Basal levels of (p)ppGpp in Enterococcus faecalis: the magic beyond the stringent response.
Basal levels of (p)ppGpp in Enterococcus faecalis: the magic beyond the stringent response.
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DOI：
10.1128/mbio.00646-13
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发表时间：
2013-09-24
期刊：
影响因子：
6.4
通讯作者：
Lemos JA
中科院分区：
文献类型：
--
作者：
Gaca AO;Kajfasz JK;Miller JH;Liu K;Wang JD;Abranches J;Lemos JA
由alarmone（p）ppGpp介导的严格反应（SR）是保守的细菌适应系统，其控制在不利条件下生存所必需的广泛代谢改变。在粪肠球菌中，（p）ppGpp的产生由双功能蛋白RSH（“Rel SpoT同源物”;也称为RelA）和单功能合成酶RelQ控制。先前对缺乏rsh、relQ或两者的粪肠球菌菌株的表征揭示，RSH负责SR的激活，并且（p）ppGpp产生的改变对细菌应激存活和毒力产生负面影响。尽管其作为SR的效应器的作用得到了很好的表征，但（p）ppGpp在平衡生长期间的意义仍然知之甚少。产生不同基础量（p）ppGpp的粪肠球菌菌株的微阵列鉴定了由（p）ppGpp的适度变化调节的几种基因和途径。值得注意的是，参与能量产生的许多基因的表达在BERSH BERRELQ [（p）ppGpp 0]菌株中被诱导，这表明缺乏基础（p）ppGpp使细胞处于“转录松弛”状态。在（p）ppGpp 0菌株的发酵概况和增加生产的H2 O2证实了观察到的转录变化。我们证实，类似于在枯草芽孢杆菌中看到的，（p）ppGpp直接抑制参与GTP生物合成的酶的活性，并且（p）ppGpp的完全丧失导致GTP稳态失调。最后，我们发现（p）ppGpp与抗生素存活率的相关性与SR无关，而是与基础（p）ppGpp库有关。总的来说，这项研究强调了平衡生长条件下基础（p）ppGpp池的关键作用，但仍未得到充分重视。耐药性细菌感染继续对公共卫生构成重大威胁，因为它限制了护理提供者可用的治疗选择。由统称为（p）ppGpp的两个修饰的鸟嘌呤核苷酸的积累介导的严格反应（SR）是高度保守的应激反应，其广泛地将细菌生理学重塑为存活状态。鉴于SR与细菌在抗生素治疗中存活的能力的强相关性以及（p）ppGpp产生与细菌感染性的直接关联，了解细菌如何产生和利用（p）ppGpp可能揭示新的抗微生物疗法开发的潜在靶点。使用多重耐药病原体粪肠球菌作为模型，我们表明，（p）ppGpp水平的微小变化，远低于触发SR所需的浓度，严重影响细菌代谢和抗生素的生存。我们的研究结果强调了基础（p）ppGpp水平对细菌代谢平衡和应激耐受性的贡献。
The stringent response (SR), mediated by the alarmone (p)ppGpp, is a conserved bacterial adaptation system controlling broad metabolic alterations necessary for survival under adverse conditions. In Enterococcus faecalis, production of (p)ppGpp is controlled by the bifunctional protein RSH (for “Rel SpoT homologue”; also known as RelA) and by the monofunctional synthetase RelQ. Previous characterization of E. faecalis strains lacking rsh, relQ, or both revealed that RSH is responsible for activation of the SR and that alterations in (p)ppGpp production negatively impact bacterial stress survival and virulence. Despite its well-characterized role as the effector of the SR, the significance of (p)ppGpp during balanced growth remains poorly understood. Microarrays of E. faecalis strains producing different basal amounts of (p)ppGpp identified several genes and pathways regulated by modest changes in (p)ppGpp. Notably, expression of numerous genes involved in energy generation were induced in the ∆rsh ∆relQ [(p)ppGpp0] strain, suggesting that a lack of basal (p)ppGpp places the cell in a “transcriptionally relaxed” state. Alterations in the fermentation profile and increased production of H2O2 in the (p)ppGpp0 strain substantiate the observed transcriptional changes. We confirm that, similar to what is seen in Bacillus subtilis, (p)ppGpp directly inhibits the activity of enzymes involved in GTP biosynthesis, and complete loss of (p)ppGpp leads to dysregulation of GTP homeostasis. Finally, we show that the association of (p)ppGpp with antibiotic survival does not relate to the SR but rather relates to basal (p)ppGpp pools. Collectively, this study highlights the critical but still underappreciated role of basal (p)ppGpp pools under balanced growth conditions. Drug-resistant bacterial infections continue to pose a significant public health threat by limiting therapeutic options available to care providers. The stringent response (SR), mediated by the accumulation of two modified guanine nucleotides collectively known as (p)ppGpp, is a highly conserved stress response that broadly remodels bacterial physiology to a survival state. Given the strong correlation of the SR with the ability of bacteria to survive antibiotic treatment and the direct association of (p)ppGpp production with bacterial infectivity, understanding how bacteria produce and utilize (p)ppGpp may reveal potential targets for the development of new antimicrobial therapies. Using the multidrug-resistant pathogen Enterococcus faecalis as a model, we show that small alterations to (p)ppGpp levels, well below concentrations needed to trigger the SR, severely affected bacterial metabolism and antibiotic survival. Our findings highlight the often-underappreciated contribution of basal (p)ppGpp levels to metabolic balance and stress tolerance in bacteria.