Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
PLoS One. 2012;7(6):e38453. doi: 10.1371/journal.pone.0038453. Epub 2012 Jun 7.
Mutation of the staphylococcal accessory regulator (sarA) limits biofilm formation in diverse strains of Staphylococcus aureus, but there are exceptions. One of these is the commonly studied strain Newman. This strain has two defects of potential relevance, the first being mutations that preclude anchoring of the fibronectin-binding proteins FnbA and FnbB to the cell wall, and the second being a point mutation in saeS that results in constitutive activation of the saePQRS regulatory system. We repaired these defects to determine whether either plays a role in biofilm formation and, if so, whether this could account for the reduced impact of sarA in Newman. Restoration of surface-anchored FnbA enhanced biofilm formation, but mutation of sarA in this fnbA-positive strain increased rather than decreased biofilm formation. Mutation of sarA in an saeS-repaired derivative of Newman (P18L) or a Newman saeRS mutant (ΔsaeRS) resulted in a biofilm-deficient phenotype like that observed in clinical isolates, even in the absence of surface-anchored FnbA. These phenotypes were correlated with increased production of extracellular proteases and decreased accumulation of FnbA and/or Spa in the P18L and ΔsaeRS sarA mutants by comparison to the Newman sarA mutant. The reduced accumulation of Spa was reversed by mutation of the gene encoding aureolysin, while the reduced accumulation of FnbA was reversed by mutation of the sspABC operon. These results demonstrate that saeRS and sarA act synergistically to repress the production of extracellular proteases that would otherwise limit accumulation of critical proteins that contribute to biofilm formation, with constitutive activation of saeRS limiting protease production, even in a sarA mutant, to a degree that can be correlated with increased enhanced capacity to form a biofilm. Although it remains unclear whether these effects are mediated directly or indirectly, studies done with an sspA::lux reporter suggest they are mediated at a transcriptional level.
葡萄球菌附属调节蛋白 (sarA) 的突变限制了多种金黄色葡萄球菌菌株的生物膜形成，但也有例外。其中之一是常见研究的 Newman 菌株。该菌株有两个潜在相关的缺陷，第一个缺陷是阻止纤维连接蛋白结合蛋白 FnbA 和 FnbB 锚定在细胞壁上的突变，第二个缺陷是 saeS 中的点突变导致 saePQRS 调控系统的组成性激活。我们修复了这些缺陷，以确定它们是否在生物膜形成中发挥作用，如果是，这是否可以解释 sarA 在 Newman 中的影响降低。表面锚定 FnbA 的恢复增强了生物膜的形成，但在这个 fnbA 阳性菌株中突变 sarA 反而增加了生物膜的形成，而不是减少。在 Newman 的 saeS 修复衍生物 (P18L) 或 Newman saeRS 突变体 (ΔsaeRS) 中突变 sarA 导致了与临床分离株观察到的类似的生物膜缺陷表型，即使没有表面锚定的 FnbA。这些表型与在 P18L 和 ΔsaeRS sarA 突变体中，与 Newman sarA 突变体相比，细胞外蛋白酶的产量增加以及 FnbA 和/或 Spa 的积累减少有关。与 aureolysin 基因的突变相比，降低 Spa 的积累被逆转，而降低 FnbA 的积累被 sspABC 操纵子的突变所逆转。这些结果表明，saeRS 和 sarA 协同作用，抑制细胞外蛋白酶的产生，否则会限制参与生物膜形成的关键蛋白的积累，即使在 sarA 突变体中，saeRS 的组成性激活也会限制蛋白酶的产生，这与增强形成生物膜的能力成正比。尽管尚不清楚这些影响是直接还是间接介导的，但使用 sspA::lux 报告基因的研究表明，它们是在转录水平上介导的。
