Characterizing Electron Transport through Living Biofilms

Microorganisms as New Sources of Energy

The use of fossil energy sources has a negative impact on the economic and socio-political stability of specific regions and countries, causing environmental changes due to the emission of greenhouse gases. Moreover, the stocks of mineral energy are limited, causing the demand for new types and forms of energy. Biomass is a renewable energy source and represents an alternative to fossil energy sources. Microorganisms produce energy from the substrate and biomass, i.e., from substances in the microenvironment, to maintain their metabolism and life. However, specialized microorganisms also produce specific metabolites under almost abiotic circumstances that often do not have the immediate task of sustaining their own lives. This paper presents the action of biogenic and biogenic–thermogenic microorganisms, which produce methane, alcohols, lipids, triglycerides, and hydrogen, thus often creating renewable energy from waste biomass. Furthermore, some microorganisms acquire new or improved properties through genetic interventions for producing significant amounts of energy. In this way, they clean the environment and can consume greenhouse gases. Particularly suitable are blue-green algae or cyanobacteria but also some otherwise pathogenic microorganisms (E. coli, Klebsiella, and others), as well as many other specialized microorganisms that show an incredible ability to adapt. Microorganisms can change the current paradigm, energy–environment, and open up countless opportunities for producing new energy sources, especially hydrogen, which is an ideal energy source for all systems (biological, physical, technological). Developing such energy production technologies can significantly change the already achieved critical level of greenhouse gases that significantly affect the climate.

In Situ Spectroelectrochemical Characterization Reveals Cytochrome-Mediated Electric Syntrophy in Geobacter Coculture

Direct interspecies electron transfer (DIET) between microbial species prevails in some key microbial consortia. However, the electron transfer mechanism(s) in these consortia is controversial due to lack of efficient characterization methods. Here, we provide an in situ anaerobic spectroelectrochemical coculture cell (in situ ASCC) to induce the formation of DIET coculture biofilm on the interdigitated microelectrode arrays and characterize the electron transfer directly. Two typical Geobacter DIET cocultures, Geobacter metallireducens and wild-type Geobacter sulfurreducens (G.m&G.s) and G. metallireducens and a G. sulfurreducens strain deficient in citrate synthase (G.m&G.s-ΔgltA), were selected. In situ Raman and electrochemical Fourier transform infrared (FTIR) spectroscopy indicated that cytochromes are abundant in the electric syntrophic coculture. Cyclic voltammetry and potential step experiment revealed a diffusion-controlled electron transfer process and the electrochemical gating measurements further demonstrated a cytochrome-mediated electron transfer in the DIET coculture. Furthermore, the G.m&G.s-ΔgltA coculture displayed a higher redox conductivity than the G.m&G.s coculture, consistent with the existence of an intimate and efficient electrical connection between these two species. Our findings provide the first report of a redox-gradient-driven electron transport facilitated by c-type cytochromes in DIET coculture, supporting the model that DIET is mediated by cytochromes and suggest a platform to explore the other DIET consortia.

Microbial fuel cells: a comprehensive review for beginners

Microbial fuel cells (MFCs) have shown immense potential as a one-stop solution for three major sustainability issues confronting the world today-energy security, global warming and wastewater management. MFCs represent a cross-disciplinary platform for research at the confluence of the natural and engineering sciences. The diversity of variables influencing performance of MFCs has garnered research interest across varied scientific disciplines since the beginning of this century. The increasing number of research publications has made it necessary to keep track of work being carried out by research groups across the globe and consolidate significant findings on a regular basis. Review articles are often the nodal points for beginners who are required to undertake an exploratory survey of literature to identify a suitable research problem. This 'review of reviews' is a ready-reckoner that directs readers to relevant reviews and research articles reporting significant developments in MFC research in the last two decades. The article also highlights the areas needing research attention which when addressed could take this technology a few more steps closer to practical implementation.