What is the Difference Between BL21 and BL21 DE3

The key difference between BL21 and BL21 DE3 is that BL21 is an E. coli B strain that does not carry the gene for T7 RNA polymerase, while BL21 DE3 is an E. coli B strain that carries the gene for T7 RNA polymerase.

E. coli B strains and their derivatives are extensively used as hosts to express high levels of recombinant protein production. Properties like protease deficiency, low acetate production at a high level of glucose, and enhanced permeability make E. coli B strains a desirable host for the production of genetically engineered recombinant proteins. BL21 and BL21 DE3 are two different E. coli B strains that are deficient in Lon protease in the cytoplasm and OmpT protease in the outer membrane. Both these strains are extensively used for recombinant protein expression. However, BL21 is only suitable for expression from promoters recognized by the E. coli RNA polymerase, such as lac, tac, trc, ParaBAD, PrhaBAD, and also the T5 promoter. On the other hand, BL21 (DE3) is suitable for expression from a T7 promoter, T7-lac promoter, or promoters recognized by E. coli RNA polymerases such as lac, tac, trc, ParaBAD, PrhaBAD, and T5 promoter.

CONTENTS

1. Overview and Key Difference
2. What is BL21  
3. What is BL21 DE3
4. Similarities – BL21 and BL21 DE3
5. BL21 vs. BL21 DE3 in Tabular Form
6. FAQ – BL21 and BL21 DE3
7. Summary – BL21 vs. BL21 DE3

What is BL21?

BL21 is an E. coli B strain that is used for recombinant protein expression. This E. coli B strain does not carry the gene for T7 RNA polymerase. Therefore, it is only suitable for expression from promoters recognized by the E. coli RNA polymerase, such as lac, tac, trc, ParaBAD, PrhaBAD, and T5 promoter.

Moreover, this specific E. coli B strain exhibits distinctive characteristics, such as high-level protein expression and straightforward induction. It can be effectively utilized in non-T7 RNA polymerase protein expression systems, enabling precise regulation of protein expression, even for highly toxic proteins.

What is BL21 DE3?

BL21 DE3 is an E. coli B strain used for recombinant protein expression. This E. coli B strain contains the λDE3 lysogen that carries the gene for T7 RNA polymerase under the control of the lacUV5 promoter. In this protein expression strain,  IPTG is normally required to maximally induce expression of the T7 RNA polymerase in order to express recombinant genes, which are cloned downstream of a T7 promoter. Moreover, BL21 (DE3) is suitable for expression from a T7 promoter, T7-lac promoter, or promoters recognized by the E. coli RNA polymerase such as lac, tac, trc, ParaBAD, PrhaBAD, and T5 promoter.

Additionally, BL21 DE3 is known for its notable attributes, including a high transformation efficiency, its specialized construction for facilitating high-level T7 expression of recombinant proteins, and the absence of protease activity in this B strain.

What are the Similarities Between BL21 and BL21 DE3?

• BL21 and BL21 DE3 are known as competent E. coli cells.
• BL21 and BL21 DE3 are two different E.coli B strains that are deficient in Lon protease in the cytoplasm and OmpT protease in the outer membrane.
• Both these strains are extensively used for recombinant protein expression.
• Both these strains are commercially easily available.

What is the Difference Between BL21 and BL21 DE3?

BL21 is an E. coli B strain that does not carry the gene for T7 RNA polymerase, while BL21 DE3 is an E. coli B strain that does carry the gene for T7 RNA polymerase. Thus, this is the key difference between BL21 and BL21 DE3. Furthermore, BL21 is only suitable for expression from promoters recognized by the E. coli RNA polymerase, such as lac, tac, trc, ParaBAD, PrhaBAD, and T5 promoter. On the other hand, BL21 DE3 is suitable for expression from a T7 promoter, T7-lac promoter, or promoters recognized by the E. coli RNA polymerase such as lac, tac, trc, ParaBAD, PrhaBAD, and T5 promoter.

The infographic below presents the differences between BL21 and BL21 DE3 in tabular form for side-by-side comparison.

FAQ: BL21 and BL21 DE3

What does DE3 mean in coli BL21?

DE3 refers to a coli B strain that contains the λDE3 lysogen that carries the gene for T7 RNA polymerase under the control of the lacUV5 promoter.

Why use BL21 DE3 cells for protein expression?

BL21 DE3 is a competent strain of high-level protein expression and easy induction. It also provides tighter control of protein expression for toxic proteins and is resistant to chloramphenicol.

What are the different types of BL21?

There are four types of coli strains: BL21 Star, Rosetta, SHuffle, and Origami.

Summary – BL21 vs. BL21 DE3

BL21 and BL21 DE3 are two different E. coli B strains that are extensively used for recombinant protein expression. BL21 is an E. coli B strain that does not carry the gene for T7 RNA polymerase, while BL21 DE3 is an E. coli B strain that carries the gene for T7 RNA polymerase. So, this summarizes the difference between BL21 and BL21 DE3.

Reference:

1. Jeong, Haeyoung, et al. “Complete Genome Sequence of Escherichia Coli Strain BL21.” Genome Announcements, U.S. National Library of Medicine.
2. Du, Fei, et al. “Regulating the T7 RNA Polymerase Expression in E. Coli BL21 (DE3) to Provide More Host Options for Recombinant Protein Production – Microbial Cell Factories.” BioMed Central, BioMed Central.

Image Courtesy:

1. “E. coli Bacteria” By NIH Image Gallery (CC BY-NC 2.0 DEED) via Flickr