Assessment of Voltage Influence in Carbon Dioxide Fixation Process by a Photo-Bioelectrochemical System under Photoheterotrophy

Sara Díaz-Rullo Edreira,Silvia Barba,Fernando Martínez,Daniel Puyol,Raúl Molina,Juan Antonio Melero,Ioanna A. Vasiliadou,Juan José Espada

doi:10.3390/microorganisms9030474

Sara Díaz-Rullo Edreira, Silvia Barba + Show 6 more

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https://doi.org/10.3390/microorganisms9030474

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Abstract

Bioelectrochemical systems are a promising technology capable of reducing CO2 emissions, a renewable carbon source, using electroactive microorganisms for this purpose. Purple Phototrophic Bacteria (PPB) use their versatile metabolism to uptake external electrons from an electrode to fix CO2. In this work, the effect of the voltage (from −0.2 to −0.8 V vs. Ag/AgCl) on the metabolic CO2 fixation of a mixed culture of PPB under photoheterotrophic conditions during the oxidation of a biodegradable carbon source is demonstrated. The minimum voltage to fix CO2 was between −0.2 and −0.4 V. The Calvin–Benson–Bassham (CBB) cycle is the main electron sink at these voltages. However, lower voltages caused the decrease in the current intensity, reaching a minimum at −0.8 V (−4.75 mA). There was also a significant relationship between the soluble carbon uptake in terms of chemical oxygen demand and the electron consumption for the experiments performed at −0.6 and −0.8 V. These results indicate that the CBB cycle is not the only electron sink and some photoheterotrophic metabolic pathways are also being affected under electrochemical conditions. This behavior has not been tested before in photoheterotrophic conditions and paves the way for the future development of photobioelectrochemical systems under heterotrophic conditions.

Highlights

The emission of anthropogenic greenhouse gases, carbon dioxide (CO2 ), is considered one of the main causes of climate change and global warming [1,2,3]
Bioelectrochemical systems (BES), which are capable of fixing CO2 by using electroactive microorganisms, are considered an environmentally friendly technology that contributes to mitigating carbon footprint concerns [4]
Evidence of biologicalmediated process is found in the reduction of the conductivity of the anode in biological experiments above −0.2 V, but is found neither in the biological experiment at −0.2 V nor in the abiotic control at −0.8 V, as shown in Supporting Information ( S1)

Summary

Introduction

The emission of anthropogenic greenhouse gases, carbon dioxide (CO2 ), is considered one of the main causes of climate change and global warming [1,2,3]. Bioelectrochemical systems (BES), which are capable of fixing CO2 by using electroactive microorganisms, are considered an environmentally friendly technology that contributes to mitigating carbon footprint concerns [4]. Purple phototrophic bacteria (PPB) are a group of microorganisms with a multitude of metabolic pathways [8,9] that have interesting applications in resource recovery from waste sources [10]. This includes their capacity to uptake external electrons in BES [11,12,13,14]. Some previous works have evidenced the capacity of PPB to uptake electrons and to incorporate them into their metabolism, demonstrating that the main metabolic pathway is the Calvin–

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