CRISPR-Cas9 is a genome editing system. CRISPR systems provides immunity to bacteria and archaea from viruses and has been adapted for use as a genome editing tool capable of knocking out genes and rewriting genetic sequences in animal, plant and fungi. CRISPR-Cas9 is being adapted to other applications outside genome editing.
Cas9 is the nuclease enzyme that does the cutting in the Type II CRISPR systems used by Streptococcus thermophilis . The function of Clustered Regularly Interspersed Short Palindromic Repeats (CRISPR) sequences that are part of a bacterial immune system, was discovered in the yogurt bacteria Streptococcus thermophilus . Phillipe Horvath and Rodolphe BarrangouRodolphe Barrangou of Danisco (later DuPont) made that discovery and in 2007 reported in Science that the bacteria incorporate sequences from phage viruses they have been exposed to as spacers in the CRISPR region which gave the bacteria resistance to those phage viruses . DuPont has patented a technique of exposing bacteria to different phage viruses and uses CRISPR sequences to tell them which ones have acquired resistance, something that helps them avoid phage viruses spoiling their yogurt .