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Electroactive microorganisms are pivotal players in mineral transformation within redox interfaces characterized by pronounced oxygen and dissolved metal gradients. Yet, their systematic cultivation from such environments remains elusive. Here, we conducted an anodic enrichment using anoxic ferruginous waters from a post-mining lake as inoculum. Weak electrogenicity ( j = ∼5 µA cm−2) depended on electroactive planktonic cells rather than anodic biofilms, with a preference for formate as electron donor. Addition of yeast extract decreased the lag phase but did not increase current densities. The enriched bacterial community varied depending on the substrate composition but mainly comprised of sulfate- and nitrate-reducing bacteria (e.g., Desulfatomaculum spp. and Stenotrophomonas spp.). A secondary enrichment strategy resulted in different bacterial communities composed of iron-reducing (e.g., Klebsiella spp.) and fermentative bacteria (e.g., Paeniclostridium spp.). Secondary electron microscopy and energy-dispersive X-ray spectroscopy results indicate the precipitation of sulfur- and iron-rich organomineral aggregates at the anode surface, presumably impeding current production. Our findings indicate that (i) anoxic waters containing geogenically derived metals can be used to enrich weak electricigens, and (ii) it is necessary to either specifically inhibit sulfate reducers. Otherwise, sulfate reducers tend to dominate over EAM during cultivation, which can lead to anode passivation due to biomineralization.

3D-printed anodes for bioelectrochemical systems are increasingly being reported. However, comparisons between 3D-printed anodes and their non-3D-printed counterparts with the same material composition are still lacking. In addition, surface roughness parameters that could be correlated with bioelectrochemical performance are rarely determined. To fill these gaps, slurries with identical composition but different mass fractions were processed into SiOC anodes by tape-casting, freeze-casting, or direct-ink writing. The current generation was investigated using electroactive biofilms enriched with Geobacter spp. Freeze-cast anodes showed more surface pores and the highest surface kurtosis of 5.7 ± 0.5, whereas tape-cast and 3D-printed anodes showed a closed surface porosity. 3D-printing was only possible using slurries 85 wt% of mass fraction. The surface pores of the freeze-cast anodes improved bacterial adhesion and resulted in a high initial (first cycle) maximum current density per geometric surface area of 9.2 ± 2.1 A m−2. The larger surface area of the 3D-printed anodes prevented pore clogging and produced the highest current density per geometric surface area of 12.0 ± 1.2 A m−2. The current density values of all anodes are similar when the current density is normalized over the entire geometric surface as determined by CT-scans. This study highlights the role of geometric surface area in normalizing current generation and the need to use more surface roughness parameters to correlate anode properties, bacterial adhesion, and current generation.

Physiological cellular parameters, like for instance latency times (lagt), duplication rates (DR), relative growth rates (RGR) and yield coefficients (YNe) are only known as endpoint measurements for electroactive microorganisms (EAM). Here we show that these can be gained non-invasively and in real-time for early-stage biofilm formation at electrodes using a microfluidic electrochemical flow-cell (EFC) allowing in vivo optical microscopy. Parameters obtained for early-stage mixed culture biofilm anodes formed at +150 mV vs. Ag/ AgCl sat. KCl are lagt of 2.31-4.58 days, DR of 0.72-1.20 × 105 cells h-1, RGR of 0.02-0.27 h-1 and YNe of 5.99-7.94 × 1012 cells mole--1. However, oxygen permeation into the EFC was a main problem remaining unsolved during the study that provides interesting lessons for future improvements.

Microbial resource mining of electroactive microorganism (EAM) is currently methodically hampered due to unavailable electrochemical screening tools. Here, we introduce an electrochemical microwell plate (ec-MP) composed of a 96 electrochemical deepwell plate and a recently developed 96-channel multipotentiostat. Using the ec-MP we investigated the electrochemical and metabolic properties of the EAM models Shewanella oneidensis and Geobacter sulfurreducens with acetate and lactate as electron donor combined with an individual genetic analysis of each well. Electrochemical cultivation of pure cultures achieved maximum current densities (jmax) and coulombic efficiencies (CE) that were well in line with literature data. The co-cultivation of S. oneidensis and G. sulfurreducens led to an increased current density of jmax of 88.57±14.04 µA cm-2 (lactate) and jmax of 99.36±19.12 µA cm-2 (lactate and acetate). Further, a decreased time period of reaching jmax and biphasic current production was revealed and the microbial electrochemical performance could be linked to the shift in the relative abundance.

Bed electrodes provide high electrode area‐to‐volume ratios representing a promising configuration for transferring bioelectrochemical systems close to industrial applications. Nevertheless, the intrinsic electrical resistance leads to a poor polarization behavior. Therefore, the distribution of Geobacter spp. and their electrochemical performance within exemplary fixed bed electrodes were investigated. A minimally invasive sampling system allowed characterization of granules from different spatial locations of bed electrodes. Cyclic voltammetry of single granules (n=63) demonstrated that the major share of electroactivity (134.3 mA L −1 ) was achieved by ca. 10% of bed volume, specifically that being close to the current collector. Nevertheless, analysis of the microbial community revealed that Geobacter spp. dominated all sampled granules. These findings clearly demonstrate the need for engineered bed electrodes to improve electron exchange between microorganisms and granules.

Porous SiOC tapes were studied as anodes for bioelectrochemical system (BES) using Geobacter spp. as electroactive microorganism (EAM). The ceramic anodes were produced by tape‐casting of poly(silsesquioxanes), tailoring the surface properties by incorporating graphite and carbon black and varying the pyrolysis temperature. By varying these parameters, the specific surface area, the hydrophilicity and the roughness  were adjusted, with the pyrolysis temperature playing a major role. When used as anodes at 0.2 V vs. Ag/AgCl sat. KCl in the BES, maximum current densities relative to the geometric surface area ( j GSA ) up to 5.8 Am ‐2 were achieved . Microbial community analysis of the biofilm shows the dominant presence of Geobacter spp. as EAM. Benchmarking the performance of the anodes of this study with anodes using the same EAM demonstrates that porous SiOC anodes are a promising class of materials, as they show j GSA comparable to carbon‐based anodes

The Front Cover shows a biofilm anode that is obtained through electrochemically driven enrichment in a one‐chamber reactor that is dominated by Geobacter but also colonized by methanogens that cross feed from cathodic hydrogen. More information can be found in the Article by B. Korth et al.

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Geobacter spp. enrichment biofilms were cultivated in batch using one-chamber and two-chamber bioelectrochemical reactors. Time-resolved substrate quantification was performed to derive physiological parameters as well as incremental coulombic efficiency (i.e., coulombic efficiency during one batch cycle, here every 6h) during early stage biofilm development. The results of one-chamber reactors revealed an intermediate acetate increase putatively due to the presence of acetogens. Total coulombic efficiencies of two-chamber reactors were considerable lower (19.6±8.3% and 49.3±13.2% for 1st and 2nd batch cycle, respectively) compared to usually reported values of mature Geobacter spp. enrichment biofilms presumably reflecting energetic requirements for biomass production (i.e., cells and extracellular polymeric substances) during early stages of biofilm development. The incremental coulombic efficiency exhibits considerable changes during batch cycles indicating shifts between phases of maximizing metabolic rates and maximizing biomass yield. Analysis based on Michaelis-Menten kinetics yielded maximum substrate uptake rates (vmax,Ac, vmax,I) and half-saturation concentration coefficients (KM,Ac,KM,I) based on acetate uptake or current production, respectively. The latter is usually reported in literature but neglects energy demands for biofilm growth and maintenance as well as acetate and electron storage. From 1st to 2nd batch cycle, vmax,Ac and KM,Ac, decreased from 0.0042–0.0051 mmol Ac− h−1 cm−2 to 0.0031–0.0037 mmol Ac− h−1 cm−2 and 1.02–2.61 mM Ac− to 0.28–0.42 mM Ac−, respectively. Furthermore, differences between KM,Ac/KM,I and vmax,Ac/vmax,I were observed providing insights into the physiology of Geobacter spp. enrichment biofilms. Notably, KM,I considerably scattered while vmax,Ac/vmax,I and KM,Ac remained rather stable indicating that acetate transport within biofilm only marginally affects reaction rates. The observed data variation mandates the requiremen

Biofilm anodes based on Geobacter enrichment in one‐chamber and two‐chamber reactors are qualitatively and quantitatively investigated. The methanogenic community of biofilms in both types of reactors consists exclusively of hydrogenotrophs, mainly the genus Methanobacterium . As qPCR demonstrates in one‐chamber reactors, the abundance of Geobacter and methanogens increases due to the presence of cathodically produced hydrogen. In two‐chamber reactors, the abundance of methanogens is decreased by 98% compared to one‐chamber reactors. Adding hydrogen gas to the anodic compartment of two‐chamber reactors recovers the abundance of methanogens and Geobacter . Ratios of methanogens/bacteria are confirmed using cofactor F 420 autofluorescence of methanogens. The impact of the reactor setup for developing primary microbial electrochemical technologies is discussed reasoning that two‐chamber reactors have to be generally favored. Yet, their use inheres a trade‐off when cultivating biofilm anodes, as the indicated syntrophic interactions between methanogens and Geobacter are reduced but pH decrease might influence microbial processes.

In der Natur sind zahlreiche biologische Prozesse mit der Übertragung von Elektronen verbunden, insbesondere die Stoffwechselprozesse zur Energiegewinnung aller Organismen. Technische Systeme zur elektrischen Energiegewinnung, zur Synthese bestimmter Produkte mittels elektrischen Stroms oder zur elektrischen Signalbildung in Messsystemen basieren auf denselben Grundprinzipien der Elektrochemie. Daher ist die Kopplung von Elektronenflüssen in biologischen und technischen Systemen nur folgerichtig und steht im Mittelpunkt der Elektrobiotechnologie.

In der Natur sind zahlreiche biologische Prozesse mit der Übertragung von Elektronen verbunden, insbesondere die Stoffwechselprozesse zur Energiegewinnung aller Organismen. Technische Systeme zur elektrischen Energiegewinnung, zur Synthese bestimmter Produkte mittels elektrischen Stroms oder zur elektrischen Signalbildung in Messsystemen basieren auf denselben Grundprinzipien der Elektrochemie. Daher ist die Kopplung von Elektronenflüssen in biologischen und technischen Systemen nur folgerichtig und steht im Mittelpunkt der Elektrobiotechnologie.

The combination of anaerobic digestion (AD) and microbial electrochemical technologies provides the opportunity to efficiently produce methane and electrical energy from complex biomass. Enhanced methane production and system stability have been reported but the causes (electrolysis or microbial–electrochemical interactions) are less understood. Using the model substrate corn silage it is demonstrated that, for conditions allowing microbiome growth and adaptation, the methane yield of combined reactors remains constant (216 (±29) mL godm−1) while a second product, electrons (q = 14.4 (±0.8) kC, jmax = 1.34 mA cm−2 geometric current density), is also generated. The combined strategy allowed up to a 27% increase in total yield while the reactor community and its dynamics over time were not affected. A typical AD composition of Firmicutes, Bacteroidetes, Proteobacteria, and Synergistetes (bacteria) as well as Methanosarcina, Methanoculleus and Methanobacterium (archaea) was found in the bulk liquid. Specific enrichments of Geobacter (anode) and Methanobacterium (cathode) were of functional relevance.