**2. Mechanism of CRISPR/Cas9 system**

The CRISPR/Cas9 system is a type II adaptive immune system in bacteria and archaea, protecting them against invading nucleic acid such as virus by cleaving the foreign DNA through specific sequence recognition [29]. The immunity is acquired through the integration of short fragment of the foreign DNA as spacer between two adjacent repeats at the proximal end of a CRISPR locus [29]. The bacterial CRISPR/Cas9 system involves three stepwise processes, namely acquisition, biogenesis and interference.
