Biotechnology Bulletin ›› 2021, Vol. 37 ›› Issue (12): 252-264.doi: 10.13560/j.cnki.biotech.bull.1985.2021-0618

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Optimization and Application of Double-plasmid CRISPR-Cas9 System in Escherichia coli

WANG Kai-kai(), WANG Xiao-lu, SU Xiao-yun(), ZHANG Jie()   

  1. State Key Laboratory of Animal Nutrition,Institute of Animal Science,Chinese Academy of Agricultural Sciences,Beijing 100193
  • Received:2021-05-11 Online:2021-12-26 Published:2022-01-19
  • Contact: SU Xiao-yun,ZHANG Jie E-mail:kkw_2012@163.com;suxiaoyun@caas.cn;zhangjie09@caas.cn

Abstract:

In recent years,the CRISPR-Cas9(clustered regularly interspaced short palindromic repeats)system has been successfully exploited as versatile genome editing tools in various microorganisms. Because the application of CRISPR-Cas9 system is restricted only by the NGG of PAM(protospacer adjacent motif)sequence,therefore CRISPR-Cas9 system can theoretically edit any site or gene on the genome harboring NGG sequence. However,for the genes that have profound effects on cell growth and metabolism,the editing efficiency would be significantly reduced or even the mutants could not be obtained. Plenty of previous reports have provided valuable strategies to reduce the off-target effects of CRISPR-Cas9 system,but the reduction of editing efficiency is far from being solved. In this study,an efficient double- plasmid CRISPR-Cas9 system was established by using plasmids with different copy numbers to regulate the concentration of homology arms and the expression of Cas9 protein and gRNA,which would make them work more collaboratively for the gene editing purpose. The experimental results showed that the pfkA(6-phosphofructokinase isozyme 1)and pfkB(6-phosphofructokinase isozyme 2)genes in glycolysis pathway and the zwf(Glucose-6-phosphate 1-dehydrogenase)gene in pentose phosphate pathway were successfully deleted using the optimized double-plasmid CRISPR-Cas9 system,with the gene deletion efficiency of up to 100%;the nagABE gene cluster was also successfully replaced by glycerol kinase gene glpK,with the gene integration efficiency of 10%. By contrast,when using the single-plasmid CRISPR-Cas9 system,the pfkB gene deletion and glpK gene integration were successful in double-plasmid CRISPR-Cas9 system,and the efficiency of deleting pfkA and zwf increased by 31% and 63% respectively. The differences in carbon source utilization between mutant and wild-type strains further indicated that the gene editing efficiency was associated with special gene activity. Results from this study demonstrated that the sufficient target gene homology arms and the over-expression of gRNA may efficiently enhance the gene editing efficiency of CRISPR-Cas9 system.

Key words: CRISPR-Cas9 system, Escherichia coli, gene editing, double-plasmid system