PhD Studentship: Coherent electron transport in energy generation processes by electrogenic microorganisms

Description: 

Supervisors: Dr C. Avignone Rossa, Dr R. Sporea, Dr A. Grüning
Leverhulme Doctoral Training Centre for Quantum Biology
University of Surrey

For the last 15 years, we have investigated bioelectrochemical systems, where electrogenic microorganisms transfer electrons to an external solid acceptor such as an electrode. If the electrode is connected via an external circuit to a cathode, an electric current is produced (of the order of mW/m2 of anode). There is an ongoing discussion about the true nature of the mechanisms involved, either electron hopping or electron tunnelling. We propose using semiconductors as opposed to metals in these systems, as the potential gradient which can be produced on the surface will allow selective growth of microorganisms with different redox potentials, and the consequent improved transfer of electrons from the microorganism to the electrical system.

Several mechanisms have been proposed for external electron transfer by bacteria to electrode. One of them involves the modification of the cell membrane to form a pilus, which acts as a nanowire that attaches to the solid electrode. It has been shown that electrons are transported along the length of those bacterial nanowires (El-Naggar et al PNAS (2010) 107(42), 18127–18131). Other work has shown electron tunnelling between FeS clusters (a quantum effect) in enzymes (cytochromes) of the same species (Wigginton et al Geochim Cosmochim Acta (2007) 71, 543–555). There are experimental methods to measure electron transfer (Xian-Wei Liu et al Sci Reports 4, 3732 DOI: 10.1038/srep03732) and models have been developed which attempt to explain the phenomena involved (Polizzi et al Faraday Discuss 155, 43–62).

In this project, you will pursue the following lines of research connecting electrogenic bacteria and quantum effects:

Explore in detail the electron transport mechanisms between membrane cytochromes and electrodes. Is this a classical conductive transport, is it ion transport, or does it involve quantum tunnelling along a series of Fe-S clusters? For example, the quantum extension of the classical Drude theory of metal conductivity shows that regularly spaced potential wells (positive metal atom core) can achieve nearly 100% electron permeability through superposition of quantum wave packets. What permeability rates can the (regular) potential wells associated with geometrical arrangement of FeS clusters in pili achieve?

So far, bio-electricity has been produced using metallic (or carbon) electrodes as the interface between the microbial electro-generation and the electric load. You will examine here how using a semiconductor as the electrode influences the microbial metabolism and therefore electron transfer.

Semiconductors are characterised by the energy-band gaps for electrons, implying that electrons in them can exist only on discrete potential / energy levels (as opposed to metals or carbon). Therefore, the electron donation process from microorganism is constrained by these potential bands. Consequently, microorganisms cannot change the energy-level at which they are donating electrons continuously, but only in discrete steps. How does this influence the metabolism of a microbial species (or the composition of a microbial community) with respect to its electrogenicity?

Quantum effects allow to have a marked potential gradient along the surface of an electrode, and therefore electrogenic microbes with a preferred donation voltage would group better in the region where this potential exists along the gradient on the electrode surface. This potential gradient will allow for a completely new and efficient way to analyse the electrogenic behaviour in a multi-species community by differentiating the electric habitat along the gradient, while all the species still share a common biochemical habitat. This would allow for new communities to evolve that perhaps can metabolise incoming organic waste more efficiently: each species could donate electrons to the electrode at their preferred potential while still allowing exchange of partial oxidised organic compounds between them.

Start date: October 2019 (with possibility of late start in January 2020)
Duration: 36 months
Application deadline: Ongoing
Funding information: All University fees are covered for the duration of the project with a stipend of approximately £15,000 per year for eligible UK/EU students.

More information and application links: https://tinyurl.com/y2jp62gj

Contact details: 
Leverhulme Doctoral Training Centre for Quantum Biology University of Surrey
Contact email address: 
C.Avignone-Rossa@surrey.ac.uk
Expiration date: 
Tuesday, October 1, 2019