Microbial Electrosyntheses - Research project evaluating the usage of electric energy for future microbial production processes

Most industrial synthesis of fuels and chemicals are currently based on the use of fossil carbon sources such as oil, gas and coal. It has long been known that these supplies are finite. Therefore, to greater extent biotechnological and chemical processes based on renewable raw materials like sugar and starch get into focus. Nevertheless, the usage of such raw materials results in a massive competition for crops between commodity and food manufacturers. A way out of this "food-or-fuel" dilemma may be microbial electrosynthesis. In this process, electrons are transferred from a cathode to microorganisms. The microorganisms use the electrons for reductive synthesis reactions (in the optimal case) based on CO2, whereby the required electrical energy should be obtained from regenerative sources. As part of the first research funding, numerous and in-depth insights were collected, which will be further investigated in the follow-up project.

The aim of the ongoing project is the further development of microbial electrosynthesis for the production of bulk chemicals. For this purpose, the knowledge gained from the first research project will be used to establish new production routes based on electroactive organisms. Alternatively, optimizations of the biofilm formation of these electroactive organisms are planned in order to increase yields. Furthermore, it is planned to make microbial electrosynthesis even more efficient by various reaction-technical optimizations (such as the use of novel reactor concepts).
The focus of the project will be on three key topics:

a)      Expansion of the product spectrum, among others through strain development
Literature describes numerous organisms that are suitable as model organisms for microbial electrosynthesis. Although these electroactive organisms have been very well studied, only a few strains are known to produce industrially relevant chemicals. Therefore, within the framework of this project, the product range of different electroactive strains should be extended by means of metabolic engineering. In addition, other organisms with interesting properties such as H2 metabolization or high solvent tolerance are being capacitated to be electroactive.

b)      Optimization of biofilm formation with appropriate monitoring
The underlying biological mechanisms for electron uptake are poorly understood. Therefore, the investigation of the interaction of the microorganisms with the cathode is a research focus of the DFI. As well biofilm formation and cell immobilization at the cathode as different techniques for biofilm stability are being investigated.

c)       Reaction engineering optimization of microbial electrosyntheses
For the extension of microbial electrosynthesis towards a photoelectrochemical production system, hydrogen production by means of photocatalysis and the cultivation of C. necator should be combined and analyzed. Furthermore, fluidized bed reactors will be investigated.

Microbial Electrosynthesis is a new interdisciplinary research field for the production of biofuels and basic chemicals from oxidized substrates such as carbon dioxide. Electrons supplied by a cathode enable the reductive synthesis of these substrates catalyzed by electroactive microorganisms. These organisms are able to interact directly with the cathode or utilize electrochemically reduced media components such as redox mediators or hydrogen. To date the biological mechanisms for the electron uptake are poorly understood (1).Therefore, our research at the DFI focuses on the interaction of electroactive microorganisms with cathodes including biofilm formation and cell immobilization on different electrode materials. Different electron uptake strategies such as the direct transfer are being compared to the indirect, mainly mediator-based electron transfer mechanisms concerning production efficiency. Bioelectrochemical reactor designs are developed and optimized to enhance microbial growth and production of chemicals helping to improve our electroactive microorganisms. A broad spectrum of molecular and microbial as well as electrochemical methods (e.g. impedance spectroscopy, cyclic voltammetry) are used to characterize the systems. The research groups Biochemical Engineering and Electrochemistry are working on this tandem project at the DFI.

(1) Sydow, A., Krieg, T., Mayer, F. et al. Appl Microbiol Biotechnol (2014) 98: 8481