Strategies for improved Escherichia coli bioprocessing performance

Abstract: Escherichia coli has a proven track record for successful production of anything from small molecules like organic acids to large therapeutic proteins, and has thus important applications in both R&D and commercial production. The versatility of this organism in combination with the accumulated knowledge of its genome, metabolism and physiology, has allowed for development of specialty strains capable of performing very specific tasks, opening up opportunities within new areas. The work of this thesis has been devoted to alter membrane transport proteins and the regulation of these, in order for E. coli to find further application within two such important areas.The first area was vaccine development, where it was investigated if E. coli could be a natural vehicle for live vaccine production. The hypothesis was that the introduction and manipulation of a protein surface translocation system from pathogenic E. coli would result in stable expression levels of Salmonella subunit antigens on the surface of laboratory E. coli. While different antigen combinations were successfully expressed on the surface of E. coli, larger proteins were affected by proteolysis, which manipulation of cultivation conditions could reduce, but not eliminate completely. The surface expressed antigens were further capable of inducing proinflammatory responses in epithelial cells.The second area was biorefining. By altering the regulation of sugar assimilation, it was hypothesized that simultaneous uptake of the sugars present in lignocellulose hydrolyzates could be achieved, thereby improving the yield and productivity of important bio-based chemicals. The dual-layered catabolite repression was identified and successfully removed in the engineered E. coli, and the compound (R)-3-hydroxybutyric acid was produced from simultaneous assimilation of glucose, xylose and arabinose.