Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated proteins (Cas) together comprise the CRISPR-Cas system. In bacteria, this system confers an adaptive immunity against invading mobile elements such as viruses and plasmids. The CRISPR-Cas9 system has emerged as a programmable and versatile tool for precise genome editing in a wide variety of organisms. In contrast, research conducted in the Department of Animal Sciences at Colorado State University focused on exploiting the CRISPR-Cas9 system for selective killing of a bacterial pathogen relevant to meat safety by targeting specific virulence genes.
The CRISPR-Cas9 system contains two key factors: the Cas9 protein, which can cleave double-stranded DNA, and guide RNA (gRNA) which is transcribed from the CRISPR sequence (Figure 1). The function of the Cas9 protein is like a pair of scissors. Guide RNA is complimentary to the target sequence and is able to guide the Cas9 protein to the sequence-specific site of cleavage. The interaction between the Cas9 protein and the target DNA leads to the creation of a double-stranded DNA break. Such DNA cleavage can be used either to edit or to kill organisms. In recent studies, CRISPR-Cas9 systems have been explored for developing sequence-specific antimicrobials, which means that by targeting the cleavage of specific sites in a genome of interest, the kill should be limited to only organisms containing that specific gene or genes.