A comparative life cycle analysis of electromicrobial production systems

Electromicrobial production (EMP) processes represent an attractive strategy for the capture and conversion of CO2 into carbon-based products. We describe the development and application of comprehensive reactor, process, and life cycle impact models to analyze three major EMP systems relying on formate, H2, and acetate as intermediate molecules. Our results demonstrate that EMP systems can achieve a smaller carbon footprint than traditional bioprocessing strategies provided the electric grid is composed of >~90% renewable energy sources. For each of the three products we consider (biomass, enzymes, and lactic acid), the H2-mediated Knallgas bacteria system achieves the lowest overall global warming potential, indicating that this EMP strategy may be best-suited for industrial efforts based on current technology. We also identify environmental hotspots and process limitations that are key sites for future engineering and research efforts for each EMP system. Our analysis demonstrates the utility of an integrated bioelectrochemical model/life cycle assessment framework in both analyzing and aiding the ecodesign of electromicrobial processes and should help guide the design of working, scalable, and sustainable systems.

Optimization of PolyHydroxyAlkanoate Bioelectrosynthesis by the thermophilic bacterium Kyrpidia spormannii

<p>The electrosynthesis of valuable compounds by biofilms on electrodes is intensively studied since few years. However, the actual biofilms growing so far on cathode produce mainly small inexpensive compounds such as acetate or ethanol. A novel Knallgas bacteria, <em>Kyrpidia spormannii</em> have been recently described to grow on cathode in thermophilic and microaerophilic conditions, producing significant amount of PolyHydroxyAlkanoates (PHAs) (Reiner et al., 2018). These PHA are promising sustainable bioplastic polymers with the potential to replace petroleum-derived plastics in a variety of applications. However, the effect of culture conditions and electrode properties on the growth of <em>K. spormannii</em> biofilm and PHA production is still unclear.</p> <p>We present in this study the successful development and operation of autotrophic biocathode whereby the electroactive biofilm was able to grow by utilizing CO<sub>2</sub> and a cathode as the sole carbon and electron source, respectively. We report for the first time, the effect of operating conditions of the Bioelectrochemical system (BES), cathode materials and cathode surface modification on current consumption, biofilm formation, PHA productivity and overall coulombic efficiency of a <em>K. spormannii</em> culture growing on electrodes. In particular, the focus of this study lies on optimization of three main operating conditions, which are the applied cathode potential, pH buffer and the oxygen concentration in the feed gas. Increased biofilm formation and PHA production was observed at an applied potential of -844mV vs. SCE, pH 6.5, O<sub>2</sub> saturation of 2.5%, and for a graphite cathode modified by CO<sub>2</sub> activation. The PHA concentration in the biofilm reached a maximum of ≈40 μg·cm<sup>-2</sup> after optimization. The resultant PHA yield reported after optimization is increased by 12.2 times in comparison to previous results. In conclusion, these findings take microbial electrosynthesis of PHA a step forward towards practical implementation.</p>

Cultivation-Independent Detection of Autotrophic Hydrogen-Oxidizing Bacteria by DNA Stable-Isotope Probing

ABSTRACTKnallgas bacteria are a physiologically defined group that is primarily studied using cultivation-dependent techniques. Given that current cultivation techniques fail to grow most bacteria, cultivation-independent techniques that selectively detect and identify knallgas bacteria will improve our ability to study their diversity and distribution. We used stable-isotope probing (SIP) to identify knallgas bacteria in rhizosphere soil of legumes and in a microbial mat from Obsidian Pool in Yellowstone National Park. When samples were incubated in the dark, incorporation of13CO2was H2dependent. SIP enabled the detection of knallgas bacteria that were not detected by cultivation, and the majority of bacteria identified in the rhizosphere soils were betaproteobacteria predominantly related to genera previously known to oxidize hydrogen. Bacteria in soil grew on hydrogen at concentrations as low as 100 ppm. AhydBhomolog encoding a putative high-affinity NiFe hydrogenase was amplified from13C-labeled DNA from both vetch and clover rhizosphere soil. The results indicate that knallgas bacteria can be detected by SIP and populations that respond to different H2concentrations can be distinguished. The methods described here should be applicable to a variety of ecosystems and will enable the discovery of additional knallgas bacteria that are resistant to cultivation.