Biohybrids for Solar Fuels: Whole-cell Photocatalysis by Non-photosynthetic Organisms

Lead Research Organisation: University of Leeds
Department Name: Institute of Membrane & Systems Biology

Abstract

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Technical Summary

We propose to tap into sunlight, an underutilised source of clean power, and address the direct exchange of electrons between bacterial cells and inorganic photocatalysts for the biophotocatalytic production of solar chemicals including fuels. Current state-of-the-art technology, referred to as "bionic leaf", relies on the transfer of energy via intermediates such as hydrogen. By contrast, recent results from the applicants indicate that cytochromes purified from the extracellular respiratory machinery of Shewanella oneidensis MR-1 (MR-1) enable direct exchange of solar energy with synthetic photosensitisers. The MR-1 extracellular respiratory machinery exchanges energy/electrons across the bacterial outer membrane. To this end, we propose a novel synthetic biology approach in which bespoke photocatalysts are directly coupled to the extracellular cytochromes of MR-1 in vivo. Modular biohybrid assemblies will be produced that use intracellular redox transformations to sustain light-driven extracellular catalysis thereby closing the redox loop and enabling self-sustaining production of solar fuels. Two proof-of-principle light-driven reactions are proposed: (a) MR-1 catalysed reductions, such as protons to hydrogen or carbon dioxide to formate, coupled to inorganic photo-oxidation of industrially-relevant alcohols to aldehydes, and (b) MR-1 catalysed oxidation of glycerol (a major underutilised by-product of biodiesel production) to ethanol coupled to the inorganic photo-reduction of carbon dioxide to formate.

Planned Impact

Societal impact
The aim of this project is to use biophysical, (bio)nanotechnological and synthetic biological approaches to study Shewanella for exploitation in the area of Industrial Biotechnology and Bioenergy. In particular, we aim to couple respiratory proteins of Shewanella to inorganic photocatalysts to harvest solar energy for novel and innovative approaches to produce value added chemicals and fuels. For instance, we will explore the solar conversion of glycerol to ethanol and formate. Glycerol is a major underutilised by-product from biodiesel. Approximately 1 kg of crude glycerol is produced for every 10 kg of biodiesel, in the US, this would equate to about 0.8 x 109 kg of glycerol in 2016.
Renewable energy is recognised as a top national strategic priority (UK White Paper on Energy). Several incidents have demonstrated the fragility of the global energy supply such as the outbreak of conflicts and civil wars in the Middle-East and the ecological and humanitarian threat of a nuclear meltdown in Fukushima, Japan. The search for alternative energy sources is therefore of major GLOBAL importance. The Paris Agreement in 2015 has set out a global strategy to minimise the impact of climate change by reducing greenhouse gas emissions. A solution to this problem has to be sought by combining a multitude of complementary 'alternative' energy sources; this research will contribute to this progress.

Technological impact
The overall concept of this proposal is microbial catalysis driven by solar energy harnessed by inorganic photocatalysts. The state-of-the-art in solar-driven microbial catalytic systems first produces hydrogen and, in a second step, uses this hydrogen as an energy vector to drive downstream bioproduction of higher value compounds, e.g. reduction of CO2 to fusel alcohols by Ralstonia. This proposal aims to advance the state-of-the-art by directly coupling the photocatalyst and microbial catalytic systems.
Our proposed research into the coupling of outer membrane proteins with inorganic photocatalysts is basic research with academic beneficiaries. However, after successful completion of this project, we envisage that our work will contribute to (a) the future design of hybrid bacterial-inorganic (photo-)catalytic systems for chemical conversions and (b) increased knowledge on the ability of Shewanella to transport electrons across the outer membrane. Conjugation between inorganic materials and biomacromolecules has wide-ranging relevance to technology, including bioenergy (as proposed here), health technology, e.g. drug delivery, and the development of novel probes for cellular localisation and trafficking. Insights from our project will also impact on biotechnology exploiting bacterial electron exchange with electrodes for which Shewanella is an important model system. Examples include; mediatorless microbial fuel cells, which run on waste carbon sources (such as in waste water) to produce electricity or hydrogen, and, selective production of reduced organic products when electrons are supplied from a cathode (microbial electrosynthesis), or, oxidised organic products when the electrons from fermentation are delivered to an anode.

Collaborations and training
This project will consolidate the recently formed partnership between Butt, Clarke (UEA), Jeuken (Leeds) and Reisner (Cambridge). The project will extent the partnership to Gralnick (USA) who will bring metabolic insight and expertise in engineering Shewanella for targeted biotransformations. Within this project we will also provide top-quality cross-disciplinary training for three BBSRC PDRAs and a research technician, to provide expertise in the development of alternative energy biotechnologies, an area of critical scientific, technological and economic importance for the future.

Publications

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Van Wonderen JH (2021) Nanosecond heme-to-heme electron transfer rates in a multiheme cytochrome nanowire reported by a spectrally unique His/Met-ligated heme. in Proceedings of the National Academy of Sciences of the United States of America

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Piper SEH (2022) Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors. in Angewandte Chemie (International ed. in English)

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Piper SEH (2022) Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors. in Angewandte Chemie (Weinheim an der Bergstrasse, Germany)

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Butt J (2023) Protein film electrochemistry in Nature Reviews Methods Primers

 
Description In this project we aimed to couple light-harvesting nanoparticles to bacteria for solar fuel production. The methodology was based on the coupling of the light-harvesting nanoparticles to a specific protein that resides on the surface of the bacterium. All objectives on the coupling of the nanoparticles to the protein and, later, to the bacteria were successful. However, our data shows that this does not result in the production of solar fuels as intended. Further study has indicated that this was due to fast charge recombination between the protein and the nanoparticles. There were a total of 7 publications as outputs from this research project, in several high-impact journals. In follow-up work, we are now aiming to change the coupling strategy between the light-harvesting nanoparticles and the protein to solve these bottlenecks.
Exploitation Route Our research findings will inform others in the engineering biology community, generally, as a case study into the benefit and challenges of attempting to harness biology to trap the energy from sunlight. Specificically, our findings about the challenges of making using of bacrteria to power redox reactions may be taken forward by others, or ourselves, in future grants and other projects.
Sectors Energy

Environment

 
Title Nanosecond heme-to-heme electron transfer rates in a multiheme cytochrome nanowire reported by a spectrally unique His/Met-ligated heme using pump-probe spectroscopy. 
Description Data from spectroscopic, electrochemical, voltammetric and computational studies as presented in van Wonderen et al 'Nanosecond heme-to-heme electron transfer rates in a multiheme cytochrome nanowire reported by a spectrally unique His/Met-ligated heme'. Data presented in the Main and Supporting Information Appendix are included. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://figshare.com/articles/dataset/van_Wonderen_et_al_PNAS_2021_Data_Sets_xlsx/16621714
 
Title Nanosecond heme-to-heme electron transfer rates in a multiheme cytochrome nanowire reported by a spectrally unique His/Met-ligated heme using pump-probe spectroscopy. van Wonderen et al 
Description Spectroscopic, electrochemical and voltammetric data desribing properties of photosensitized MtrC proteins. The data are presented as figures in van Wonderen et al 'Nanosecond heme-to-heme electron transfer rates in a spectrally unique His/Met-ligated heme', the manuscript and supporting information appendix. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://figshare.com/articles/dataset/Nanosecond_heme-to-heme_electron_transfer_rates_in_a_multiheme...
 
Title Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors Piper et al 
Description Data from spectroscopy and gas chromatography with corresponding plots of analyte concentration with time. Data from dynamic light scattering and mass spectrometry (LC-MS) 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
URL https://figshare.com/articles/dataset/Photocatalytic_Removal_of_the_Greenhouse_Gas_Nitrous_Oxide_by_...
 
Title Research data supporting "Size-dependent activity of carbon dots for photocatalytic H2 generation in combination with a molecular Ni cocatalyst" 
Description Data for publication, including UV-vis data, H2 evolution data, IR spectra, and PL spectra. The data set is organised by Figures and each folder contains a specific readme.txt file that provides detailed explanations. Publication abstract: Carbon dots (CDs) are low-cost light-absorbers in photocatalytic multicomponent systems, but their wide size distribution has hampered rational design and the identification of the factors that lead to their best performance. To address this challenge, we report herein the novel use of gel filtration size exclusion chromatography to separate amorphous, graphitic, and graphitic N-doped CDs depending on their lateral size to study the effect of their size on photocatalytic H2 evolution with a DuBois type Ni cocatalyst. Transmission electron microscopy and dynamic light scattering confirm size-dependent separation, while UV-vis and fluorescence spectroscopy of the more monodisperse fractions show a distinct response which computational modelling attributed to a complex interplay between CD size and optical properties. A size-dependent effect on the photocatalytic H2 evolution performance of the CDs in combination with a molecular Ni cocatalyst is demonstrated with a maximum activity at approximately 2-3 nm CD diameter. Overall, size separation leads to a two-fold increase in the specific photocatalytic activity for H2 evolution using the monodisperse CDs compared to the as synthesized polydisperse samples, highlighting the size-dependent effect on photocatalytic activity towards H2 evolution. 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/357252