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Mortimer, Zahara (2024) Nutritional profile optimisation of carbon dioxide fixing bacteria by molecular engineering. EngD thesis, University of Nottingham.

PDF (Nutritional Profile Optimisation of Carbon Dioxide Fixing Bacteria by Molecular Engineering) (Thesis - as examined) - Repository staff only until 18 July 2026. Subsequently available to Repository staff only - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader Download (11MB)

Abstract

A global dilemma has evolved concerning the sustainability of supplying global energy demand and feeding a growing global population, predicted to increase by 2 billion towards 2050. The production of greenhouse gases (GHG) driven by anthropogenic activity is the dominant contributor to the global climate change effect observed, with energy related carbon dioxide (CO2) emissions remaining at their highest in 2022 since before 1990. Simultaneously, approximately 10 % of the current global population suffer from hunger, despite one third of food resources being wasted annually. The capacity of bacteria to biologically sequester CO2 whilst generating a protein source offers a potential strategy to alleviate the energy and food insecurity dilemma described. Cupriavidus necator H16 is a model bacteria capable of fixing CO2 using hydrogen (H2) as an energy source, hence is referred to as a hydrogen oxidising bacteria (HOB). Further, C. necator H16 is amenable to genetic modification with various molecular tools available to optimise the strain, conferring the strain’s potential as a CO2 utilising production chassis. Alternative protein sources derived from bacteria, denoted single cell protein (SCP), are attractive due to their ability to utilise waste as feedstocks, minimal arable land requirement and potential to achieve high protein yields. Notably, this research project was conducted in collaboration with the carbon recycling biotechnology company, Deep Branch®, whose platform is centralised around harnessing CO2 fixing bacteria to generate an optimised protein product, Proton™, for animal feed.

In this work, the wildtype C. necator H16 was initially evaluated as a potential alternative protein source amongst a range of physiologically diverse bacteria strains, conferring variable inter-species protein quality (DIAAS = 55.4 – 107.8 %) and digestibility (54.3 – 88.5 %) in in vitro human digestions (INFOGEST method). The relatively high presence of nucleic acids represents a major constraint to the application of SCP for human consumption, however this has not been reported with regard to feed inclusion. Therefore, C. necator H16, in addition to a novel HOB isolate (Paracoccus pantotrophus sp.), were respectively assessed as protein ingredients in a simulated Atlantic Salmon gut (SalmoSim®), predicting > 86 % in vivo digestibility. Additionally, the impact of heat treatment on SCP sources prior to SalmoSim® digestions was negligible. In in vivo, no difference in growth performance (p > 0.05) of zebrafish (Danio rerio) fed on complete diets partially replaced (27.7 % total feed) with bacteria SCP were observed relative to a fish meal control diet. Notably, the storage compound polyhydroxybutyrate (PHB) which is natively produced by both HOB strains did not adversely affect feed performance of SCP diets in vivo relative to fish meal control despite the compounds indigestibility.

Finally, to optimise the wildtype C. necator H16 as a SCP production chassis, Transposon Directed Insertion-site Sequencing (TraDIS) was employed to produce essential gene lists associated with the utilisation of various feedstocks (CO2/H2, fructose, formate and glycerol) and PHB production respectively. To identify essential genes for PHB deficiency and accumulation phenotypes, TraDIS was combined with a physical cell sorting method, Fluorescence Activated Cell Sorting (FACS), which offers an alternative to fitness-based selection of mutants and allows the study of phenotypes not obligately associated with survival. Collectively, these TraDIS experiments were executed with the intention of identifying novel gene targets in C. necator H16 for molecular engineering.

Item Type:	Thesis (University of Nottingham only) (EngD)
Supervisors:	Zhang, Ying Parr, Tim Salter, Andrew Irons, Robin Woods, Craig Krabben, Preben
Keywords:	Cupriavidus necator H16, Hydrogen oxiding bacteria, Single cell protein, Polyhydroxybutyrate, Transposons
Subjects:	T Technology > TP Chemical technology > TP 368 Food processing and manufacture
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	78297
Depositing User:	Mortimer, Zahara
Date Deposited:	31 Oct 2024 10:15
Last Modified:	31 Oct 2024 10:15
URI:	https://eprints.nottingham.ac.uk/id/eprint/78297

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