Enhancement of anaerobic lysine production in Corynebacterium glutamicum electrofermentations

Abstract

It has been suggested that application of electric potential can affect lysine producing fermentations, although experimental evidence is lacking. To study this hypothesis we used the lysine producer Corynebacterium glutamicum ZW04, and we exposed it to 12 different conditions regarding anaerobic gas environment, applied electrode potential (cathodic, open circuit, anodic), redox mediator and nitrate presence. The gas environment was found to play a major role, with CO leading to double the lysine concentrations and yields when compared to N. Electrode potentials also played a major role, with reductive conditions doubling the titers and increasing the yields of lysine up to 4 times. Addition of the redox mediator anthraquinone-2-sulfonate (AQ2S) under the presence of CO and reductive conditions led to additional doubling of the titers, although the yields were not altered considerably. This study demonstrates for the first time that cathodic electrode conditions combined with CO and AQ2S as a redox mediator can significantly improve both the yields and the titers of lysine production of a C. glutamicum lysine producing strain, reaching levels that have only been achieved under aerobic conditions.

Anodic electro‐fermentation: Anaerobic production of L‐Lysine by recombinant Corynebacterium glutamicum

“…On the other hand, under oxidative conditions its redox potential is too negative to allow acceptance of electrons from the terminal components of the cellular electron transport chain of C. glutamicum (Kracke et al, ). Interestingly lysine concentrations and yields observed by us were comparable to those reported in the same study but under reductive conditions (Xafenias et al, ), in spite of the fact that in that study a further optimized production strain was used. This strain carried two additional beneficial mutations for lysine production (Ohnishi et al, ), yet no better outcome was achieved.…”

“…Xafenias et al () recently tested anthraquinone‐2‐sulfonate (AQ2S) as a mediator to increase the production of lysine under oxidative and reductive conditions in a BES. In contrast to our study, no growth could be observed but different effects on different metabolic products were described.…”

“…In C. glutamicum this should in principle allow anaerobic growth and production (Kracke, Vassilev, & Krömer, 2015). A recent study describes the incubation of C. glutamicum in a BES under reductive conditions to enhance anaerobic lysine production (Xafenias, Kmezik, & Mapelli, 2017), however, under these electron "feeding" conditions no growth could be observed. Here we provide the L-lysine producing strain C. glutamicum lysC (Kim, Heinzle, & Wittmann, 2006) with the extracellular electron acceptor ferricyanide, a mediator with a positive redox potential (+0.44V vs. standard hydrogen electrode).…”

Bioelectricity Generation by Corynebacterium glutamicum with Redox-Hydrogel-Modified Carbon Electrode

“…C. glutamicum, an important Gram-positive industrial bacterium, can utilize oxygen as a preferable terminal electron acceptor in its respiratory system [7][8][9]. Manipulation of the redox metabolism of C. glutamicum connected with a cathode in a bioelectrochemical reactor system resulted in higher yields of the target product (l-lysine) when supplemented with AQDS [10]. Such results suggest that direct electron transfer between C. glutamicum and an electrode might be difficult.…”

Enhanced electron transfer of different mediators for strictly opposite shifting of metabolism in Clostridium pasteurianum grown on glycerol in a new electrochemical bioreactor

“…Few studies have been carried out to examine electron transfer or utilization in BES with suspended microorganisms (Harnisch, Rosa, Kracke, Virdis, & Krömer, ), mostly in classic BES, such as the popular H‐cell reactors, which are hardly applicable for industrial bioprocesses and have inherent shortcomings for the control of culture conditions and quantification of electron transfer (Utesch & Zeng, ). Indirect electron transfer via mediators in suspension culture is an alternative process, where even none‐electroactive microorganisms can be influenced for enhanced production of valuable products (Aulenta, Di Maio, Ferri, & Majone, ; Choi, Um, & Sang, ; Xafenias, Kmezik, & Mapelli, ). Kracke, Virdis, Bernhardt, Rabaey, and Krömer () first reported a metabolic shift in Clostridium autoethanogenum towards more reduced products because of the electron supply in BES dependent on the redox potentials (RPs) of utilized mediators and intracellular electron acceptors (Kracke et al, ).…”