On the Effectiveness and Challenges of Electrosynthesis Strategies in Escherichia coli

Conventional bioprocesses that aim to convert CO2 to fuels and chemicals do so through a supply chain that begins with agricultural products such as corn, intermediaries like dextrose, and eventually produce chemicals by fermentation. However, it has long been desired that bioprocesses be established to convert CO2 point source emissions to chemicals. Fundamentally, this is a thermodynamics problem since the use of CO2 as a feedstock requires an efficient mechanism to deliver energy to produce chemicals. The focus of this work is to examine several strategies for microbial electrosynthesis, the delivery of electrical energy to microbial cell factories, for producing chemicals. The study encompasses four areas type of microbial electrosynthesis and the results are summarized here: 1) Experimental work was performed to evaluate the affect of neutral red mediated charge transfer in mutant strains of Escherichia coli for the purpose of producing succinic acid. The results of this task showed wild-type cells exhibited the greatest molar increase in succinate yield with an 89% increase while an ldhA deficient strain showed 40% increase. The lack of direct charge transfer was implicated as the cause since an electron balance was not able to account for an increase in succinate. 2) We explored the use of mediators such has formate that can be generated from carbon dioxide and renewable electricity as a carbon source for cell growth and chemical production. An auxotrophic strategy was employed to engineer formate assimilation, and growth rate on formate as a C1 donor for folate was determined to be 0.33 h-1. This was 78% of the wild-type strain. 3) We developed a framework for analyzing how metabolic pathways can be efficiently engineered into microbes to produce chemicals. This orthogonality framework showed ethylene glycol to be a highly promising substrate for electrosynthesis applications. 4) Finally, a bioprocess for the conversion of ethylene glycol to glycolic acid was characterized and its suitability to replace glucose as a feedstock was examined. The maximum glycolate titres for the best performing conditions reached 10.6 g/L. The highest substrate uptake rate for ethylene glycol was determined to be ca. 5 mmol/gDW-h.

Department dc:contributor.department

Chemical Engineering Applied Chemistry

Year dc:date.issued

2017

Author dc:creator

• Pandit, Aditya Vikram

Advisor dc:contributor.advisor

• Mahadevan, Radhakrishnan

• Escherichia coli
• ethylene glycol
• glycolic acid
• metabolic engineering
• orthogonality

Handle dc:identifier.uri

http://hdl.handle.net/1807/98810

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/98810