Mutacin IV

Objective: To investigate the types of sepM gene mutations and their distribution in clinical isolates of Streptococcus mutans (S. mutans) and explore the association of sepM gene mutation with the capacity of mutacin Ⅳ production by S. mutans. Objective: We assessed the capacity of mutacin Ⅳ production in 80 clinical isolates of S. mutans using an inhibition zone assay. The minimum spanning tree and phylogenetic tree of these isolates were constructed using core genome multilocus sequence typing and maximum likelihood method, respectively. GeneMarkS software was used to predict the coding genes of these isolates, and the predicted genes were blasted against the sepM gene sequence of the reference genome UA159 to determine sepM gene mutations and their distribution characteristics in the clinical isolates. The mutation types affecting mutacin Ⅳ production were identified by analyzing the differentially distributed mutations between mutacin Ⅳ-producing isolates and mutacin Ⅳ-free isolates and by comparing the inhibition zones between isolates with sepM gene mutations and those without mutations. Objective: Among the 80 clinical isolates of S. mutans, 25 isolates were capable of mutacin Ⅳ production and 55 did not produce mutacin Ⅳ. The minimum spanning tree showed that the allelic differences were less among the mutacin Ⅳproducing isolates than among the mutacin Ⅳ-free isolates, and the origins of the mutacin Ⅳ-producing isolates were similar. We identified a total of 34 single base mutations in the 80 clinical isolates, and among them, C31T (P=0.001), G533A (P < 0.001), C756T (P=0.025), and C1036T (P=0.003) showed significant differential distributions between the mutacin Ⅳ-producing and mutacin Ⅳ-free isolates. These differentially distributed mutations were positively correlated with the capacity of mutacin Ⅳ production of the bacteria.

Objective: To analyze the role of small RNA srn821798 in posttranscriptional regulation of mutacin IV expression in Streptococcus mutans. Methods: The potential target genes of srn821978 were predicted using RNAhybrid, RNAPredator and IntaRNA. We collected 10 Streptococcus mutans (S.muans) strains with high expression of mutacin IV and another 10 S.muans strains that did not express mutacin IV screened by inhibition zone test, and the expression levels of srn821798 and the candidate target genes in these strains were detected by qPCR. Using synthesized mimics and inhibitors of srn821798, we constructed S.muans strains with high or low srn821798 expression via electroporation based on the standard strain of S.muans UA159, and analyzed the expression levels of srn821798 and its candidate target genes in these strains. We also examined the binding ability of srn821798 to its target gene sepM using electrophoresis and a dual- luciferase reporter system. Results: The expression levels of the candidate target genes of srn821798 including sepM, comD, comE, nlmA and nlmB were significantly higher while the expression level of srn821798 was significantly lower in clinical S.muans strains with high expression of mutacin IV than in those without mutacin IV expression (P < 0.05). Although the expression levels of the candidate target genes in strains with up- regulated or down- regulated srn821798 expression did not differ significantly from those in the standard strain, the expression level of sepM showed a trend of differential distribution, and srn821798 was predicted to have a strong binding ability to sepM action site.

Streptococcus mutans (S. mutans) is a serious microbe causing dental caries. Mutacin IV is an effective bacteriocin produced by S. mutans to antagonize numerous non-mutans streptococcal species. However, the posttranscriptional regulation of mutacin IV remains unclear. This study aimed to analyze the effect of small RNA srn225147 on mutacin IV. The functional prediction suggested that srn225147 is involved in the production of mutacin IV, an important secondary metabolite. According to RNAhybrid and RNAPredator prediction, the mutacin IV formation-associated gene comD is a target of srn225147. We further analyzed the roles of srn225147 and comD in 20 S. mutans clinical strains with high production of mutacin IV (High-IV group) and lacking mutacin IV (None-IV group). Levels of comD expression were significantly higher in the High-IV group, whereas the Non-IV group showed relatively higher expression of srn225147, with a negative correlation observed between srn225147 and comD. Moreover, compared to the mimic negative control (NC) group, comD expression was decreased at 400-fold srn225147 overexpression but increased at approximately 1400-fold overexpression. Although the production of mutacin IV in the 1400-fold change srn225147 mimic group was larger than that in the 400-fold change mimic group, there was no significant difference in the production of mutacin IV between the srn225147 mimic group and mimic NC group. These results indicate that srn225147 has a two-way regulation effect on the expression of comD but that its regulation in the production of mutacin IV is weak.