21EngBio: Engineering Biology for Molecular Precursor Production

Lead Research Organisation: The University of Manchester
Department Name: Chemistry

Abstract

Alkoxysilanes are silicon-containing compounds that are used in the production of a huge variety of consumer and industrial products including machine parts, electronic components, adhesives, abrasives and ceramics. For example, a type of ceramic called silicon carbide has received much interest recently as it is used in several high-technology applications. This material can conduct electricity at very high voltages and currents, and hence it is used in the power transmission components of wind turbines and electric vehicles. Its extreme hardness and heat resistance means that it has also found uses in the aerospace industry for rocket nozzles and heat shielding, as well as in personal and vehicular armour plating in the defence and security sector.

However, the production of these alkoxysilanes is currently very energy intensive, relatively inefficient and environmentally unfriendly. Specifically, their production employs refined silicon, which is itself produced by the smelting of quartz rock with coal at very high temperatures in a furnace. This silicon is then reacted with chlorine (a very toxic and corrosive gas) and an alcohol to finally produce the desired alkoxysilanes. An additional issue with the current process is that quartz of suitable quality is mainly available in two places on the globe, in Norway and the central USA. It is anticipated that it may be difficult for these sources to meet the growing demand of the manufacturing sector in the coming years. There is therefore a need to develop alternative methods of producing alkoxysilanes that are more eco-friendly and are not reliant on limited quartz reserves.

In fact, silicon is an abundant element in nature and is found in most minerals. Many plants also absorb silicon from the soil. Though there have been several attempts in the past 40 years to produce alkoxysilanes directly from these crude minerals or plant matter, they have been hampered by the difficulty in removing unwanted metal contaminants from these raw materials.

It has been known for many years that some species of marine sponges incorporate silicon into their skeletons by condensing water soluble forms of silicon that are found in seawater. This process is facilitated by an enzyme termed 'silicatein', which enables the formation of silicon-oxygen chemical bonds under mild biological conditions. Notably, more recent research has shown that the enzyme can be used to produce simple alkoxysilanes under laboratory conditions. This project will expand on these early findings to develop a biologically-inspired route to the production of alkoxysilanes that will be cheap, widely available and environmentally sustainable.
Specifically, this project will genetically modify a harmless bacterium so that it produces modified versions of silicatein enzymes that have greater ability to produce industrially relevant alkoxysilanes. The host bacteria will then further genetically modified, so that it presents these enzymes on their surface. In doing so, the bacteria can themselves perform the reaction without needing to extract the enzyme from the bacteria. The work will also focus on the isolation of these alkoxysilanes with a high degree of purity (free from trace metals) by harnessing the enzyme's natural preference for reacting only with silicon. Finally, a process will be developed that combines fermentation of sugars by yeasts to produce alcohol, with the engineered bacteria, so that by only adding crude minerals and sugar, the desired alkoxysilanes can be produced in a single process.

By demonstrating how enzymes and bacteria can be used like a chemical factory, this project will demonstrate how biology can be harnessed to address what is essentially an engineering challenge - the improved production of an industrial chemical of high economic value.

Technical Summary

Tetraalkoxysilanes (TROS) are a family of compounds containing a silicon atom that have a tremendous range of applications. However, many advanced applications in the energy, aerospace and defence sectors demand very high purity silanes that should be free of trace metal contaminants, which degrade the performance of the materials. To produce such high purity feedstocks, a series of energy intensive steps are employed: (1) the mining and refining of quartz into metallic silicon; (2) the reaction of silicon with chlorine to give tetrachlorosilane and finally; (3) alcoholysis of tetrachlorosilane to give the desired product.

It is well-known that rice plants uptake soluble silicates and deposit them in their tissues as silica nanoparticles, which can comprise as much as 20% of its dry weight. Thus, such plant-based silicates could be used as renewable resource for the production of high purity alkoxysilanes. It has also been known for many years that some marine sponges incorporate silicon into their skeletons by polymerising dissolved silicates into inorganic silica. This polymerisation is catalysed by a family of enzymes termed the silicateins, which the applicant has shown can catalyse the condensation of alcohols and silanols to produce simple alkoxysilanes under laboratory conditions.

This project will expand on these early findings to develop a biologically-inspired route to the production of alkoxysilanes that will be cheap and environmentally sustainable. Thus, this project will: (1) recombinantly engineer silicateins with improved activity towards tetraethoxysilane, as an exemplar TROS; (2) harness the selectivity of the silicateins to enable the use of crude silicate sources (e.g. rice husks); (3) engineer E. coli to display silicatein on its surface and demonstrate whole-cell biocatalysis; and (4) demonstrate the use of membrane compartmentalisation for the integrated production of TEOS using ethanol produced from the in situ fermentation of glucose.

Publications

10 25 50
 
Description The goal of this research was to investigate the whether an enzyme (biological catalyst) from a marine sponge was able to catalyse the synthesis of small organic molecules containing silicon atoms. This research is significant because such molecules are used as chemical feedstocks for the manufacture of inorganic materials such as electronic components. However, the existing routes for the production of these "organosilicon" molecules is not eco-friendly. This research has demonstrated that these enzymes are indeed able to catalyse the formation of these organosilicon molecules.
In the process of carrying out this research several ancillary discoveries were also made, such as chemical tests to detect whether enzymes are carrying out chemical reactions where silicon-oxygen bonds are being formed.
Exploitation Route Further research to elaborate on the initial findings would be an interesting avenue of research, to demonstrate that practically useful amounts of organosilicon compounds are produced, and that these compounds can be used for the fabrication of materials.
Sectors Chemicals

Manufacturing

including Industrial Biotechology

 
Description Mechanism-Structure-Sequence Relationships in Silicon-Processing Enzymes
Amount £201,710 (GBP)
Funding ID RPG-2022-084 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 02/2023 
End 07/2026
 
Description The effects of organosilicon compounds in plant food production and safety
Amount $4,912 (USD)
Funding ID WAG-1291314601 
Organisation British Council 
Sector Charity/Non Profit
Country United Kingdom
Start 05/2022 
End 12/2023
 
Title Spectrophotometric reagents for silicon-oxygen bond hydrolysis 
Description Enzymes are now harnessed for a plethora of industrial processes and chemical syntheses. However, one frontier area that remains understudied is the enzymatic manipulation of 'inorganic' compounds and specifically organosilicon chemistry. These reagents were designed to addresses the issue of accurately measuring the catalytic efficiency of any enzyme that may be capable of hydrolysing silicon-oxygen bonds, which is crucial to any effort directed at the discovery of new enzymes that are capable of this reaction, or the recombinant engineering of enzymes towards this end. By developing novel spectrophotometrically active substrates and optimizing assay conditions, we anticipate that our findings will offer valuable insights into the biocatalysis of Si-O bonds and contribute to the field of enzymatic assay development. 
Type Of Material Technology assay or reagent 
Year Produced 2024 
Provided To Others? Yes  
Impact Reagents are being shared with other research groups. A publication detailing their design, procedures on their usage and biochemical characteristics is currently under review at time of writing. 
 
Description David Churchill, Korea Advanced Institute of Science & Technology (KAIST) 
Organisation Korea Advanced Institute of Science and Technology (KAIST)
Country Korea, Republic of 
Sector Academic/University 
PI Contribution The development and characterisation of enzymatic assays using reagents supplied by KAIST.
Collaborator Contribution The supply of bespoke synthesised reagents for the development of enzymatic assays.
Impact None yet
Start Year 2023
 
Description Defence Science and Technology Laboratory - Christopher Hawkins 
Organisation Defence Science & Technology Laboratory (DSTL)
Country United Kingdom 
Sector Public 
PI Contribution Provided briefings into research results
Collaborator Contribution Partner provided information input into the strategic need for project.
Impact Input into the preparation of this BBSRC Engineering Biology proposal
Start Year 2021
 
Description Open University, UK - Prof. Peter G. Taylor 
Organisation Open University
Country United Kingdom 
Sector Academic/University 
PI Contribution Experimental research into the topic of silicon biochemistry, including intellectual input, access to laboratory facilities, project administration.
Collaborator Contribution Intellectual input into the topic of silicon biochemistry.
Impact Research papers published, opportunities for wider networking with SMEs related to this area of research.
Start Year 2018