Problem with construction of deletion mutant (Bacteria)
Posted 20 April 2011 - 01:36 AM
I am trying to construct a few deletion mutants of Corynebacterium glutamicum using the integration vector pK19mobsacB. I amplified the gene having the desired deletion using overlapping pcr, cloned it into pK19mobsacB and transformed into E. coli S17-1.
The recombinant plasmid was introduced into Corynebacterium glutamicum using either electroporation or conjugation. After electroporation, the cells were plated in LBHIS/Km10 plates and I was getting very few number of colonies compared to that in conjugation. In the case of conjugation, the cells were plated in LB/Km/Nx plates and I got quite number of colonies within the second day of incubation itself.
For the double cross over, I followed two different protocols.
1. Picked up one of the kanamycin-resistant colonies and grew in BHI medium with 2% glucose and 5 mM sodium azide.
2. The cells were plated in LBHIS/Suc10 (10% sucrose) plates.
1. Picked up‘6’ colonies and put each in LB and cultivated o/n at 30℃
2. Plating: LB/suc10 (10-1 to 10-4 dilution)
Fifty colonies from LBHIS/Suc or LB/Suc10 were streak plated to LB plate and then to LB/Km10 plates. Unfortunately, all my colonies are kanamycin-resistant. It means that double cross over has not happened? Then how could the cells grow in sucrose medium? It is a bit cofusing to me (I have confirmed the sacB gene in the vector by sequencing it before starting the experiment). I did colony pcr to confirm the colonies and could know that all the colonies harbor the wild-type gene.I repeated the protocol many times, but the result is same.
Could anyone help me to solve this problem? I would really thankful to you.
Regards & Have a good day!!!
Posted 20 April 2011 - 06:55 AM
Posted 20 April 2011 - 04:45 PM
Yes, sacB is lethal to C. glutamicum in the presence of sucrose and the cells attain sucrose-resistance after second cross over.
Posted 21 April 2011 - 03:03 AM
Yes..SacB is expressed in C.glutamicum.