between SQDG, PC, PG and DGTS concentrations and chlorophyll-a concentrations and algal abundances indicated that eukaryotic primary producers were the predominant source of IPLs at this site. However, whilst IPL concentrations in the water were closely tied to total algal abundances, the rapid succession of different algal groups blooming throughout the year did not result in major shifts in IPL composition. This shows that the most commonly occurring IPLs have limited chemotaxonomic potential, and highlights the need to use targeted assays of more specific biomarker IPLs. [ABSTRACT FROM AUTHOR]

The diazotrophic community in microbial mats growing along the shore of the North Sea barrier island Schiermonnikoog (The Netherlands) was studied using microscopy, lipid biomarkers, stable carbon (δC) and nitrogen (δN) isotopes as well as by constructing and analyzing 16S rRNA gene libraries. Depending on their position on the littoral gradient, two types of mats were identified, which showed distinct differences regarding the structure, development and composition of the microbial community. Intertidal microbial mats showed a low species diversity with filamentous non-heterocystous Cyanobacteria providing the main mat structure. In contrast, supratidal microbial mats showed a distinct vertical zonation and a high degree of species diversity. Morphotypes of non-heterocystous Cyanobacteria were recognized as the main structural component in these mats. In addition, unicellular Cyanobacteria were frequently observed, whereas filamentous heterocystous Cyanobacteria occurred only in low numbers. Besides the apparent visual dominance of cyanobacterial morphotpyes, 16S rRNA gene libraries indicated that both microbial mat types also included members of the Proteobacteria and the Cytophaga-Flavobacterium-Bacteroides group as well as diatoms. Bulk δN isotopes of the microbial mats ranged from +6.1‰ in the lower intertidal to −1.2‰ in the supratidal zone, indicating a shift from predominantly nitrate utilization to nitrogen fixation along the littoral gradient. This conclusion was supported by the presence of heterocyst glycolipids, representing lipid biomarkers for nitrogen-fixing heterocystous Cyanobacteria, in supratidal but not in intertidal microbial mats. The availability of combined nitrogen species might thus be a key factor in controlling and regulating the distribution of the diazotrophic microbial community of Schiermonnikoog. [ABSTRACT FROM AUTHOR]

Abstract: Mud volcanoes (MVs) are formed by expulsion due to lateral or vertical compression of overpressured fluids in the sub-surface. Their sediments are characterized by a specific lithology called mud breccia, which is composed of inorganic and organic matter sourced from different sedimentary units and transported from the sub-surface to the seafloor. Biomarker lipid distributions were determined for sediment cores collected from the Kazakov, NIOZ and Odessa MVs in the Sorokin Trough, northeastern Black Sea. This revealed different mud breccia sources that are directly linked to the location of the fracture zones or diapiric folds formed by tectonic compression. The Kazakov MV shows biomarker characteristics of relatively mature organic matter, likely related to the Maycopian Shale Formation. The NIOZ and Odessa MVs contain immature organic matter derived from much shallower sediments overpressed by rising Maycopian diapirs. In the mud breccia from the NIOZ MV, biomarkers clearly record two different mud eruption episodes reflected in distinct distributions from unrelated sedimentary facies. Hence, the study shows that, although the organic matter of a mud breccia is sourced from a complex mixture of lithofacies, the collective biomarker signal reveals specific signatures of the sedimentary sections that contributed most to the migrated fluid. [Copyright &y& Elsevier]