Overview
The Horsfall lab believe in a circular economy, and this links all the work carried out in our lab. Unlike the current economic model the circular economy sees waste not as a problem, but a raw material to be fed back into the system (Fig 1). As well as turning waste from industrial processes into useful materials we are also interested in doing the same for contaminants on polluted land, adding value to the process of decontamination. One way we achieve this is by using bacteria to convert heavy metal contaminants into metallic nanoparticles which have many applications in medicine and industry, including catalysts in hydrogen fuels cells and as anti-microbial agents. We use Synthetic Biology- applying engineering principles to biology such as interchangeable, modular DNA parts- to engineer bacteria able to convert many different metals into nanoparticles, and to control that process. Another focus for the lab is on lignin, a large molecule that is hard to break down but nevertheless is made of many useful compounds. It is a very common molecule in plants, and is found in waste from sources such as the paper industry. We are also combining our two main focuses in another project where we are enhancing the breakdown of lignin by using nanoparticles produced from waste by our bacteria.
We are a multi-disciplinary lab with expertise in genetics, microbiology, biochemistry, biotechnology, nanotechnology and environmental science.
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Figure 1: The circular economy

Production of copper nanoparticles (BBSRC; Diageo; IBioIC)
Whisky distillation is performed in copper stills and as a result produces copper-contaminated byproducts. These byproducts also contain a lot of spent grain and yeast which could otherwise be reused, such as for animal feed. We are currently using a species of
Morganella bacteria to reduce the copper ions and convert them into nanoparticles. We have already demonstrated that Morganella can produce nanoparticles of zero-valency copper (Cu0), and by manipulating pH levels we are able to control nanoparticle morphology, resulting in nanoparticles of uniform size and shape (Fig 2). Our current focus is on investigating the mechanism behind nanoparticle formation by studying the effects of copper on the proteome, allowing us to select target proteins and apply synthetic biology tools to increase the efficiency and utility of nanoparticle production. We are also developing methods which will allow us to maximise the removal of copper from distillery byproducts.
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Figure 2: Uniform copper nanoparticles produced by the bacterium Morganella

Lignin degradation (EPSRC; Presidential Special Scholarship Scheme for Innovation and Development, Federal Government of Nigeria)
Lignin is a major component of plant biomass whose enzymatic degradation results in the production of valuable renewable products such as vanillin (food flavouring), adipic acid (nylon precursor), and biofuels, offering an alternative to compounds derived from fossil fuels. Lignin is also very abundant, being present in many waste sources such as wheat stalks from the food industry. However lignin is a very large and complex molecule that is difficult to degrade due to the strong linkages present in its structure, exhibiting strong resistance to chemical and enzymatic degradation. We are currently investigating the use of enzymes from microorganisms that are naturally able to break lignin down, and genetically engineering bacteria and yeast to produce high yields of these enzymes.

As well as the enzymatic degradation of lignin we are also investigating the application of our biogenic nanoparticles to enhance the conversion of lignin into valuable renewable products with potential uses such as catalysts.

Cleaning Land for Wealth (CL4W) (EPSRC)
We are part of a consortium of five UK universities which is developing ways to incentivise the decontamination of land. The decontamination process involves the use of phytoremediation to remove heavy metals from the land; the resulting plant material will then be processed to remove the heavy metals, and the now decontaminated biomass harvested of all its useful components, such as lignin (see Lignin degradation project above). Any remaining biomass can be efficiently burned for energy. Our lab’s role in the project is in dealing with the heavy metals extracted from the plants.
We use a number of different bacterial strains to convert the accumulated heavy metals into nanoparticles. This not only converts the metals into a form that can be easily removed from a solution; the nanoparticles themselves are often high-value materials having uses such as catalysts and anti-microbials. We are currently able to produce nanoparticles of a number of different metals; the anaerobic bacterium
Desulfovibrio is able to produce zero-valent platinum and palladium nanoparticles (Fig 3), as well as nickel sulphide. We have investigated the proteome of cells exposed to Pd and Pt and are now working towards ascertaining each protein’s role in nanoparticle production, with an eye towards being able to control nanoparticle formation at the genetic level. We have also engineered a strain of E. coli that is able to survive high concentrations of arsenic(V) and produce an insoluble form of arsenic attached to the cell wall, making it easier to remove arsenic contamination from a solution (Fig 4).
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Figure 3: Pt (left) and Pd (right) nanoparticles produced by Desulfovibrio.

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Figure 4: Large arsenic structures bound to the surface of engineered E. coli.