Microbial fuel cells (MFCs) are a promising technology to recover electrical energy from different types of waste. However, the power density of MFCs for practical applications is limited by the anode performance, mainly resulting from low bacterial loading capacity and low extracellular electron transfer (EET) efficiency. In this study, an open three-dimensional (3D) structured electrode was fabricated using a natural loofah sponge as the precursor material. The loofah sponge was directly converted into a continuous 3D macroporous carbon material via a simple carbonization procedure. The loofah sponge carbon (LSC) was decorated with nitrogen-enriched carbon nanoparticles by cocarbonizing polyaniline-hybridized loofah sponges to improve their microscopic structures. The macroscale porous structure of the LSCs greatly increased the bacterial loading capacity. The microscale coating of carbon nanoparticles favored EET due to the enhanced interaction between the bacteria and the anode. By using a single-chamber MFC equipped with the fabricated anode, a power density of 1090 ± 72 mW m(-2) was achieved, which is much greater than that obtained by similarly sized traditional 3D anodes. This study introduces a promising method for the fabrication of high-performance anodes from low-cost, sustainable natural materials.

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Mass transport within a cathode, including OH(-) transport and oxygen diffusion, is important for the performance of air-cathode microbial fuel cells (MFCs). However, little is known regarding how mass transport profiles are associated with MFC performance and how they are affected by biofilm that inevitably forms on the cathode surface. In this study, the OH(-) and oxygen profiles of a cathode biofilm were probed in situ in an MFC using microelectrodes. The pH of the catalyst layer interface increased from 7.0 ± 0.1 to 9.4 ± 0.3 in a buffered MFC with a bare cathode, which demonstrates significant accumulation of OH(-) in the cathode region. Furthermore, the pH of the interface increased to 10.0 ± 0.3 in the presence of the local biofilm, which indicates that OH(-) transport was severely blocked. As a result of the significant OH(-) accumulation, the maximum power density of the MFC decreased from 1.8 ± 0.1 W/m(2) to 1.5 ± 0.08 W/m(2). In contrast, oxygen crossover, which was significant under low current flow conditions, was limited by the cathode biofilm. As a result of the blocked oxygen crossover, higher MFC coulombic efficiency (CE) was achieved in the presence of the cathode biofilm. These results indicate that enhanced OH(-) transport and decreased oxygen crossover would be beneficial for high-performance MFC development.

Herbicides are one of the most widely used chemicals in agriculture. While they are known to be harmful to non-target organisms, the effects of herbicides on the composition and functioning of soil microbial communities remain unclear. Here we show that application of three widely used herbicides—glyphosate, glufosinate and dicamba—increase the prevalence of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soil microbiomes without clear changes in the abundance, diversity and composition of bacterial communities. Mechanistically, these results could be explained by a positive selection for more tolerant genotypes that acquired several mutations in previously well-characterized herbicide and antibiotic resistance genes. Moreover, herbicide exposure increased cell membrane permeability and conjugation frequency of multidrug resistance plasmids, promoting ARG movement between bacteria. A similar pattern was found in agricultural soils across eleven provinces in China, where herbicide application, and the levels of glyphosate residues in soils, were associated with increased ARG and MGE abundances relative to herbicide-free control sites. Together, our results show that herbicide application can enrich ARGs and MGEs by changing the genetic composition of soil microbiomes, potentially contributing to the global antimicrobial resistance problem in agricultural environments.

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Conventional biodecolorization of azo dyes is often limited by the lack of sustainable and bioavailable electron donors in aqueous environments. This limitation may be overcome by light-excited photoelectrons that drive the microbial reduction of azo dyes. Here, we innovatively developed a surface-precipitated Geobacter sulfurreducens− CdS biohybrid for the bioreduction of methyl orange (MO), a typical azo dye, driven by light. This biohybrid system exhibited the maximum kinetic constant at 1.441 h −1 , which is, to the best of our knowledge, the highest value reported thus far for MO biodecolorization. The intermittent illumination results indicated that G. sulfurreducens could directly use extracellular photoelectrons (rather than electrons from organics oxidization by strains) in order to perform decolorization on the bacterial cell surface. This can be attributed to the direct electron transfer from CdS nanoparticles to G. sulfurreducens. In addition, OmcB was identified as a key outermembrane protein that may act as a capacitor to modulate electron transfer from CdS to MO. This biohybrid catalytic approach may serve as a new strategy for azo dye degradation in oligotrophic surface waters and can deepen our knowledge on interactions between light, semiconductors and micro-organisms.

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Spectroelectrochemistry has been found to be an efficient technique for revealing extracellular electron transfer (EET) mechanism of electroactive biofilms (EABs). Herein, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor for monitoring EABs in situ. The sensor uses a tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber and coated with nanoscale gold film for high-efficiency SPR excitation. The wavelength shift of the surface plasmon resonance (SPR) over the fiber surface clearly identifies the electrochemical activity of the surface localized (adjacent to the electrode interface) bacterial cells in EABs, which differs from the "bulk" detections of the conventional electrochemical measurements. A close relationship between the variations of redox state of the EABs and the changes of the SPR under potentiostatic conditions has been achieved, pointing to a new way to study the EET mechanism of the EABs. Benefiting from its compact size, high sensitivity, and ease of use, together with remote operation ability, the proposed sensor opens up a multitude of opportunities for monitoring EABs in various hard-to-reach environments.