| 摘要: | 感染性心內膜炎 (Infective endocarditis) 是一種感染性的心血管疾病，具有很高的復發率及死亡率。轉糖鏈球菌是引起齲齒的主要病原體，也是感染性心內膜炎的伺機性病原體。相較於在口腔中生物膜的形成依賴於葡聚醣，心臟瓣膜上細胞外DNA (eDNA) 依賴性的生物膜形成在感染性心內膜炎的發病機制中扮演至關重要的角色。而我們先前研究發現，細菌自體溶解素 (AtlA) 在感染性心內膜炎中eDNA依賴性的生物膜形成中發揮關鍵作用。此外，我們發現血漿中的鈣離子透過促進AtlA 的 N 端加工來增強細菌 eDNA 釋放和 eDNA 依賴性生物膜形成，進而形成AtlA 的成熟型態。為了研究鈣離子調節 AtlA 成熟的機制，先前的研究分析了 atlA操縱組其中各自的作用，並確定 thmA 是 AtlA 成熟和生物膜形成的潛在貢獻者。然而在本篇研究發現是由 thmA 極性突變體表現出形成 AtlA 成熟型態和生物膜的能力降低，而非 thmA 非極性突變體，而這也代表下游基因 Smu. 694、Smu. 695 和Smu. 696 有機會參與 AtlA 介導的生物膜形成。有趣的是，三種單一突變株只有Smu. 695 突變體形成生物膜的能力下降。更有趣的是，將 thmA-Smu. 694 回補至thmA 極性突變株會造成細菌彼此分離和形成生物膜的能力下降。若將 thmA- Smu.695 回補至 thmA 極性突變株後，可以發現形成 AtlA 成熟型態和形成生物膜的能力都有恢復。此外，將 Smu. 695 回補至 Smu. 695 突變體和 thmA 極性突變體皆會增加生物膜。同時，藉由反轉錄聚合?連鎖反應證明 thmA 到 Smu. 696 四個基因可成為一組操縱組，且屬於 atlA 操縱組。這些發現表示 Smu. 694 和 Smu. 695 在參與AtlA 依賴性生物膜形成中，兩者作用相反。Smu. 694 和 Smu. 695 在 AtlA 成熟和eDNA 依賴性生物膜形成中具有一定影響性以及潛在機制和其他功能。
Infective endocarditis (IE) is an infectious disease of the cardiovascular system that carries a high recurrence and mortality rate. Streptococcus mutans, a major pathogen for causing dental caries, is also an opportunistic pathogen for IE. In contrast to the glucandependent biofilm formation in the oral cavity, to develop the extracellular DNA (eDNA)-dependent biofilm on heart valves plays a crucial role in the pathogenesis of IE. Our previous studies have demonstrated that the bacterial autolysin (AtlA) plays a pivotal role in eDNA-dependent biofilm formation in IE. Additionally, we found that a plasma component, calcium ions, enhances bacterial eDNA release and eDNA-dependent biofilm formation by promoting the N-terminal processing of AtlA, resulting in the maturation form of AtlA. To investigate the mechanism of calcium ions-regulated AtlA maturation,
a previous study analyzed the roles of the components in the atlA operon and identified thmA as a potential contributor to AtlA maturation and biofilm formation. However, our study revealed that only the thmA polar mutant, not the thmA nonpolar mutant, exhibited a reduced ability to form the mature form of AtlA and the biofilm. This suggests the involvement of downstream genes, including Smu. 694, Smu. 695, and Smu. 696, in AtlAmediated biofilm formation. Interestingly, only the Smu. 695-deficient mutant of these three single-mutant strains showed reduction in their ability to form the biofilm. More interestingly, Complementation of thmA-Smu. 694 in the thmA polar mutant strain
reduced the bacterial ability to separate from each other and form the biofilm, while complementation of thmA-Smu. 695 restored the ability of the thmA polar mutant strain to form the mature form of AtlA and to develop a biofilm. In addition, complementation of Smu. 695 in both Smu. 695-deficient mutant and thmA polar mutant strain enhance the biofilm. Meanwhile, thmA-Smu. 696 was a four-gene operon and belonged to atlA operon confirmed by RT-PCR. These findings suggest opposite roles for Smu. 694 and Smu. 695 in AtlA-dependent biofilm formation. Smu. 694 and Smu. 695 had implications as well as potential mechanisms and other functions in AtlA maturation and eDNA-dependent
biofilm formation. |
