Extracellular DNA (eDNA) is a biofilm component that contributes to the formation and structural stability of biofilms. Streptococcus mutans, a major cariogenic bacterium, induces eDNA-dependent biofilm formation under specific conditions. Since cell death can result in the release and accumulation of DNA, the dead cells in biofilms are a source of eDNA. However, it remains unknown how eDNA is released from dead cells and is localized within S. mutans biofilms. We focused on cell death induced by the extracellular signaling peptide called competence-stimulating peptide (CSP). We demonstrate that nucleic acid release into the extracellular environment occurs in a subpopulation of dead cells. eDNA production induced by CSP was highly dependent on the lytF gene, which encodes an autolysin. Although lytF expression was induced bimodally by CSP, lytF-expressing cells further divided into surviving cells and eDNA-producing dead cells. Moreover, we found that lytF-expressing cells were abundant near the bottom of the biofilm, even when all cells in the biofilm received the CSP signal. Dead cells and eDNA were also abundantly present near the bottom of the biofilm. The number of lytF-expressing cells in biofilms was significantly higher than that in planktonic cultures, which suggests that adhesion to the substratum surface is important for the induction of lytF expression. The deletion of lytF resulted in reduced adherence to a polystyrene surface. These results suggest that lytF expression and eDNA production induced near the bottom of the biofilm contribute to a firmly attached and structurally stable biofilm.

中文翻译：

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变形链球菌生物膜中刺激能力的肽依赖性局部细胞死亡和细胞外DNA产生。

细胞外DNA（eDNA）是生物膜的组成部分，有助于生物膜的形成和结构稳定性。变形链球菌是一种主要的致癌细菌，在特定条件下可诱导eDNA依赖性生物膜形成。由于细胞死亡会导致DNA的释放和积累，因此生物膜中的死细胞是eDNA的来源。但是，如何从死亡细胞释放eDNA以及如何在变形链球菌生物膜中定位eDNA仍然是未知的。我们专注于由称为能力刺激肽（CSP）的细胞外信号肽诱导的细胞死亡。我们证明了释放到细胞外环境中的核酸发生在死亡细胞的亚群中。CSP诱导的eDNA产生高度依赖lytF基因，编码自溶素。尽管lytF表达是由CSP双峰诱导的，但表达lytF的细胞进一步分为存活细胞和产生eDNA的死亡细胞。而且，我们发现，即使当生物膜中的所有细胞都接收到CSP信号时，在生物膜的底部附近仍表达lytF的细胞大量存在。死细胞和eDNA也大量存在于生物膜底部附近。生物膜中表达lytF的细胞数量显着高于浮游培养中的数量，这表明与基底表面的粘附对于诱导lytF表达很重要。lytF的缺失导致对聚苯乙烯表面的附着力降低。这些结果表明，在生物膜底部附近诱导的lytF表达和eDNA产生有助于牢固附着和结构稳定的生物膜。