title: Investigation of the impact of Tat export pathway enhancement on E. coli culture, protein production and early stage recovery.
abstract: The twin arginine translocation (Tat) pathway occurs naturally in E. coli and has the distinct ability to translocate folded proteins across the inner membrane of the cell. It has the potential to export commercially useful proteins that cannot be exported by the ubiquitous Sec pathway. To better understand the bioprocess potential of the Tat pathway, this article addresses the fermentation and downstream processing performances of E. coli strains with a wild-type Tat system exporting the over-expressed substrate protein FhuD. These were compared to strains cell-engineered to over-express the Tat pathway, since the native export capacity of the Tat pathway is low. This low capacity makes the pathway susceptible to saturation by over-expressed substrate proteins, and can result in compromised cell integrity. However, there is concern in the literature that over-expression of membrane proteins, like those of the Tat pathway, can impact negatively upon membrane integrity itself. Under controlled fermentation conditions E. coli cells with a wild-type Tat pathway showed poor protein accumulation, reaching a periplasmic maximum of only 0.5 mg L⁻¹ of growth medium. Cells over-expressing the Tat pathway showed a 25% improvement in growth rate, avoided pathway saturation, and showed 40-fold higher periplasmic accumulation of FhuD. Moreover, this was achieved whilst conserving the integrity of cells for downstream processing: experimentation comparing the robustness of cells to increasing levels of shear showed no detrimental effect from pathway over-expression. Further experimentation on spheroplasts generated by the lysozyme/osmotic shock method--a scaleable way to release periplasmic protein--showed similar robustness between strains. A scale-down mimic of continuous disk-stack centrifugation predicted clarifications in excess of 90% for both intact cells and spheroplasts. Cells over-expressing the Tat pathway performed comparably to cells with the wild-type system. Overall, engineering E. coli cells to over-express the Tat pathway allowed for greater periplasmic yields of FhuD at the fermentation scale without compromising downstream processing performance.
authors: The Advanced Centre for Biochemical Engineering, Department of Biochemical Engineering, University College London, Torrington Place, London WC1E 7JE, UK.
authors: Steven D
authors: SD
authors: Branston
authors: Cristina F R O
authors: CF
authors: Matos
authors: Robert B
authors: RB
authors: Freedman
authors: Colin
authors: C
authors: Robinson
authors: Eli
authors: E
authors: Keshavarz-Moore
mesh_terms: D000595:Amino Acid Sequence; D018988:Bacterial Translocation; D001431:Bacteriological Techniques; D061249:Batch Cell Culture Techniques / Q000379:methods*; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D002498:Centrifugation; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D005285:Fermentation; D007218:Industrial Microbiology / Q000379:methods*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D019897:Periplasm / Q000378:metabolism; D033902:Periplasmic Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000502:physiology; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D013104:Spheroplasts / Q000378:metabolism; D014783:Viscosity
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D033902:Periplasmic Binding Proteins; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; C408585:twin-arginine translocase complex, E coli; C069969:fhuD protein, E coli