UBC Theses and Dissertations
An investigation of a temperature-sensitive intein with regards to its use as metabolic control element for bioprocess enhancement Korvin, Daniel
Bioprocesses based on metabolically engineered microbes have become tremendously important in recent decades as a platform for the synthesis of complex molecules. Substantial research effort has been devoted to the improvement of microbial strains involved, and while this has enhanced some metrics of strain performance dramatically, namely product yield with respect to substrate and biomass, achieving similar results with other aspects has remained elusive. Improving productivity, the rate at which a modified strain can synthesize a product of interest, in particular has presented an engineering challenge despite its obvious value to the economics of a process and has typically only been done through bioprocess optimization. A strategy that could yield the desired result is strain engineering to better integrate with the bioprocess context in which it is used. The work described in this thesis has sought to achieve that goal by providing a method to the operating engineer to dynamically control the induction of genes associated with product formation. More specifically, a T7 RNA polymerase was modified by the insertion of a mutant variant of the S cerevisiae Vacuolar membrane ATPase(VMA) intein. This mutant intein will only splice out of its host only under conditions of reduced temperature, which in effect makes the polymerase active only after a temperature shift from 37℃ to 18℃ degrees. This creates a strict demarcation between biomass accumulation and product synthesis, only allowing this transition to be made at an optimal point during fermentation, as chosen by the operating engineer. Using lycopene biosynthesis as a case study and applying this approach, it was found that a productivity improvement of approximately 15% over an uncontrolled strain was attained. It was also found that a remarkable degree of control stringency was conferred upon the system, with no premature product synthesis detected under any condition investigated.These results are expanded upon to generate a series of simple mathematical models, with the aim of describing how such a dynamic metabolic control element might be expected to perform in a more generalized context, and to provide a means by which to more quantitatively assess the strain’s performance.
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