CRISPR-Cas9 Nickase-Assisted Genome Editing in Lactobacillus casei.

has drawn increasing attention as a health-promoting probiotic, while effective genetic manipulation tools are often not available, e.g., the single-gene knockout in still depends on the classic homologous recombination-dependent double-crossover strategy, which is quite labor-intensive and time-consuming. In the present study, a rapid and precise genome editing plasmid, pLCNICK, was established for genome engineering based on CRISPR-Cas9 In addition to the P-Cas9 and P-sgRNA (single guide RNA) expression cassettes, pLCNICK includes the homologous arms of the target gene as repair templates. The ability and efficiency of chromosomal engineering using pLCNICK were evaluated by in-frame deletions of four independent genes and chromosomal insertion of an enhanced green fluorescent protein (eGFP) expression cassette at the locus. The efficiencies associated with in-frame deletions and chromosomal insertion is 25 to 62%. pLCNICK has been proved to be an effective, rapid, and precise tool for genome editing in , and its potential application in other lactic acid bacteria (LAB) is also discussed in this study. The lack of efficient genetic tools has limited the investigation and biotechnological application of many LAB. The CRISPR-Cas9 nickase-based genome editing in , an important food industrial microorganism, was demonstrated in this study. This genetic tool allows efficient single-gene deletion and insertion to be accomplished by one-step transformation, and the cycle time is reduced to 9 days. It facilitates a rapid and precise chromosomal manipulation in and overcomes some limitations of previous methods. This editing system can serve as a basic technological platform and offers the possibility to start a comprehensive investigation on As a broad-host-range plasmid, pLCNICK has the potential to be adapted to other species for genome editing.