Response of Streptococcus pyogenes to Nutritional Stress

描述（由申请人提供）：化脓性链球菌（A组链球菌，GAS）引起人体各种感染，包括皮肤，喉咙，深层组织，甚至血液。虽然这些部位富含多肽和蛋白质，但这种多营养不良生物所必需的游离氨基酸并不丰富。对这种自然环境的适应性反应的分子细节尚未完全探索。因此，这种反应需要在一个将基本代谢过程与毒力基因表达联系起来的调控网络水平上加以理解，并使生物体能够以动态的方式利用富含蛋白质的宿主环境。基于近年来在GAS基因组学方面取得的进展，本研究提出(i)通过使用DNA微阵列技术进行全球转录分析，在全基因组范围内确定GAS氨基酸饥饿反应的广度。这种方法将允许描述严格（RelA+）和宽松菌株（RelA-）在实验室培养基中的氨基酸饥饿反应，以及在全面水平上模拟或构成体内情况的条件。CodY是一种多效性转录抑制因子，可感知细胞的营养状态，为了将这种严格的反应与CodY的活性联系起来，本研究提出（ii）确定CodY的靶基因及其转录模式作为相关决定的鸟苷多磷酸水平的函数。虽然这种方法可以在应答基因的转录调控水平上理解对营养应激的反应，但本研究的第三个目的是（iii）确定亚基因、基因和操纵子水平上的mRNA降解模式，并探索mRNA半衰期改变的分子机制。这将提供转录稳定性如何受到环境条件影响的信息。综上所述，这项研究应该产生一个全面的适应性反应网络，以应对GAS可能与其宿主相关的关键环境条件。这些知识将有助于了解致病机制，甚至可能导致治疗或预防链球菌感染的新方法。

DESCRIPTION (provided by applicant): Streptococcus pyogenes (group A streptococcus, GAS) causes various infections of humans including the skin, throat, deep tissue, and even the bloodstream. Although these sites are rich in peptides and proteins, free amino acids, which are essential for this polyauxotrophic organism, are not abundant. The molecular details of the adaptive response to such natural environments are incompletely explored. This response needs to be understood, therefore, at the level of a regulatory network that links basic metabolic processes to virulence gene expression and enables the organism in a dynamic way to take advantage of protein-rich host environments. Based on the advances made in the genomics of GAS in recent years, this study proposes to (i) determine the breadth of the amino acid starvation response of GAS on a genome-wide scale, by global transcription profiling using DNA microarray technology. This approach will allow description of the amino acid starvation response of stringent (RelA+) and relaxed strains (RelA-) in laboratory media as well as in conditions that mimic or constitute in-vivo situations at a comprehensive level. To link the stringent response to the activity of CodY, a pleiotropic transcriptional repressor that senses the nutritional state of the cell, this study proposes to (ii) identify the target genes of CodY and their transcription pattern as a function of the relA-determined guanosine polyphosphate level. While this approach will enable the response to nutritional stress to be understood at the level of transcriptional regulation of the responsive genes, the third aim of this study proposes to (iii) determine global mRNA degradation patterns at the sub-genic, genic and operonic levels and explore molecular mechanisms involved in the alteration of mRNA half-lives. This will provide information about how transcript stability is influenced by environmental conditions. Taken together, this research should result in a comprehensive network of adaptive responses to a key environmental condition that GAS may encounter in association with their host. This knowledge will help understand pathogenetic mechanisms and may even lead to new approaches for treatment or prevention of streptococcal infections.