Chowdhury Nityananda, Kwan Brian W, Wood Thomas K
Department of Chemical Engineering, Pennsylvania, Pennsylvania State University, University Park, 16802-4400, USA.
Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania, 16802-4400, USA.
Sci Rep. 2016 Feb 3;6:20519. doi: 10.1038/srep20519.
Most bacterial cells are stressed, and as a result, some become tolerant to antibiotics by entering a dormant state known as persistence. The key intracellular metabolite that has been linked to this persister state is guanosine tetraphosphate (ppGpp), the alarmone that was first linked to nutrient stress. In Escherichia coli, ppGpp redirects protein production during nutrient stress by interacting with RNA polymerase directly and by inhibiting several proteins. Consistently, increased levels of ppGpp lead to increased persistence; but, the mechanism by which elevated ppGpp translates into persistence has not been determined. Hence, we explored persistence in the absence of ppGpp so that the underlying mechanism of persister cell formation could be explored. We found that persister cells still form, although at lower levels, in the absence of ppGpp. Additionally, the toxin/antitoxin systems that we investigated (MqsR, MazF, GhoT, and YafQ) remain able to increase persistence dramatically in the absence of ppGpp. By overproducing each E. coli protein from the 4287 plasmid vectors of the ASKA library and selecting for increased persistence in the absence of ppGpp (via a relA spoT mutant), we identified five new proteins, YihS, PntA, YqjE, FocA, and Zur, that increase persistence simply by reducing cell growth.
大多数细菌细胞都处于应激状态,因此,一些细菌通过进入一种称为持留态的休眠状态而对抗生素产生耐受性。与这种持留态相关的关键细胞内代谢物是四磷酸鸟苷(ppGpp),这种警报素最初与营养应激有关。在大肠杆菌中,ppGpp在营养应激期间通过直接与RNA聚合酶相互作用并抑制几种蛋白质来重新定向蛋白质合成。一致地,ppGpp水平的升高导致持留性增加;但是,ppGpp水平升高转化为持留性的机制尚未确定。因此,我们探索了在没有ppGpp的情况下的持留性,以便探究持留细胞形成的潜在机制。我们发现,在没有ppGpp的情况下,持留细胞仍然会形成,尽管形成水平较低。此外,我们研究的毒素/抗毒素系统(MqsR、MazF、GhoT和YafQ)在没有ppGpp的情况下仍然能够显著增加持留性。通过从ASKA文库的4287个质粒载体中过量表达每种大肠杆菌蛋白质,并在没有ppGpp的情况下(通过relA spoT突变体)选择增加持留性,我们鉴定出了五种新的蛋白质,即YihS、PntA、YqjE、FocA和Zur,它们仅通过降低细胞生长就增加了持留性。