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Ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryotomography

Subramanian, Poorna and Pirbadian, Sahand and El-Naggar, Mohamed Y. and Jensen, Grant J. (2018) Ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryotomography. Proceedings of the National Academy of Sciences of the United States of America, 115 (14). E3246-E3255. ISSN 0027-8424. PMCID PMC5889646. http://resolver.caltech.edu/CaltechAUTHORS:20170619-134442390

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Abstract

Bacterial nanowires have garnered recent interest as a proposed extracellular electron transfer (EET) pathway that links the bacterial electron transport chain to solid-phase electron acceptors away from the cell. Recent studies showed that Shewanella oneidensis MR-1 produces outer membrane (OM) and periplasmic extensions that contain EET components and hinted at their possible role as bacterial nanowires. However, their fine structure and distribution of cytochrome electron carriers under native conditions remained unclear, making it difficult to evaluate the potential electron transport (ET) mechanism along OM extensions. Here, we report high-resolution images of S. oneidensis OM extensions, using electron cryotomography (ECT). We developed a robust method for fluorescence light microscopy imaging of OM extension growth on electron microscopy grids and used correlative light and electron microscopy to identify and image the same structures by ECT. Our results reveal that S. oneidensis OM extensions are dynamic chains of interconnected outer membrane vesicles (OMVs) with variable dimensions, curvature, and extent of tubulation. Junction densities that potentially stabilize OMV chains are seen between neighboring vesicles in cryotomograms. By comparing wild type and a cytochrome gene deletion mutant, our ECT results provide the likely positions and packing of periplasmic and outer membrane proteins consistent with cytochromes. Based on the observed cytochrome packing density, we propose a plausible ET path along the OM extensions involving a combination of direct hopping and cytochrome diffusion. A mean-field calculation, informed by the observed ECT cytochrome density, supports this proposal by revealing ET rates on par with a fully packed cytochrome network.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1073/pnas.1718810115DOIArticle
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5889646/PubMed CentralArticle
http://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1718810115/-/DCSupplementalPublisherSupporting Information
http://dx.doi.org/10.1101/103242DOIDiscussion Paper
ORCID:
AuthorORCID
Jensen, Grant J.0000-0003-1556-4864
Alternate Title:The ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryo-tomography
Additional Information:© 2018 National Academy of Sciences. Published under the PNAS license. Edited by E. Peter Greenberg, University of Washington, Seattle, WA, and approved February 21, 2018 (received for review November 6, 2017). We thank Dr. Yi-Wei Chang and Dr. Matthew Swulius for help with preparing Fig. 7 B and C, respectively. We are grateful to Dr. Sean J. Elliott for providing the SAXS model file for MtrA (41) used in Fig. 7B and to Dr. Jeffrey A. Gralnick for providing the cytochrome mutant strain. We thank Dr. Catherine Oikonomou for helping edit the manuscript. P.S. acknowledges support by the Caltech Center for Environmental Microbial Interactions. Work in the laboratory of G.J.J. is supported by the Howard Hughes Medical Institute. The in vivo OM extension imaging platform and mapping of EET proteins are funded by the Air Force Office of Scientific Research Presidential Early Career Award for Scientists and Engineers (FA955014-1-0294, to M.Y.E.-N.). Modeling of ET kinetics and partial support for S.P. are funded by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy through Grant DE-FG02-13ER16415 (to M.Y.E.-N.). Author contributions: P.S., S.P., M.Y.E.-N., and G.J.J. designed research; P.S. and S.P. performed research; P.S. and S.P. analyzed data; and P.S., S.P., M.Y.E.-N., and G.J.J. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1718810115/-/DCSupplemental.
Group:Caltech Center for Environmental Microbial Interactions (CEMI)
Funders:
Funding AgencyGrant Number
Caltech Center for Environmental Microbial Interactions (CEMI)UNSPECIFIED
Howard Hughes Medical Institute (HHMI)UNSPECIFIED
Air Force Office of Scientific Research (AFOSR)FA955014-1-0294
Department of Energy (DOE)DE-FG02-13ER16415
Subject Keywords:extracellular electron transport; electron cryotomography; membrane cytochromes; bacterial nanowires; Shewanella
PubMed Central ID:PMC5889646
Record Number:CaltechAUTHORS:20170619-134442390
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170619-134442390
Official Citation:Ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryotomography Poorna Subramanian, Sahand Pirbadian, Mohamed Y. El-Naggar, Grant J. Jensen Proceedings of the National Academy of Sciences Apr 2018, 115 (14) E3246-E3255; DOI: 10.1073/pnas.1718810115
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78333
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Jun 2017 20:55
Last Modified:23 Apr 2019 00:17

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