Material–Microbe Interfaces for Solar-Driven CO2 Bioelectrosynthesis

Enhancing the electrochemical conversion of carbon dioxide to value-added products on zinc oxide-MXene nanocomposite

Developing efficient and sustainable catalysts for CO2 electroreduction is critical to addressing the rising atmospheric CO2 levels and mitigating climate change. This study presents a novel ZnO-MXene (Ti2C) nanocomposite as a high-performance electrocatalyst for CO2 conversion, offering a strategic approach for generating valuable carbon-based feedstocks. The ZnO-MXene nanocomposites were synthesized via the wet impregnation method and comprehensively characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). Electrochemical performance was assessed through linear sweep voltammetry (LSV), cyclic voltammetry (CV), and controlled potential coulometry, with gas chromatography employed for product quantification. ZnO-MX10 and ZnO-MX2.5 exhibited high selectivity for CH4 (79.3 % Faradaic efficiency, FE) at -0.56 VRHE and CO (76.8 % FE) at -0.78 VRHE, while significantly suppressing competing H2 evolution. The synergistic interaction between ZnO and MXene enhances charge transfer, increases active sites, and improves surface area, leading to superior electrochemical performance. Overall, this work introduces a novel ZnO-MXene nanocomposite with dual selectivity for CO and CH4, enhanced electroactive surface, and long-term stability. Unlike conventional Zn-based catalysts, which exhibit either limited selectivity or rapid degradation, our composite achieves 79.3 % Faradaic efficiency for CH4 and 76.8 % for CO, while suppressing H2 evolution. This unique tunability and stability make ZnO-MXene an attractive alternative to noble metal-based electrocatalysts.

Recent Progress in Developing Conjugated Polymer-Microorganism Biohybrids for Semi-Artificial Photosynthetic Energy Conversion

Semi-artificial photosynthesis, which merges the precision of synthetic materials with the catalytic versatility of biological systems, offers a transformative route to solar-driven chemical fuel production and sustainable energy conversion. Conjugated polymers, with their high molar absorption coefficients, broad spectral responsiveness, and tunable semiconducting properties, have emerged as key components in advancing semi-artificial photosynthetic biohybrids. Their capacity for targeted surface modification not only facilitates enhanced interfacing with biological catalysts but also optimizes charge transfer across the bio-synthetic interface. This review traces the evolution of conjugated polymer-based biohybrids, highlighting recent advancements that extend microbial light harvesting, support cellular resilience against environmental stress, and optimize charge transfer via precise structure-activity relationships. Furthermore, this review explores the challenges and opportunities in this field, offering a roadmap for the design of durable and high-performance biohybrid systems. Through the integration of conjugated polymers and microorganisms, this review outlines a strategic approach for solar-driven chemical energy conversion, paving the way for eco-friendly energy solutions.

Photocatalytic material-microorganism hybrid systems in water decontamination

Biological processes are widely used technologies for water decontamination, but they are often limited by insufficient bioavailable carbon sources or biorecalcitrant contaminants. The recently developed photocatalytic material-microorganism hybrid (PMH) system combines the light-harvesting capacities of photocatalytic materials with specific enzymatic activities of whole cells, efficiently achieving solar-to-chemical conversion. By integrating the benefits of both photocatalysis and biological processes, the PMH system shows great potential for water decontamination. While recent reviews have focused primarily on its application in green energy development, this review emphasizes the latest advancements in PMH systems for water decontamination, covering various applications, key considerations, and synergistic mechanisms. This review aims to provide a fundamental understanding of the PMH system and explore its broader potential in environmental remediation.

Cyborg microbe biohybrids with metal-organic coating layers: Strategies, functionalisation and potential applications

The integration of living microbes, specifically bacteria and fungi, with metal-organic nanocoatings has led to the recent development of cyborg microbe biohybrids, which show excellent adaptability and functionality for a wide range of potential applications in biotechnology and medicine. This review discusses the strategies, functionalisation, and applications of these biohybrids, which are categorised into two types of coatings: metal-organic frameworks (MOFs) and metal-phenolic networks (MPNs). Key advances in their synthetic approaches via in-situ and pre-synthesised coatings are crucially addressed, and yet the methodology details and specific advantages are highlighted. Despite the notable advancements, there are various limitations and challenges, such as determination of the long-term viability and stability of the biohybrids, insufficient work on their theranostic applications and essentially scaling-up difficulties for industrial and clinical translation. The latest advancements in the biohybrids and related technology have established a critical foundation for enhancing innovative studies through the strong interdisciplinary teamwork.

Supramolecular Reconstruction of Self-Assembling Photosensitizers for Enhanced Photocatalytic Hydrogen Evolution

Natural photosynthetic systems require spatiotemporal organization to optimize photosensitized reactions and maintain overall efficiency, involving the hierarchical self-assembly of photosynthetic components and their stabilization through synergistic interactions. However, replicating this level of organization is challenging due to the difficulty in efficiently communicating supramolecular nano-assemblies with nanoparticles or biological architectures, owing to their dynamic instability. Herein, we demonstrate that the supramolecular reconstruction of self-assembled amphiphilic rhodamine B nanospheres (RN) through treatment with metal-phenolic coordination complexes results in the formation of a stable hybrid structure. This reconstructed structure enhances electron transfer efficiency, leading to improved photocatalytic performance. Due to the photoluminescence quenching property of RN and its electronic synergy with tannic acid (T) and zirconium (Z), the supramolecular complexes of hybrid nanospheres (RNTxZy) with Pt nanoparticles or a biological workhorse, Shewanella oneidensis MR-1, showed marked improvement in photocatalytic hydrogen production. The supramolecular hybrid particles with a metal-phenolic coordination layer showed 5.6- and 4.0-fold increases, respectively, in the productivities of hydrogen evolution catalyzed by Pt (Pt/RNTxZy) and MR-1 (M/RNTxZy), respectively. These results highlight the potential for further advancements in the structural and photochemical control of supramolecular nanomaterials for energy harvesting and bio-hybrid systems.

Harnessing microbes to pioneer environmental biophotoelectrochemistry

In seeking sustainable environmental strategies, microbial biophotoelectrochemistry (BPEC) systems represent a significant advancement. In this review, we underscore the shift from conventional bioenergy systems to sophisticated BPEC applications, emphasizing their utility in leveraging solar energy for essential biochemical conversions. Recent progress in BPEC technology has facilitated improved photoelectron transfer and system stability, resulting in substantial advancements in carbon and nitrogen fixation, degradation of pollutants, and energy recovery from wastewater. Advances in system design and synthetic biology have expanded the potential of BPEC for environmental clean-up and sustainable energy generation. We also highlight the challenges of environmental BPEC systems, ranging from performance improvement to future applications.

Fully Stretchable Microbial Fuel Cell with 75% Stretchability

A decent stretchability is of paramount significance to operate microbial fuel cell (MFC) under mechanically dynamic conditions. However, it remains a grand challenge to fabricate fully stretchable MFC without compromising its power output. Here, using Shewanella oneidensis MR-1 (S. oneidensis) as the model electrogenic bacteria, the study demonstrates a fully stretchable MFC device that can operate with a stretchability of 75%. The design takes advantage of a stretchable and ion-conductive polyurethane membrane, which encapsulates the biohybrids composed of S. oneidensis and reduced graphene oxide (rGO) on the polydimethylsiloxane (PDMS) current collector for synchronous stretching. It is discovered that the "stretchable" living biohybrids can sustain an adaptive bio-current output under stretching/releasing stimulation. The design also employs a stretchable air cathode. The stabilized peak power density of the stretchable MFC follows an increasing trend with the applied strain, and reaches 5.0 ± 0.7, 5.9 ± 0.9, 6.2 ± 1.1, 6.6 ± 1.4 µW cm-2 at strains of 0%, 25%, 50%, and 75%, respectively (n = 3). At 75% strain, the stretchable MFC yields a maximum current output of 104 ± 27 µA cm-2 and an open-circuit voltage of 283 ± 30 mV (n = 3). The results provide insights to design stretchable MFCs to power the next-generation on-skin devices, soft robotics, and sustainable electronics.

Assembly strategies for microbe-material hybrid systems in solar energy conversion

Microbe-material hybrid systems which facilitate the solar-driven synthesis of high-value chemicals, harness the unique capabilities of microbes, maintaining the high-selectivity catalytic abilities, while concurrently incorporating exogenous materials to confer novel functionalities. The effective assembly of both components is essential for the overall functionality of microbe-material hybrid systems. Herein, we conducted a critical review of microbe-material hybrid systems for solar energy conversion focusing on the perspective of interface assembly strategies between microbes and materials, which are categorized into five types: cell uptake, intracellular synthesis, extracellular mineralization, electrostatic adsorption, and cell encapsulation. Moreover, this review elucidates the mechanisms by which microbe-material hybrid systems convert elementary substrates, such as carbon dioxide, nitrogen, and water, into high-value chemicals or materials for energy generation.

Eradicating the Photogenerated Holes in a Photocatalyst-Microbe Hybrid System: A Review

Finding advanced technologies to store solar energy in chemical bonds efficiently is of great significance for the sustainable development of our society. The recently reported photocatalyst-microbe hybrid (PMH) system couples photocatalysts intimately with microbes and endows heterotrophic microbes with light-harvesting capacity. Generally, when PMH systems are exposed to light, photocatalytic reactions occur on the surface of photocatalysts and the photogenerated electrons enter microbial cells to promote the generation of energy carriers (such as nicotinamide adenine dinucleotide phosphate hydrogen and adenosine triphosphate) and the following chemical synthesis. PMH system applications have expanded from synthesizing value-added products (chemicals, fuels, and polymers) to treating pollutants. However, the successful operation of the PMH system relies on the timely eradication of the photogenerated holes as they recombine with the photogenerated electrons and cause the photocorrosion of the photocatalyst. This review summarizes the strategies for scavenging the photogenerated holes in PMH systems and provides insight into the current gaps and outlooks for future opportunities in this field.

Redox and Energy Homeostasis Enabled by Photocatalytic Material-Microbial Interfaces

Material-microbial interfaces offer a promising future in sustainable and efficient chemical-energy conversions, yet the impacts of these artificial interfaces on microbial metabolisms remain unclear. Here, we conducted detailed proteomic and metabolomic analyses to study the regulations of microbial metabolism induced by the photocatalytic material-microbial interfaces, especially the intracellular redox and energy homeostasis, which are vital for sustaining cell activity. First, we learned that the materials have a heavier weight in perturbing microbial metabolism and inducing distinctive biological pathways, like the expression of the metal-resisting system, than light stimulations. Furthermore, we observed that the materials-microbe interfaces can maintain the delicate redox balance and the energetic status of the microbial cells since the intracellular redox cofactors and energy currencies show stable levels as naturally inoculated microbes. These observations ensure the possibility of energizing microbial activities with artificial materials-microbe interfaces for diverse applications and also provide guides for future designs of materials-microbe hybrids to guard microbial activities.

Engineering of bespoke photosensitiser-microbe interfaces for enhanced semi-artificial photosynthesis

Biohybrid systems for solar fuel production integrate artificial light-harvesting materials with biological catalysts such as microbes. In this perspective, we discuss the rational design of the abiotic-biotic interface in biohybrid systems by reviewing microbes and synthetic light-harvesting materials, as well as presenting various approaches to coupling these two components together. To maximise performance and scalability of such semi-artificial systems, we emphasise that the interfacial design requires consideration of two important aspects: attachment and electron transfer. It is our perspective that rational design of this photosensitiser-microbe interface is required for scalable solar fuel production. The design and assembly of a biohybrid with a well-defined electron transfer pathway allows mechanistic characterisation and optimisation for maximum efficiency. Introduction of additional catalysts to the system can close the redox cycle, omitting the need for sacrificial electron donors. Studies that electronically couple light-harvesters to well-defined biological entities, such as emerging photosensitiser-enzyme hybrids, provide valuable knowledge for the strategic design of whole-cell biohybrids. Exploring the interactions between light-harvesters and redox proteins can guide coupling strategies when translated into larger, more complex microbial systems.

Bioelectricity and CO2-to-butyrate production using photobioelectrochemical cells with bio-hydrogel

Bio-photoelectrochemical cell (BPEC) is an emerging technology that can convert the solar energy into electricity or chemicals. However, traditional BPEC depending on abiotic electrodes is challenging for microbial/enzymatic catalysis because of the inefficient electron exchange. Here, electroactive bacteria (Shewanella loihica PV-4) were used to reduce graphene oxide (rGO) nanosheets and produce co-assembled rGO/Shewanella biohydrogel as a basic electrode. By adsorbing chlorophyll contained thylakoid membrane, this biohydrogel was fabricated as a photoanode that delivered maximum photocurrent 126 μA/cm3 under visible light. Impressively, the biohydrogel could be served as a cathode in BPEC by forming coculture system with genetically edited Clostridium ljungdahlii. Under illumination, the BPEC with above photoanode and cathode yielded ∼ 5.4 mM butyrate from CO2 reduction, 169 % increase compared to dark process. This work provided a new strategy (nanotechnology combined with synthetic biology) to achieve efficient bioelectricity and valuable chemical production in PBEC.

Engineering extracellular electron transfer pathways of electroactive microorganisms by synthetic biology for energy and chemicals production

The excessive consumption of fossil fuels causes massive emission of CO2, leading to climate deterioration and environmental pollution. The development of substitutes and sustainable energy sources to replace fossil fuels has become a worldwide priority. Bio-electrochemical systems (BESs), employing redox reactions of electroactive microorganisms (EAMs) on electrodes to achieve a meritorious combination of biocatalysis and electrocatalysis, provide a green and sustainable alternative approach for bioremediation, CO2 fixation, and energy and chemicals production. EAMs, including exoelectrogens and electrotrophs, perform extracellular electron transfer (EET) (i.e., outward and inward EET), respectively, to exchange energy with the environment, whose rate determines the efficiency and performance of BESs. Therefore, we review the synthetic biology strategies developed in the last decade for engineering EAMs to enhance the EET rate in cell-electrode interfaces for facilitating the production of electricity energy and value-added chemicals, which include (1) progress in genetic manipulation and editing tools to achieve the efficient regulation of gene expression, knockout, and knockdown of EAMs; (2) synthetic biological engineering strategies to enhance the outward EET of exoelectrogens to anodes for electricity power production and anodic electro-fermentation (AEF) for chemicals production, including (i) broadening and strengthening substrate utilization, (ii) increasing the intracellular releasable reducing equivalents, (iii) optimizing c-type cytochrome (c-Cyts) expression and maturation, (iv) enhancing conductive nanowire biosynthesis and modification, (v) promoting electron shuttle biosynthesis, secretion, and immobilization, (vi) engineering global regulators to promote EET rate, (vii) facilitating biofilm formation, and (viii) constructing cell-material hybrids; (3) the mechanisms of inward EET, CO2 fixation pathway, and engineering strategies for improving the inward EET of electrotrophic cells for CO2 reduction and chemical production, including (i) programming metabolic pathways of electrotrophs, (ii) rewiring bioelectrical circuits for enhancing inward EET, and (iii) constructing microbial (photo)electrosynthesis by cell-material hybridization; (4) perspectives on future challenges and opportunities for engineering EET to develop highly efficient BESs for sustainable energy and chemical production. We expect that this review will provide a theoretical basis for the future development of BESs in energy harvesting, CO2 fixation, and chemical synthesis.

Co-NC@Co-NP hierarchical nanoforest steering charge exchange efficiency at biotic-abiotic interface for microbial electrochemical carbon reduction

Converting anthropogenic carbon dioxide (CO2) to value-added products using bio-electrochemical conversions represents a promising strategy for producing sustainable fuel. However, the reaction kinetics are hindered by insufficient attachment of microorganisms and limited charge extraction at the bioinorganic interface. A hierarchical nanoforest with doped cobalt‑nitrogen-doped carbon covering cobalt nanoparticle (Co-NC@Co-NP) was integrated with a CO2-to-CH4 conversion microbiome for methane production to address these shortcomings. In-situ nanoforests were developed on the nanosheet by chemical vapor deposition with Co nanoparticles catalyzed. The bio-nanowire-like carbon nanotubes enhanced the electrostatic force for microbe enrichment via the tip effect, providing a maximum of 3.6-fold electron-receiving microbes to utilize reducing equivalents. The Co-NC@Co-NP enhanced the direct electron transfer between microbes and electrodes, reducing the adoption of energy barriers for heme-like proteins. Thus, the optimized electron transfer pathway improved selectivity by a factor of 2.0 compared to the pristine nanosheet biohybrid. Furthermore, the adjusted microbial community structure provided sufficient methanogenesis genes to match the strong electron flow, achieving maximal methane production rates (311.1 mmol/m2/day at -0.9 V vs. Ag/AgCl), 8.62 times higher than those of the counterpart nanosheet biohybrid (36.06 mmol/m2/day). This work demonstrates a comprehensive assessment of biotic-abiotic energy transfer, which may serve as a guiding principle for designing efficient bio-electrochemical systems.

Fe3 O4 nanozyme coating enhances light-driven biohydrogen production in self-photosensitized Shewanella oneidensis-CdS hybrid systems

Solar-driven biohybrid systems that produce chemical energy are a valuable objective in ongoing research. However, reactive oxygen species (ROS) that accompany nanoparticle production under light radiation severely affect the efficiency of biohybrid systems. In this study, we successfully constructed a two-hybrid system, Shewanella oneidensis-CdS and S. oneidensis-CdS@Fe3 O4 , in a simple, economical, and gentle manner. With the Fe3 O4 coating, ROS were considerably eliminated; the hydroxyl radical, superoxide radical, and hydrogen peroxide contents were reduced by 66.7%, 65.4%, and 72%, respectively, during light-driven S. oneidensis-CdS hydrogen production. S. oneidensis-CdS@Fe3 O4 showed a 2.6-fold higher hydrogen production (70 h) than S. oneidensis-CdS. Moreover, the S. oneidensis-CdS system produced an additional 367.8 μmol g-dcw-1 (70 h) of hydrogen compared with S. oneidensis during irradiation. The apparent quantum efficiencies of S. oneidensis-CdS and S. oneidensis-CdS@Fe3 O4 were 6.2% and 11.5%, respectively, exceeding values previously reported. In conclusion, a stable nanozyme coating effectively inhibited the cytotoxicity of CdS nanoparticles, providing an excellent production environment for bacteria. This study provides a rational strategy for protecting biohybrid systems from ROS toxicity and contributes to more efficient solar energy conversion in the future.

Light-driven biohybrid system utilizes N2 for photochemical CO2 reduction

Attempting to couple photochemical CO₂ reduction with N₂ fixation is usually difficult, because the reaction conditions for these two processes are typically incompatible. Here, we report that a light-driven biohybrid system can utilize abundant, atmospheric N₂ to produce electron donors via biological nitrogen fixation, to achieve effective photochemical CO₂ reduction. This biohybrid system is constructed by incorporating molecular cobalt-based photocatalysts into N₂-fixing bacteria. It is found that N₂-fixing bacteria can convert N₂ into reductive organic nitrogen and create a localized anaerobic environment, which allows the incorporated photocatalysts to continuously perform photocatalytic CO₂ reduction under aerobic conditions. Specifically, the light-driven biohybrid system displays a high formic acid production rate of over 1.41 × 10^-14 mol h^-1 cell^-1 under visible light irradiation, and the organic nitrogen content undergoes an over-3-fold increase within 48 hours. This work offers a useful strategy for coupling CO₂ conversion with N₂ fixation under mild and environmentally benign conditions.

Engineering Outer Membrane Vesicles to Increase Extracellular Electron Transfer of Shewanella oneidensis

Outer membrane vesicles (OMVs) of Gram-negative bacteria play an essential role in cellular physiology. The underlying regulatory mechanism of OMV formation and its impact on extracellular electron transfer (EET) in the model exoelectrogenShewanella oneidensis MR-1 remain unclear and have not been reported. To explore the regulatory mechanism of OMV formation, we used the CRISPR-dCas9 gene repression technology to reduce the crosslink between the peptidoglycan (PG) layer and the outer membrane, thus promoting the OMV formation. We screened the target genes that were potentially beneficial to the outer membrane bulge, which were classified into two modules: PG integrity module (Module 1) and outer membrane component module (Module 2). We found that downregulation of the penicillin-binding protein-encoding gene pbpC for peptidoglycan integrity (Module 1) and the N-acetyl-d-mannosamine dehydrogenase-encoding gene wbpP involved in lipopolysaccharide synthesis (Module 2) exhibited the highest production of OMVs and enabled the highest output power density of 331.3 ± 1.2 and 363.8 ± 9.9 mW m-2, 6.33- and 6.96-fold higher than that of the wild-typeS. oneidensis MR-1 (52.3 ± 0.6 mW m-2), respectively. To elucidate the specific impacts of OMV formation on EET, OMVs were isolated and quantified for UV-visible spectroscopy and heme staining characterization. Our study showed that abundant outer membrane c-type cytochromes (c-Cyts) including MtrC and OmcA and periplasmic c-Cyts were exposed on the surface or inside of OMVs, which were the vital constituents responsible for EET. Meanwhile, we found that the overproduction of OMVs could facilitate biofilm formation and increase biofilm conductivity. To the best of our knowledge, this study is the first to explore the mechanism of OMV formation and its correlation with EET of S. oneidensis, which paves the way for further study of OMV-mediated EET.

Green Conversion of Carbon Dioxide and Sustainable Fuel Synthesis

Carbon capture and use may provide motivation for the global problem of mitigating global warming from substantial industrial emitters. Captured CO2 may be transformed into a range of products such as methanol as renewable energy sources. Polymers, cement, and heterogeneous catalysts for varying chemical synthesis are examples of commercial goods. Because some of these components may be converted into power, CO2 is a feedstock and excellent energy transporter. By employing collected CO2 from the atmosphere as the primary hydrocarbon source, a carbon-neutral fuel may be created. The fuel is subsequently burned, and CO2 is released into the atmosphere like a byproduct of the combustion process. There is no net carbon dioxide emitted or withdrawn from the environment during this process, hence the name carbon-neutral fuel. In a world with net-zero CO2 emissions, the anthroposphere will have attained its carbon hold-up capacity in response to a particular global average temperature increase, such as 1.5 °C. As a result, each carbon atom removed from the subsurface (lithosphere) must be returned to it, or it will be expelled into the atmosphere. CO2 removal technologies, such as biofuels with carbon sequestration and direct air capture, will be required to lower the high CO2 concentration in the atmosphere if the Paris Agreement’s ambitious climate targets are to be realized. In a carbon-neutral scenario, CO2 consumption with renewable energy is expected to contribute to the displacement of fossil fuels. This article includes a conceptual study and an evaluation of fuel technology that enables a carbon-neutral chemical industry in a net-zero-CO2-emissions environment. These are based on the use of collected CO2 as a feedstock in novel chemical processes, along with “green” hydrogen, or on the use of biomass. It will also shed light on innovative methods of green transformation and getting sustainable, environmentally friendly energy.

Ultrafast extraction of uranium from seawater using photosensitized biohybrid system with bioinspired cascaded strategy

The highly effective utilization of uranium resources in global seawater is a viable method to satisfy the rising demands for fueling nuclear energy industry. Herein, inspired by the multi-mechanisms of the marine bacteria for uranium immobilization, CdS nanoparticles are deposited on the cell of marine bacterial strain Bacillus velezensis UUS-1 to create a photosensitized biohybrid system UUS-1/CdS. This system achieves high uranium extraction efficiency using a cascaded strategy, where the bacterial cells guarantee high extraction selectivity and the photosensitive CdS nanoparticles realize cascading photoreduction of high soluble U(VI) to low soluble U(IV) to enhance extraction capacity. As one of the fastest-acting adsorbents in natural seawater, a high extraction capacity for uranium of 7.03 mg g^-1 is achieved with an ultrafast extraction speed of 4.69 mg g^-1 d^-1. The cascaded strategy promisingly improves uranium extraction performance and pioneers a new direction for the design of adsorbents to extract uranium from seawater.

Enrichment of hydrogen-oxidizing bacteria using a hybrid biological-inorganic system

Hybrid biological-inorganic (HBI) systems comprising inorganic water-splitting catalysts and aerobic hydrogen-oxidizing bacteria (HOB) have previously been used for CO₂ conversion. In order to identify new biocatalysts for CO₂ conversion, the present study used an HBI system to enrich HOB directly from environmental samples. Three sediment samples (from a brackish water pond, a beach, and a tide pool) and two activated sludge samples (from two separate sewage plants) were inoculated into HBI systems using a cobalt phosphorus (Co-P) alloy and cobalt phosphate (CoPi) as inorganic catalysts with a fixed voltage of 2.0 V. The gas composition of the reactor headspaces and electric current were monitored. An aliquot of the reactor medium was transferred to a new reactor when significant consumption of H₂ and CO₂ was detected. This process was repeated twice (with three reactors in operation for each sample) to enrich HOB. Increased biomass concomitant with increased H₂ and CO₂ consumption was observed in the third reactor, indicating enrichment of HOB. 16S rRNA gene amplicon sequencing demonstrated enrichment of sequences related to HOB (including bacteria from Mycobacterium, Hydrogenophaga, and Xanthobacter genera) over successive sub-cultures. Finally, four different HOB belonging to the Mycobacterium, Hydrogenophaga, Xanthobacter, and Acidovorax genera were isolated from reactor media, representing potential candidates as HBI system biocatalysts.

Photodriven Chemical Synthesis by Whole-Cell-Based Biohybrid Systems: From System Construction to Mechanism Study

By simulating natural photosynthesis, the desirable high-value chemical products and clean fuels can be sustainably generated with solar energy. Whole-cell-based photosensitized biohybrid system, which innovatively couples the excellent light-harvesting capacity of semiconductor materials with the efficient catalytic ability of intracellular biocatalysts, is an appealing interdisciplinary creature to realize photodriven chemical synthesis. In this review, we summarize the constructed whole-cell-based biohybrid systems in different application fields, including carbon dioxide fixation, nitrogen fixation, hydrogen production, and other chemical synthesis. Moreover, we elaborate the charge transfer mechanism studies of representative biohybrids, which can help to deepen the current understanding of the synergistic process between photosensitizers and microorganisms, and provide schemes for building novel biohybrids with less electron transfer resistance, advanced productive efficiency, and functional diversity. Further exploration in this field has the prospect of making a breakthrough on the biotic-abiotic interface that will provide opportunities for multidisciplinary research.

Cucurbit[10]uril-based supramolecular radicals: Powerful arms to kill facultative anaerobic bacteria

Two water-soluble supramolecular complexes (CB[10]⊃PSA and CB[10]⊃TPE-cyc) are constructed based on the host-guest interaction between cucurbit[10]uril (CB[10]) and perylene diimide derivative (PSA) or tetracationic cyclophane (TPE-cyc). Attributing to the matched redox potential, both supramolecular complexes can be specifically reduced into corresponding supramolecular radical cations or anions by facultative anaerobic E. coli. Benefiting from the strong near-infrared (NIR) absorption, CB[10]⊃PSA radical anions and CB[10]⊃TPE-cyc radical cations act as efficient NIR photosensitizers and perform an excellent antimicrobial activity (close to 100%) via PTT. In addition, the biocompatibility of TPE-cyc is notably improved under the protection of CB[10], guaranteeing its biosafety for in vivo application. CB[10]⊃PSA radical anions and CB[10]⊃TPE-cyc radical cations are in situ generated in the E. coli-infected abscess of mice and effectively inhibit the bacterial infection without obvious system toxicity. It is anticipated that this supramolecular strategy may pave a new way for the selective bacteria inhibition to regulate the balance of different bacterial flora.

Recent Advances In Microbe-Photocatalyst Hybrid Systems for Production of Bulk Chemicals: A Review

Solar-driven biocatalysis technologies can combine inorganic photocatalytic materials with biological catalysts to convert CO₂, light, and water into chemicals, offering the promise of high energy efficiency and a broader product scope than that of natural photosynthesis. Solar energy is the most abundant renewable energy source on earth, but it cannot be directly utilized by current industrial microorganisms. Therefore, the establishment of a solar-driven bio-catalysis platform, a bridge between solar energy and heterotrophic microorganisms, can dramatically increase carbon flux in biomanufacturing systems and consequently may revolutionize the biorefinery. This review first discusses the main applications of microbe-photocatalyst hybrid (MPH) systems in biorefinery processes. Then, various strategies to improve the electron transfer by microorganisms at the inorganic photocatalytic material interface are discussed, especially biohybrid systems based on autotrophic or heterotrophic bacteria and photocatalytic materials. Finally, we discuss the current challenges and offer potential solutions for the development of MPH systems.

Novel approaches to energize microbial biocatalysts

An efficient and cheap energization of microbial biocatalysts is essential in current biotechnological processes. A promising alternative to the use of common organic or inorganic electron donors is the semiconductor nanoparticles (SNs) that absorb light and transfer electrons (photoelectrons) behaving as artificial photosynthetic systems (biohybrid systems). Excited photoelectrons generated by illuminated SNs are highly reductive and readily accepted by membrane-bound proteins and electron shuttles to drive specific cell reduction processes and energy generation in microbes. However, the operational mechanisms of these hybrid systems are still poorly understood, especially at the material-microbe interface, and therefore the design and production of efficient biohybrids are challenging. Some major limitations/challenges and future prospects of SNs as microbial energization systems are discussed.

Using synthetic biology to improve photosynthesis for sustainable food production

Photosynthesis is responsible for the primary productivity and maintenance of life on Earth, boosting biological activity and contributing to the maintenance of the environment. In the past, traditional crop improvement was considered sufficient to meet food demands, but the growing demand for food coupled with climate change has modified this scenario over the past decades. However, advances in this area have not focused on photosynthesis per se but rather on fixed carbon partitioning. In short, other approaches must be used to meet an increasing agricultural demand. Thus, several paths may be followed, from modifications in leaf shape and canopy architecture, improving metabolic pathways related to CO₂ fixation, the inclusion of metabolic mechanisms from other species, and improvements in energy uptake by plants. Given the recognized importance of photosynthesis, as the basis of the primary productivity on Earth, we here present an overview of the latest advances in attempts to improve plant photosynthetic performance. We focused on points considered key to the enhancement of photosynthesis, including leaf shape development, RuBisCO reengineering, Calvin-Benson cycle optimization, light use efficiency, the introduction of the C₄ cycle in C₃ plants and the inclusion of other CO₂ concentrating mechanisms (CCMs). We further provide compelling evidence that there is still room for further improvements. Finally, we conclude this review by presenting future perspectives and possible new directions on this subject.

Enhancing Biohybrid CO2 to Multicarbon Reduction via Adapted Whole-Cell Catalysts

Catalytic CO₂ conversion to renewable fuel is of utmost importance to establish a carbon-neutral society. Bioelectrochemical CO₂ reduction, in which a solid cathode interfaces with CO₂-reducing bacteria, represents a promising approach for renewable and sustainable fuel production. The rational design of biocatalysts in the biohybrid system is imperative to effectively reduce CO₂ into valuable chemicals. Here, we introduce methanol adapted Sporomusa ovata (S. ovata) to enhance the slow metabolic activity of wild-type microorganisms to our semiconductive silicon nanowires (Si NWs) array for efficient CO₂ reduction. The adapted whole-cell catalysts enable an enhancement of CO₂ fixation with a superior faradaic efficiency on the poised Si NWs cathode. The synergy of the high-surface-area cathode and the adapted strain achieves a CO₂-reducing current density of 0.88 ± 0.11 mA/cm², which is 2.4-fold higher than the wild-type strain. This new generation of biohybrids using adapted S. ovata also decreases the charge transfer resistance at the cathodic interface and facilitates the faster charge transfer from the solid electrode to bacteria.

A review of recent advances in engineering bacteria for enhanced CO2 capture and utilization

Carbon dioxide (CO₂) is emitted into the atmosphere due to some anthropogenic activities, such as the combustion of fossil fuels and industrial output. As a result, fears about catastrophic global warming and climate change have intensified. In the face of these challenges, conventional CO₂ capture technologies are typically ineffective, dangerous, and contribute to secondary pollution in the environment. Biological systems for CO₂ conversion, on the other hand, provide a potential path forward owing to its high application selectivity and adaptability. Moreover, many bacteria can use CO₂ as their only source of carbon and turn it into value-added products. The purpose of this review is to discuss recent significant breakthroughs in engineering bacteria to utilize CO₂ and other one-carbon compounds as substrate. In the same token, the paper also summarizes and presents aspects such as microbial CO₂ fixation pathways, engineered bacteria involved in CO₂ fixation, up-to-date genetic and metabolic engineering approaches for CO₂ fixation, and promising research directions for the production of value-added products from CO₂. This review's findings imply that using biological systems like modified bacteria to manage CO₂ has the added benefit of generating useful industrial byproducts like biofuels, pharmaceutical compounds, and bioplastics. The major downside, from an economic standpoint, thus far has been related to methods of cultivation. However, thanks to genetic engineering approaches, this can be addressed by large production yields. As a result, this review aids in the knowledge of various biological systems that can be used to construct a long-term CO₂ mitigation technology at an industrial scale, in this instance bacteria-based CO₂capture/utilization technology.

Anaerobic self-assembly of a regenerable bacteria-quantum dot hybrid for solar hydrogen production

Inorganic-biological hybrid systems (bio-hybrids), comprising fermentative bacteria and inorganic semiconductor photosensitizers for synergistic utilization of solar energy and organic wastes, offer opportunities for sustainable fuel biosynthesis, but the low quantum efficiency, photosensitizer biotoxicity and inability for self-regeneration are remaining hurdles to practical application. Here, we unveil a previously neglected role of oxygen in suppressing the biosynthesis of cadmium selenide quantum dots (CdSe QDs) and the metabolic activities of Escherichia coli, and accordingly propose a simple oxygen-regulation strategy to enable the self-assembly of bacterial-QD hybrids for efficient solar hydrogen production. Shifting from aerobic to anaerobic biosynthesis significantly lowered the intracellular reactive oxygen species level and increased NADPH and thiol-protein production, enabling a two-order-of-magnitude higher bio-QD synthesis rate and resulting in CdSe-rich products. Bacteria with abundant biocompatible intracellular bio-QDs naturally formed a highly active and self-regenerable bio-hybrid and achieved a quantum efficiency of 28.7% for hydrogen production under visible light, outperforming all the existing bio-hybrids. It also exhibited high stability during cyclic operation and robust performance for treating real wastewater under simulated sunlight. Our work provides valuable new insights into the metallic nanomaterial biosynthesis process to guide the design of self-assembled bio-hybrids towards sustainable energy and environmental applications.

Modular configurations of living biomaterials incorporating nano-based artificial mediators and synthetic biology to improve bioelectrocatalytic performance: A review

Currently, the industrial application of bioelectrochemical systems (BESs) that are incubated with natural electrochemically active microbes (EABs) is limited due to inefficient extracellular electron transfer (EET) by natural EABs. Notably, recent studies have identified several novel living biomaterials comprising highly efficient electron transfer systems allowing unparalleled proficiency of energy conversion. Introduction of these biomaterials into BESs could fundamentally increase their utilization for a wide range of applications. This review provides a comprehensive assessment of recent advancements in the design of living biomaterials that can be exploited to enhance bioelectrocatalytic performance. Further, modular configurations of abiotic and biotic components promise a powerful enhancement through integration of nano-based artificial mediators and synthetic biology. Herein, recent advancements in BESs are synthesized and assessed, including heterojunctions between conductive nanomaterials and EABs, in-situ hybrid self-assembly of EABs and nano-sized semiconductors, cytoprotection in biohybrids, synthetic biological modifications of EABs and electroactive biofilms. Since living biomaterials comprise a broad range of disciplines, such as molecular biology, electrochemistry and material sciences, full integration of technological advances applied in an interdisciplinary framework will greatly enhance/advance the utility and novelty of BESs. Overall, emerging fundamental knowledge concerning living biomaterials provides a powerful opportunity to markedly boost EET efficiency and facilitate the industrial application of BESs to meet global sustainability challenges/goals.

Anthraquinone-2-Sulfonate as a Microbial Photosensitizer and Capacitor Drives Solar-to-N2O Production with a Quantum Efficiency of Almost Unity

Semiartificial photosynthesis shows great potential in solar energy conversion and environmental application. However, the rate-limiting step of photoelectron transfer at the biomaterial interface results in an unsatisfactory quantum yield (QY, typically lower than 3%). Here, an anthraquinone molecule, which has dual roles of microbial photosensitizer and capacitor, was demonstrated to negotiate the interface photoelectron transfer via decoupling the photochemical reaction with a microbial dark reaction. In a model system, anthraquinone-2-sulfonate (AQS)-photosensitized Thiobacillus denitrificans, a maximum QY of solar-to-nitrous oxide (N₂O) of 96.2% was achieved, which is the highest among the semiartificial photosynthesis systems. Moreover, the conversion of nitrate into N₂O was almost 100%, indicating the excellent selectivity in nitrate reduction. The capacitive property of AQS resulted in 82-89% of photoelectrons released at dark and enhanced 5.6-9.4 times the conversion of solar-to-N₂O. Kinetics investigation revealed a zero-order- and first-order- reaction kinetics of N₂O production in the dark (reductive AQS-mediated electron transfer) and under light (direct photoelectron transfer), respectively. This work is the first study to demonstrate the role of AQS in photosensitizing a microorganism and provides a simple and highly selective approach to produce N₂O from nitrate-polluted wastewater and a strategy for the efficient conversion of solar-to-chemical by a semiartificial photosynthesis system.

A critical review on microbe-electrode interactions towards heavy metal ion detection using microbial fuel cell technology

Implicit interaction of electroactive microbes with solid electrodes is an interesting phenomenon in nature, which supported development of bioelectrochemical systems (BESs), especially the microbial fuel cell (MFCs) for valorization of low-value waste streams into bioelectricity. Intriguingly, the metabolism of interacted microbes with electrode is affected by the microenvironment at electrodes, which influences the current response. For instance, when heavy metal ions (HMIs) are imposed in the medium, the current production decreases due to their intrinsic toxic effect. This event provides an immense opportunity to utilize MFC as a sensor to selectively detect HMIs in the environment, which has been explored vastly in recent decade. In this review, we have concisely discussed the microbial interaction with electrodes and mechanism of detection of HMIs using an MFC. Recent advancement in sensing elements and their application is elaborated with a future perspective section for follow-up research and development in this field.

Self-sustained ammonium recovery from wastewater and upcycling for hydrogen-oxidizing bacteria-based power-to-protein conversion

Microbial protein (MP) production by autotrophic hydrogen-oxidizing bacteria is regarded as a potentially sustainable approach to mitigate food crisis, water pollution, and climate change. Herein, a hybrid biological-inorganic (HBI) system which coupled energy-neutral ammonium recovery and in-situ upcycling for MP production was demonstrated. No energy and acids/bases were needed for ammonium recovery and pH control. The system was tested with different amounts of CO₂ supply and operated at different operational modes (microbial fuel cell or microbial electrolysis cell mode). 0.381 g/L of biomass containing 64.79% of crude protein was produced using the recovered nitrogen and therefore led to 76.8% of ammonium recovery and 84.6% of COD removal from real municipal wastewater. The system although not yet optimal in terms of efficiency has a meaning in alleviating food crisis and environmental issues. Altogether, this study offers insight into developing an energy and resource-efficient power-to-protein process to supplement conventional food production globally.

A review of recent advances in electrode materials for emerging bioelectrochemical systems: From biofilm-bearing anodes to specialized cathodes

Bioelectrochemical systems (BES), mainly microbial fuel cells (MEC) and microbial electrolysis cells (MFC), are unique biosystems that use electroactive bacteria (EAB) to produce electrons in the form of electric energy for different applications. BES have attracted increasing attention as a sustainable, low-cost, and neutral-carbon option for energy production, wastewater treatment, and biosynthesis. Complex interactions between EAB and the electrode materials play a crucial role in system performance and scalability. The electron transfer processes from the EAB to the anode surface or from the cathode surface to the EAB have been the object of numerous investigations in BES, and the development of new materials to maximize energy production and overall performance has been a hot topic in the last years. The present review paper discusses the advances on innovative electrode materials for emerging BES, which include MEC coupled to anaerobic digestion (MEC-AD), Microbial Desalination Cells (MDC), plant-MFC (P-MFC), constructed wetlands-MFC (CW-MFC), and microbial electro-Fenton (BEF). Detailed insights on innovative electrode modification strategies to improve the electrode transfer kinetics on each emerging BES are provided. The effect of materials on microbial population is also discussed in this review. Furthermore, the challenges and opportunities for materials scientists and engineers working in BES are presented at the end of this work aiming at scaling up and industrialization of such versatile systems.

Electrosynthesis, modulation, and self-driven electroseparation in microbial fuel cells

Microbial electrosynthesis (MES) represents a sustainable platform that converts waste into resources, using microorganisms within an electrochemical cell. Traditionally, MES refers to the oxidation/reduction of a reactant at the electrode surface with externally applied potential bias. However, microbial fuel cells (MFCs) generate electrons that can drive electrochemical reactions at otherwise unbiased electrodes. Electrosynthesis in MFCs is driven by microbial oxidation of organic matter releasing electrons that force the migration of cationic species to the cathode. Here, we explore how electrosynthesis can coexist within electricity-producing MFCs thanks to electro-separation of cations, electroosmotic drag, and oxygen reduction within appropriately designed systems. More importantly, we report on a novel method of in situ modulation for electrosynthesis, through additional “pin” electrodes. Several MFC electrosynthesis modulating methods that adjust the electrode potential of each half-cell through the pin electrodes are presented. The innovative concept of electrosynthesis within the electricity producing MFCs provides a multidisciplinary platform converting waste-to-resources in a self-sustainable way.

Recent advances in the improvement of bi-directional electron transfer between abiotic/biotic interfaces in electron-assisted biosynthesis system

As an important biosynthesis technology, electron-assisted biosynthesis (EABS) system can utilize exogenous electrons to regulate the metabolic network of microorganisms, realizing the biosynthesis of high value-added chemicals and CO₂ fixation. Electrons play crucial roles as the energy carriers in the EABS process. In fact, efficient interfacial electron transfer (ET) is the decisive factor to realize the rapid energy exchange, thus stimulating the biosynthesis of target metabolic products. However, due to the interfacial resistance of ET between the abiotic solid electrode and biotic microbial cells, the low efficiency of interfacial ET has become a major bottleneck, further limiting the practical application of EABS system. As the cell membrane is insulated, even the cell membrane embedded electron conduit (no matter cytochromes or channel protein for shuttle transferring) to increase the cell membrane conductivity, the ET between membrane electron conduit and electrode surface is kinetically restricted. In this review, the pathway of bi-directional interfacial ET in EABS system was summarized. Furthermore, we reviewed representative milestones and advances in both the anode outward interfacial ET (from organism to electrode) and cathode inward interfacial ET (from electrode to organism). Here, new insights from the perspectives of material science and synthetic biology were also proposed, which were expected to provide some innovative opinions and ideas for the following in-depth studies.

Enhanced Light-Driven Hydrogen Production by Self-Photosensitized Biohybrid Systems

Storage of solar energy as hydrogen provides a platform towards decarbonizing our economy. One emerging strategy for the production of solar fuels is to use photocatalytic biohybrid systems that combine the high catalytic activity of non-photosynthetic microorganisms with the high light-harvesting efficiency of metal semiconductor nanoparticles. However, few such systems have been tested for H₂ production. We investigated light-driven H₂ production by three novel organisms, Desulfovibrio desulfuricans, Citrobacter freundii, and Shewanella oneidensis, self-photosensitized with cadmium sulfide nanoparticles, and compared their performance to Escherichia coli. All biohybrid systems produced H₂ from light, with D. desulfuricans-CdS demonstrating the best activity overall and outperforming the other microbial systems even in the absence of a mediator. With this system, H₂ was continuously produced for more than 10 days with a specific rate of 36 μmol g_dcw ^-1  h^-1 . High apparent quantum yields of 23 % and 4 % were obtained, with and without methyl viologen, respectively, exceeding values previously reported.

An insight into the bioelectrochemical photoreduction of CO2 to value-added chemicals

Goal of sustainable carbon neutral economy can be achieved by designing an efficient CO₂ reduction system to generate biofuels, in particular, by mimicking the mechanism of natural photosynthesis using semiconducting nanomaterials interfaced with electroactive bacteria (EAB) in a photosynthetic microbial electrosynthesis (PMES) system. This review paper presents an overview of the recent advancements in the biohybrid photoanode and photocathode materials. We discuss the reaction mechanism observed at photoanode and photocathode to enhance our understanding on the solar driven MES. We extend the discussion by showcasing the potential activity of EABs toward high selectivity and production rates for desirable products by manipulating their genomic sequence. Additionally, the critical challenges associated in scaling up the PMES system including the strategies for diminution of reactive oxygen species, low solubility of CO₂ in the typical electrolytes, low selectivity of product species are presented along with the suggestions of alternative strategies to achieve economically viable generation of (bio)commodities.

Status Update on Bioelectrochemical Systems: Prospects for Carbon Electrode Design and Scale-Up

Bioelectrochemical systems (BES) employ enzymes, subcellular structures or whole electroactive microorganisms as biocatalysts for energy conversion purposes, such as the electrosynthesis of value-added chemicals and power generation in biofuel cells. From a bioelectrode engineering viewpoint, customizable nanostructured carbonaceous matrices have recently received considerable scientific attention as promising electrode supports due to their unique properties attractive to bioelectronics devices. This review demonstrates the latest advances in the application of nano- and micro-structured carbon electrode assemblies in BES. Specifically, in view of the gradual increase in the commercial applicability of these systems, we aim to address the stability and scalability of different BES designs and to highlight their potential roles in a circular bioeconomy.

Extracellular electron transfer across bio-nano interfaces for CO2 electroreduction

Acetogenic bacteria represent a class of organisms capable of converting reducing equivalents and carbon dioxide into products with carbon-carbon bonds. Materials-based bio-electrochemical approaches are attractive for supplying biological organisms directly with grid-supplied electrons to convert carbon dioxide to value-added chemicals. Carbon nanotube-modified biocathodes have emerged as promising candidates for microbial electrosynthesis with high yields of carbon product formation, but a fundamental understanding of extracellular charge transfer at this electrode-biofilm interface is still lacking. Here, we utilize solid-state interfaces between semiconducting single-walled carbon nanotubes (s-SWCNT) and a model acetogenic bacterium for mechanistic studies of electro-catalytic CO2 conversion to acetate. Studies of bacteria/s-SWCNT interactions in a transistor-based device suggest direct extracellular electron transfer (EET) at the bio-nano interface. Deuterium isotope labeling experiments confirmed that the availability of electrochemically produced H2 as a redox mediator does not limit the efficiency of EET and CO2 electro-reduction for C. ljungdahlii biofilms, suggesting the primary reducing equivalents are the electrons delivered across the electrode/bacterium interface or involvement of biological redox mediators. Additional isotope labeling studies demonstrate high Faradaic efficiency for CO2 electro-reduction at the SWCNT/bacterium interface. These results provide important information about EET across the bacterium/material interface in a model biocathode.

Photo-augmented PHB production from CO2 or fructose by Cupriavidus necator and shape-optimized CdS nanorods

Particulate photocatalysts developed for the solar energy-driven reduction of the greenhouse gas CO₂ have a small product range and low specificity. Hybrid photosynthesis expands the number of products with photocatalysts harvesting sunlight and transferring charges to microbes harboring versatile metabolisms for bioproduction. Besides CO₂, abiotic photocatalysts have been employed to increase microbial production yields of reduced compounds from organic carbon substrates. Most single-reactor hybrid photosynthesis systems comprise CdS assembled in situ by microbial activity. This approach limits optimization of the morphology, crystal structure, and crystallinity of CdS for higher performance, which is usually done via synthesis methods incompatible with life. Here, shape and activity optimized CdS nanorods were hydrothermally produced and subsequently applied to Cupriavidus necator for the heterotrophic and autotrophic production of the bioplastic polyhydroxybutyrate (PHB). C. necator with CdS NR under light produced 1.5 times more PHB when compared to the same bacterium with suboptimal commercially-available CdS. Illuminated C. necator with CdS NR synthesized 1.41 g PHB from fructose over 120 h and 28 mg PHB from CO₂ over 48 h. Interestingly, the beneficial effect of CdS NR was specific to C. necator as the metabolism of other microbes often employed for bioproduction including yeast and bacteria was negatively impacted. These results demonstrate that hybrid photosynthesis is more productive when the photocatalyst characteristics are optimized via a separated synthesis process prior to being coupled with microbes. Furthermore, bioproduction improvement by CdS-based photocatalyst requires specific microbial species highlighting the importance of screening efforts for the development of performant hybrid photosynthesis.

Bacterial Redox Potential Powers Controlled Radical Polymerization

Microbes employ a remarkably intricate electron transport system to extract energy from the environment. The respiratory cascade of bacteria culminates in the terminal transfer of electrons onto higher redox potential acceptors in the extracellular space. This general and inducible mechanism of electron efflux during normal bacterial proliferation leads to a characteristic fall in bulk redox potential (E_h), the degree of which is dependent on growth phase, the microbial taxa, and their physiology. Here, we show that the general reducing power of bacteria can be subverted to induce the abiotic production of a carbon-centered radical species for targeted bioorthogonal molecular synthesis. Using two species, Escherichia coli and Salmonella enterica serovar Typhimurium as model microbes, a common redox active aryldiazonium salt is employed to intervene in the terminal respiratory electron flow, affording radical production that is mediated by native redox-active molecular shuttles and active bacterial metabolism. The aryl radicals are harnessed to initiate and sustain a bioorthogonal controlled radical polymerization via reversible addition-fragmentation chain transfer (BacRAFT), yielding a synthetic extracellular matrix of "living" vinyl polymers with predetermined molecular weight and low dispersity. The ability to interface the ubiquitous reducing power of bacteria into synthetic materials design offers a new means for creating engineered living materials with promising adaptive and self-regenerative capabilities.

Enhancing Biosynthesis and Manipulating Flux in Whole Cells with Abiotic Catalysis

Metabolic engineering uses genetic strategies to drive flux through desired pathways. Recent work with electrochemical, photochemical, and chemocatalytic setups has revealed that these systems can also expand metabolic pathways and manipulate flux in whole cells. Electrochemical systems add or remove electrons from metabolic pathways to direct flux to more- or less-reduced products. Photochemical systems act as synthetic light-harvesting complexes and yield artificial photosynthetic organisms. Biocompatible chemocatalysis increases product scope, streamlines syntheses, and yields single-flask processes to deliver products that would be challenging to synthesize through biosynthetic means alone. Here, we exclusively highlight systems that combine abiotic systems with living whole cells, taking particular note of strategies that enable the merger of these typically disparate systems.

Cadmium sulfide nanoparticles-assisted intimate coupling of microbial and photoelectrochemical processes: Mechanisms and environmental applications

Intimate coupling of microbial extracellular electron transfer (EET) and photoelectrochemical processes is an emerging research area with great potential to circumvent many disadvantages associated with traditional techniques that depend on independent microbial or photocatalysis treatment. Microbial EET processes involve microorganism oxidation of extracellular electron donors for respiration and synchronous reduction of extracellular electron acceptors to form an integrated respiratory chain. Coupled microbial EET-photoelectrochemical technologies greatly improve energy conversion efficiency providing both economic and environmental benefits. Among substitutes for semiconductor photocatalysts, cadmium sulfide nanoparticles (CdS NPs) possess several attractive properties. Specifically, CdS NPs have suitable electrical conductivity, large specific surface area, visible light-driven photocatalysis capability and robust biocompatibility, enabling them to promote hybrid microbial-photoelectrochemical processes. This review highlights recent advances in intimately coupled CdS NPs-microbial extracellular electron transfer systems and examines the mechanistic pathways involved in photoelectrochemical transformations. Finally, the prospects for emerging applications utilizing hybrid CdS NPs-based microbial-photoelectrochemical technologies are assessed. As such, this review provides a rigorous fundamental analysis of electron transport dynamics for hybrid CdS NPs-microbial photoelectrochemical processes and explores the applicability of engineered CdS NPs-biohybrids for future applications, such as in environmental remediation and clean-energy production.