Cathodes enhance Corynebacterium glutamicum growth with nitrate and promote acetate and formate production

Abstract

The industrially important Corynebacterium glutamicum can only incompletely reduce nitrate into nitrite which then accumulates and inhibits growth. Herein we report that cathodes can resolve this problem and enhance glucose fermentation and growth by promoting nitrite reduction. Cell growth was inhibited at relatively high potentials but was significant when potentials were more reductive (-1.20V with anthraquinone-2-sulfonate as redox mediator or -1.25V vs. Ag/AgCl). Under these conditions, glucose was consumed up to 6 times faster and acetate was produced at up to 11 times higher yields (up to 1.1mol/mol-glucose). Acetate concentrations are the highest reported so far for C. glutamicum under anaerobic conditions, reaching values up to 5.3±0.3g/L. Herein we also demonstrate for the first time formate production (up to 3.4±0.3g/L) by C. glutamicum under strongly reducing conditions, and we attribute this to a possible mechanism of CO2 bioreduction that was electrochemically triggered.

Tuning Redox Potential of Anthraquinone-2-Sulfonate (AQS) by Chemical Modification to Facilitate Electron Transfer From Electrodes in Shewanella oneidensis

“…The amperometric i-t curve and cyclic voltammetry (CV) were monitored using a Chenhua CHI1030C potentiostat ( Xafenias et al, 2016 ) . The potential of amperometric curve was imposed at −0.65 V (vs. Ag/AgCl).…”

“…Unless otherwise specified, the CV assays were carried out in a conventional three-electrode system at a scan rate of 100 mV/s, in which the electrolyte was consisted of deoxygenated M9 buffer (pH 7.0) ( Elgrishi et al, 2018 ). Current density and Coulombic efficiency in MES were calculated using the following equations ( Steinbusch et al, 2010 ; Xafenias et al, 2016 ): where I means current record, S means surface area of carbon cloth , M means the number of moles of products, n means the number of electrons in each reaction, and F is Faraday’s constant (96,485 C/mol of electrons). The production of succinate was analyzed by a high-performance liquid chromatography (HPLC) method on an Agilent 1,100 Series HPLC system equipped with a cation exchange column (Aminex HPX87-H, Bio-Rad, United States) as described previously ( Bursac et al, 2017 ).…”

“…Unless otherwise specified, the CV assays were carried out in a conventional three-electrode system at a scan rate of 100 mV/s, in which the electrolyte was consisted of deoxygenated M9 buffer (pH 7.0) (Elgrishi et al, 2018). Current density and Coulombic efficiency in MES were calculated using the following equations (Steinbusch et al, 2010;Xafenias et al, 2016):…”

“…S. oneidensis MR-1 employs several different strategies to capture electrons from the cathode, including cytochromes, nanowires and extracellular ESs ( Tremblay and Zhang, 2015 ). Nowadays, many ESs have been found to improve the electron transport capacity from a cathode to microbes, such as neutral red (NR), riboflavin (RF), anthraquinone-2-sulfonate (AQS) and methyl viologen (MV) ( Choi et al, 2012 ; Harrington et al, 2015a ; Tokunou et al, 2016 ; Xafenias et al, 2016 ).…”