变异链球菌sepM基因中存在与变链素IV形成相关的突变类型

Association of sepM gene mutation with mutacin IV production by Streptococcus mutans

目的了解sepM基因在变异链球菌临床株中的突变类型及其分布特征;探索sepM基因突变与变异链球菌变链素IV形成能力的关系。方法采用抑菌圈法检测80株变异链球菌临床株的变链素IV形成能力,根据核心基因组多位点序列分型方法构建这80株变异链球菌临床株的最小生成树,根据最大似然法构建这80个样本的进化树。采用GeneMarkS软件预测这些菌株的编码基因,并将预测到的基因与参考基因组UA159的sepM基因序列进行比对,了解sepM基因在变异链球菌临床株中的突变类型及其分布特征。通过分析变链素IV形成组和无变链素IV形成组菌株中差异分布的突变类型及比较突变组和无突变组菌株中抑菌圈的大小,明确与变链素IV形成相关的突变类型。结果 80株变异链球菌临床株中有变链素IV形成(变链素IV形成组)和无变链素IV形成(无变链素IV形成组)的菌株各25和55株。最小生成树结果提示变链素IV形成组菌株之间的等位基因差异少于变链素IV形成组和无变链素形成组组间菌株,并且变链素IV形成组菌株间起源类似。80株变异链球菌临床株中共检测到34个单碱基突变位点,其中有4个碱基突变(C31T、G533A、C756T、C1036T)在组间存在差异(P分别为0.001、<0.001、0.025及0.003)。这些差异分布的突变均与变链素IV的形成呈正相关。结论变异链球菌临床株sepM基因中存在与变链素IV形成相关的突变类型。

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.Methods 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.Results 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 IV producing 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.Conclusion sepM gene mutations that affect the capacity of mutacin IV production are present in the clinical strains of S.mutans.