Predicting and experimental evaluating bio-electrochemical synthesis — A case study with Clostridium kluyveri

Abstract

Microbial electrosynthesis is a highly promising application of microbial electrochemical technologies for the sustainable production of organic compounds. At the same time a multitude of questions need to be answered and challenges to be met. Central for its further development is using appropriate electroactive microorganisms and their efficient extracellular electron transfer (EET) as well as wiring of the metabolism to EET. Among others, Clostridia are believed to represent electroactive microbes being highly promising for microbial electrosynthesis. We investigated the potential steps and challenges for the bio-electrochemical fermentation (electro-fermentation) of mid-chain organic acids using Clostridium kluyveri. Starting from a metabolic model the potential limitations of the metabolism as well as beneficial scenarios for electrochemical stimulation were identified and experimentally investigated. C. kluyveri was shown to not be able to exchange electrons with an electrode directly. Therefore, exogenous mediators (2-hydroxy-1,4-naphthoquinone, potassium ferrocyanide, neutral red, methyl viologen, methylene blue, and the macrocyclic cobalt hexaamine [Co(trans-diammac)]) were tested for their toxicity and electro-fermentations were performed in 1L bioreactors covering 38 biotic and 8 abiotic runs. When using C. kluyveri and mediators, maximum absolute current densities higher than the abiotic controls were detected for all runs. At the same time, no significant impact on the cell metabolism (product formation, carbon recovery, growth rate) was found. From this observation, we deduce general potential limitations of electro-fermentations with C. kluyveri and discuss strategies to successfully overcome them.

Metabolic Network Analysis of Microbial Methane Utilization for Biomass Formation and Upgrading to Bio-Fuels

“…Metabolic networks of the different organisms (Komagataella phaffii formerly Pichia pastoris, Saccharomyces cerevisiae, Escherichia coli, Bacillus subtilis, Corynebacterium glutamicum, Cupriavidus necator formerly Ralstonia eutropha and Clostridium autoethanogenum) were modified from published stoichiometric network analyses (Melzer et al, 2009;Lopar et al, 2013Lopar et al, , 2014Ternon et al, 2014;Unrean, 2014;Kracke et al, 2016;Koch et al, 2017; to fulfill the requirements of this elementary flux mode analysis. Specifically, the networks were integrated with methane assimilation pathways, compiled as follows:…”

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

“…Among them, NR and MV are the most studied ones, especially in fermentations with Clostridia (Du, Jiang, Yu, Tang, & Yang, ; Peguin, Goma, Delorme, & Soucaille, ; Reimann, Biebl, & Deckwer, ). However, in the studies of Choi et al () and Koch et al () with C. tyrobutyricum and C. kluyveri in a cathodic BES no effect of MV was observed, which was attributed to the membrane impermeability of reduced MV (Choi et al, ; Koch et al, ). In contrast, a membrane binding of NR and electron transfer from cathode to C. tyrobutyricum was reported for reduced NR (Choi et al, ), whereas oxidized NR was reported to even inhibit the growth of C. kluyveri (Koch et al, ).…”

“…However, in the studies of Choi et al () and Koch et al () with C. tyrobutyricum and C. kluyveri in a cathodic BES no effect of MV was observed, which was attributed to the membrane impermeability of reduced MV (Choi et al, ; Koch et al, ). In contrast, a membrane binding of NR and electron transfer from cathode to C. tyrobutyricum was reported for reduced NR (Choi et al, ), whereas oxidized NR was reported to even inhibit the growth of C. kluyveri (Koch et al, ). With its low RP (−0.525 V vs. Ag/AgCl) NR is suitable to provide electrons to intracellular electron consuming redoxsystems (Harrington et al, ).…”

Integrating Electrochemistry Into Bioreactors: Effect of the Upgrade Kit on Mass Transfer, Mixing Time and Sterilizability

“…Using the upgrade kit, two-chamber 1 L electrobioreactors based on batch stirred tank reactors (BSTR) were achieved (see Figure 1 and Figure SI 1). We demonstrated that the material and design of electrodes and other components of the 1 L electrobioreactors can be achieved allowing research on several pure cultures of electroactive microorganisms, e.g., Gluconobacter oxidans (Gimkiewicz et al, 2016), Clostridium kluyveri (Koch et al, 2017), Shewanella oneidensis (Rosa et al, 2017), and genetically modified E. coli (Mayr et al, 2019). However, to what extent the insertion of electrodes, an inlay creating two chambers, and the use of an adapted stirrer as well as removal of chicanes resulted in change of fluid dynamics remained unclear, and is addressed within this study.…”