Spectroscopic elucidation of energy transfer in hybrid inorganic-biological organisms for solar-to-chemical production

Unlocking interfacial electron transfer in biophotoelectrochemical processes: Role of extracellular polymeric substances in aquatic environments

The biophotoelectrochemical process (BPECs) integrates the light-absorbing capabilities of nano-semiconductors with the catalytic efficiency of microorganisms, demonstrating significant potential for the development, utilization, transformation, and ecological restoration of water resources. In aquatic environments, extracellular polymeric substances (EPS) serve as a critical interfacial barrier between microorganisms and semiconductor materials, with the underlying electron transfer mechanisms playing a pivotal role in determining the efficiency of bio-photochemical reactions. Despite their importance, the rapidity and complexity of the electron transfer process within EPS pose significant challenges to a comprehensive understanding of BPECs. In this study, an in-situ characterization strategy was employed to rapidly and accurately analyze the components and pathways of photogenerated electron transfer involving EPS at interfaces. The findings indicate that EPS significantly accelerates the transfer of photogenerated electrons within BPECs. Specifically, proteins and redox-active substances within EPS act as efficient conduits for electron transfer, accounting for up to 84.2% of the increased speed in electron transfer rates at bio-abiotic interfaces. Conversely, polysaccharides within EPS impede the electron transfer process but serve as substrates that facilitate methane (CH4) production. The in-situ characterization approach used in this research provides valuable insights into the interfacial electron transfer mechanisms of EPS in BPECs, emphasizing their relevance in aquatic environments. This study establishes a theoretical framework for designing high-performance BPECs, with significant implications for the energy utilization of water resources and the transformation of water pollutants.

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.

Boosting microalgae-based carbon sequestration with the artificial CO2 concentration system

Global warming caused by CO2 emissions has been considered as one of the major challenges of this century. In an endeavor to control and reduce CO2 emissions, a series of Carbon dioxide Capture, Utilization, and Storage (CCUS) technologies have been developed specifically for the sequestration of CO2 from atmospheric air. Microalgae, as versatile and universal photosynthetic microorganisms, represent a promising avenue for biological CO2 sequestration. Nevertheless, further advancements are necessary to optimize microalgae-based carbon sequestration technology in terms of light reaction and dark reaction. This review discusses the current status of microalgae-based artificial CO2 sequestration technique, with a particular focus on the selection of CO2-resistant species, optimization of cultivation for CO2 sequestration, design of carbon concentration reactor, and the potential of synthetic biology to enhance CO2 solubility and biofixation efficiency. Furthermore, a discussion of Life cycle assessment and Techno-economic analysis regarding microalgae-based carbon capture was performed. The aim of this comprehensive review is to stimulate further research into microalgae-based CO2 sequestration, addressing challenges and opportunities for future development.

Recent Progress in Designing Nanomaterial Biohybrids for Artificial Photosynthesis

In natural photosynthesis, solar energy is utilized to convert water and CO2 into energy-rich compounds. However, in practice, the maximum quantum efficiency of natural photosynthesis is limited to 6.0%. Conversely, artificial photosynthesis (AP) systems utilize solar energy to convert CO2 into biosynthetic solar fuels and value-added chemicals. To mimic natural photosystems, AP integrates light-harvesting chemical catalysts with the enzyme-mediated biological catalysis occurring in microorganisms. Similar to solar energy-based optoelectronic power sources, AP has also been recognized as a promising option for reducing carbon emissions generated by the fossil fuel-based power sector. Typical quantum efficiency of AP is 5-10%; in some cases, it exceeds 20%. Recent advancements have focused on nanomaterial biohybrids (NBHs), combining nanomaterial-based photocatalysts/photosensitizers with microorganisms/enzymes for enhanced oxidation/reduction reactions. The synergistic interaction between nanomaterials and microorganisms, facilitated by their comparable size and tunable surface properties, enables improved solar energy absorption, charge separation, and conversion. NBHs offer a versatile platform for sustainable solar energy harvesting and conversion, overcoming the limitations of natural and fully abiotic photosynthesis systems. This review highlights recent breakthroughs in diverse platforms of sunlight and visible light-driven NBH-based AP systems for CO2 fixation, H2 production, water splitting, and value-added chemical synthesis. The synthesis strategies, operating mechanisms, and challenges are highlighted.

Harnessing Near-Infrared Light for Enhanced Solar Hydrogen Production from Escherichia coli Interfaced with Biocompatible Low-Bandgap Conjugated Polymer Nanosheets

The efficient conversion of solar energy into clean hydrogen fuel presents a promising pathway for sustainable energy production. However, utilizing the full solar spectrum, particularly the near-infrared (NIR) region, remains underexplored in photosynthetic biohybrid systems. In this study, biocompatible, low-bandgap conjugated polymer nanosheets (PyTT-tBAL-HAB) are developed to integrate with non-photosynthetic, non-genetically engineered Escherichia coli (E. coli) for enhanced solar-driven biological hydrogen production. The PyTT-tBAL-HAB nanosheets exhibit unique NIR light absorption properties. Integrating these nanosheets with E. coli facilitates efficient electron transfer, resulting in a 1.96-fold increase in hydrogen production rate under NIR light. Consequently, this photosynthetic biohybrid system achieves a quantum efficiency of 18.36% at 940 nm. This study demonstrates the potential of using low-bandgap conjugated polymer nanosheets as advanced photosensitizers in semi-artificial photosynthetic systems, offering a robust platform for the effective utilization of the solar spectrum.

Multienergy Codriven Electron Transfer Across the Nano-Bio Interface for Efficient Photobiocatalysis

Integrating biocatalysis with nanophotocatalysis provides a promising pathway to address the knotty environmental and energy problems. However, energy loss during the transfer of extracellular electrons across the nano-bio interface seriously limits the efficiency of whole-cell-based photobiocatalytic systems. Herein, we demonstrate an integrated multienergy codriven reaction platform containing BaTiO3 nanoparticles (BTO) for harvesting mechanical energy from flowing water to elevate the interfacial electric field, BiVO4 quantum dots (BQD) for harvesting light energy to generate photocarriers, and Geobacter sulfurreducens (GS) for accepting photoelectrons to accomplish the biocatalytic reactions. The synergism between the piezoelectric and photoelectric fields significantly promotes the cross-membrane transport of photoelectrons, contributing to enhanced acetate metabolism, electron transfer, and energy synthesis of GS microbes. Such well-designed BQD/BTO-GS hybrids result in the simultaneous degradation of organic contaminants and detoxification of heavy metals in water with approximately 100% treatment efficiency. The rates of tetracycline (TC) oxidation and Cr(VI) reduction are determined to be 32.8 and 9.58 times higher than that of GS biocatalysis, respectively. Our photobiocatalytic platform exhibits an exceptional apparent quantum yield of 15.54% at 400 nm, exceeding those of most reported abiotic-biotic photobiocatalytic systems. Further investigation verifies the extensibility of our multienergy codriven strategy to the other nano-bio hybrids for enhancing the biocatalytic efficiencies (such as methanogenesis, CO2 fixation, and denitrification), thus offering an inspiring platform for energy and environmental applications. This work not only presents crucial insights into the mechanism of the water-energy nexus but also provides a paradigm for the construction of sustainable reaction systems via multienergy harnessing.

Spatially resolved charge-transfer kinetics at the quantum dot-microbe interface using fluorescence lifetime imaging microscopy

Integrating the optoelectronic properties of quantum dots (QDs) with biological enzymatic systems to form microbe-semiconductor biohybrids offers promising prospects for both solar-to-chemical conversion and light-modulated biochemical processes. Developing these nano-bio hybrid systems necessitates a deep understanding of charge-transfer dynamics at the nano-bio interface. Photoexcited carrier transfer from QDs to microbes is driven by complex interactions, with emerging insights into the relevant thermodynamic and kinetic factors. The heterogeneities of both microbes and QD ensembles pose significant challenges in mechanistic understanding, which is critical for designing advanced nano-bio hybrids. We used fluorescence lifetime imaging microscopy to analyze charge transfer between a CdSe QD film and Shewanella oneidensis microbes. We correlated the spatiotemporal fluorescence data with an analytical model. Our analysis revealed two distinct distributions of QD de-excitation pathways. The characteristics of these distributions: 1) a faster transfer rate ([Formula: see text]), with a lower acceptor number ([Formula: see text]) and 2) a slower transfer rate ([Formula: see text]) with a higher acceptor number ([Formula: see text]). We assign these distributions to the indirect and direct electron transfer mechanisms, respectively. Our findings demonstrate how spectroscopic imaging can uncover fundamental electron transfer mechanisms at complex interfaces, offering valuable design principles for future nano-bio hybrids.

Live-cell synthesis of biocompatible quantum dots

Quantum dots (QDs) exhibit fluorescence properties with promising prospects for biomedical applications; however, the QDs synthesized in organic solvents shows poor biocompatibility, limiting their use in biological systems. We developed an approach for synthesizing QDs in live cells by coupling a series of intracellular metabolic pathways in a precise spatial and temporal sequence. We have validated this approach in yeast (Saccharomyces cerevisiae), Staphylococcus aureus, Michigan Cancer Foundation-7 (MCF-7) and Madin-Darby canine kidney (MDCK) cells. The intracellularly synthesized QDs are inherently stable and biocompatible, making them suitable for the direct in situ labeling of cells and cell-derived vesicles. Here, we provide an optimized workflow for the live-cell synthesis of QDs by using S. cerevisiae, S. aureus or MCF-7 cells. In addition, we detail a cell-free aqueous synthetic system (quasi-biosynthesis) containing enzymes, electrolytes, peptides and coenzymes, which closely mimics the intracellular synthetic conditions used in our cell culture system. In this solution, we synthesize biocompatible ultrasmall QDs that are easier to purify and characterize than those synthesized in cells. The live-cell-synthesized QDs can be used for bioimaging and microvesicle detection, whereas the quasi-biosynthesized QDs are suitable for applications such as biodetection, biolabeling and real-time imaging. The procedure can be completed in 3-4 d for live-cell QD synthesis and 2 h for the quasi-biosynthesis of QDs. The procedure is suitable for users with expertise in chemistry, biology, materials science and synthetic biology. This approach encourages interested researchers to engage in the field of QDs and develop further biomedical applications.

The cytotoxicity of photoexcited CdS in an E. coli-CdS hybrid system and the roles of the sacrificial agent to reduce this toxic effect

This study investigates the biosynthesis of CdS nanoparticles (NPs) by Escherichia coli CD-2 to develop an E. coli-CdS hybrid system. The hybrid system was exposed to light in the presence and absence of cysteine (Cys) as a sacrificial agent. The finding revealed that in the absence of Cys, photo-induced holes led to a sharp increase in oxidative stress, disrupting the oxidative/antioxidative balance within bacterial cells. Consequently, cellular components were oxidized under elevated oxidative stress, lending to functional loss. This oxidative damage resulted in reduced cell viability, and in severe cases, cell disruption. Fortunately, the inclusion of the sacrificial agent alleviated these toxic effects. Cys quenched the photo-induced holes, markedly lowering oxidative stress within the cells. This mitigation enabled the maintenance of essential cellular functions during treatment. The majority of bacterial cells preserved their vitality and utilized the extra photoelectrons for cell growth under these conditions.

Powering the Future: Unveiling the Secrets of Semiconductor Biointerfaces in Biohybrids for Semiartificial Photosynthesis

Developing technology for sustainable chemical and fuel production is a key focus of scientific research. Semiartificial photosynthesis is a promising approach, pairing "electric microbes" with artificial light absorbers (semiconductors) to convert N2, CO2, and water into value-added products using sunlight. Mimicking natural photosynthesis is done with semiconductors acting as electron donors or sinks for microbes. This method enables the production of multicarbon (C2+) chemicals (e.g., ethanol and caproic acid) and ammonia with high efficiency and selectivity. Despite significant progress, commercial-scale applications remain elusive due to fundamental challenges. This Review covers advances in semiartificial photosynthesis and highlights that there is no clear mechanistic understanding underpinning the production of chemicals using the combination of light, semiconductors, and microbes. Does the mechanism rely on H2 uptake, do the microbes eat electrons directly from the light absorbers, or is it a combination of both? It focuses on overcoming bottlenecks using advanced spectroscopy, microscopy, and synthetic biology tools to study charge transfer kinetics between microbial cell membranes and semiconductors. Understanding this interaction is crucial for increasing solar-to-chemical (STC) efficiencies, necessary for industrial use. This Review also outlines future research directions and techniques to advance this field, aiming to achieve net-zero climate goals through multidisciplinary efforts.

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.

Polymer semiconductor films and bacteria hybrid artificial bio-leaves

Bio-artificial photosynthetic systems can reduce CO2 into multicarbon compounds by simulating natural photosynthesis. Here, inspired by organic photovoltaic structures, we demonstrate a bio-artificial photosynthetic system based on the hybridization of polymer semiconductor films and bacteria. The study suggests that the polymer-based semiconductor film can efficiently drive the non-photosynthetic bacteria to convert CO2 to acetate. By systematically characterizing the charge transport behavior of the bio-artificial photosynthetic system, the bulk-heterojunction structure and charge transport layers are proven to enhance the system performance markedly. The scalable floating artificial bio-leaf system can produce acetate to gram scale in a week. Notably, the semiconductor film is easy to recycle and maintains stable performance, showing good sustainable production capability of the system. A quasi-solid-state artificial bio-leaf is successfully prepared using agar to simulate the morphology and function of natural leaves. Last, the acetate production converted from CO2 was used to grow yeast for food production, thus achieving a complete simulation of natural photosynthesis.

Particle on a Rod: Surface-Tethered Catalyst on CdS Nanorods for Enzymatically Active Nicotinamide Cofactor Generation

The photochemical generation of nicotinamide cofactor 1,4-NADH, facilitated by inorganic photosensitizers, emerges as a promising model system for investigating charge transfer phenomena at the interface of semiconductors and bacteria, with implications for enhancing photosynthetic biohybrid systems (PBSs). However, extant semiconductor nanocrystal model systems suffer from achieving optimal conversion efficiency under visible light. This study investigates quasi-one-dimensional CdS nanorods as superior light absorbers, surface modified with catalyst Cp*Rh(4,4'-COOH-bpy)Cl2 to produce enzymatically active NADH. This model subsystem facilitates easy product isolation and achieves a turnover frequency (TOF) of 175 h-1, one of the highest efficiencies reported for inorganic photosensitizer-based nicotinamide cofactor generation. Charge transfer kinetics, fundamental for catalytic solar energy conversion, range from 106 to 108 s-1 for this system highlighting the superior electron transfer capabilities of NRs. This model ensures efficient cofactor production and offers critical insights into advancing systems that mimic natural photosynthesis for sustainable solar-to-chemical synthesis.

Engineering Shewanella oneidensis-Carbon Felt Biohybrid Electrode Decorated with Bacterial Cellulose Aerogel-Electropolymerized Anthraquinone to Boost Energy and Chemicals Production

Interfacial electron transfer between electroactive microorganisms (EAMs) and electrodes underlies a wide range of bio-electrochemical systems with diverse applications. However, the electron transfer rate at the biotic-electrode interface remains low due to high transmembrane and cell-electrode interfacial electron transfer resistance. Herein, a modular engineering strategy is adopted to construct a Shewanella oneidensis-carbon felt biohybrid electrode decorated with bacterial cellulose aerogel-electropolymerized anthraquinone to boost cell-electrode interfacial electron transfer. First, a heterologous riboflavin synthesis and secretion pathway is constructed to increase flavin-mediated transmembrane electron transfer. Second, outer membrane c-Cyts OmcF is screened and optimized via protein engineering strategy to accelerate contacted-based transmembrane electron transfer. Third, a S. oneidensis-carbon felt biohybrid electrode decorated with bacterial cellulose aerogel and electropolymerized anthraquinone is constructed to boost the interfacial electron transfer. As a result, the internal resistance decreased to 42 Ω, 480.8-fold lower than that of the wild-type (WT) S. oneidensis MR-1. The maximum power density reached 4286.6 ± 202.1 mW m-2, 72.8-fold higher than that of WT. Lastly, the engineered biohybrid electrode exhibited superior abilities for bioelectricity harvest, Cr6+ reduction, and CO2 reduction. This study showed that enhancing transmembrane and cell-electrode interfacial electron transfer is a promising way to increase the extracellular electron transfer of EAMs.

Proteomic and metabolic analysis of Moorella thermoacetica-g-C3N4 nanocomposite system for artificial photosynthesis

Artificial photosynthesis by microbe-semiconductor biohybrid systems has been demonstrated as a valuable strategy in providing sustainable energy and in carbon fixation. However, most of the developed biohybrid systems for light harvesting employ heavy metal materials, especially cadmium sulfide (CdS), which normally cause environmental pollution and restrict the widespread of the systems. Herein, we constructed an environmentally friendly biohybirid system based on a typical acetogenic bacteria, Moorella thermoacetica, coupling with a carbon-based semiconductor, graphitic carbon nitride (g-C3N4), to realize light-driven carbon fixation. The proposed biohybrid system displayed outstanding acetate productivity with a quantum yield of 2.66 ± 0.43 %. Non-targeted proteomic analysis indicated that the physiological activity of the bacteria was improved, coupling with the non-toxic material. We further proposed the mechanisms of energy generation, electron transfer and CO2 fixation of the irradiated biohybrid system by proteomic and metabolomic characterization. With the photoelectron generated in g-C3N4 under illumination, CO2 is finally converted to acetate via the Wood-Ljungdahl pathway (WLP). Other associated pathways were also proved to be activated, providing extra energy or substrates for acetate production. The study reveals that the future focus of the development of biohybrid systems for light harvesting can be on the metal-free biocompatible material, which can activate the expression of the key enzymes involved in the electron transfer and carbon metabolism under light irradiation.

Revisiting Solar Energy Flow in Nanomaterial-Microorganism Hybrid Systems

Nanomaterial-microorganism hybrid systems (NMHSs), integrating semiconductor nanomaterials with microorganisms, present a promising platform for broadband solar energy harvesting, high-efficiency carbon reduction, and sustainable chemical production. While studies underscore its potential in diverse solar-to-chemical energy conversions, prevailing NMHSs grapple with suboptimal energy conversion efficiency. Such limitations stem predominantly from an insufficient systematic exploration of the mechanisms dictating solar energy flow. This review provides a systematic overview of the notable advancements in this nascent field, with a particular focus on the discussion of three pivotal steps of energy flow: solar energy capture, cross-membrane energy transport, and energy conversion into chemicals. While key challenges faced in each stage are independently identified and discussed, viable solutions are correspondingly postulated. In view of the interplay of the three steps in affecting the overall efficiency of solar-to-chemical energy conversion, subsequent discussions thus take an integrative and systematic viewpoint to comprehend, analyze and improve the solar energy flow in the current NMHSs of different configurations, and highlighting the contemporary techniques that can be employed to investigate various aspects of energy flow within NMHSs. Finally, a concluding section summarizes opportunities for future research, providing a roadmap for the continued development and optimization of NMHSs.

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.

Operando Spectroscopic Elucidation of the Bubble Sunshade Effect in Inorganic-Biological Hybrids for Photosynthetic Hydrogen Production

Hydrogen production by photosynthetic hybrid systems (PBSs) offers a promising avenue for renewable energy. However, the light-harvesting efficiency of PBSs remains constrained due to unclear intracellular kinetic factors. Here, we present an operando elucidation of the sluggish light-harvesting behavior for existing PBSs and strategies to circumvent them. By quantifying the spectral shift in the structural color scattering of individual PBSs during the photosynthetic process, we observe the accumulation of product hydrogen bubbles on their outer membrane. These bubbles act as a sunshade and inhibit light absorption. This phenomenon elucidates the intrinsic constraints on the light-harvesting efficiency of PBSs. The introduction of a tension eliminator into the PBSs effectively improves the bubble sunshade effect and results in a 4.5-fold increase in the light-harvesting efficiency. This work provides valuable insights into the dynamics of transmembrane transport gas products and holds the potential to inspire innovative designs for improving the light-harvesting efficiency of PBSs.

Electron-Transport-Chain-Mediated Selective Growth of Gold Nanocrystals in the Intermembrane Space of Live Microbial Cells

Hybridization of microbial cells with inorganic nanoparticles that could dramatically improve cellular functions such as electron transfer has been realized by the random attachment or stochastic entry of the nanoparticles. Clearly, the selective growth of inorganic nanoparticles on target functional organelles is ideal for such hybridization. Here, we report the selective growth of gold nanocrystals in the intermembrane space (IMS) of Escherichia coli by exploiting the electron transport chain (ETC). We systematically show that gold ions are permeated through porins in the outer membrane of E. coli and further reduced to gold nanocrystals by the ETC in live E. coli. We directly observe that the resulting gold nanocrystals exist only in the IMS by transmission electron microscopy measurements of cross-sectioned E. coli. Molecular dynamics simulations suggest that once gold ions are reduced to small nuclei by the ETC, the nuclei can be stably physisorbed onto ETC complexes, further supporting the ETC-mediated growth. Finally, we show that the ATP synthesis of E. coli where gold nanocrystals are formed in the IMS is up to 9 times higher than that of E. coli alone. We believe that our work can significantly contribute to not only improving microbial metabolic functions for biological energy conversion but also restoring physiological dysfunctions of microbial cells for biomedicine.

Electromagnetic Field Drives the Bioelectrocatalysis of γ-Fe2O3-Coated Shewanella putrefaciens CN32 to Boost Extracellular Electron Transfer

The microbial hybrid system modified by magnetic nanomaterials can enhance the interfacial electron transfer and energy conversion under the stimulation of a magnetic field. However, the bioelectrocatalytic performance of a hybrid system still needs to be improved, and the mechanism of magnetic field-induced bioelectrocatalytic enhancements is still unclear. In this work, γ-Fe2O3 magnetic nanoparticles were coated on a Shewanella putrefaciens CN32 cell surface and followed by placing in an electromagnetic field. The results showed that the electromagnetic field can greatly boost the extracellular electron transfer, and the oxidation peak current of CN32@γ-Fe2O3 increased to 2.24 times under an electromagnetic field. The enhancement mechanism is mainly due to the fact that the surface modified microorganism provides an elevated contact area for the high microbial catalytic activity of the outer cell membrane's cytochrome, while the magnetic nanoparticles provide a networked interface between the cytoplasm and the outer membrane for boosting the fast multidimensional electron transport path in the magnetic field. This work sheds fresh scientific light on the rational design of magnetic-field-coupled electroactive microorganisms and the fundamentals of an optimal interfacial structure for a fast electron transfer process toward an efficient bioenergy conversion.

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.

From mechanism to application: Decrypting light-regulated denitrifying microbiome through geometric deep learning

Regulation on denitrifying microbiomes is crucial for sustainable industrial biotechnology and ecological nitrogen cycling. The holistic genetic profiles of microbiomes can be provided by meta-omics. However, precise decryption and further applications of highly complex microbiomes and corresponding meta-omics data sets remain great challenges. Here, we combined optogenetics and geometric deep learning to form a discover-model-learn-advance (DMLA) cycle for denitrification microbiome encryption and regulation. Graph neural networks (GNNs) exhibited superior performance in integrating biological knowledge and identifying coexpression gene panels, which could be utilized to predict unknown phenotypes, elucidate molecular biology mechanisms, and advance biotechnologies. Through the DMLA cycle, we discovered the wavelength-divergent secretion system and nitrate-superoxide coregulation, realizing increasing extracellular protein production by 83.8% and facilitating nitrate removal with 99.9% enhancement. Our study showcased the potential of GNNs-empowered optogenetic approaches for regulating denitrification and accelerating the mechanistic discovery of microbiomes for in-depth research and versatile applications.

Organic Semiconducting Polymers for Augmenting Biosynthesis and Bioconversion

Solar-driven biosynthesis and bioconversion are essential for achieving sustainable resources and renewable energy. These processes harness solar energy to produce biomass, chemicals, and fuels. While they offer promising avenues, some challenges and limitations should be investigated and addressed for their improvement and widespread adoption. These include the low utilization of light energy, the inadequate selectivity of products, and the limited utilization of inorganic carbon/nitrogen sources. Organic semiconducting polymers offer a promising solution to these challenges by collaborating with natural microorganisms and developing artificial photosynthetic biohybrid systems. In this Perspective, we highlight the latest advancements in the use of appropriate organic semiconducting polymers to construct artificial photosynthetic biohybrid systems. We focus on how these systems can enhance the natural photosynthetic efficiency of photosynthetic organisms, create artificial photosynthesis capability of nonphotosynthetic organisms, and customize the value-added chemicals of photosynthetic synthesis. By examining the structure-activity relationships and emphasizing the mechanism of electron transfer based on organic semiconducting polymers in artificial photosynthetic biohybrid systems, we aim to shed light on the potential of this novel strategy for artificial photosynthetic biohybrid systems. Notably, these coupling strategies between organic semiconducting polymers and organisms during artificial photosynthetic biohybrid systems will pave the way for a more sustainable future with solar fuels and chemicals.

Making the connections: physical and electric interactions in biohybrid photosynthetic systems

Biohybrid photosynthesis systems, which combine biological and non-biological materials, have attracted recent interest in solar-to-chemical energy conversion. However, the solar efficiencies of such systems remain low, despite advances in both artificial photosynthesis and synthetic biology. Here we discuss the potential of conjugated organic materials as photosensitisers for biological hybrid systems compared to traditional inorganic semiconductors. Organic materials offer the ability to tune both photophysical properties and the specific physicochemical interactions between the photosensitiser and biological cells, thus improving stability and charge transfer. We highlight the state-of-the-art and opportunities for new approaches in designing new biohybrid systems. This perspective also summarises the current understanding of the underlying electron transport process and highlights the research areas that need to be pursued to underpin the development of hybrid photosynthesis systems.

Microalgae-material hybrid for enhanced photosynthetic energy conversion: a promising path towards carbon neutrality

Photosynthetic energy conversion for high-energy chemicals generation is one of the most viable solutions in the quest for sustainable energy towards carbon neutrality. Microalgae are fascinating photosynthetic organisms, which can directly convert solar energy into chemical energy and electrical energy. However, microalgal photosynthetic energy has not yet been applied on a large scale due to the limitation of their own characteristics. Researchers have been inspired to couple microalgae with synthetic materials via biomimetic assembly and the resulting microalgae-material hybrids have become more robust and even perform new functions. In the past decade, great progress has been made in microalgae-material hybrids, such as photosynthetic carbon dioxide fixation, photosynthetic hydrogen production, photoelectrochemical energy conversion and even biochemical energy conversion for biomedical therapy. The microalgae-material hybrid offers opportunities to promote artificially enhanced photosynthesis research and synchronously inspires investigation of biotic-abiotic interface manipulation. This review summarizes current construction methods of microalgae-material hybrids and highlights their implication in energy and health. Moreover, we discuss the current problems and future challenges for microalgae-material hybrids and the outlook for their development and applications. This review will provide inspiration for the rational design of the microalgae-based semi-natural biohybrid and further promote the disciplinary fusion of material science and biological science.

Single-cell multimodal imaging uncovers energy conversion pathways in biohybrids

Microbe-semiconductor biohybrids, which integrate microbial enzymatic synthesis with the light-harvesting capabilities of inorganic semiconductors, have emerged as promising solar-to-chemical conversion systems. Improving the electron transport at the nano-bio interface and inside cells is important for boosting conversion efficiencies, yet the underlying mechanism is challenging to study by bulk measurements owing to the heterogeneities of both constituents. Here we develop a generalizable, quantitative multimodal microscopy platform that combines multi-channel optical imaging and photocurrent mapping to probe such biohybrids down to single- to sub-cell/particle levels. We uncover and differentiate the critical roles of different hydrogenases in the lithoautotrophic bacterium Ralstonia eutropha for bioplastic formation, discover this bacterium's surprisingly large nanoampere-level electron-uptake capability, and dissect the cross-membrane electron-transport pathways. This imaging platform, and the associated analytical framework, can uncover electron-transport mechanisms in various types of biohybrid, and potentially offers a means to use and engineer R. eutropha for efficient chemical production coupled with photocatalytic materials.

Periplasmic biomineralization for semi-artificial photosynthesis

Semiconductor-based biointerfaces are typically established either on the surface of the plasma membrane or within the cytoplasm. In Gram-negative bacteria, the periplasmic space, characterized by its confinement and the presence of numerous enzymes and peptidoglycans, offers additional opportunities for biomineralization, allowing for nongenetic modulation interfaces. We demonstrate semiconductor nanocluster precipitation containing single- and multiple-metal elements within the periplasm, as observed through various electron- and x-ray-based imaging techniques. The periplasmic semiconductors are metastable and display defect-dominant fluorescent properties. Unexpectedly, the defect-rich (i.e., the low-grade) semiconductor nanoclusters produced in situ can still increase adenosine triphosphate levels and malate production when coupled with photosensitization. We expand the sustainability levels of the biohybrid system to include reducing heavy metals at the primary level, building living bioreactors at the secondary level, and creating semi-artificial photosynthesis at the tertiary level. The biomineralization-enabled periplasmic biohybrids have the potential to serve as defect-tolerant platforms for diverse sustainable applications.

Direct Visualization and Restoration of Metallic Ion-Induced Subcellular Ultrastructural Remodeling

Analysis of cellular ultrastructure dynamics and metal ions' fate can provide insights into the interaction between living organisms and metal ions. Here, we directly visualize the distribution of biogenic metallic aggregates, ion-induced subcellular reorganization, and the corresponding regulation effect in yeast by the near-native 3D imaging approach, cryo-soft X-ray tomography (cryo-SXT). By comparative 3D morphometric assessment, we observe the gold ions disrupting cellular organelle homeostasis, resulting in noticeable distortion and folding of vacuoles, apparent fragmentation of mitochondria, extreme swelling of lipid droplets, and formation of vesicles. The reconstructed 3D architecture of treated yeast demonstrates ∼65% of Au-rich sites in the periplasm, a comprehensive quantitative assessment unobtained by TEM. We also observe some AuNPs in rarely identified subcellular sites, namely, mitochondria and vesicles. Interestingly, the amount of gold deposition is positively correlated with the volume of lipid droplets. Shifting the external starting pH to near-neutral results in the reversion of changes in organelle architectures, boosting the amount of biogenic Au nanoparticles, and increasing cell viability. This study provides a strategy to analyze the metal ions-living organism interaction from subcellular architecture and spatial localization perspectives.

Enhanced production of amylase, pyruvate and phenolic compounds from glucose by light-driven Aspergillus niger-CuS nanobiohybrids

BACKGROUND

The demand for value-added compounds such as amylase, pyruvate and phenolic compounds produced by biological methods has prompted the rapid development of advanced technologies for their enhanced production. Nanobiohybrids (NBs) make use of both the microbial properties of whole-cell microorganisms and the light-harvesting efficiency of semiconductors. Photosynthetic NBs were constructed that link the biosynthetic pathways of Aspergillus niger with CuS nanoparticles.

RESULTS

In this work, NB formation was confirmed by negative values of the interaction energy, i.e., 2.31 × 10⁸ to -5.52 × 10⁸ kJ mol^-1 for CuS-Che NBs, whereas for CuS-Bio NBs the values were -2.31 × 10⁸ to -4.62 × 10⁸ kJ mol^-1 for CuS-Bio NBs with spherical nanoparticle interaction. For CuS-Bio NBs with nanorod interaction, it ranged from -2.3 × 10⁷ to -3.47 × 10⁷ kJ mol^-1 . Further, the morphological changes observed by scanning electron microscopy showed the presence of the elements Cu and S in the energy-dispersive X-ray spectra and the presence of CuS bonds in Fourier transform infrared spectroscopy indicate NB formation. In addition, the quenching effect in photoluminescence studies confirmed NB formation. Production yields of amylase, phenolic compounds and pyruvate amounted to 11.2 μmol L^-1, 52.5 μmol L^-1 and 28 nmol μL^-1, respectively, in A. niger-CuS Bio NBs on the third day of incubation in the bioreactor. Moreover, A niger cells-CuS Bio NBs had amino acids and lipid yields of 6.2 mg mL^-1 and 26.5 mg L^-1, respectively. Furthermore, probable mechanisms for the enhanced production of amylase, pyruvate and phenolic compounds are proposed.

CONCLUSION

Aspergillus niger-CuS NBs were used for the production of the amylase enzyme and value-added compounds such as pyruvate and phenolic compounds. Aspergillus niger-CuS Bio NBs showed a greater efficiency compared to A. niger-CuS Che NBs as the biologically produced CuS nanoparticles had a higher compatibility with A. niger cells. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

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.

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.

Solar-driven methanogenesis with ultrahigh selectivity by turning down H2 production at biotic-abiotic interface

Integration of methanogens with semiconductors is an effective approach to sustainable solar-driven methanogenesis. However, the H₂ production rate by semiconductors largely exceeds that of methanogen metabolism, resulting in abundant H₂ as side product. Here, we report that binary metallic active sites (namely, NiCu alloys) are incorporated into the interface between CdS semiconductors and Methanosarcina barkeri. The self-assembled Methanosarcina barkeri-NiCu@CdS exhibits nearly 100% CH₄ selectivity with a quantum yield of 12.41 ± 0.16% under light illumination, which not only exceeds the reported biotic-abiotic hybrid systems but also is superior to most photocatalytic systems. Further investigation reveal that the Ni-Cu-Cu hollow sites in NiCu alloys can directly supply hydrogen atoms and electrons through photocatalysis to the Methanosarcina barkeri for methanogenesis via both extracellular and intracellular hydrogen cycles, effectively turning down the H₂ production. This work provides important insights into the biotic-abiotic hybrid interface, and offers an avenue for engineering the methanogenesis process.

Microbe-mediated transformation of metal sulfides: Mechanisms and environmental significance

Microorganisms play a key role in the natural circulation of various constituent elements of metal sulfides. Some microorganisms (such as Thiobacillus ferrooxidans) can promote the oxidation of metal sulfides to increase the release of heavy metals. However, other microorganisms (such as Desulfovibrio vulgaris) can transform heavy metals into metal sulfides crystals. Therefore, insight into the metal sulfides transformation mediated by microorganisms is of great significance to environmental protection. In this review, first, we discuss the mechanism and influencing factors of microorganisms transforming heavy metals into metal sulfides crystals in different environments. Then, we explore three microbe-mediated transformation forms of heavy metals to metal sulfides and their environmental applications: (1) transformation to metal sulfides precipitation for metal resource recovery; (2) transformation to metal sulfides nanoparticles (NPs) for pollutant treatment; (3) transformation to "metal sulfides-microbe" biohybrid system for clean energy production and pollutant remediation. Finally, we further provide critical views on the application of microbe-mediated metal sulfides transformation in the environmental field and discuss the need for future research.

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.

Biocatalytic conversion of sunlight and carbon dioxide to solar fuels and chemicals

This review discusses the progress in the assembly of photosynthetic biohybrid systems using enzymes and microbes as the biocatalysts which are capable of utilising light to reduce carbon dioxide to solar fuels. We begin by outlining natural photosynthesis, an inspired biomachinery to develop artificial photosystems, and the rationale and motivation to advance and introduce biological substrates to create more novel, and efficient, photosystems. The case studies of various approaches to the development of CO2-reducing microbial semi-artificial photosystems are also summarised, showcasing a variety of methods for hybrid microbial photosystems and their potential. Finally, approaches to investigate the relatively ambiguous electron transfer mechanisms in such photosystems are discussed through the presentation of spectroscopic techniques, eventually leading to what this will mean for the future of microbial hybrid photosystems.

Photosynthesis of Acetate by Sporomusa ovata-CdS Biohybrid System

Sporomusa ovata, a typical electroautotrophic microorganism, has been utilized in bioelectrosynthesis for carbon dioxide fixation to multicarbon organic chemicals. However, additional photovoltaic devices are normally needed to convert photo energy to electric energy to power the carbon dioxide fixation, which restricts the overall energy conversion efficiency. Herein, we report Sporomusa ovata-CdS biohybrids for artificial photosynthesis driven by light without any other power source. The quantum yield can reach 16.8 ± 9%, and the active duration time of the system can last for 5 days. During the artificial photosynthesis, carbon dioxide is first reduced to formate and finally converted to acetate via the Wood-Ljungdahl pathway. The carbon dioxide fixation, electron transfer, energy metabolism, and reactive oxygen species damage repair processes in the biohybrid system were characterized by proteomic analysis. Key enzymes, e.g., flavoprotein, ferredoxin, formate-tetrahydrofolate ligase, 5-methyltetrahydrofolate:corrinoid iron-sulfur protein methyltransferase, thioredoxin, and rubrerythrin, were found up-regulated in the biohybrid system. The findings are helpful in understanding the mechanism of the artificial photosynthesis and useful for the development of new biohybrid systems using genetically engineered microbes in the future. The study is expected to boost the development of bioabiotic hybrid system in solar energy harvest.

Engineering Acetogenic Bacteria for Efficient One-Carbon Utilization

C1 gases, including carbon dioxide (CO₂) and carbon monoxide (CO), are major contributors to climate crisis. Numerous studies have been conducted to fix and recycle C1 gases in order to solve this problem. Among them, the use of microorganisms as biocatalysts to convert C1 gases to value-added chemicals is a promising solution. Acetogenic bacteria (acetogens) have received attention as high-potential biocatalysts owing to their conserved Wood–Ljungdahl (WL) pathway, which fixes not only CO₂ but also CO. Although some metabolites have been produced via C1 gas fermentation on an industrial scale, the conversion of C1 gases to produce various biochemicals by engineering acetogens has been limited. The energy limitation of acetogens is one of the challenges to overcome, as their metabolism operates at a thermodynamic limit, and the low solubility of gaseous substrates results in a limited supply of cellular energy. This review provides strategies for developing efficient platform strains for C1 gas conversion, focusing on engineering the WL pathway. Supplying liquid C1 substrates, which can be obtained from CO₂, or electricity is introduced as a strategy to overcome the energy limitation. Future prospective approaches on engineering acetogens based on systems and synthetic biology approaches are also discussed.

Effects of cadmium sulfide nanoparticles on sulfate bioreduction and oxidative stress in Desulfovibrio desulfuricans

Sulfate-containing wastewater has a serious threat to the environment and human health. Microbial technology has great potential for the treatment of sulfate-containing wastewater. It was found that nano-photocatalysts could be used as extracellular electron donors to promote the growth and metabolic activity of non-photosynthetic microorganisms. However, nano-photocatalysts could also induce oxidative stress and damage cells. Therefore, the interaction mechanism between photosynthetic nanocatalysts and non-photosynthetic microorganisms is crucial to determine the regulatory strategies for microbial wastewater treatment technologies. In this paper, the mechanism and regulation strategy of cadmium sulfide nanoparticles (CdS NPs) on the growth of sulfate-reducing bacteria and the sulfate reduction process were investigated. The results showed that the sulfate reduction efficiency could be increased by 6.4% through CdS NPs under light conditions. However, the growth of Desulfovibrio desulfuricans C09 was seriously inhibited by 55% due to the oxidative stress induced by CdS NPs on cells. The biomass and sulfate reduction efficiency could be enhanced by 6.8% and 5.9%, respectively, through external addition of humic acid (HA). At the same time, the mechanism of the CdS NPs strengthening the sulfate reduction process by sulfate bacteria was also studied which can provide important theoretical guidance and technical support for the development of microbial technology combined with extracellular electron transfer (EET) for the treatment of sulfate-containing wastewater.

Light-driven carbon dioxide reduction to methane by Methanosarcina barkeri in an electric syntrophic coculture

The direct conversion of CO₂ to value-added chemical commodities, thereby storing solar energy, offers a promising option for alleviating both the current energy crisis and global warming. Semiconductor-biological hybrid systems are novel approaches. However, the inherent defects of photocorrosion, photodegradation, and the toxicity of the semiconductor limit the application of these biohybrid systems. We report here that Rhodopseudomonas palustris was able to directly act as a living photosensitizer to drive CO₂ to CH₄ conversion by Methanosarcina barkeri under illumination after coculturing. Specifically, R. palustris formed a direct electric syntrophic coculture with M. barkeri. Here, R. palustris harvested solar energy, performed anoxygenic photosynthesis using sodium thiosulfate as an electron donor, and transferred electrons extracellularly to M. barkeri to drive methane generation. The methanogenesis of M. barkeri in coculture was a light-dependent process with a production rate of 4.73 ± 0.23 μM/h under light, which is slightly higher than that of typical semiconductor-biohybrid systems (approximately 4.36 μM/h). Mechanistic and transcriptomic analyses showed that electrons were transferred either directly or indirectly (via electron shuttles), subsequently driving CH₄ production. Our study suggests that R. palustris acts as a natural photosensitizer that, in coculture with M. barkeri, results in a new way to harvest solar energy that could potentially replace semiconductors in biohybrid systems.

Harnessing electrical-to-biochemical conversion for microbial synthesis

Electrical-to-biochemical conversion (E2BC) drives cell metabolism for biosynthesis and has become a promising way to realize green biomanufacturing. This review discusses the following aspects: 1. the natural E2BC processes and their underlying E2BC mechanism; 2. development of artificial E2BC for tunable microbial electrosynthesis; 3. design of electrobiochemical systems using self-powered, light-assisted, and nano-biohybrid approaches; 4. synthetic biology methods for efficient microbial electrosynthesis. This review also compares E2BC with electrocatalysis-biochemical conversion (EC2BC), as both strategies may lead to future carbon negative green biomanufacturing.

Bioinspired Artificial Photosynthetic Systems

Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents recent advances towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid/electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.

De Novo Approach to Encapsulating Biocatalysts into Synthetic Matrixes: From Enzymes to Microbial Electrocatalysts

Biocatalysts hold great promise in chemical and electrochemical reactions. However, biocatalysts are prone to inhospitable physiochemical conditions. Encapsulating biocatalysts into a synthetic host matrix can improve their stability and activity, and broaden their operational conditions. In this Review, we summarize the emerging de novo approaches to encapsulating biocatalysts into synthetic matrixes. Here, de novo means that embedding of biocatalysts and construction of matrixes take place simultaneously. We discuss the advantages and limitations of the de novo approach. On the basis of the nature of the biocatalysts and the synthetic frameworks, we specifically focus on two aspects: (1) encapsulation of enzymes (in vitro) in metal-organic frameworks and (2) encapsulation of microbial electrocatalysts (in vivo) on the electrode. For both cases, we discuss how the encapsulation improves biocatalysts' performance (stability, viability, activity, and etc.). We also highlight the benefit of encapsulation in facilitating the transport of charge carriers in microbial electrocatalysis.

Pushing the methodological envelope in understanding the photo/electrosynthetic materials-microorganism interface

Biohybrid photo/electrosynthetic systems synergize microbial metabolic pathways and inorganic materials to generate the fuels and chemicals to power our society. They aim to combine the strengths of product selectivity from biological cells and efficient charge generation and light absorption of inorganic materials. However crucial mechanistic questions still remain. In this review we address significant knowledge gaps that must be closed and recent efforts to do so to push biohybrid systems closer to applicability. In particular, we focus on noteworthy advances that have recently been made in applying state-of-the-art analytical spectroscopic, electrochemical, and microelectronic techniques to help pinpoint key complexities of the microbe-materials interface. We discuss the basic function of these techniques, how they have been translated over to study biohybrid systems, and which key insights and implications have been extracted. Finally, we delve into the key advances necessary for the design of next generation biohybrid energy conversion systems.

Molecular insights and future frontiers in cell photosensitization for solar-driven CO2 conversion

The conversion of CO2 to value-added products powered with solar energy is an ideal solution to establishing a closed carbon cycle. Combining microorganisms with light-harvesting nanomaterials into photosynthetic biohybrid systems (PBSs) presents an approach to reaching this solution. Metabolic pathways precisely evolved for CO2 fixation selectively and reliably generate products. Nanomaterials harvest solar light and biocompatibly associate with microorganisms owing to similar lengths scales. Although this is a nascent field, a variety of approaches have been implemented encompassing different microorganisms and nanomaterials. To advance the field in an impactful manner, it is paramount to understand the molecular underpinnings of PBSs. In this perspective, we highlight studies inspecting charge uptake pathways and singularities in photosensitized cells. We discuss further analyses to more completely elucidate these constructs, and we focus on criteria to be met for designing photosensitizing nanomaterials. As a result, we advocate for the pairing of microorganisms with naturally occurring and highly biocompatible mineral-based semiconductor nanomaterials.

Artificial-regulated synthesis of nanocrystals in live cells

Live cells, as reservoirs of biochemical reactions, can serve as amazing integrated chemical plants where precursor formation, nucleation and growth of nanocrystals, and functional assembly can be carried out accurately following an artificial program. It is crucial but challenging to deliberately direct intracellular pathways to synthesize desired nanocrystals that cannot be produced naturally in cells, because the relevant reactions exist in different spatiotemporal dimensions and will never encounter spontaneously. This article summarizes progress in the introduction of inorganic functional nanocrystals into live cells via the ‘artificial-regulated space–time-coupled live-cell synthesis’ strategy. We also describe ingenious bio-applications of the nanocrystal–cell systems, and quasi-biosynthesis strategies expanded from live-cell synthesis. Artificial-regulated live-cell synthesis—which involves the interdisciplinary application of biology, chemistry, nanoscience and medicine—will enable researchers to better exploit the unanticipated potentialities of live cells and open up new directions in synthetic biology.

Biophotoelectrochemistry for renewable energy and environmental applications

Biophotoelectrochemistry (BPEC) is an interdisciplinary research field and combines bioelectrochemistry and photoelectrochemistry through the utilization of the catalytic abilities of biomachineries and light harvesters to accomplish the production of energy or chemicals driven by solar energy. The BPEC process may act as a new approach for sustainable green chemistry and waste minimization. This review provides the state-of-the-art introduction of BPEC basics and systems, with a focus on light harvesters and biocatalysts, configurations, photoelectron transfer mechanisms, and the potential applications in energy and environment. Several examples of BPEC applications are discussed including H2 production, CO2 reduction, chemical synthesis, pollution control, and biogeochemical cycle of elements. The challenges about BPEC systems are identified and potential solutions are proposed. The review aims to encourage further research of BPEC toward development of practical BPEC systems for energy and environmental applications.

Degradation of low-concentration perfluorooctanoic acid via a microbial-based synergistic method: assessment of the feasibility and functional microorganisms

Perfluorooctanoic acid (PFOA) is persistent in the environment. The activities of microorganisms alone are insufficient for the decomposition of PFOA, but microorganisms can contribute positively to the degradation of PFOA in synergistic systems. Herein, a synergistic system combining photocatalytic decay with microbial degradation of the transformation products was applied to degrade 500.0 μg L^-1 PFOA. The microorganisms increased the total removed percentage by 30.7% to a final percentage of 79.7 ± 9.4% in comparison with the photocatalytic method alone. Moreover, an additional 44.2% of removed total organic carbon and additional defluorination percentage of 24.5% were obtained after the synergistic tests. The 16S RNA sequencing analysis indicated that Stenotrophomonas, Bacillus, Pseudomonas, and Brevundimonas were highly enriched in the functional microbial community, which was simultaneously shaped by photocatalysis and substances. This study found it would be feasible to use a synergistic method containing photocatalysis and a microbial community for the degradation of low-concentrations of PFOA, and the results provided a reference to modified the removal efficiency of the synergistic system by looking insight into the relationship between the functional microbial community and PFOA.

Acetogenic bacteria utilize light-driven electrons as an energy source for autotrophic growth

To develop an efficient artificial photosynthesis system using acetogen-nanoparticle hybrids, the efficiency of the electron–hole pair generation of nanoparticles must be enhanced to demonstrate extracellular electron utilization by the acetogen. Here we verified that Clostridium autoethanogenum, an industrially relevant acetogen, could use electrons generated from size- and structure-controlled chemically synthesized cadmium sulfide nanoparticles displayed on the cell surface under light-exposure conditions. In addition, transcriptomic analysis showed that the electrons generated from nanoparticles were largely transported to the intracellular matrix via the metal ion or flavin-binding proteins. These results illustrate the potential to increase the CO₂-fixing efficiency of nanoparticle-based artificial photosynthesis by engineering cellular processes related to electron transfer generated from the cathode.

Acetogenic bacteria use cellular redox energy to convert CO₂ to acetate using the Wood–Ljungdahl (WL) pathway. Such redox energy can be derived from electrons generated from H₂ as well as from inorganic materials, such as photoresponsive semiconductors. We have developed a nanoparticle-microbe hybrid system in which chemically synthesized cadmium sulfide nanoparticles (CdS-NPs) are displayed on the cell surface of the industrial acetogen Clostridium autoethanogenum. The hybrid system converts CO₂ into acetate without the need for additional energy sources, such as H₂, and uses only light-induced electrons from CdS-NPs. To elucidate the underlying mechanism by which C. autoethanogenum uses electrons generated from external energy sources to reduce CO₂, we performed transcriptional analysis. Our results indicate that genes encoding the metal ion or flavin-binding proteins were highly up-regulated under CdS-driven autotrophic conditions along with the activation of genes associated with the WL pathway and energy conservation system. Furthermore, the addition of these cofactors increased the CO₂ fixation rate under light-exposure conditions. Our results demonstrate the potential to improve the efficiency of artificial photosynthesis systems based on acetogenic bacteria integrated with photoresponsive nanoparticles.

Whole-Cell-Based Photosynthetic Biohybrid Systems for Energy and Environmental Applications

With the increasing awareness of sustainable development, energy and environment are becoming two of the most important issues of concern to the world today. Whole-cell-based photosynthetic biohybrid systems (PBSs), an emerging interdisciplinary field, are considered as attractive biosynthetic platforms with great prospects in energy and environment, combining the superiorities of semiconductor materials with high energy conversion efficiency and living cells with distinguished biosynthetic capacity. This review presents a systematic discussion on the synthesis strategies of whole-cell-based PBSs that demonstrate a promising potential for applications in sustainable solar-to-chemical conversion, including light-facilitated carbon dioxide reduction and biohydrogen production. In the end, the explicit perspectives on the challenges and future directions in this burgeoning field are discussed.