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Title: Metabolic Characterization and Engineering of Streptomyces lividans Producing Heterologous Proteins (Metabole karakterisering en engineering van Streptomyces lividans voor heterologe eiwitproductie)
Other Titles: Metabolic Characterization and Engineering of Streptomyces lividans Producing Heterologous Proteins
Authors: Lule, Ivan
Issue Date: 18-Dec-2012
Abstract: Streptomycetes have become attractive hosts for heterologous protein production due to for instance, their ability to efficiently secrete their proteins in the extracellular environment. Among these microbes, Streptomyces lividans, known to have a reduced restriction-modification barrier, has been used more extensively for heterologous protein production. Hitherto, studies on metabolic characterization and engineering of S. lividans for heterologous protein production are limited, and of these, few are performed in (upscale) controlled fermentation environments. Without metabolomics, the metabolic impact/load that heterologous protein production exerts on the central carbon metabolism of S. lividans remains loosely understood, and can not easily be relieved.Therefore, the general objective of this dissertation was to characterize the growth and metabolism of S. lividans producing heterologous proteins in (upscale) controlled fermentation environments. The study is further extended to assess the effect of overexpressing the gene (pck) encoding phosphoenolpyruvate carboxykinase on heterologous protein production in S. lividans. A genome scale metabolic network model of wild-type S. lividans was extended to include mouse tumor necrosis factor-alpha (mTNF-alpha) production. The resulting model matrix was mathematically analyzed to check for its inherent properties and sensitivity to key measurable fluxes. Results obtained showed that model sensitivity to mTNF-alpha was tenfold higher than biomass production, while the latter was at least tenfold more sensitive than the measurable amino acid fluxes. Metabolic characterization of recombinant S. lividans, in comparison with the wild-type S. lividans, was done to assess metabolic impact based on both extracellular metabolomics and constraint-based modeling. Results obtained showed that the metabolic impact due to heterologous protein production results in lower substrate uptake and slower growth, the former an indication for metabolic channeling. The metabolic impact is widely-distributed in the genome of S. lividans, causing a great shift in its performance. Critical exchange fluxes in the recombinant cell’s or model’s performance have been identified as biomass, mTNF-alpha, histidine, valine and alanine. Finally, based on metabolic engineering techniques, it was revealed that pck overexpression in S. lividans TK24 results in up to 1.7-fold increase in hTNF-alpha production. The major findings in this dissertation are an indication of metabolic shifts within the recombinant cell as well as a positive correlation between the explored metabolic engineering approach and heterologous protein production.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Laboratory of Molecular Bacteriology (Rega Institute)
Chemical and Biochemical Process Technology and Control Section
Chemical Engineering - miscellaneous

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