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Reconstructing the evolution of BL21 into C41 reveals rapid adaptability of a widely used E. coli strain
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. (Jan-Willem de Gier)
(English)Manuscript (preprint) (Other academic)
National Category
Biochemistry and Molecular Biology
URN: urn:nbn:se:su:diva-94992OAI: diva2:657540
Available from: 2013-10-20 Created: 2013-10-20 Last updated: 2013-10-21Bibliographically approved
In thesis
1. From protein production to genome evolution in Escherichia coli
Open this publication in new window or tab >>From protein production to genome evolution in Escherichia coli
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of my Ph.D. studies was to improve production yields of membrane- and secretory proteins in the widely used E. coli protein production strain BL21(DE3). In this strain expression of the gene encoding the protein of interest is driven by the powerful T7 RNA polymerase (T7 RNAP) whose gene is located on the chromosome and under control of the strong, IPTG-inducible lacUV5 promoter. Unfortunately, the production of many membrane and secretory proteins is 'toxic' to BL21(DE3), resulting in poor growth and low production yields.

To understand this ‘toxicity’, the BL21(DE3) derived mutant strains C41(DE3) and C43(DE3) were characterized. Somehow, these strains can efficiently produce many ‘toxic’ membrane and secretory proteins. We showed that mutations weakening the lacUV5 promoter are responsible for this. These mutations result in a slower onset of protein production upon the addition of IPTG, which avoids saturating the Sec-translocon capacity. The Sec-translocon is a protein-conducting channel in the cytoplasmic membrane mediating the biogenesis of membrane proteins and translocation of secretory proteins. Next, we constructed a BL21(DE3)-derivative, Lemo21(DE3), in which the activity of T7 RNAP can be precisely controlled by titrating in its natural inhibitor T7 lysozyme using the rhamnose promoter system. In Lemo21(DE3), the expression level of genes encoding membrane and secretory proteins can be set such that the Sec-translocon capacity is not saturated. This is key to optimizing membrane and secretory protein production yields. Finally, reconstructing the evolution of C41(DE3) from BL21(DE3) in real time showed that during its isolation C41(DE3) had acquired mutations critical for surviving the starvation conditions used, and provided insight in how the mutations in the lacUV5 promoter had occurred.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2013. 59 p.
Escherichia coli, BL21(DE3), protein production, membrane proteins, secretory proteins, genome evolution
National Category
Biochemistry and Molecular Biology
Research subject
urn:nbn:se:su:diva-94993 (URN)978-91-7447-786-3 (ISBN)
Public defence
2013-11-22, Magnelisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2013-10-30 Created: 2013-10-20 Last updated: 2013-10-29Bibliographically approved

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