Anode potential influences the structure and function of anodic electrode and electrolyte-associated microbiomes.

Paul G Dennis,Bernardino Virdis,Phil Hugenholtz,Inka Vanwonterghem,Alif Hassan,Korneel Rabaey,Gene W Tyson

doi:10.1038/srep39114

Paul G Dennis, Bernardino Virdis + Show 5 more

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https://doi.org/10.1038/srep39114

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Abstract

Three bioelectrochemical systems were operated with set anode potentials of +300 mV, +550 mV and +800 mV vs. Standard Hydrogen Electrode (SHE) to test the hypothesis that anode potential influences microbial diversity and is positively associated with microbial biomass and activity. Bacterial and archaeal diversity was characterized using 16 S rRNA gene amplicon sequencing, and biofilm thickness was measured as a proxy for biomass. Current production and substrate utilization patterns were used as measures of microbial activity and the mid-point potentials of putative terminal oxidases were assessed using cyclic voltammetry. All measurements were performed after 4, 16, 23, 30 and 38 days. Microbial biomass and activity differed significantly between anode potentials and were lower at the highest potential. Anodic electrode and electrolyte associated community composition was also significantly influenced by anode potential. While biofilms at +800 mV were thinner, transferred less charge and oxidized less substrate than those at lower potentials, they were also associated with putative terminal oxidases with higher mid-point potentials and generated more biomass per unit charge. This indicates that microbes at +800 mV were unable to capitalize on the potential for additional energy gain due to a lack of adaptive traits to high potential solid electron acceptors and/or sensitivity to oxidative stress.

Highlights

Three bioelectrochemical systems were operated with set anode potentials of +300 mV, +550 mV and +800 mV vs. Standard Hydrogen Electrode (SHE) to test the hypothesis that anode potential influences microbial diversity and is positively associated with microbial biomass and activity
The most commonly described Bioelectrochemical systems (BESs) is the microbial fuel cell (MFC), in which electrical power is generated via microbial decomposition of organic matter at an anode coupled with cathodic reduction of an electron acceptor at more positive potential
Microorganisms should obtain more energy when coupling respiration to more oxidising anodes as long as they can harvest the energy via generation of ATP by producing additional proton motive force[3]

Summary

Introduction

Three bioelectrochemical systems were operated with set anode potentials of +300 mV, +550 mV and +800 mV vs. Standard Hydrogen Electrode (SHE) to test the hypothesis that anode potential influences microbial diversity and is positively associated with microbial biomass and activity. While biofilms at +800 mV were thinner, transferred less charge and oxidized less substrate than those at lower potentials, they were associated with putative terminal oxidases with higher mid-point potentials and generated more biomass per unit charge This indicates that microbes at +800 mV were unable to capitalize on the potential for additional energy gain due to a lack of adaptive traits to high potential solid electron acceptors and/or sensitivity to oxidative stress. Thermodynamics dictates that microorganisms should obtain more energy when using anodes at higher electrochemical potentials, as long as they can use the energy to generate additional proton motive force[3] If this is the case, anode potential should be positively associated with current generation and microbial biomass, and influence microbial diversity; the relationship between anode potential and microbial community structure and function is not clear[4]. Relationships, in which current remains similar at approximately 300 mV, 700 mV and 900 mV but drops significantly at 600 mV9 or peaks between approximately −50 mV to +400 mV and declines sharply outside of this range[4,10]

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