Extracellular electron transfer is the key process underpinning the development of bioelectrochemical systems for the production of energy or added-value compounds. Thermincola potens JR is a promising Gram-positive bacterium to be used in these systems because it is thermophilic. In this paper, we describe the structural and functional properties of the nonaheme cytochrome OcwA, which is the terminal reductase of this organism. The structure of OcwA, determined at 2.2-Å resolution, shows that the overall fold and organization of the hemes are not related to other metal reductases and instead are similar to those of multiheme cytochromes involved in the biogeochemical cycles of nitrogen and sulfur. We show that, in addition to solid electron acceptors, OcwA can also reduce soluble electron shuttles and oxyanions. These data reveal that OcwA can work as a multipurpose respiratory enzyme allowing this organism to grow in environments with rapidly changing availability of terminal electron acceptors without the need for transcriptional regulation and protein synthesis. IMPORTANCE Thermophilic Gram-positive organisms were recently shown to be a promising class of organisms to be used in bioelectrochemical systems for the production of electrical energy. These organisms present a thick peptidoglycan layer that was thought to preclude them to perform extracellular electron transfer (i.e., exchange catabolic electrons with solid electron acceptors outside the cell). In this paper, we describe the structure and functional mechanisms of the multiheme cytochrome OcwA, the terminal reductase of the Gram-positive bacterium Thermincola potens JR found at the cell surface of this organism. The results presented here show that this protein can take the role of a respiratory “Swiss Army knife,” allowing this organism to grow in environments with soluble and insoluble substrates. Moreover, it is shown that it is unrelated to terminal reductases found at the cell surface of other electroactive organisms. Instead, OcwA is similar to terminal reductases of soluble electron acceptors. Our data reveal that terminal oxidoreductases of soluble and insoluble substrates are evolutionarily related, providing novel insights into the evolutionary pathway of multiheme cytochromes.

Electroactive microorganisms have attracted significant interest for the development of novel biotechnological systems of low ecological footprint. These can be used for the sustainable production of energy, bioremediation of metal-contaminated environments and production of added-value products. Currently, almost 100 microorganisms from the Bacterial and Archaeal domains are considered electroactive, given their ability to efficiently interact with electrodes in microbial electrochemical technologies. Cell-surface exposed conductive proteins are key players in the electron transfer between cells and electrodes. Interestingly, it seems that among the electroactive organisms identified so far, these cell-surface proteins fall into one of four groups. In this review, the different types of cell-surface conductive proteins found in electroactive organisms will be overviewed, focusing on their structural and functional properties.

Natural‐derived polymers are used to coat liquid‐core capsules layer by layer to encapsulate cells. Human osteoblast‐like cells (SaOs‐2) are encapsulated in such spherical devices using a three‐step methodology: i) ionotropic gelation to produce alginate beads encapsulating the cells; ii) layer‐by‐layer coating using water‐soluble chitosan and alginate; and iii) core liquefaction. Cells remain viable for 3 d after the encapsulation procedure, suggesting that the developed capsules possess a semipermeable, nanostructured coating. All of the capsules exhibit a spherical shape, smooth surface and liquid‐core characteristics. All of the processes are conducted under mild conditions and physiological pH. We consider that the methodology employed in the development of the capsules obtained from natural‐based biomaterials has potential to find applicability in the development of scaffolds or cell carriers in tissue engineering and regenerative medicine.

Electrochemical single nano-impacts of electroactive Shewanella oneidensis bacteria at a 7 μm diameter carbon fibre ultramicroelectrode in an aqueous potassium phosphate buffer (pH = 7.2) solution containing a redox active probe (potassium ferro-or ferricyanide) is reported. We present chronoamperometric measurements recorded at the ultramicroelectrode polarized at the potential of the steady-state current of the redox probe in solution (oxidation for K 4 Fe(CN) 6 or reduction for K 3 Fe(CN) 6 ) in the presence of bacteria. The shape of current transients associated to single bacteria nano-impacts is compared and discussed as a function of the redox probe in solution and of the ultramicroelectrode applied potential.

As a powerful tool, nanoenzyme electrocatalyst broadens the ways to explore bioinspired solutions to the world's energy and environmental concerns. Efforts of fashioning novel nanoenzymes for effective electrode functionalization is generating innovative viable catalysts with high catalytic activity, low cost, high stability and versatility, and ease of production. High chemo‐selectivity and broad functional group tolerance of nanoenzyme with an intrinsic enzyme like activity make them an excellent environmental tool. The catalytic activities and kinetics of nanoenzymes that benefit the development of nanoenzyme‐based energy and environmental technologies by effectual electrode functionalization are discussed in this article. Further, a deep‐insight on recent developments in the state‐of‐art of nanoenzymes either in terms of electrocatalytic redox reactions (viz. oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction and hydrogen evolution reaction) or environmental remediation /treatment of wastewater/or monitoring of a variety of pollutants. The complex interdependence of the physicochemical properties and catalytic characteristics of nanoenzymes are discussed along with the exciting opportunities presented by nanomaterial‐based core structures adorned with nanoparticle active‐sites shell for enhanced catalytic processes. Thus, such modular architecture with multi‐enzymatic potential introduces an immense scope of making its economical scale‐up for multielectron‐fuel or product recovery and multi‐pollutant or pesticide remediation as reality.