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NanoSIMS imaging reveals metabolic stratification within current-producing biofilms

Chadwick, Grayson L. and Jiménez-Otero, Fernanda and Gralnick, Jeffrey A. and Bond, Daniel R. and Orphan, Victoria J. (2019) NanoSIMS imaging reveals metabolic stratification within current-producing biofilms. Proceedings of the National Academy of Sciences of the United States of America, 116 (41). pp. 20716-20724. ISSN 0027-8424. PMCID PMC6789570. doi:10.1073/pnas.1912498116.

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Metal-reducing bacteria direct electrons to their outer surfaces, where insoluble metal oxides or electrodes act as terminal electron acceptors, generating electrical current from anaerobic respiration. Geobacter sulfurreducens is a commonly enriched electricity-producing organism, forming thick conductive biofilms that magnify total activity by supporting respiration of cells not in direct contact with electrodes. Hypotheses explaining why these biofilms fail to produce higher current densities suggest inhibition by formation of pH, nutrient, or redox potential gradients; but these explanations are often contradictory, and a lack of direct measurements of cellular growth within biofilms prevents discrimination between these models. To address this fundamental question, we measured the anabolic activity of G. sulfurreducens biofilms using stable isotope probing coupled to nanoscale secondary ion mass spectrometry (nanoSIMS). Our results demonstrate that the most active cells are at the anode surface, and that this activity decreases with distance, reaching a minimum 10 µm from the electrode. Cells nearest the electrode continue to grow at their maximum rate in weeks-old biofilms 80-µm-thick, indicating nutrient or buffer diffusion into the biofilm is not rate-limiting. This pattern, where highest activity occurs at the electrode and declines with each cell layer, is present in thin biofilms (<5 µm) and fully grown biofilms (>20 µm), and at different anode redox potentials. These results suggest a growth penalty is associated with respiring insoluble electron acceptors at micron distances, which has important implications for improving microbial electrochemical devices as well as our understanding of syntrophic associations harnessing the phenomenon of microbial conductivity.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Chadwick, Grayson L.0000-0003-0700-9350
Jiménez-Otero, Fernanda0000-0003-1583-6495
Gralnick, Jeffrey A.0000-0001-9250-7770
Bond, Daniel R.0000-0001-8083-7107
Orphan, Victoria J.0000-0002-5374-6178
Additional Information:© 2019 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). Edited by Susan L. Brantley, Pennsylvania State University, University Park, PA, and approved August 29, 2019 (received for review July 24, 2019). This publication was supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research (DE-SC0016469) and the NASA Astrobiology Institute, Award NNA13AA92A (to V.J.O.) and the Simons Foundation (Program: Life Sciences-Simons Collaboration on Principles of Microbial Ecosystems; Award 542393). D.R.B. and J.A.G. were supported by National Science Foundation Dimensions of Biodiversity program DEB 1542513. G.L.C. was supported by NIH/NRSA Training Grant T32 GM007616. F.J.O. was supported by the Mexican National Council for Science and Technology and the Office of Naval Research Award N000141612194. We thank Dr. Gail Celio for training and loan of the UMN Imaging facilities, Dr. Ryan Hunter for assistance developing a biofilm staining and embedding protocol, and Dr. Yunbin Guan for assistance with the nanoSIMS analysis. Author contributions: G.L.C., F.J.O., J.A.G., D.R.B., and V.J.O. designed research; G.L.C. and F.J.O. performed research; G.L.C. and F.J.O. analyzed data; and G.L.C., F.J.O., J.A.G., D.R.B., and V.J.O. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0016469
Simons Foundation542393
NIH Predoctoral FellowshipT32 GM007616
Consejo Nacional de Ciencia y Tecnología (CONACyT)UNSPECIFIED
Office of Naval Research (ONR)N000141612194
Subject Keywords:Geobacter sulfurreducens; nanoSIMS; extracellular electron transfer; electrode reduction; stable isotope tracers
Issue or Number:41
PubMed Central ID:PMC6789570
Record Number:CaltechAUTHORS:20190923-160449911
Persistent URL:
Official Citation:NanoSIMS imaging reveals metabolic stratification within current-producing biofilms. Grayson L. Chadwick, Fernanda Jiménez Otero, Jeffrey A. Gralnick, Daniel R. Bond, Victoria J. Orphan. Proceedings of the National Academy of Sciences Oct 2019, 116 (41) 20716-20724; DOI: 10.1073/pnas.1912498116
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98815
Deposited By: Tony Diaz
Deposited On:24 Sep 2019 01:41
Last Modified:16 Nov 2021 17:41

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