Bacterial extracellular electron transfer: a powerful route to the green biosynthesis of inorganic nanomaterials for multifunctional applications

In Situ Biosynthesis of FeS Nanoparticles Boosts Current Generation in Bioelectrochemical Systems Through Efficient Electron Transfer

The utility of electrochemical active biofilm in bioelectrochemical systems has received considerable attention for harvesting energy and chemical products. However, the slow electron transfer between biofilms and electrodes hinders the enhancement of performance and still remains challenging. Here, using Fe3O4 /L-Cys nanoparticles as precursors to induce biomineralization, a facile strategy for the construction of an effective electron transfer pathway through biofilm and biological/inorganic interface is proposed, and the underlying mechanisms are elucidated. Taking advantage of an on-chip interdigitated microelectrode array (IDA), the conductive current of biofilm that is related to the electron transfer process within biofilm is characterized, and a 2.10-fold increase in current output is detected. The modification of Fe3O4/L-Cys on the electrode surface facilitates the electron transfer between the biofilm and the electrode, as the bio/inorganic interface electron transfer resistance is only 16% compared to the control. The in-situ biosynthetic Fe-containing nanoparticles (e.g., FeS) enhance the transmembrane EET and the EET within biofilm, and the peak conductivity increases 3.4-fold compared to the control. The in-situ biosynthesis method upregulates the genes involved in energy metabolism and electron transfer from the transcriptome analysis. This study enriches the insights of biosynthetic nanoparticles on electron transfer process, holding promise in bioenergy conversion.

Microalgae-bacteria nexus for environmental remediation and renewable energy resources: Advances, mechanisms and biotechnological applications

Microalgae and bacteria, known for their resilience, rapid growth, and proximate ecological partnerships, play fundamental roles in environmental and biotechnological advancements. This comprehensive review explores the synergistic interactions between microalgae and bacteria as an innovative approach to address some of the most pressing environmental issues and the demands of clean and renewable freshwater and energy sources. Studies indicated that microalgae-bacteria consortia can considerably enhance the output of biotechnological applications; for instance, various reports showed during wastewater treatment the COD removal efficiency increased by 40%-90.5 % due to microalgae-bacteria consortia, suggesting its great potential amenability in biotechnology. This review critically synthesizes research works on the microalgae and bacteria nexus applied in the advancements of renewable energy generation, with a special focus on biohydrogen, reclamation of wastewater and desalination processes. The mechanisms of underlying interactions, the environmental factors influencing consortia performance, and the challenges and benefits of employing these bio-complexes over traditional methods are also discussed in detail. This paper also evaluates the biotechnological applications of these microorganism consortia for the augmentation of biomass production and the synthesis of valuable biochemicals. Furthermore, the review sheds light on the integration of microalgae-bacteria systems in microbial fuel cells for concurrent energy production, waste treatment, and resource recovery. This review postulates microalgae-bacteria consortia as a sustainable and efficient solution for clean water and energy, providing insights into future research directions and the potential for industrial-scale applications.

Green Synthesis of Silver Nanoparticles Mediated by Punica granatum Peel Waste: An Effective Additive for Natural Rubber Latex Nanofibers Enhancement

Pomegranate waste poses an environmental challenge in Arequipa. Simultaneously, interest in sustainable materials like natural rubber latex (NRL) is growing, with Peruvian communities offering a promising source. This study explores the green synthesis of silver nanoparticles (AgNPs) using pomegranate peel extract and their incorporation into NRL nanofibers for enhanced functionalities. An eco-friendly process utilized silver nitrate and pomegranate peel extract as a reducing and capping agent to synthesize AgNPs. The resulting AgNPs and NRL/AgNPs nanofibers were characterized using imaging and spectroscopic techniques such as UV-vis, TGA, FTIR, XRD, Raman, SEM, and DLS. Green-synthesized AgNPs were spherical and crystalline, with an average diameter of 59 nm. They showed activity against K. pneumoniae, E. coli, B. cereus, and S. aureus (IC50: 51.32, 4.87, 27.72, and 69.72 µg/mL, respectively). NRL and NRL/AgNPs nanofibers (300-373 nm diameter) were successfully fabricated. The composite nanofibers exhibited antibacterial activity against K. pneumoniae and B. cereus. This study presents a sustainable approach by utilizing pomegranate waste for AgNP synthesis and NRL sourced from Peruvian communities. Integrating AgNPs into NRL nanofibers produced composites with antimicrobial properties. This work has potential applications in smart textiles, biomedical textiles, and filtration materials where sustainability and antimicrobial functionality are crucial.

Modularized Engineering of Shewanella oneidensis MR-1 for Efficient and Directional Synthesis of 5-Aminolevulinic Acid

Shewanella oneidensis MR-1 has found widespread applications in pollutant transformation and bioenergy production, closely tied to its outstanding heme synthesis capabilities. However, this significant biosynthetic potential is still unexploited so far. Here, we turned this bacterium into a highly-efficient bio-factory for green synthesis of 5-Aminolevulinic Acid (5-ALA), an important chemical for broad applications in agriculture, medicine, and the food industries. The native C5 pathway genes of S. oneidensis was employed, together with the introduction of foreign anti-oxidation module, to establish the 5-ALA production module, resulting 87-fold higher 5-ALA yield and drastically enhanced tolerance than the wild type. Furthermore, the metabolic flux was regulated by using CRISPR interference and base editing techniques to suppress the competitive pathways to further improve the 5-ALA titer. The engineered strain exhibited 123-fold higher 5-ALA production capability than the wild type. This study not only provides an appealing new route for 5-ALA biosynthesis, but also presents a multi-dimensional modularized engineering strategy to broaden the application scope of S. oneidensis.

Revisiting the smart metallic nanomaterials: advances in nanotechnology-based antimicrobials

Despite significant advancements in diagnostics and treatments over the years, the problem of antimicrobial drug resistance remains a pressing issue in public health. The reduced effectiveness of existing antimicrobial drugs has prompted efforts to seek alternative treatments for microbial pathogens or develop new drug candidates. Interestingly, nanomaterials are currently gaining global attention as a possible next-generation antibiotics. Nanotechnology holds significant importance, particularly when addressing infections caused by multi-drug-resistant organisms. Alternatively, these biomaterials can also be combined with antibiotics and other potent biomaterials, providing excellent synergistic effects. Over the past two decades, nanoparticles have gained significant attention among research communities. Despite the complexity of some of their synthesis strategies and chemistry, unrelenting efforts have been recorded in synthesizing potent and highly effective nanomaterials using different approaches. With the ongoing advancements in nanotechnology, integrating it into medical procedures presents novel approaches for improving the standard of patient healthcare. Although the field of nanotechnology offers promises, much remains to be learned to overcome the several inherent issues limiting their full translation to clinics. Here, we comprehensively discussed nanotechnology-based materials, focusing exclusively on metallic nanomaterials and highlighting the advances in their synthesis, chemistry, and mechanisms of action against bacterial pathogens. Importantly, we delve into the current challenges and prospects associated with the technology.

Bacterially synthesized superfine tellurium nanoneedles as an antibacterial and solar-thermal still for efficient purification of polluted water

Bacterial biosynthesis of nanomaterials has several advantages (e.g., reduced energy inputs, lower cost, negligible environmental pollution) compared with traditional approaches. Various nanomaterials have been produced by bacteria. However, reports on using the bacterial biosynthesis of nanomaterials for applications with solar-thermal agents are scarce due to their narrow optical absorption. Herein, for the first time, we proposed a bacterial biosynthesis of broad-absorbing tellurium nanoneedles and demonstrated their effectiveness for solar-thermal evaporation and antibacterial applications. By simple biosynthesis within bacteria (Shewanella oneidensis MR-1), tellurium nanoneedles achieved a superfine configuration with a length-to-diameter ratio of nearly 20 and broad-spectrum absorbance. After integrating tellurium nanoneedles into a porous polyvinyl-alcohol scaffold, a solar-thermal still named TSAS-3 realized a high evaporation rate of 2.25 kg m-2 h-1 and solar-thermal conversion efficiency of 81% upon 1-Sun illumination. Based on these unique properties, the scaffold displayed good performances in seawater desalination, multiple wastewater treatment, and antibacterial applications. This work provides a simple and feasible strategy for the use of microbial-synthesized nanomaterials in solar-driven water purification and antibacterial applications.

Green Synthesis of Novel Silver Nanoparticles Using Salvia blepharophylla and Salvia greggii: Antioxidant and Antidiabetic Potential and Effect on Foodborne Bacterial Pathogens

In the face of evolving healthcare challenges, the utilization of silver nanoparticles (AgNPs) has emerged as a compelling solution due to their unique properties and versatile applications. The aim of this study was the synthesis and characterization of novel AgNPs (SB-AgNPs and SG-AgNPs, respectively) using Salvia blepharophylla and Salvia greggii leaf extracts and the evaluation of their antimicrobial, antioxidant, and antidiabetic activities. Several analytical instrumental techniques were utilized for the characterization of SB-AgNPs and SG-AgNPs, including UV-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transmission infrared (FT-IR) spectroscopy, energy-dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). FTIR analysis identified various functional groups in the leaf extracts and nanoparticles, suggesting the involvement of phytochemicals as reducing and stabilizing agents. High-resolution TEM images displayed predominantly spherical nanoparticles with average sizes of 52.4 nm for SB-AgNPs and 62.5 nm for SG-AgNPs. Both SB-AgNPs and SG-AgNPs demonstrated remarkable antimicrobial activity against Gram-positive bacteria Staphylococcus aureus and Listeria monocytogenes and Gram-negative bacteria Salmonella typhimurium and Escherichia coli. SB-AgNPs and SG-AgNPs also exhibited 90.2 ± 1.34% and 89.5 ± 1.5% DPPH scavenging and 86.5 ± 1.7% and 80.5 ± 1.2% α-amylase inhibition, respectively, at a concentration of 100 μg mL-1. Overall, AgNPs synthesized using S. blepharophylla and Salvia greggii leaf extracts may serve as potential candidates for antibacterial, antioxidant, and antidiabetic agents. Consequently, this study provides viable solutions to mitigate the current crisis of antibiotic resistance and to efficiently combat antimicrobial infections and Type 2 diabetes.

Lactiplantibacillus plantarum uses ecologically relevant, exogenous quinones for extracellular electron transfer

IMPORTANCE

While quinones are essential for respiratory microorganisms, their importance for microbes that rely on fermentation metabolism is not understood. This gap in knowledge hinders our understanding of anaerobic microbial habitats, such in mammalian digestive tracts and fermented foods. We show that Lactiplantibacillus plantarum, a model fermentative lactic acid bacteria species abundant in human, animal, and insect microbiomes and fermented foods, uses multiple exogenous, environmental quinones as electron shuttles for a hybrid metabolism involving EET. Interestingly, quinones both stimulate this metabolism as well as cause oxidative stress when extracellular electron acceptors are absent. We also found that quinone-producing, lactic acid bacteria species commonly enriched together with L. plantarum in food fermentations accelerate L. plantarum growth and medium acidification through a mainly quinone- and EET-dependent mechanism. Thus, our work provides evidence of quinone cross-feeding as a key ecological feature of anaerobic microbial habitats.

Transcriptome Analysis Reveals the Inhibitory Effect of Cu2+ on Polyferric Sulfate Floc Reduction by Shewanella putrefaciens CN32

Polyferric sulfate (PFS), an economical coagulant widely used for removing heavy metal contaminants from water, is susceptible to reduction and transformation by iron-reducing bacteria prevalent in sediments. However, the effect of heavy metal ions adsorbed in PFS flocs on this biological process remains unclear. According to our results, compared with other heavy metal cations (e.g., Cu2+, Cd2+, Zn2+, Ni2+, Pb2+, and Co2+), Cu2+ had a stronger inhibitory effect on PFS floc reduction by Shewanella putrefaciens CN32, a typical dissimilatory iron-reducing bacterium. The presence of Cu2+ remarkably influenced the global transcription of CN32, resulting in 782 upregulated genes and 713 downregulated genes that are mainly annotated in energy production, amino acid metabolism, protein biosynthesis, and oxidation‒reduction processes. The anaerobic TCA cycle for energy (electron) production was significantly activated in the presence of Cu2+, while the transcription of many genes related to the extracellular electron transfer pathway was downregulated, which is responsible for the decreased Fe3+ reduction. Moreover, the pathways of assimilatory sulfate reduction and subsequent cysteine biosynthesis were significantly enriched, which is hypothesized to result in the consumption of abundant energy produced from the enhanced anaerobic TCA cycle, revealing a strategy to address the oxidative stress caused by Cu2+. This work elucidates the unusual suppressive effects of Cu2+ on the microbial reduction of PFS flocs, which reveals the high resistance of PFS flocs to microbial destruction when used to treat Cu2+ pollution in water, thus demonstrating their tremendous practical prospects.

Living electrochemical biosensing: Engineered electroactive bacteria for biosensor development and the emerging trends

Bioelectrical interfaces made of living electroactive bacteria (EAB) provide a unique opportunity to bridge biotic and abiotic systems, enabling the reprogramming of electrochemical biosensing. To develop these biosensors, principles from synthetic biology and electrode materials are being combined to engineer EAB as dynamic and responsive transducers with emerging, programmable functionalities. This review discusses the bioengineering of EAB to design active sensing parts and electrically connective interfaces on electrodes, which can be applied to construct smart electrochemical biosensors. In detail, by revisiting the electron transfer mechanism of electroactive microorganisms, engineering strategies of EAB cells for biotargets recognition, sensing circuit construction, and electrical signal routing, engineered EAB have demonstrated impressive capabilities in designing active sensing elements and developing electrically conductive interfaces on electrodes. Thus, integration of engineered EAB into electrochemical biosensors presents a promising avenue for advancing bioelectronics research. These hybridized systems equipped with engineered EAB can promote the field of electrochemical biosensing, with applications in environmental monitoring, health monitoring, green manufacturing, and other analytical fields. Finally, this review considers the prospects and challenges of the development of EAB-based electrochemical biosensors, identifying potential future applications.

Structural Determinants of Redox Conduction Favor Robustness over Tunability in Microbial Cytochrome Nanowires

Structural determinants of a 103-fold variation in electrical conductivity for helical homopolymers of tetra-, hexa-, and octa-heme cytochromes (named Omc- E, S, and Z, respectively) from Geobacter sulfurreducens are investigated with the Pathways model for electron tunneling, classical molecular dynamics, and hybrid quantum/classical molecular mechanics. Thermally averaged electronic couplings for through-space heme-to-heme electron transfer in the "nanowires" computed with density functional theory are ≤0.015 eV. Pathways analyses also indicate that couplings match within a factor of 5 for all "nanowires", but some alternative tunneling routes are found involving covalent protein backbone bonds (Omc- S and Z) or propionic acid-ligating His H-bonds on adjacent hemes (OmcZ). Reorganization energies computed from electrostatic vertical energy gaps or a version of the Marcus continuum expression parameterized on the total (donor + acceptor) solvent-accessible surface area typically agree within 20% and fall within the range 0.48-0.98 eV. Reaction free energies in all three "nanowires" are ≤|0.28| eV, even though Coulombic interactions primarily tune the site redox energies by 0.7-1.2 eV. Given the conserved energetic parameters, redox conductivity differs by < 103-fold among the cytochrome "nanowires". Redox currents do not exceed 3.0 × 10-3 pA at a physiologically relevant 0.1 V bias, with the slowest electron transfers being on a (μs) timescale much faster than typical (ms) enzymatic turnovers. Thus, the "nanowires" are proposed to be functionally robust to variations in structure that provide a habitat-customized protein interface. The 30 pA to 30 nA variation in conductivity previously reported from atomic force microscopy experiments is not intrinsic to the structures and/or does not result from the physiologically relevant redox conduction mechanism.

Effects of Different Nanoparticles on Microbes

Nanoparticles widely exist in nature and may be formed through inorganic or organic pathways, exhibiting unique physical and chemical properties different from those of bulk materials. However, little is known about the potential consequences of nanomaterials on microbes in natural environments. Herein, we investigated the interactions between microbes and nanoparticles by performing experiments on the inhibition effects of gold, ludox and laponite nanoparticles on Escherichia coli in liquid Luria–Bertani (LB) medium at different nanoparticle concentrations. These nanoparticles were shown to be effective bactericides. Scanning electron microscopy (SEM) images revealed the distinct aggregation of cells and nanoparticles. Transmission electron microscopy (TEM) images showed considerable cell membrane disruption due to nanoparticle accumulation on the cell surfaces, resulting in cell death. We hypothesized that this nanoparticle accumulation on the cell surfaces not only disrupted the cell membranes but also physically blocked the microbes from accessing nutrients. An iron-reducing bacterium, Shewanella putrefaciens, was tested for its ability to reduce the Fe (III) in solid ferrihydrite (HFO) or aqueous ferric citrate in the presence of laponite nanoparticles. It was found that the laponite nanoparticles inhibited the reduction of the Fe (III) in solid ferrihydrite. Moreover, direct contact between the cells and solid Fe (III) coated with the laponite nanoparticles was physically blocked, as confirmed by SEM images and particle size measurements. However, the laponite particles had an insignificant effect on the extent of aqueous Fe (III) bioreduction but slightly enhanced the rate of bioreduction of the Fe (III) in aqueous ferric citrate. The slightly increased rate of bioreduction by laponite nanoparticles may be due to the removal of inhibitory Fe (II) from the cell surface by its sorption onto the laponite nanoparticle surface. This result indicates that the scavenging of toxic heavy metals, such as Fe (II), by nanoparticles may be beneficial for microbes in the environment. On the other hand, microbial cells are also capable of detoxifying nanoparticles by coagulating nanoparticles with extracellular polymeric substances or by changing nanoparticle morphologies. Hence, the interactions between microbes and nanoparticles in natural environments should receive more attention.

Utilizing a divalent metal ion transporter to control biogenic nanoparticle synthesis

Biogenic synthesis of inorganic nanomaterials has been demonstrated for both wild and engineered bacterial strains. In many systems the nucleation and growth of nanomaterials is poorly controlled and requires concentrations of heavy metals toxic to living cells. Here, we utilized the tools of synthetic biology to engineer a strain of Escherichia coli capable of synthesizing cadmium sulfide nanoparticles from low concentrations of reactants with control over the location of synthesis. Informed by simulations of bacterially-assisted nanoparticle synthesis, we created a strain of E. coli expressing a broad-spectrum divalent metal transporter, ZupT, and a synthetic CdS nucleating peptide. Expression of ZupT in the outer membrane and placement of the nucleating peptide in the periplasm focused synthesis within the periplasmic space and enabled sufficient nucleation and growth of nanoparticles at sub-toxic levels of the reactants. This strain synthesized internal CdS quantum dot nanoparticles with spherical morphology and an average diameter of approximately 3.3 nm.

ONE-SENTENCE SUMMARY

Expression of a metal ion transporter regulates synthesis of cadmium sulfide nanoparticles in bacteria.

Physiological Benefits of Oxygen-Terminating Extracellular Electron Transfer

Extracellular electron transfer (EET) is a process via which certain microorganisms, such as bacteria, exchange electrons with extracellular materials by creating an electrical link across their membranes. EET has been studied for the reactions on solid materials such as minerals and electrodes with implication in geobiology and biotechnology. EET-capable bacteria exhibit broad phylogenetic diversity, and some are found in environments with various types of electron acceptors/donors not limited to electrodes or minerals. Oxygen has also been shown to serve as the terminal electron acceptor for EET of Pseudomonas aeruginosa and Faecalibacterium prausnitzii. However, the physiological significance of such oxygen-terminating EETs, as well as the mechanisms underlying them, remain unclear. In order to understand the physiological advantage of oxygen-terminating EET and its link with energy metabolism, in this review, we compared oxygen-terminating EET with aerobic respiration, fermentation, and electrode-terminating EET. We also summarized benefits and limitations of oxygen-terminating EET in a biofilm setting, which indicate that EET capability enables bacteria to create a niche in the anoxic zone of aerobic biofilms, thereby remodeling bacterial metabolic activities in biofilms.

Assessing Thermal Response of Redox Conduction for Anti-Arrhenius Kinetics in a Microbial Cytochrome Nanowire

A micrometers-long helical homopolymer of the outer-membrane cytochrome type S (OmcS) from Geobacter sulfurreducens is proposed to transport electrons to extracellular acceptors in an ancient respiratory strategy of biogeochemical and technological significance. OmcS surprisingly exhibits higher conductivity upon cooling (anti-Arrhenius kinetics), an effect previously attributed to H-bond restructuring and heme redox potential shifts. Herein, the temperature sensitivity of redox conductivity is more thoroughly examined with conventional and constant-redox and -pH molecular dynamics and quantum mechanics/molecular mechanics. A 30 K drop in temperature constituted a weak perturbation to electron transfer energetics, changing electronic couplings (⟨H_mn⟩), reaction free energies (ΔG_mn), reorganization energies (λ_mn), and activation energies (E_a) by at most |0.002|, |0.050|, |0.120|, and |0.045| eV, respectively. Changes in ΔG_mn reflected -0.07 ± 0.03 V shifts in redox potentials that were caused in roughly equal measure by altered electrostatic interactions with the solvent and protein. Changes in intraprotein H-bonding reproduced the earlier observations. Single-particle diffusion and multiparticle steady-state flux models, parametrized with Marcus theory rates, showed that biologically relevant incoherent hopping cannot qualitatively or quantitatively describe electrical conductivity measured by atomic force microscopy in filamentous OmcS. The discrepancy is attributed to differences between solution-phase simulations and solid-state measurements and the need to model intra- and intermolecular vibrations explicitly.

Evidence and Mechanisms of Selenate Reduction to Extracellular Elemental Selenium Nanoparticles on the Biocathode

Intracellular selenium nanoparticles (SeNPs) production is a roadblock to the recovery of selenium from biological water treatment processes because it is energy intensive to break microbial cells and then separate SeNPs. This study provided evidence of significantly more extracellular SeNP production on the biocathode (97-99%) compared to the conventional reactors (1-90%) using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. The cathodic microbial community analysis showed that relative abundance of Azospira oryzae, Desulfovibrio, Stenotrophomonas, and Rhodocyclaceae was <1% in the inoculum but enriched to 10-21% for each group when the bioelectrochemical reactor reached a steady state. These four groups of microorganisms simultaneously produce intracellular and extracellular SeNPs in conventional biofilm reactors per literature review but prefer to produce extracellular SeNPs on the cathode. This observation may be explained by the cellular energetics: by producing extracellular SeNPs on the biocathode, microbes do not need to transfer selenate and the electrons from the cathode into the cells, thereby saving energy. Extracellular SeNP production on the biocathode is feasible since we found high concentrations of C-type cytochrome, which is well known for its ability to transfer electrons from electrodes to microbial cells and reduce selenate to SeNPs on the cell membrane.

Nanomaterials in bioelectrochemical devices: on applications enhancing their positive effect

Electrochemical biosensors and biofuel cells are finding an ever-increasing practical application due to several advantages. Biosensors are miniature measuring devices, which can be used for on-the-spot analyses, with small assay times and sample volumes. Biofuel cells have dual benefits of environmental cleanup and electric energy generation. Application of nanomaterials in biosensor and biofuel-cell devices increases their functioning efficiency and expands spheres of use. This review discusses the potential of nanomaterials in improving the basic parameters of bioelectrochemical systems, including the sensitivity increase, detection lower-limit decrease, detection-range change, lifetime increase, substrate-specificity control. In most cases, the consideration of the role of nanomaterials links a certain type of nanomaterial with its effect on the bioelectrochemical device upon the whole. The review aims at assessing the effects of nanomaterials on particular analytical parameters of a biosensor/biofuel-cell bioelectrochemical device.

Recent advances in electro-fermentation technology: A novel approach towards balanced fermentation

Biotransformation of organic substrates via acidogenic fermentation (AF) to high-value products such as C1-C6 carboxylic acids and alcohol serves as platform chemicals for various industrial applications. However, the AF technology suffers from low product titers due to thermodynamic constraints. Recent studies suggest that augmenting AF redox potential can regulate the metabolic pathway and provide seamless electron flow by lowering the activation energy barrier, thus positively influencing the substrate utilization rate, product yield, and speciation. Hence, the augmented AF system with an exogenous electricity supply is termed as electro-fermentation (EF), which has enormous potential to strengthen the fermentation technology domain. Therefore, this critical review systematically discusses the current understanding of EF with a special focus on the extracellular electron transfer mechanism of electroactive bacteria and provides perspectives and research gaps to further improve the technology for green chemical synthesis, sustainable waste management, and circular bio-economy.

Gentle Patterning Approaches toward Compatibility with Bio-Organic Materials and Their Environmental Aspects

Advances in material science, bioelectronic, and implantable medicine combined with recent requests for eco-friendly materials and technologies inevitably formulate new challenges for nano- and micropatterning techniques. Overall, the importance of creating micro- and nanostructures is motivated by a large manifold of fundamental and applied properties accessible only at the nanoscale. Lithography is a crucial family of fabrication methods to create prototypes and produce devices on an industrial scale. The pure trend in the miniaturization of critical electronic semiconducting components has been recently enhanced by implementing bio-organic systems in electronics. So far, significant efforts have been made to find novel lithographic approaches and develop old ones to reach compatibility with delicate bio-organic systems and minimize the impact on the environment. Herein, such delicate materials and sophisticated patterning techniques are briefly reviewed.

Electrogenic Bacteria Promise New Opportunities for Powering, Sensing, and Synthesizing

Considerable research efforts into the promises of electrogenic bacteria and the commercial opportunities they present are attempting to identify potential feasible applications. Metabolic electrons from the bacteria enable electricity generation sufficient to power portable or small-scale applications, while the quantifiable electric signal in a miniaturized device platform can be sensitive enough to monitor and respond to changes in environmental conditions. Nanomaterials produced by the electrogenic bacteria can offer an innovative bottom-up biosynthetic approach to synergize bacterial electron transfer and create an effective coupling at the cell-electrode interface. Furthermore, electrogenic bacteria can revolutionize the field of bioelectronics by effectively interfacing electronics with microbes through extracellular electron transfer. Here, these new directions for the electrogenic bacteria and their recent integration with micro- and nanosystems are comprehensively discussed with specific attention toward distinct applications in the field of powering, sensing, and synthesizing. Furthermore, challenges of individual applications and strategies toward potential solutions are provided to offer valuable guidelines for practical implementation. Finally, the perspective and view on how the use of electrogenic bacteria can hold immeasurable promise for the development of future electronics and their applications are presented.

Biogenic iron sulfide functioning as electron-mediating interface to accelerate dissimilatory ferrihydrite reduction by Shewanella oneidensis MR-1

Microbially driven iron and sulfur geochemical cycles co-exist ubiquitously in subsurface environments and are of environmental relevance. Shewanella species (dissimilatory metal-reducing bacteria) are capable of reducing Fe(III)-(oxyhydr)oxide minerals and diverse sulfur sources using corresponding metabolic pathways and producing FeS secondary minerals. In spite of the ability in promoting bacterial extracellular electron transfer (EET), the specific role of FeS in mediating EET between microbe/mineral interface is still unclear. In this work, the electron-mediating function of biogenic FeS on promoting the reduction of ferrihydrite by S. oneidensis MR-1 using thiosulfate as sulfur source was investigated in terms of Fe(III) reduction percentage, X-ray diffraction and scanning electron microscopy. The results showed that the microbial ferrihydrite reduction was pH-dependent and positively correlated with the addition of thiosulfate. In the presence of thiosulfate, biogenic FeS in nano-scale were formed and deposited on the surfaces of S. oneidensis MR-1 and ferrihydrite to build an interfacial electron transfer bridge between them. The addition of either thiosulfate and in-vitro FeS could rescue the entirely inactivated ability of the mutant (△omcA/mtrC) in ferrihydrite reduction to some extent, but which was obviously inferior to the wild-type strain. Meanwhile, the effect of the biogenic FeS in-situ coating on the surfaces of S. oneidensis MR-1 cells on promoting microbial ferrihydrite reduction was significantly superior to the in-vitro ones. Thus, the in-situ formed biogenic FeS secondary minerals were demonstrated to mediate and accelerate interfacial electron transfer from S. oneidensis MR-1 cells to ferrihydrite through interfacing with the bacterial EET routes, especially Mtr pathway. This work provides an insight into the secondary minerals-mediating interfacial electron transfer between microbes and minerals in the presence of biological S (-II), which has important biogeochemical and environmental implications.

Prospects and applications of synergistic noble metal nanoparticle-bacterial hybrid systems

Hybrid systems composed of living cells and nanomaterials have been attracting great interest in various fields of research ranging from materials science to biomedicine. In particular, the interfacing of noble metal nanoparticles and bacterial cells in a single architecture aims to generate hybrid systems that combine the unique physicochemical properties of the metals and biological attributes of the microbial cells. While the bacterial cells provide effector and scaffolding functions, the metallic component endows the hybrid system with multifunctional capabilities. This synergistic effort seeks to fabricate living materials with improved functions and new properties that surpass their individual components. Herein, we provide an overview of this research field and the strategies for obtaining hybrid systems, and we summarize recent biological applications, challenges and current prospects in this exciting new arena.

Insights into the Biosynthesis of Nanoparticles by the Genus Shewanella

The exploitation of microorganisms for the fabrication of nanoparticles (NPs) has garnered considerable research interest globally. The microbiological transformation of metals and metal salts into respective NPs can be achieved under environmentally benign conditions, offering a more sustainable alternative to chemical synthesis methods. Species of the metal-reducing bacterial genus Shewanella are able to couple the oxidation of various electron donors, including lactate, pyruvate, and hydrogen, to the reduction of a wide range of metal species, resulting in biomineralization of a multitude of metal NPs. Single-metal-based NPs as well as composite materials with properties equivalent or even superior to physically and chemically produced NPs have been synthesized by a number of Shewanella species. A mechanistic understanding of electron transfer-mediated bioreduction of metals into respective NPs by Shewanella is crucial in maximizing NP yields and directing the synthesis to produce fine-tuned NPs with tailored properties. In addition, thorough investigations into the influence of process parameters controlling the biosynthesis is another focal point for optimizing the process of NP generation. Synthesis of metal-based NPs using Shewanella species offers a low-cost, eco-friendly alternative to current physiochemical methods. This article aims to shed light on the contribution of Shewanella as a model organism in the biosynthesis of a variety of NPs and critically reviews the current state of knowledge on factors controlling their synthesis, characterization, potential applications in different sectors, and future prospects.