Most living organisms require zinc for survival; however, excessive amounts of this trace element can be toxic. Therefore, the frequent fluctuations of salivary zinc, caused by the low physiological level and the frequent introduction of exogenous zinc ions, present a serious challenge for bacteria colonizing the oral cavity. Streptococcus mutans is considered one of the main bacterial pathobiont in dental caries. Here, we verified the role of a P-type ATPase ZccE as the main zinc-exporting transporter in S. mutans and delineated the effects of zinc toxification caused by zccE deletion in the physiology of this bacterium. The deletion of the gene zccE severely impaired the ability of S. mutans to grow under high zinc stress conditions. Intracellular metal quantification using inductively coupled plasma optical emission spectrometer revealed that the zccE mutant exhibited approximately two times higher zinc accumulation than the wild type when grown in the presence of a subinhibitory zinc concentration. Biofilm formation analysis revealed less single-strain biofilm formation and competitive weakness in the dual-species biofilm formed with Streptococcus sanguinis for zccE mutant under high zinc stress. The quantitive reverse transcription polymerase chain reaction test revealed decreased expressions of gtfB, gtfC, and nlmC in the mutant strain under excessive zinc treatment. Collectively, these findings suggest that ZccE plays an important role in the zinc detoxification of S. mutans and that zinc is a growth-limiting factor for S. mutans within the dental biofilm.

中文翻译：

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ZccE，一种有助于变异链球菌生物膜形成和竞争力的 P 型 ATP 酶

大多数生物体都需要锌才能生存；但是，过量的这种微量元素可能有毒。因此，由于生理水平低下和外源锌离子的频繁引入而导致的唾液锌的频繁波动，对口腔定植的细菌提出了严峻的挑战。变形链球菌被认为是龋齿的主要致病菌之一。在这里，我们验证了 P 型 ATP 酶 ZccE 作为变形链球菌中主要锌输出转运蛋白的作用，并描述了由zccE缺失引起的锌中毒在该细菌生理学中的作用。基因zccE的缺失严重损害了S. mutans的能力在高锌胁迫条件下生长。使用电感耦合等离子体发射光谱仪对细胞内金属进行定量表明，当在亚抑制性锌浓度下生长时，zccE突变体的锌积累量比野生型高约两倍。生物膜形成分析表明，在高锌胁迫下，zccE突变体的单菌株生物膜形成较少，而血链球菌形成的双物种生物膜存在竞争弱点。定量逆转录聚合酶链反应检测显示gtfB、gtfC和nlmC的表达降低在过量锌处理下的突变菌株中。总的来说，这些发现表明 ZccE 在变形链球菌的锌解毒中起重要作用，并且锌是牙齿生物膜内变形链球菌的生长限制因子。