Improving the carbon efficiency in the bio-production of citramalic acid in Escherichia coli

Lebeau, Juliana Laurence Dominique (2018) Improving the carbon efficiency in the bio-production of citramalic acid in Escherichia coli. PhD thesis, University of Nottingham.

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Methacrylic acid (MAA) is a bulk chemical used in the synthesis of acrylic polymers as well as for the manufacture of many different products such as resins, and paints. However, the industrial manufacturing processes for MAA production involve toxic raw materials that are reliant on availability and economic variability of petroleum derived compounds. Global consumption and market of acrylics keep growing, rendering constant production processes as well as price stability highly desirable.

To date, there is no direct bio-process available for the biosynthesis of MAA itself. Fortunately, a bio-production route of citramalic acid, which was previously demonstrated to be converted readily to MAA in a simple chemical patented hot pressurised water process, was demonstrated in Escherichia coli with promising titres of product (130 g/L). The enzyme citramalate synthase was used, and catalysed the condensation of two central cellular metabolites, pyruvate and acetyl-CoA, to (R)-citramalate in a one-step reaction. However, the biocatalytic reaction is limited by the availability of the starting materials. Acetyl-CoA is mainly produced via the decarboxylation of pyruvate, resulting in losing carbon by the formation of CO2, and is known as one of the major limitation for the development of cost-effective microbial bio-production of commodity bio-chemicals.

In this thesis, E. coli strains were engineered to be able to co-consume carbohydrate and/or non-carbohydrate sources, in order to address the metabolic limitation due to pyruvate decarboxylation. In E. coli, both acetate and ethanol are directly linked to acetyl-CoA via different reversible enzyme pathways and were thus identified as potential external sources of acetyl-CoA. The introduction of either an acetate or an ethanol assimilation pathway with the appropriate co-feeding of glucose/acetate or glucose/ethanol resulted in increasing the specific productivities of (R)-citramalate in E. coli up to 50% in comparison to bio-production systems based on glucose only. Thus, acetate and ethanol co-feeding strategies provided promising outcomes for the bio-production of MAA.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hall, Stephen J.
Stephens, Gill
Keywords: Biotechnology, microbiology, synthetic biology, citramalate, fermentation
Subjects: T Technology > TP Chemical technology
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 49947
Depositing User: Lebeau, Juliana
Date Deposited: 13 Jul 2018 04:40
Last Modified: 13 Jul 2020 04:30

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