Abstract
Microbial electrochemical technologies (METs) have a number of potential technological applications. In this work, we report the use of screen-printed electrodes (SPEs) as a tool to analyze the microbial electroactivity by using Geobacter sulfurreducens as a model microorganism. We took advantage of the small volume required for the assays (75 μL) and the disposable nature of the manufactured strips to explore short-term responses of microbial extracellular electron transfer to conductive materials under different scenarios. The system proved to be robust for identifying the bioelectrochemical response, while avoiding complex electrochemical setups, not available in standard biotechnology laboratories. We successfully validated the system for characterizing the response of Geobacter sulfurreducens in different physiological states (exponential phase, stationary phase, and steady state under continuous culture conditions) revealing different electron transfer responses. Moreover, a combination of SPE and G. sulfurreducens resulted to be a promising biosensor for quantifying the levels of acetate, as well as for performing studies in real wastewater. In addition, the potential of the technology for identifying electroactive consortia was tested, as an example, with a mixed population with nitrate-reducing capacity. We therefore present SPEs as a novel low-cost platform for assessing microbial electrochemical activity at the microscale level.
Highlights
Since the discovery in the last decade of electrode-respiring microbes, such as Geobacter sulfurreducens and some species of Shewanella [1,2], there has been an increasing interest in their potential applications for designing several types of microbial electrochemical technologies (METs), like electricity production from wastewater in microbial fuel cells (MFC), bioremediation in microbial electroremediating cells (MERCs) [3], electrosynthesis, or biosensing [4]
With the aim of standardize our methodology, a preliminary study was performed by increasing thecell concentration of G. sulfurreducens and measuring the current production using carbon screen-printed electrode (SPE)
The results presented in this work demonstrate that screen-printed disposable electrodes can be used as a novel platform to assess within minutes the electron transfer capacities of electroactive microorganisms in quick drop assays that only require microlitres of culture samples
Summary
Since the discovery in the last decade of electrode-respiring microbes, such as Geobacter sulfurreducens and some species of Shewanella [1,2], there has been an increasing interest in their potential applications for designing several types of microbial electrochemical technologies (METs), like electricity production from wastewater in microbial fuel cells (MFC), bioremediation in microbial electroremediating cells (MERCs) [3], electrosynthesis, or biosensing [4]. Many attempts to optimize METs have been focused on reactor design and operational aspects [5,6] Different electrochemical approaches, such as chronoamperometric assays, cyclic voltammetry (CV), sometimes coupled to spectroscopic techniques as infrared (IR) or Raman [7,8,9], have been applied for the study of this fascinating phenomenon. All of these have helped to investigate and analyze electroactive microorganisms and learn valuable information about how microbial physiology at different hierarchical levels affects the capability of electron transfer to solid electrodes at the whole biofilm, single cell and sub-cell (molecular) level [10,11,12]. This is partially due to difficulties in monitoring METs or the requirement of rather complex experimental setups for growing bacteria in electrochemical environments with limited access to microbial tools [13,14]
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