Expression of a cryptic secondary sigma factor gene unveils natural competence for DNA transformation in Staphylococcus aureus.
Expression of a cryptic secondary sigma factor gene unveils natural competence for DNA transformation in Staphylococcus aureus.
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DOI：
10.1371/journal.ppat.1003003
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发表时间：
2012
期刊：
影响因子：
6.7
通讯作者：
Msadek T
中科院分区：
文献类型：
--
作者：
Morikawa K;Takemura AJ;Inose Y;Tsai M;Nguyen Thi le T;Ohta T;Msadek T
作为一种主要的人类病原体，金黄色葡萄球菌是否能够发展出通过DNA转化的自然能力一直是一个问题。我们之前的研究表明，一种新的葡萄球菌次级sigma因子（SigH）可能是能力发展的关键组成部分，但相应的基因似乎是隐藏的，因为在标准实验室条件下的生长过程中无法检测到其表达。在这里，我们发现了两种不同的机制，允许在一小部分细菌细胞群中激活叹息的产生。第一种是染色体基因重复重排以低频率自发发生[≤10−5]，产生新的嵌合性sigH基因的表达。第二种涉及通过上游反向重复序列的转录后调控，有效地抑制了叹息基因的表达。重要的是，我们首次证明了产生活性叹息的金黄色葡萄球菌细胞能够通过质粒或染色体DNA进行转化，这需要表达受叹息控制的能力基因。此外，利用N315 MRSA菌株的DNA，我们成功地通过自然转化将全长SCCmecII元件转移到甲氧西林敏感菌株中，从而使所得到的金黄色葡萄球菌转化物具有甲氧西林抗性。综上所述，我们提出了一个独特的葡萄球菌能力调控模型，该模型可以帮助解释这种重要病原体通过水平基因转移获得抗生素抗性基因。金黄色葡萄球菌是引起广泛感染的主要人类病原体，多种抗生素耐药菌株的出现强调了这一点，全世界高达60%的菌株对甲氧西林耐药（耐甲氧西林金黄色葡萄球菌或MRSA）。事实上，与mrsa相关的感染现在是美国死亡的主要原因之一，突出表明这种细菌对人类健康构成的威胁越来越大。许多细菌有能力通过摄取细胞外DNA获得新的遗传特征，包括抗生素耐药性，这种现象被称为自然遗传转化或能力。我们已经表明，叹息葡萄球菌sigma因子可能是能力发展的关键组成部分，但其基因在标准实验室条件下不表达。在这里，我们发现了两种不同的机制，允许激活金黄色葡萄球菌的叹息生产：染色体基因重复重排和通过上游反向重复序列的转录后调控。重要的是，我们首次证明了金黄色葡萄球菌细胞产生活性的SigH能够通过质粒或染色体DNA自然转化，并且我们能够通过染色体DNA转化赋予甲氧西林对甲氧西林敏感菌株的抗性。金黄色葡萄球菌依赖叹气的能力发展可以帮助解释抗生素抗性基因的获得和所谓的“超级细菌”的兴起。
It has long been a question whether Staphylococcus aureus, a major human pathogen, is able to develop natural competence for transformation by DNA. We previously showed that a novel staphylococcal secondary sigma factor, SigH, was a likely key component for competence development, but the corresponding gene appeared to be cryptic as its expression could not be detected during growth under standard laboratory conditions. Here, we have uncovered two distinct mechanisms allowing activation of SigH production in a minor fraction of the bacterial cell population. The first is a chromosomal gene duplication rearrangement occurring spontaneously at a low frequency [≤10−5], generating expression of a new chimeric sigH gene. The second involves post-transcriptional regulation through an upstream inverted repeat sequence, effectively suppressing expression of the sigH gene. Importantly, we have demonstrated for the first time that S. aureus cells producing active SigH become competent for transformation by plasmid or chromosomal DNA, which requires the expression of SigH-controlled competence genes. Additionally, using DNA from the N315 MRSA strain, we successfully transferred the full length SCCmecII element through natural transformation to a methicillin-sensitive strain, conferring methicillin resistance to the resulting S. aureus transformants. Taken together, we propose a unique model for staphylococcal competence regulation by SigH that could help explain the acquisition of antibiotic resistance genes through horizontal gene transfer in this important pathogen. Staphylococcus aureus is a major human pathogen responsible for a broad spectrum of infections, emphasized by the emergence of multiple antibiotic-resistant strains with up to 60% of strains worldwide resistant to methicillin (Methicillin Resistant Staphylococcus aureus or MRSA). Indeed, MRSA-related infections are now one of the leading causes of death in the USA, highlighting the growing threat this bacterium poses to human health. Many bacteria have the ability to acquire novel genetic characteristics, including antibiotic resistance, through the uptake of extracellular DNA, a phenomenon known as natural genetic transformation or competence. We have shown that the SigH staphylococcal sigma factor is a likely key component for competence development, but that its gene is not expressed under standard laboratory conditions. Here, we have uncovered two distinct mechanisms allowing activation of SigH production in S. aureus: a chromosomal gene duplication rearrangement and post-transcriptional regulation through an upstream inverted repeat sequence. Importantly, we have demonstrated for the first time that S. aureus cells producing active SigH become competent for natural transformation by plasmid or chromosomal DNA, and we were able to confer methicillin resistance to a methicillin-sensitive strain by transformation with chromosomal DNA. SigH-dependent competence development in S. aureus could help explain the acquisition of antibiotic resistance genes and the rise of the so-called “superbug."
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