Thesis

Metabolic analysis of genetically engineered micro-organisms

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Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13316
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Abstract
  • The Aspergilli are important industrial microorganisms used for the production of organic acids and enzymes. In this project the main objective was to increase productivity in industrial micro-organisms grown on glucose as the sole carbon source by expressing A. niger genes coding for the enzyme 6-phosphofructo-1-kinase (PFK). A. terreus was chosen as the recipient organism as it is closely related to A. niger and would hopefully be receptive to expression of A. niger genes. The project aimed to engineer the metabolism of A. terreus to use features of A. niger such as its high productivity and yield which, along with optimisation of production and fermentation media has resulted in up to 80% of substrate (sucrose) being converted into the product, citric acid. Using this knowledge it is anticipated that the rates of glucose utilisation and glycolysis will be increased so that the precursors for the production of industrially important products are produced in higher yields by A. terreus. When glucose is utilised during a fermentation, A. terreus is known to produce itaconic acid at low pH and lovastatin and other secondary metabolities at higher pH. However, when a starting pH of 6.5 was used that would favour lovastatin production, a novel pathway of glucose catabolism was demonstrated in this study by both wild type A. terreus (without any strain development) and by transformants containing the A. niger genes encoding PFK. Gluconic acid was produced by A. terreus at high yields (up to 0.7 mole per mole of glucose consumed). Although A. niger is used on an industrial scale to biomanufacture gluconic acid, this is the first demonstration of gluconic acid production by A. terreus. The implications for fermentation control with A. terreus when used for the production of secondary metabolites at high pH are explored. Although glucose utilisation was not clearly different between the parental and modified strains, the modified strain produced less gluconic acid than the parental strain. This was found to be glucose concentration-dependent because accumulated gluconic acid could be utilised when glucose was exhausted in the fermentation medium. This knowledge furnishes new strategies for metabolite production with A. terreus . The major significance of study is the realisation of A. terreus as a potential novel producer organism for gluconic acid which has many and varied uses as a bulk chemical. Employing the new understandings of glucose catabolism by A. terreus, new strategies for secondary metabolite production could be anticipated with glucose feeding employing pH as a feedback regulation. This research work was funded by the European Commission under the international project ANTICO (Aspergillus Niger Transformed Into Commercial Organisms.
Resource Type
DOI
Date Created
  • 2012
Former identifier
  • 967039

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