Metabolic engineering for gaseous biofuels production

  • Emilia Wojcik

Student thesis: Phd


Due to world population growth and climate change, there is an urgent necessity to develop renewable, sustainable and carbon-neutral sources of energy. Biofuels, or fuels produced from biomass, are a focus of research into novel energy sources. A large diversity of biofuel molecules has been produced through metabolic engineering of microorganisms, which is defined as the modification of cellular metabolism to achieve a specific outcome. Propane is an excellent biofuel target: it is compatible with existing infrastructure for liquefied petroleum gas (LPG) and used in a wide variety of applications, such as cooking, heating and as a motor fuel. Propane is easily removed from a bacterial culture due to its gaseous state, and there is no need for its extraction. Additionally, propane can be produced from waste feedstocks which absorb CO2 as they grow, therefore contributing towards the goal of carbon neutrality of biofuels. The aims of this thesis were to develop biocatalysts and microbial strains for propane production, and to explore the potential of CO2-absorbing waste feedstocks to support the growth of industrial microbial hosts. Chlorella variabilis fatty acid photodecarboxylase (CvFAP) is a blue-light photoenzyme which decarboxylates fatty acids to alkanes, and was used in this study as a biocatalyst for propane production. A CvFAP variant with 16-fold propane production in vivo was generated through protein engineering. Two alternative feedstocks, brown macroalgae and cyanobacterial biomass, were explored for their potential to support the growth of Escherichia coli and Halomonas. Halomonas is a salt-loving bacterium, and an emerging industrial microbial host. The enzyme Bgl1b was shown to convert laminarin, a polysaccharide found in brown macroalgae, to glucose, and Bgl1b-expressing strains of E. coli and Halomonas were constructed. The natural ability of Halomonas to grow on mannitol, a sugar alcohol found in brown macroalgae, was exploited to produce propane from cells grown solely on mannitol-rich algal extract. Halomonas was also shown to produce propane while growing on lysed cyanobacterial biomass. The insights gained from this project about CvFAP as a biocatalyst, and macroalgal and cyanobacterial biomass as feedstock sources for E. coli and Halomonas, provide a foundation for future work on developing microbial propane production platforms.
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorDavid Leys (Supervisor) & Nigel Scrutton (Supervisor)

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