An in-situ surface electrochemistry approach toward whole-cell studies: Charge transfer between Geobacter sulfurreducens and electrified metal/electrolyte interfaces through linker molecules

Electrochemical reactivity and structure properties of electrogenic bacteria, Geobacter sulfurreducens (Gs) were studied to explore the heterogeneous electron transfer at the bacteria/electrode interface using electrochemical and in-situ spectroscopic techniques. The redox behavior of Gs adsorbed on a gold electrode, which is modified with a ω-functionalized self-assembled monolayer (SAM) of alkanethiols, depends strongly on the terminal group. The latter interacts directly with outermost cytochromes embedded into the outer membrane of the Gs cells. The redox potential of bacterial cells bound electrostatically to a carboxyl-terminated SAM is close to that observed for bacteria attached to a bare gold electrode, revealing a high electronic coupling at the cell/SAM interface. The redox potentials of bacterial cells adsorbed on amino- and pyridyl-terminated SAMs are significantly different suggesting that the outermost cytochromes changes their conformation upon adsorption on these SAMs. No redox activity of Gs was found with CH3-, N(CH3)3+- and OH-terminated SAMs. Complementary in-situ spectroscopic studies on bacteria/SAMs/Au electrode assemblies were carried out to monitor structure changes of the bacterial cells upon polarization. Spectro-electrochemical techniques revealed the electrochemical turnover of the oxidized and reduced states of outer membrane cytochromes (OMCs) in Gs, providing evidence that the OMCs are responsible for the direct electron transfer to metal electrodes, such as gold or silver, during the electricity production. Furthermore, we observed spectroscopic signatures of the native structure of the OMCs and no conformational change during the oxidation/reduction process of the microorganisms. These findings indicate that the carboxyl-anchoring group provides biocompatible conditions for the outermost cytochromes of the Gs, which facilitate the heterogeneous electron transfer at the microorganism/electrode interface.

Auswirkungen der Klimaänderung auf die schweizerische Wasserkraftnutzung

Hydraulic power contributes for a large part to electricity production in Switzerland. However, hydropower could be strongly affected by climate change. For that reason, the project CCWasserkraft – which results are summarised here – has been launched. In different studies, important aspects of the interactions between climate, hydrology and hydropower were investigated. Comprehensive simulations in representative catchments allowed quantifying the impacts of climate change on discharge and hydropower production. Finally, the results were extrapolated to whole Switzerland. The results show that significant changes are likely in the near future 2021–2050: an increase of hydropower production is projected for the winter half year, whereas stagnation or a decrease is expected in the summer half year. On the whole, the yearly hydropower production should remain constant or could even increase slightly. Projections for 2070–2099 remain uncertain. However, hydropower production from highly glaciated catchments located in southern and eastern Valais as well as catchments south of the Alps is expected to decline.