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Imaging organic-mineral aggregates formed by Fe(II)oxidizing bacteria using Helium Ion Microscopy James Martin Byrne, Matthias Schmidt, Tina Gauger, Casey Bryce, and Andreas Kappler Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.8b00077 • Publication Date (Web): 05 Mar 2018 Downloaded from http://pubs.acs.org on March 7, 2018
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Environmental Science & Technology Letters
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Imaging organic-mineral aggregates formed by Fe(II)-oxidizing bacteria
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using Helium Ion Microscopy
3 James M Byrne1*, Matthias Schmidt2, Tina Gauger1, Casey Bryce1, Andreas Kappler1
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University of Tuebingen, Center for Applied Geoscience, Geomicrobiology, Sigwartstrasse 10, 72076, Tuebingen
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Department of Isotope Biogeochemistry, ProVIS - Centre for Chemical Microscopy, Helmholtz Centre for Environmental Research GmbH – UFZ, Permoserstrasse 15, 04318, Leipzig, Germany
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*corresponding author:
[email protected] 11 12 13
1 ACS Paragon Plus Environment
Environmental Science & Technology Letters
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Abstract
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Helium ion microscopy (HIM) has been used to image the development of mineralized twisted stalks
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produced by a neutrophilic, microaerophilic Fe(II)-oxidizing bacteria of the class Zetaproteobacteria.
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HIM is a relatively new type of microscopy which has several advantages over conventional scanning
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electron microscopy (SEM) due to its higher spatial resolution and the fact that samples can be
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imaged without coating (e.g. with Pt/Au). Here, we use HIM to show the development of nanometer-
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and micrometer-sized twisted stalk features consisting of organic material and Fe(III) minerals which
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appear to be loosely bound to the bacterial cells. These appendages are thought to be essential for
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eliminating Fe(III) waste produced during Fe(II) oxidation by sorbing Fe(III) and transporting it away
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from the cell. The results show the initial formation of long, precipitate free stalks. After just 2 days,
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these became encrusted with spikey lepidocrocite crystals, and by 1 month the characteristic
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twisted shape was almost indiscernible. These results demonstrate the high quality of images which
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can be obtained with Helium ion microscopy from organic and mineral structures produced by
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bacteria without the requirement to sputter coat samples with conductive metals and can thus be
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considered to be more representive of how these structures would exist in the environment.
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Environmental Science & Technology Letters
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Introduction
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Electron microscopy has long been used for studying biological materials such as bacteria at high
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resolution 1. Transmission electron microscopy (TEM) provides high-resolution information of
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intracellular organelles, but is restricted to very thin samples (
