Genome editing in Streptococcus mutans through self-targeting CRISPR arrays

Streptococcus mutans is the primary etiological agent of human dental caries. Its major virulence factors, glucosyltransferases (Gtfs), utilize sucrose to synthesize extracellular polysaccharides (EPS), leading to the formation of dental plaque biofilm. The current study was designed to develop a novel self-targeting gene editing technology that targeted gtfs to inhibit biofilms formation. The CRISPR-Cas system (ie, clustered regularly interspaced short palindromic repeat, with CRISPR-associated proteins) provides sequence-specific protection against foreign genetic materials in archaea and bacteria, and has been widely developed for genomic engineering. The first aim of this study was to test whether components of the CRISPR-Cas9 system from S mutans UA159 is necessary to defend against foreign DNA. The data showed that a suitable PAM site, tracrRNA, Cas9, and RNase III are indispensable elements to perform normal function of S mutans CRISPR-Cas9 system. Based on these results, we designed self-targeting CRISPR arrays (containing spacer sequences identifying with gtfB) and cloned them onto plasmids. Afterward, we transformed the plasmids and editing templates into UA159 (self-targeting) to acquire desired mutants. Our data showed that this technology performed well and was able to successfully edit gtfB or gtfBgtfC genes. This resulted in high reduction in EPS synthesis and was able to breakdown biofilm formation, which is also a promising tool for dental clinics in order to prevent the formation of S mutans biofilms in the future.