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2008 Annual Science Report

Marine Biological Laboratory Reporting  |  JUL 2007 – JUN 2008

Iron Oxidation - Shaping the Past and Present Environments

Project Summary

This year the Edwards Lab completed and published most outstanding results from her NAI projects. Of notable success was the completion of several aspects concerning the abundance and diversity of life on basaltic rocks, including several methods-based studies that examine in detail the biases associated with different approaches used by ourselves, and in other labs as reported in the literature (Santelli et al., 2008; Orcutt et al., in review, Wang and Edwards, in review). The publication by Santelli et al. in Nature resulted in considerable publicity including and NSF press release and associated artists rendition of microbial life on rocks in the deep sea (Fig. 1).

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

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A highly diverse and abundant epilithic and endolithic microbial community exists on basaltic lavas from the East Pacific Rise as shown in

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a, The EPR at 9u N is characterized by lava flows, such as pillow basalts that outcrop at the sea floor. Scale bar, 40 cm. b, c, Photographs showing the range of volcanic samples used in this study from fresh and glassy (b) to more altered and oxide-coated ©. Scale bars, 2 cm (b) and 4 cm ©. d, e, Scanning electron microscopy (SEM) images of different presumed cellular morphologies, such as coccoidal (d) and filamentous (e) structures that were observed on ferromanganese-oxide-encrusted and iron-oxide-coated samples. Scale bars, 5 mm.

Relative bacterial richness from several environmental studies shown through rarefaction analyses.

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a, Species richness of Bacteria inhabiting EPR seafloor lavas (cumulative results) is compared with that of other ocean environments, such as the Sargasso Sea6 (partial curve), a MAR hydrothermal vent in situ growth chamber7, an EPR hydrothermal white smoker spire5, Nankai Trough deep-sea sediments8, and EPR deep sea water. The bacterial richness of the EPR basalts is also compared to a basalt-hosted community from Hawaii and other known high richness environments (b), such as a farm soil9 (partial curve) and a hypersaline microbial mat from the Guerrero Negro10 (partial curve). Partial rarefaction curves are shown for visualization purposes; however, complete data sets were used in calculating curve projections. c, Rarefaction curves for the individual EPR and Hawaii basalt clone libraries. A partial curve is shown for HI-LPP (total clones5246). Comparative studies in a and b are based on near full-length 16S rRNA gene sequences, and most studies are the sum of several environmental samples. OTUs are defined at a sequence similarity of 97%.
FG, fresh glass; LSR, Loihi seamount South Rift; LPP, Loihi seamount Pisces Peak; SP1 & SP2, South Point samples.

One other major area of advancement should be noted here. Three other completed papers relate to the discovery of a novel biogenic mineral structure produced by iron-oxidizing bacteria (Toner et al., in review (a)), which we think is being stabilized by organic ligands that are structural components of the mineral (this paper is in revision following very positive reviews in Geochimica Cosmochimica Acta). This line of query led us to test for the presence of ligands in hydrothermal plume material, where we ideed have found evidence for Fe(II) and Fe(III) ligands that appear to chance the thermodynamic stability properties of this metal (Toner et al., in review (b)) (this paper is in revsion following very positive review in Nature Geosciences). Finally, we have explored the isotopic signatures associated with hydrothermal systems in the deep sea where Fe oxidizing bacteria are active (Rouxel et al., 2008).

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Iron spectromicroscopy of a particle aggregate collected from the Tica vent sediment trap. (A) STXM image collected at Fe 2p3/2 edge (707.6 eV). The Fe 2p NEXAFS spectra extracted from areas 1-3 (outlined in white) are displayed in panel (B), along with Fe(II) and Fe(III) reference spectra from pyrrhotite and ferrihydrite reference minerals, respectively. The presence and amplitude of the two Fe 2p3/2-edge peaks is indicative of the relative proportions of Fe(II) (at 707.6 eV) and Fe(III) (at 709.5 eV) present in the areas of interest. The distributions of Fe(III) and Fe(II) within the aggregate were mapped by performing singular value decomposition analysis of the Fe spectra and are displayed in panels C and D, respectively. (E) STXM image collected at the C 1s edge (300 eV), arrow highlights rope-like morphologies present in the Corg matrix. (F) C distribution map (at 288.5 eV) within the particle aggregate. Data were recorded in the photon energy ranges: (1) pyrrhotite, 700-730 eV; (2) ferrihydrite, 700-735 eV; and, (3) experimental spectra, 700-729 eV. Spectra from areas 1 and 2 are multiplied by 4 and 2, respectively, for display purposes. The scale bars are 1 μm.

    Katrina Edwards Katrina Edwards
    Olivier Rouxel

    Objective 6.1
    Environmental changes and the cycling of elements by the biota, communities, and ecosystems