Engineering extracellular electron transfer to promote simultaneous brewing wastewater treatment and chromium reduction.

Microbial fuel cell (MFC) technology has been developed for wastewater treatment in the anodic chamber, and heavy metal reduction in the cathodic chamber. However, the limited extracellular electron transfer (EET) rate of exoelectrogens remained a constraint for practical applications of MFCs. Here, a MFC system that used the electricity derived from anodic wastewater treatment to drive cathodic Cr6+ reduction was developed, which enabled an energy self-sustained approach to efficiently address Cr6+ contamination. This MFC system was achieved by screening exoelectrogens with a superior EET rate, promoting the exoelectrogenic EET rate, and constructing a conductive bio-anode. Firstly, Shewanella algae-L3 was screened from brewing wastewater acclimatized sludge, which generated power density of 566.83 mW m-2. Secondly, to facilitate EET rate, flavin synthesis gene operon ribADEHC was overexpressed in engineered S. algae-L3F to increase flavins biosynthesis, which promoted the power density to 1233.21 mW m-2. Thirdly, to facilitate interface electron transfer, carbon nanotube (CNT) was employed to construct a S. algae-L3F-CNT bio-anode, which further enhanced power density to 3112.98 mW m-2. Lastly, S. algae-L3F-CNT bio-anode was used to harvest electrical energy from brewing wastewater to drive cathodic Cr6+ reduction in MFC, realizing 71.43% anodic COD removal and 98.14% cathodic Cr6+ reduction. This study demonstrated that enhanced exoelectrogenic EET could facilitate cathodic Cr6+ reduction in MFC.

Recent advances in enrichment, isolation, and bio-electrochemical activity evaluation of exoelectrogenic microorganisms.

Exoelectrogenic microorganisms (EEMs) catalyzed the conversion of chemical energy to electrical energy via extracellular electron transfer (EET) mechanisms, which underlay diverse bio-electrochemical systems (BES) applications in clean energy development, environment and health monitoring, wearable/implantable devices powering, and sustainable chemicals production, thereby attracting increasing attentions from academic and industrial communities in the recent decades. However, knowledge of EEMs is still in its infancy as only ∼100 EEMs of bacteria, archaea, and eukaryotes have been identified, motivating the screening and capture of new EEMs. This review presents a systematic summarization on EEM screening technologies in terms of enrichment, isolation, and bio-electrochemical activity evaluation. We first generalize the distribution characteristics of known EEMs, which provide a basis for EEM screening. Then, we summarize EET mechanisms and the principles underlying various technological approaches to the enrichment, isolation, and bio-electrochemical activity of EEMs, in which a comprehensive analysis of the applicability, accuracy, and efficiency of each technology is reviewed. Finally, we provide a future perspective on EEM screening and bio-electrochemical activity evaluation by focusing on (i) novel EET mechanisms for developing the next-generation EEM screening technologies, and (ii) integration of meta-omics approaches and bioinformatics analyses to explore nonculturable EEMs. This review promotes the development of advanced technologies to capture new EEMs.

[Design and applications of synthetic electroactive microbial consortia].

Synthetic electroactive microbial consortia, which include exoelectrogenic and electrotrophic communities, catalyze the exchange of chemical and electrical energy in cascade metabolic reactions among different microbial strains. In comparison to a single strain, a community-based organisation that assigns tasks to multiple strains enables a broader feedstock spectrum, faster bi-directional electron transfer, and greater robustness. Therefore, the electroactive microbial consortia held great promise for a variety of applications such as bioelectricity and biohydrogen production, wastewater treatment, bioremediation, carbon and nitrogen fixation, and synthesis of biofuels, inorganic nanomaterials, and polymers. This review firstly summarized the mechanisms of biotic-abiotic interfacial electron transfer as well as biotic-biotic interspecific electron transfer in synthetic electroactive microbial consortia. This was followed by introducing the network of substance and energy metabolism in a synthetic electroactive microbial consortia designed by using the "division-of-labor" principle. Then, the strategies for engineering synthetic electroactive microbial consortiums were explored, which included intercellular communications optimization and ecological niche optimization. We further discussed the specific applications of synthetic electroactive microbial consortia. For instance, the synthetic exoelectrogenic communities were applied to biomass generation power technology, biophotovoltaics for the generation of renewable energy and the fixation of CO2. Moreover, the synthetic electrotrophic communities were applied to light-driven N2 fixation. Finally, this review prospected future research of the synthetic electroactive microbial consortia.