Identifying target processes for microbial electrosynthesis by elementary mode analysis

Abstract

BackgroundMicrobial electrosynthesis and electro fermentation are techniques that aim to optimize microbial production of chemicals and fuels by regulating the cellular redox balance via interaction with electrodes. While the concept is known for decades major knowledge gaps remain, which make it hard to evaluate its biotechnological potential. Here we present an in silico approach to identify beneficial production processes for electro fermentation by elementary mode analysis. Since the fundamentals of electron transport between electrodes and microbes have not been fully uncovered yet, we propose different options and discuss their impact on biomass and product yields.ResultsFor the first time 20 different valuable products were screened for their potential to show increased yields during anaerobic electrically enhanced fermentation. Surprisingly we found that an increase in product formation by electrical enhancement is not necessarily dependent on the degree of reduction of the product but rather the metabolic pathway it is derived from. We present a variety of beneficial processes with product yield increases of maximal 36% in reductive and 84% in oxidative fermentations and final theoretical product yields up to 100%. This includes compounds that are already produced at industrial scale such as succinic acid, lysine and diaminopentane as well as potential novel bio-commodities such as isoprene, para-hydroxybenzoic acid and para-aminobenzoic acid. Furthermore, it is shown that the way of electron transport has major impact on achievable biomass and product yields. The coupling of electron transport to energy conservation could be identified as crucial for most processes.ConclusionsThis study introduces a powerful tool to determine beneficial substrate and product combinations for electro-fermentation. It also highlights that the maximal yield achievable by bio electrochemical techniques depends strongly on the actual electron transport mechanisms. Therefore it is of great importance to reveal the involved fundamental processes to be able to optimize and advance electro fermentations beyond the level of lab-scale studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-014-0410-2) contains supplementary material, which is available to authorized users.

Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply

“…However, a detailed discussion of metabolic electron transfer and possible interactions with an electrode are discussed in a preceding work from our group [18]. By analysing the electron feed from a cathode to the cellular metabolism theoretically, we identified the entry point of electrons into the microbial metabolism as a step of major importance for MES processes [18, 19]. It was shown that depending on the metabolic reaction that is directly related to extracellular electron supply, different effects on cellular redox and energy yields might be achieved.…”

Elektrobioraffinerien: Synergien zwischen elektrochemischen und mikrobiologischen Stoffumwandlungen nutzbar machen

“…B. Lit. [47,48] Bioprozesse sind oftmals durch die Anreicherung von Metaboliten, also Zwischenprodukten (Intermediaten) oder Produkten per se,l imitiert. Eine Steuerung findet auch in Elektrofermentationen Anwendung (z.…”

Plugging in microbial metabolism for industrial applications

“…Depending on the electrode potential, an excess of redox cofactors (such as NADH and NADPH) may be produced when an electrode is utilised as an electron acceptor, or in ATP production when being utilised as an electron acceptor 17 .…”