Living electronics: A catalogue of engineered living electronic components

Biology leverages a range of electrical phenomena to extract and store energy, control molecular reactions and enable multicellular communication. Microbes, in particular, have evolved genetically encoded machinery enabling them to utilize the abundant redox-active molecules and minerals available on Earth, which in turn drive global-scale biogeochemical cycles. Recently, the microbial machinery enabling these redox reactions have been leveraged for interfacing cells and biomolecules with electrical circuits for biotechnological applications. Synthetic biology is allowing for the use of these machinery as components of engineered living materials with tuneable electrical properties. Herein, we review the state of such living electronic components including wires, capacitors, transistors, diodes, optoelectronic components, spin filters, sensors, logic processors, bioactuators, information storage media and methods for assembling these components into living electronic circuits.

Bioremediation of selenium-contaminated soil using earthworm Eisenia fetida: Effects of gut bacteria in feces on the soil microbiome

Selenium (Se) contamination in the soil poses a food safety risk to humans. The present study was to investigate the role of earthworm Eisenia fetida in soil Se remediation. When exposed to selenite at 4 mg Se/kg, E. fetida efficiently concentrated Se in tissues (24.53 mg Se/kg dry weight), however, only accounting for a minor portion of the added Se. Microbial analysis shows 12 out of 15 functional genera became more abundant in the worm-inhabited soil when exposed to Se, suggesting E. fetida contributed to Se remediation mainly by introducing Se-reducing bacteria to the soil via feces, which were dominated by the genera Pseudomonas (∼62.65%) and Aeromonas (∼29.99%), whose abundance was also significantly boosted in the worm-inhabited soil. However, when isolated from worm feces at 200 mg Se/L, Pseudomonas strains only displayed a high tolerance to Se rather than removal capacity. In contrast, among 4 isolated Aeromonas strains, A. caviae rapidly removing 85.74% of the added selenite, mainly through accumulation (67.38%), while A. hydrophila and A. veronii were more effective at volatilizing Se (27.77% and 24.54%, respectively), and A. media performed best by reducing Se by ∼49.00% under anaerobic conditions. Overall, our findings have highlighted the importance of E. fetida as a key contributor of functional bacteria to the soil microbiome, building a strong foundation for the development of an earthworm-soil system for Se bioremediation.

Selenium (Se) recovery for technological applications from environmental matrices based on biotic and abiotic mechanisms

Selenium (Se) is an essential element with application in manufacturing from food to medical industries. Water contamination by Se is of concern due to anthropogenic activities. Recently, Se remediation has received increasing attention. Hence, different types of remediation techniques are listed in this work, and their potential for Se recovery is evaluated. Sorption, co-precipitation, coagulation and precipitation are effective for low-cost Se removal. In photocatalytic, zero-valent iron and electrochemical systems, the above mechanisms occur with reduction as an immobilization and detoxification process. In combination with magnetic separation, the above techniques are promising for Se recovery. Biological Se oxyanions reduction has been widely recognized as a cost-effective method for Se remediation, simultaneously generating biosynthetic Se nanoparticles (BioSeNPs). Increasing the extracellular production of BioSeNPs and controlling their morphology will benefit its recovery. However, the mechanism of the microbial production of BioSeNPs is not well understood. Se containing products from both microbial reduction and abiotic methods need to be refined to obtain pure Se. Eco-friendly and cost-effective Se refinery methods need to be developed. Overall, this review offers insight into the necessity of shifting attention from Se remediation to Se recovery.

Antibacterial effect of copper nanoparticles produced in a Shewanella-supported non-external circuit bioelectrical system on bacterial plant pathogens

The inhibition of copper nanoparticles produced in a nec_BES to plant pathogens was investigated in this study.

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

Synthesis of inorganic nanomaterials such as metal nanoparticles (MNPs) using various biological entities as smart nanofactories has emerged as one of the foremost scientific endeavors in recent years. The biosynthesis process is environmentally friendly, cost-effective and easy to be scaled up, and can also bring neat features to products such as high dispersity and biocompatibility. However, the biomanufacturing of inorganic nanomaterials is still at the trial-and-error stage due to the lack of understanding for underlying mechanism. Dissimilatory metal reduction bacteria, especially Shewanella and Geobacter species, possess peculiar extracellular electron transfer (EET) features, through which the bacteria can pump electrons out of their cells to drive extracellular reduction reactions, and have thus exhibited distinct advantages in controllable and tailorable fabrication of inorganic nanomaterials including MNPs and graphene. Our aim is to present a critical review of recent state-of-the-art advances in inorganic biosynthesis methodologies based on bacterial EET using Shewanella and Geobacter species as typical strains. We begin with a brief introduction about bacterial EET mechanism, followed by reviewing key examples from literatures that exemplify the powerful activities of EET-enabled biosynthesis routes towards the production of a series of inorganic nanomaterials and place a special emphasis on rationally tailoring the structures and properties of products through the fine control of EET pathways. The application prospects of biogenic nanomaterials are then highlighted in multiple fields of (bio-) energy conversion, remediation of organic pollutants and toxic metals, and biomedicine. A summary and outlook are given with discussion on challenges of bio-manufacturing with well-defined controllability.

Developments in the study and applications of bacterial transformations of selenium species

Microbial bio-transformations of the essential trace element selenium are now recognized to occur among a wide variety of microorganisms. These transformations are used to convert this element into its assimilated form of selenocysteine, which is at the active center of a number of key enzymes, and to produce selenium nanoparticles, quantum dots, metal selenides, and methylated selenium species that are indispensable for biotechnological and bioremediation applications. The focus of this review is to present the state-of-the-art of all aspects of the investigations into the bacterial transformations of selenium species, and to consider the characterization and biotechnological uses of these transformations and their products.

Biological Metabolism Synthesis of Metal Oxides Nanorods from Bacteria as a Biofactory toward High-Performance Lithium-Ion Battery Anodes

Increasing awareness toward environmental remediation and renewable energy has led to a vigorous demand for exploring a win-win strategy to realize the eco-efficient conversion of pollutants ("trash") into energy-storage nanomaterials ("treasure"). Inspired by the biological metabolism of bacteria, Acidithiobacillus ferrooxidans (A. ferrooxidans) is successfully exploited as a promising eco-friendly sustainable biofactory for the controllable fabrication of α-Fe₂ O₃ nanorods via the oxidation of soluble ferrous irons to insoluble ferric substances (Jarosite, KFe₃ (SO₄ )₂ (OH)₆ ) and a facile subsequent heat treatment. It is demonstrated that the stable solid electrolyte interphase layers and marvelous cracks in situ formed in biometabolic α-Fe₂ O₃ nanorods play important roles that not only significantly enhance the structure stability but also facilitate electron and ion transfer. Consequently, these biometabolic α-Fe₂ O₃ nanorods deliver a superior stable capacity of 673.9 mAh g^-1 at 100 mA g^-1 over 200 cycles and a remarkable multi-rate capability that observably prevails over the commercial counterpart. It is highly expected that such biological synthesis strategies can shed new light on an emerging field of research interconnecting biotechnology, energy technology, environmental technology, and nanotechnology.

Biosynthesis of Nanomaterials by Shewanella Species for Application in Lithium Ion Batteries

Nanomaterials exhibit extraordinary properties based on their size, shape, chemical composition, and crystal structure. Owing to their unique properties nanomaterials are preferred over their bulk counterparts for a number of applications. Although conventional physical and chemical routes were established for the massive production of nanomaterials, there are some drawbacks such as environmental burden and high cost that cannot be disregarded. Recently, there has been great interest toward the green synthesis of inorganic nanomaterials. It has been reported that dissimilatory metal reduction by microorganisms is a cost-effective process to remediate toxic organic and inorganic compounds under anaerobic conditions. Particularly, members of the Shewanella genus have been utilized to produce various biogenic nanomaterials with unique micro/nanostructured morphologies through redox transformations as well as to remove harmful metals and metalloids in eco-efficient and environment-friendly methods under ambient conditions. In the present mini-review, we specifically address the active utilization of microbial respiration processes for the synthesis of novel functional biogenic nanomaterials by the members of the Shewanella genus. This biosynthetic method may provide alternative approaches to produce electrode materials for sustainable energy storage applications.

Morphology-tunable tellurium nanomaterials produced by the tellurite-reducing bacterium Lysinibacillus sp. ZYM-1

Although tellurite is highly toxic to organisms, elemental tellurium nanomaterials (TeNMs) have many uses. The microbe-mediated reduction of tellurite to Te(0) has been shown to be a green and cost-effective approach for turning waste into wealth. However, it is difficult to tune the morphology of biogenic nanomaterials. In this study, a series of experiments was conducted to investigate the factors influencing tellurite reduction by the tellurite-reducing bacterium Lysinibacillus sp. ZYM-1, including pH, tellurite concentration, temperature, and heavy metal ions. The optimal removal efficiency of tellurite was respectively achieved at pH 8, 0.5 mM tellurite, and 40 °C. All of the tested metal ions retarded the reduction of tellurite, especially Cd²⁺ and Co²⁺, which completely inhibited its reduction. Further characterization of the biogenic TeNMs indicated that their morphology could be tuned by the tellurite concentration, pH, temperature, and organic solvents used. Regular Te nanosheets were produced using 5 mM tellurite. The TeNMs were primarily synthesized in the cell membrane. Hexagonal Te nanoplates, nanorods, nanoflowers, and nanobranches were synthesized when combining membrane fractions with tellurite and NADH. The diverse morphologies are assumed to be induced by the synergy between the reduction kinetics and the protein structure. Therefore, this study confirmed that the bacterium can tune the morphology of TeNMs, broadening the potential application of biogenic TeNMs.

One Dimensional Silver-based Nanomaterials: Preparations and Electrochemical Applications

One dimensional (1D) silver-based nanomaterials have a great potential in various fields because of their high specific surface area, high electric conductivity, optoelectronic properties, mechanical flexibility and high electro-catalytic efficiency. In this Review, the preparations of 1D silver-based nanomaterials is classified by structure composed of simple silver nanowires/rods/belts/tubes, core-shells, and hybrids. The latest applications based on 1D silver nanomaterials and their composite materials are summarized systematically including electrochemical capacitors, lithium-ion/lithium-oxygen batteries, electrochemical sensors and electrochemical catalysis. The preparation process, tailored material properties and electrochemical applications are discussed.

Selenium biomineralization for biotechnological applications

Selenium (Se) is not only a strategic element in high-tech electronics and an essential trace element in living organisms, but also a potential toxin with low threshold concentrations. Environmental biotechnological applications using bacterial biomineralization have the potential not only to remove selenium from contaminated waters, but also to sequester it in a reusable form. Selenium biomineralization has been observed in phylogenetically diverse microorganisms isolated from pristine and contaminated environments, yet it is one of the most poorly understood biogeochemical processes. Microbial respiration of selenium is unique because the microbial cells are presented with both soluble (SeO(4)(2-) and SeO(3)(2-)) and insoluble (Se(0)) forms of selenium as terminal electron acceptor. Here, we highlight selenium biomineralization and the potential biotechnological uses for it in bioremediation and wastewater treatment.

Shewanella-mediated biosynthesis of manganese oxide micro-/nanocubes as efficient electrocatalysts for the oxygen reduction reaction

Developing efficient electrocatalysts for the oxygen reduction reaction (ORR) is critical for promoting the widespread application of fuel cells and metal-air batteries. Here, we develop a biological low-cost, ecofriendly method for the synthesis of Mn2 O3 micro-/nanocubes by calcination of MnCO3 precursors in an oxygen atmosphere. Microcubic MnCO3 precursors with an edge length of 2.5 μm were fabricated by dissimilatory metal-reducing Shewanella loihica PV-4 in the presence of MnO4 (-) as the sole electron acceptor under anaerobic conditions. After calcining the MnCO3 precursors at 500 and 700 °C, porous Mn2 O3 -500 and Mn2 O3 -700 also showed microcubic morphology, while their edge lengths decreased to 1.8 μm due to thermal decomposition. Moreover, the surfaces of the Mn2 O3 microcubes were covered by granular nanoparticles with average diameters in the range of 18-202 nm, depending on the calcination temperatures. Electrochemical measurements demonstrated that the porous Mn2 O3 -500 micro-/nanocubes exhibit promising catalytic activity towards the ORR in an alkaline medium, which should be due to a synergistic effect of the overlapping molecular orbitals of oxygen/manganese and the hierarchically porous structures that are favorable for oxygen absorption. Moreover, these Mn2 O3 micro-/nanocubes possess better stability than commercial Pt/C catalysts and methanol-tolerance property in alkaline solution. Thus the Shewanella-mediated biosynthesis method we provided here might be a new strategy for the preparation of various transition metal oxides as high-performance ORR electrocatalysts at low cost.

Biologically based method for the synthesis of Hg–Se nanostructures by Shewanella spp

Living organisms, especially microorganisms, have the potential to offer cheap and benign synthetic routes for the production of nanomaterials.

A facile bacterial assisted electrochemical self-assembly of polypyrrole micro-pillars: towards underwater low adhesive superoleophobicity

By taking advantage of bacterial extracellular electron transfer behavior, a facile method was developed to fabricate oriented polypyrrole micro-pillars (PPy-MP) with nanoscale surface roughness. Microbes acted as a living conductive template on which PPy was in situ polymerized. The as-prepared PPy-MP exhibit the distinctive underwater low adhesive superoleophobicity which is attributable to the unique hierarchical micro/nano-structures and the high surface energy by doping with inorganic small anions.

Mercury capture into biogenic amorphous selenium nanospheres produced by mercury resistant Shewanella putrefaciens 200

Shewanella putrefaciens 200, resistant to high concentration of Hg(II), was selected for co-removal of mercury and selenium from aqueous medium. Biogenic Hg(0) reduced from Hg(II) by S. putrefaciens 200 was captured into extracellular amorphous selenium nanospheres, resulting in the formation of stable HgSe nanoparticles. This bacterial reduction could be a new strategy for mercury removal from aquatic environments without secondary pollution of mercury methylation or Hg(0) volatilization.

Draft genome sequence of Shewanella sp. strain HN-41, which produces arsenic-sulfide nanotubes

The dissimilatory metal reducing bacterium Shewanella sp. strain HN-41 was first reported to produce novel photoactive As-S nanotubes via reduction of As(V) and S(2)O(3)(2-) under anaerobic conditions. Here we report the draft genome sequence and annotation of strain HN-41.