Difference Between BL21 and DH5 Alpha

The key difference between BL21 and DH5 Alpha is that BL21 is a protease deficient genetically engineered competent E. coli cell used primarily for protein expression, while DH5 Alpha is a genetically engineered competent E. coli cell with recA1 mutation used primarily for plasmid transformation.

E. coli is one of the famous organisms of choice for recombinant protein production. It has become the most popular expression platform over the years. It is also used as a cell factory. BL21 and DH5 Alpha are two genetically engineered E. coli cells currently used for protein expression and plasmid transformation, respectively.

CONTENTS

1. Overview and Key Difference
2. What is BL21  
3. What is DH5 Alpha
4. Similarities – BL21 and DH5 Alpha
5. BL21 vs DH5 Alpha in Tabular Form
6. Summary – BL21 vs DH5 Alpha

What is BL21?

BL21 is a protease deficient genetically engineered competent E .coli cell primarily used for protein expression. E. coli BL21 is a bacterial cell derived from the B strain. It has defects of Lon protease and ompT outer membrane protease. It is commonly used for recombinant protein expression because it normally brings stability to expressed proteins. BL21 is useful for protein expression with pCold I-IV DNA and pCold TF DNA. But this competent E. coli cell is not intended for a protein expression system using T7 promoter such as pET system. The reason behind this is BL21 does not express T7 RNA polymerase. Additionally, it is not recommended to use for construction or preparation of plasmid since it does not have recA mutation.

BL21 was first described by Studier in 1986 after various modifications of B line. BL21 cells are deficient in the LON protease, which degrades many foreign proteins. Furthermore, it is missing another gene that codes for the outer membrane protease (OmpT) whose function is to degrade extracellular proteins. A lack of these proteins triggers the successful production of foreign protein in E. coli BL21 cells. Furthermore, hsdSB mutation in these cells prevents foreign DNA methylation and disruption in the BL21 cells.

What is DH5 Alpha?

DH5 Alpha is a genetically engineered competent E. coli cell with recA1 mutation that is primarily used for plasmid transformation. DH5 Alpha E. coli cells are genetically engineered by American biologist Douglas Hanahan to maximize the efficiency of transformation. DH5 Alpha cell has three distinct mutations: recA1, endA1, and lacZΔM15. recA1 is a single point mutation that replaces glycine 160 with and an aspartic acid residue in the recA polypeptide. This mutation disables the activity of the recombinases and inactivates homologous recombination. endA1 mutation inactivates an intracellular endonuclease which prevents it from degrading the inserted plasmid.

Moreover, lacZΔM15 mutation enables blue-white screening of transformed cells. These cells are competent cells. They are often used with calcium chloride transformation to insert the desired plasmid. It was identified by recent research that the DH5 Alpha cell with the Hanahan method was the most efficient competent cell for plasmid transformation.

What are the Similarities Between BL21 and DH5 Alpha?

• BL21 and DH5 Alpha are two genetically engineered E .coli
• Both are competent cells.
• They consist of distinct mutations.
• Both have no natural habitat.
• These are used for laboratory purposes such as expression studies and cloning procedures.

What is the Difference Between BL21 and DH5 Alpha?

BL21 is a protease deficient genetically engineered competent E. coli cell primarily used for protein expression. On the other hand, DH5 Alpha is a genetically engineered competent E. coli cell with recA1 mutation primarily used for plasmid transformation. So, this is the key difference between BL21 and DH5 Alpha. Furthermore, BL21 E. coli cell does not have recA1 mutation, while DH5 Alpha E. coli cell does have recA1 mutation.

The following infographic lists the differences between BL21 and DH5 Alpha in tabular form.

Summary – BL21 vs DH5 Alpha

The non-pathogenic strains of E. coli are genetically developed by scientists for laboratory expression studies and cloning purposes. BL21 and DH5 Alpha are two genetically engineered E. coli cells. BL21 is primarily used for protein expression studies. On the other hand, DH5 Alpha is primarily used for plasmid transformation purposes. Thus, this is the summary of the difference between BL21 and DH5 Alpha.

Reference:

1. “BL21 Competent E. Coli.” New England Biolabs: Reagents for the Life Sciences Industry.
2. “DH5-Alpha Chemically Competent E. Coli Cells.” GoldBio.

Image Courtesy:

1. “Analysis-of-Human-Cytomegalovirus-Encoded-SUMO-Targets-and-Temporal-Regulation-of-SUMOylation-of-pone.0103308.g001” By Kim E, Kim Y, Kim Y, Lee M, Hayward G, Ahn J – “Analysis of Human Cytomegalovirus-Encoded SUMO Targets and Temporal Regulation of SUMOylation of the Immediate-Early Proteins IE1 and IE2 during Infectio” PLOS ONE. DOI:10.1371/journal.pone.0103308. PMID 25050850. PMC: 4106884 (CC BY 4.0) via Commons Wikimedia
2. “DH5-alpha colonies growing on an amp plate” By balapagos (CC BY-SA 2.0) via Flickr