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Bremen, Germany

Braun S.,University of Aarhus | Morono Y.,Japan Agency for Marine - Earth Science and Technology | Becker K.W.,Organic Geochemistry Group | Hinrichs K.-U.,Organic Geochemistry Group | And 3 more authors.
Geochimica et Cosmochimica Acta | Year: 2016

Microbial biomolecules, typically from the cell envelope, can provide crucial information about distribution, activity, and adaptations of sub-seafloor microbial communities. However, when cells die these molecules can be preserved in the sediment on timescales that are likely longer than the lifetime of their microbial sources. Here we provide for the first time measurements of the cellular content of biomolecules in sedimentary microbial cells. We separated intact cells from sediment matrices in samples from surficial, deeply buried, organic-rich, and organic-lean marine sediments by density centrifugation. Amino acids, amino sugars, muramic acid, and intact polar lipids were analyzed in both whole sediment and cell extract, and cell separation was optimized and evaluated in terms of purity, separation efficiency, taxonomic resemblance, and compatibility to high-performance liquid chromatography and mass spectrometry for biomolecule analyses. Because cell extracts from density centrifugation still contained considerable amounts of detrital particles and non-cellular biomolecules, we further purified cells from two samples by fluorescence-activated cell sorting (FACS). Cells from these highly purified cell extracts had an average content of amino acids and lipids of 23-28 fg cell-1 and 2.3 fg cell-1, respectively, with an estimated carbon content of 19-24 fg cell-1. In the sediment, the amount of biomolecules associated with vegetative cells was up to 70-fold lower than the total biomolecule content. We find that the cellular content of biomolecules in the marine subsurface is up to four times lower than previous estimates. Our approach will facilitate and improve the use of biomolecules as proxies for microbial abundance in environmental samples and ultimately provide better global estimates of microbial biomass. © 2016 Elsevier Ltd.

Heuer V.B.,Organic Geochemistry Group | Kruger M.,Bundesanstalt fur Geowissenschaften und Rohstoffe | Elvert M.,Organic Geochemistry Group | Hinrichs K.-U.,Organic Geochemistry Group
Organic Geochemistry | Year: 2010

Acetate is an important intermediate in the anaerobic degradation of organic matter and highly relevant for the cycling of carbon in nature. The water soluble C2 compound is produced by fermentation of organic matter as well as by reduction of CO2 with H2 via the acetyl-CoA pathway (acetogenesis) and serves as an important substrate for a variety of microorganisms including sulfate reducing bacteria and methanogenic archaea. The relative importance of the different metabolic processes in acetate production and consumption is thought to be reflected in the stable carbon isotopic composition of pore water acetate. δ13C values of acetate have been shown to be highly variable in marine sediments, ranging from -85‰ to -3‰, and distinct isotopic fractionations have previously been reported to be associated with fermentation, acetogenesis and acetoclastic methanogenesis in pure microbial cultures. Aiming to better understand the stable carbon isotope biogeochemistry of sedimentary acetate, this study investigates if process related carbon isotopic signals of acetate are also expressed in the pore water pool of complex freshwater environments. We report findings from incubation experiments with lake sediments, in which we manipulated the relative importance of single processes by addition of specific substrates and inhibitors. In particular, we found: (a) δ13C values of acetate closely resembled δ13C values of total organic carbon in the sediment's solid phase (TOC) where fermentation was the dominant process; (b) a distinct 13C enrichment of the acetate pool relative to δ13CTOC where acetate was consumed by acetoclastic methanogenesis; and (c) a distinct 13C depletion of acetate relative to both δ13CTOC and δ13C values of dissolved inorganic carbon (DIC) where high levels of H2 stimulated acetogenesis. Our study provides further evidence for the diagnostic value of the stable carbon isotope chemistry of acetate for the detection of biogeochemical processes in natural systems. © 2009 Elsevier Ltd. All rights reserved.

Lu X.,Organic Geochemistry Group | Lu X.,Wuhan University | Liu X.-L.,Organic Geochemistry Group | Liu X.-L.,Massachusetts Institute of Technology | And 8 more authors.
Organic Geochemistry | Year: 2015

Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH-GDGTs), with one or two hydroxyl groups in one of the biphytanyl moieties, are major compounds in planktonic Thaumarchaeota, and occur widely in marine and lacustrine sediments. In order to examine their potential as an indicator of local variation in sea surface temperature (SST), we collected 70 surface sediments from the Chinese coastal seas (CCSs), including 16 from the Yangtze Estuary, to determine their tetraether lipid composition. The proportion of OH-GDGTs relative to total isoprenoid GDGTs increased with latitude from 1.8% to 12.8% and correlated strongly with SST, as indicated from redundancy analysis. The variation in OH-GDGT composition was best captured by the weighted average number of cyclopentane moieties in OH-GDGT-1 and -2 (RI-OH), which correlated significantly with both summer and autumn SST and was associated with minimum residual SST relative to remote sensing data. The large input of terrigenous organic matter to the Yangtze Estuary appears to have no significant influence on the OH-GDGT based proxy. Our study suggests that RI-OH could serve as a useful proxy for recording warm seasonal SST in the CCSs. A global surface sediment compilation further indicates that RI-OH and its derivative, RI-OH', which additionally contains OH-GDGT-0, may be used to estimate SST in warm (ca.>. 15. °C annual mean SST) and cold (ca. 15. °C) environments, respectively. © 2015 Elsevier Ltd.

Liu X.-L.,Organic Geochemistry Group | Liu X.-L.,University of Bremen | Lipp J.S.,Organic Geochemistry Group | Lipp J.S.,University of Bremen | And 6 more authors.
Geochimica et Cosmochimica Acta | Year: 2012

Hydroxylated glycerol dialkyl glycerol tetraethers (hydroxy-GDGTs) were detected in marine sediments of diverse depositional regimes and ages. Mass spectrometric evidence, complemented by information gleaned from two-dimensional (2D) 1H- 13C nuclear magnetic resonance (NMR) spectroscopy on minute quantities of target analyte isolated from marine sediment, allowed us to identify one major compound as a monohydroxy-GDGT with acyclic biphytanyl moieties (OH-GDGT-0). NMR spectroscopic and mass spectrometric data indicate the presence of a tertiary hydroxyl group suggesting the compounds are the tetraether analogues of the widespread hydroxylated archaeol derivatives that have received great attention in geochemical studies of the last two decades. Three other related compounds were assigned as acyclic dihydroxy-GDGT (2OH-GDGT-0) and monohydroxy-GDGT with one (OH-GDGT-1) and two cyclopentane rings (OH-GDGT-2). Based on the identification of hydroxy-GDGT core lipids, a group of previously reported unknown intact polar lipids (IPLs), including the ubiquitously distributed H341-GDGT (Lipp J. S. and Hinrichs K. -U. (2009) Structural diversity and fate of intact polar lipids in marine sediments. Geochim. Cosmochim. Acta 73, 6816-6833), and its analogues were tentatively identified as glycosidic hydroxy-GDGTs. In addition to marine sediments, we also detected hydroxy-GDGTs in a culture of Methanothermococcus thermolithotrophicus. Given the previous finding of the putative polar precursor H341-GDGT in the planktonic marine crenarchaeon Nitrosopumilus maritimus, these compounds are synthesized by representatives of both cren- and euryarchaeota. The ubiquitous distribution and apparent substantial abundance of hydroxy-GDGT core lipids in marine sediments (up to 8% of total isoprenoid core GDGTs) point to their potential as proxies. © 2012 Elsevier Ltd.

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