School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia.
Infect Immun. 2011 Nov;79(11):4550-8. doi: 10.1128/IAI.05644-11. Epub 2011 Aug 29.
During infection, Streptococcus pneumoniae exists mainly in sessile biofilms rather than in planktonic form, except during sepsis. The capacity to form biofilms is believed to be important for nasopharyngeal colonization as well as disease pathogenesis, but relatively little is known about the regulation of this process. Here, we investigated the effect of exogenous iron [Fe(III)] as well as the role of luxS (encoding S-ribosylhomocysteine lyase) on biofilm formation by S. pneumoniae D39. Fe(III) strongly enhanced biofilm formation at concentrations of ≥50 μM, while Fe(III) chelation with deferoxamine was inhibitory. Importantly, Fe(III) also upregulated the expression of luxS in wild-type D39. A luxS-deficient mutant (D39luxS) failed to form a biofilm, even with Fe(III) supplementation, whereas a derivative overexpressing luxS (D39luxS+) exhibited enhanced biofilm formation capacity and could form a biofilm without added Fe(III). D39luxS exhibited reduced expression of the major Fe(III) transporter PiuA, and the cellular [Fe(III)] was significantly lower than that in D39; in contrast, D39luxS+ had a significantly higher cellular [Fe(III)] than the wild type. The release of extracellular DNA, which is an important component of the biofilm matrix, also was directly related to luxS expression. Similarly, genetic competence, as measured by transformation frequency as well as the expression of competence genes comD, comX, comW, cglA, and dltA and the murein hydrolase cbpD, which is associated with fratricide-dependent DNA release, all were directly related to luxS expression levels and were further upregulated by Fe(III). Moreover, mutagenesis of cbpD blocked biofilm formation. We propose that competence, fratricide, and biofilm formation are closely linked in pneumococci, and that luxS is a central regulator of these processes. We also propose that the stimulatory effects of Fe(III) on all of these parameters are due to the upregulation of luxS expression, and that LuxS provides for a positive Fe(III)-dependent amplification loop by increasing iron uptake.
在感染期间，肺炎链球菌主要以静止的生物膜形式存在，而不是浮游形式，除非发生败血症。形成生物膜的能力被认为对鼻咽定植以及疾病发病机制很重要，但相对而言，人们对这一过程的调控知之甚少。在这里，我们研究了外源性铁[Fe(III)]以及 luxS（编码 S-核糖基高半胱氨酸裂解酶）对肺炎链球菌 D39 生物膜形成的影响。Fe(III)在浓度≥50 μM 时强烈促进生物膜形成，而用去铁胺螯合 Fe(III)则具有抑制作用。重要的是，Fe(III)也上调了野生型 D39 中 luxS 的表达。luxS 缺陷突变体（D39luxS）即使补充 Fe(III)也无法形成生物膜，而过表达 luxS 的衍生物（D39luxS+）则表现出增强的生物膜形成能力，并且可以在没有添加 Fe(III)的情况下形成生物膜。D39luxS 表现出主要 Fe(III)转运蛋白 PiuA 的表达减少，细胞内[Fe(III)]明显低于 D39；相比之下，D39luxS+的细胞内[Fe(III)]明显高于野生型。细胞外 DNA 的释放，这是生物膜基质的一个重要组成部分，也与 luxS 的表达直接相关。同样，遗传转化能力，通过转化频率以及与细胞自溶相关的 DNA 释放有关的 comD、comX、comW、cglA 和 dltA 以及 murein 水解酶 cbpD 的表达来衡量，都与 luxS 的表达水平直接相关，并进一步被 Fe(III)上调。此外，cbpD 的突变阻止了生物膜的形成。我们提出，遗传转化能力、细胞自溶和生物膜形成在肺炎链球菌中密切相关，而 luxS 是这些过程的中央调节剂。我们还提出，Fe(III)对所有这些参数的刺激作用是由于 luxS 表达的上调，而 LuxS 通过增加铁摄取提供了一个积极的 Fe(III)依赖性放大环。
