Deletion of csn2 gene affects acid tolerance and exopolysaccharide synthesis in Streptococcus mutans

Csn2 is an important protein of the CRISPR-Cas system. The physiological function of this protein and its regulatory role inStreptococcus mutans, as the primary causative agent of human dental caries, is still unclear. In this study, we investigated whethercsn2deletion would affectS. mutansphysiology and virulence gene expression. We used microscopic imaging, acid killing assays, pH drop, biofilm formation, and exopolysaccharide (EPS) production tests to determine whethercsn2deletion influencedS. mutanscolony morphology, acid tolerance/production, and glucan formation abilities. Comparisons were made between quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) data from the UA159 andcsn2deletion strain to determine the impact ofcsn2knockout onS. mutansgene expression. The results showed that deletion ofS. mutanscsn2changed its colony morphotype and made it more sensitive to acid. The expression levels of aciduricity genes, includingleuA,leuB,leuC, andleuD, were significantly down-regulated. Acid adaptation restored the aciduricity ofcsn2mutant and enhanced the ability to synthesize EPS. The expression levels of EPS synthesis-related genes, includinggtfCandgtfD, were significantly up-regulated after acid adaptation. In summary, deletion ofS. mutanscsn2exerted multiple effects on the virulence traits of this pathogen, including acid tolerance and EPS formation, and that these alterations could partially be attributed to changes in gene expression upon loss ofcsn2. Understanding the function ofcsn2inS. mutansmight lead to novel strategies to prevent or treat imbalances in oral microbiota that may favor diseases.