title: In situ electrochemical enrichment and isolation of a magnetite-reducing bacterium from a high pH serpentinizing spring.
abstract: Serpentinization is a geologic process that produces highly reduced, hydrogen-rich fluids that support microbial communities under high pH conditions. We investigated the activity of microbes capable of extracellular electron transfer in a terrestrial serpentinizing system known as 'The Cedars'. Measuring current generation with an on-site two-electrode system, we observed daily oscillations in current with the current maxima and minima occurring during daylight hours. Distinct members of the microbial community were enriched. Current generation in lab-scale electrochemical reactors did not oscillate, but was correlated with carbohydrate amendment in Cedars-specific minimal media. Gammaproteobacteria and Firmicutes were consistently enriched from lab electrochemical systems on δ-MnO2and amorphous Fe(OH)3at pH 11. However, isolation of an electrogenic strain proved difficult as transfer cultures failed to grow after multiple rounds of media transfer. Lowering the bulk pH in the media allowed us to isolate a Firmicutes strain (Paenibacillus sp.). This strain was capable of electrode and mineral reduction (including magnetite) at pH 9. This report provides evidence of the in situ activity of microbes using extracellular substrates as sinks for electrons at The Cedars, but also highlights the potential importance of community dynamics for supporting microbial life through either carbon fixation, and/or moderating pH stress.
authors.affiliation: Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
authors.forename: Annette R
authors.initials: AR
authors.lastname: Rowe
authors.affiliation: Department of Applied and Chemical Engineering, University of Tokyo, Tokyo, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Yoshimura
authors.affiliation: Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
authors.forename: Doug E
authors.initials: DE
authors.lastname: LaRowe
authors.affiliation: Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
authors.forename: Lina J
authors.initials: LJ
authors.lastname: Bird
authors.affiliation: Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.|Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
authors.forename: Jan P
authors.initials: JP
authors.lastname: Amend
authors.affiliation: Center for Green Research on Energy and Environmental Materials, National Institute for Material Sciences, Tsukuba, Ibaraki, 305-0047, Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Hashimoto
authors.affiliation: Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Nealson
authors.affiliation: Center for Green Research on Energy and Environmental Materials, National Institute for Material Sciences, Tsukuba, Ibaraki, 305-0047, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Okamoto
mesh_terms: D004579:Electron Transport / Q000502:physiology*; D052203:Ferrosoferric Oxide / Q000378:metabolism*; D000068536:Bacillota / Q000302:isolation & purification / Q000378:metabolism*; D020563:Gammaproteobacteria / Q000302:isolation & purification / Q000378:metabolism*; D006859:Hydrogen / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D012336:RNA, Ribosomal, 16S
chemical_list: D012336:RNA, Ribosomal, 16S; D006859:Hydrogen; D052203:Ferrosoferric Oxide