微生物学通报  2023, Vol. 50 Issue (5): 2204−2214

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文章信息

谢兆邦, 刘欢, 雷化雨, 史懿乐, 赵燕妮
XIE Zhaobang, LIU Huan, LEI Huayu, SHI Yile, ZHAO Yanni
非编码小RNA对细菌毒力及耐药性的调控作用研究进展
sRNA's regulation of bacterial virulence and antibiotic resistance
微生物学通报, 2023, 50(5): 2204-2214
Microbiology China, 2023, 50(5): 2204-2214
DOI: 10.13344/j.microbiol.china.220736

文章历史

收稿日期: 2022-08-07
接受日期: 2022-12-23
网络首发日期: 2023-01-30
非编码小RNA对细菌毒力及耐药性的调控作用研究进展
谢兆邦 , 刘欢 , 雷化雨 , 史懿乐 , 赵燕妮     
陕西科技大学食品科学与工程学院, 陕西  西安    710016
摘要: 近年来的研究发现,细菌非编码小RNA (small non-coding RNA, sRNA)对其不同生理进程起到了重要的调控作用。随着大量sRNA被发现并鉴定,细菌sRNA的功能被逐步阐明,其可在转录后水平广泛调控细菌的生理代谢、毒力及耐药性等。本文综述了sRNA对细菌毒力和耐药性调控作用的研究进展,对揭示细菌转录后水平毒力及耐药性调控机制具有一定意义。
关键词: 细菌非编码小RNA    细菌毒力    耐药性    
sRNA's regulation of bacterial virulence and antibiotic resistance
XIE Zhaobang , LIU Huan , LEI Huayu , SHI Yile , ZHAO Yanni     
School of Food Biological Engineering, Shaanxi University of Science & Technology, Xi'an 710016, Shaanxi, China
Abstract: It has been revealed that bacterial small non-coding RNAs are post-transcriptional regulatory molecules that tune important processes in bacterial physiology, such as the metabolism, virulence, and antibiotic resistance. In this paper, we review sRNAs' regulation of bacterial virulence and antibiotic resistance, which is of significance for revealing the post-transcriptional mechanism of bacterial virulence and drug resistance.
Keywords: sRNA    bacterial virulence    antibiotic resistance    

生物体内的RNA可分为编码RNA和非编码RNA (non-coding RNA, ncRNA),与作为蛋白质翻译模板的编码RNA不同,非编码RNA极为广泛地调控着生物体内的重要生命活动,包括DNA的转录与失活、基因的表达与关闭等,目前在真核生物体内已发现了数千条非编码RNA[1]。与真核生物相同,在原核生物甚至是病毒体内也存在一些非编码RNA片段,被称作非编码小RNA (small non-coding RNA, sRNA),从转录后水平影响原核生物的生理代谢以及致病菌的毒力和耐药性等。

1 sRNA

sRNA是一类存在于原核生物细胞内,长度通常在40–500个核苷酸之间,由DNA转录但不编码蛋白质的RNA分子[2]。sRNA通常由位于两个开放阅读框之间的非编码序列转录而来,也有小部分是从mRNA的头部或尾部非翻译区剪切而来[3]。这些sRNA具有各不相同的生物学功能,根据作用机制可将其分为3类,如表 1所示。

表 1 不同sRNA的作用机制 Table 1 The action mechanisms of various sRNAs
机制特点
Mechanism characteristics
实例
Example
作用机制
Action mechanism
参考文献
References
自身具有特殊活性
Self-special activity
M1 RNA 作为RNase P的催化亚单位参与tRNA前体的剪切
As a catalytic subunit of RNase P, it participates in the splicing of tRNA precursors
[2]
tmRNA 同时具有tRNA和mRNA的功能
Both tRNA and mRNA functions
[2]
4.5S RNA 与核糖体结合,使翻译得到的蛋白质向内质网或细菌质膜转移
It combines with ribosomes to transfer translated proteins to endoplasmic reticulum or bacterial plasma membrane
[3]
与蛋白质相互作用
Interaction with protein
RsmY/RsmZ 与RsmA蛋白结合,降低RsmA对其靶标mRNA翻译的抑制
It combines with RsmA protein to reduce the inhibition of RsmA on target mRNA translation
[4]
6S RNA 与RNA聚合酶(S70)结合改变其活性,抑制细菌在高pH环境下生存必需基因pspF的转录
It combines with RNA polymerase (S70) to change its activity, thus inhibiting the transcription of pspF, a gene necessary for bacteria to survive in high pH environment
[5]
CsrB/CsrC 与转录后调控因子CsrA蛋白结合,抑制其与目的基因的结合
It combines with the post transcriptional regulator CsrA protein and inhibits its binding to the target gene
[6]
与mRNA配对结合
Paired binding with mRNA
PrrF 在伴侣蛋白Hfq蛋白的协助下,与antR mRNA结合后抑制其翻译,从而调节铜绿假单胞菌的群体感应和毒力因子的产生
With the help of the chaperone Hfq protein, it combines with antR mRNA and inhibits its translation, thus regulating the population sensing and virulence factor production of Pseudomonas aeruginosa
[7]
STnc150 与鼠伤寒沙门氏菌中的fimA mRNA结合,抑制其翻译,降低细菌的入侵能力
It combines with fimA mRNA in Salmonella typhimurium to inhibit its translation, thus reducing the invasive ability of bacteria
[8]
LhrC 与编码单增李斯特菌进入非吞噬细胞所需的黏附素的lapB mRNA结合,抑制其翻译,从而降低细菌毒力
It combines with lapB mRNA encoding the adhesin required by Listeria monocytogenes to enter non-phagocytic cells and inhibits its translation, thus reducing bacterial virulence
[9]
RyhB 与多种mRNA配对,协助RNase E降解结合的mRNA
It pairs with a variety of mRNA to helps RNase E degrade the combined mRNA
[10]
Spot42 galE mRNA结合,干扰galK基因的转录
It combines with galE mRNA, thus interfering with the transcription of galK gene
[11]
DsrA/RprA rpoS mRNA结合,暴露其核糖体结合位点,促进其翻译,从而影响大肠杆菌的毒力
It combines with rpoS mRNA, exposes its ribosomal binding site and promotes its translation, thus affecting the virulence of Escherichia coli
[12]
OxyS flhA mRNA配对,封闭其核糖体结合位点,抑制其翻译
It pairs with flhA mRNA, blocks its ribosomal binding site and inhibits its translation
[13]
Qrr luxR mRNA结合,封闭其核糖体结合位点,抑制其翻译,进而抑制溶藻弧菌毒力因子——碱性丝氨酸蛋白酶的表达
It combines with luxR mRNA, blocks its ribosomal binding site and inhibits its translation, thus inhibiting the expression of basic serine protease, a virulence factor of Vibrio alginolyticus
[14]
2 sRNA对细菌毒力调控作用的研究进展

目前,绝大部分病原菌中均发现有sRNA存在,而且通过多种途径在转录后水平调控细菌毒力及致病性。

2.1 sRNA调控细菌自身基因表达影响毒力

2.1.1 大肠杆菌

大肠杆菌(Escherichia coli)是一种模式微生物,也是sRNA研究最为全面的细菌,目前已从中发现了上百种sRNA,而且多数参与了大肠杆菌毒力及致病性的调控。大肠杆菌的碳储存调节器(carbon storage regulator, Csr)系统将大肠杆菌的碳代谢与其他生理活动联系起来[15],调节蛋白CsrA是Csr系统的中心组件,能够调控糖原生物合成、运动性、群体感应、醋酸盐代谢和鞭毛合成等,在毒力调控中发挥着重要作用,而sRNA分子CsrB/CsrC能够负反馈调节CsrA蛋白的活性,从而调控大肠杆菌的多种代谢途径影响其毒力[6]

对于大多数致病性细菌而言,铁代谢与其侵染能力密切相关,铁摄取调节蛋白(ferric uptake regulator, Fur)是细菌重要的毒力调控因子,可通过调控sRNA的转录,全局性地调控细菌铁稳态,满足细菌在富铁/缺铁不同状态下的铁需求;在大肠杆菌中,sRNA RyhB参与了铁稳态的调控,在富铁条件下,Fe2+-Fur蛋白与ryhB基因结合,抑制RyhB的转录;而在缺铁条件下,Fur蛋白与Fe2+解离后失去活性,ryhB基因的转录抑制被解除,转录得到的RyhB与多种编码非必需铁结合蛋白的mRNA结合后,诱导RNase E降解被结合的mRNA,从而降低大肠杆菌对铁的需求和消耗,提高其对宿主限铁环境的适应性[16]。此外,RyhB还对大肠杆菌的定殖能力具有调控作用,研究发现ΔryhB突变株在小鼠膀胱内的定殖能力较原始菌株显著下降[17]

志贺氏毒素(Shiga toxin, Stx)是肠出血性大肠杆菌(enterohemorrhagic Escherichia coli)的主要毒力因子,分为Stx1和Stx2两类,可与宿主细胞膜上的受体球丙糖酰基鞘氨醇(globotriaosylceramide, Gb3)结合,使核糖体28S rRNA 3ʹ端腺苷酸脱嘌呤,抑制蛋白质合成,从而导致细胞死亡;而sRNA StxS能够直接与stx1B mRNA的核糖体结合位点结合而抑制其翻译,使得Stx1的合成下调67%;此外,StxS还可与稳定期压力响应调控因子σS 5ʹUTR区配对结合进而激活其表达,使得肠出血性大肠杆菌在基本培养基中生长时稳定期细胞密度上升20%[18]

尿路致病性大肠杆菌(uropathogenic Escherichia coli)中的sRNA RyfA能够通过控制细菌1型和p型菌毛相关蛋白的合成,从而影响其在尿路中的定殖能力;实验结果表明,尿路致病性大肠杆菌的ΔryfA缺失株在小鼠膀胱和肾脏内的定殖率分别下降至原始菌株的1/146和1/10 000[19]

2.1.2 铜绿假单胞菌

铜绿假单胞菌(Pseudomonas aeruginosa)是一种常见且分布广泛的致病菌,在自然界及人体皮肤、肠道和呼吸道中均有发现,其毒力系统的表达受到复杂而精细的调控网络控制。GacS/GacA双组分系统对铜绿假单胞菌的毒力至关重要,其能够通过正调控氰化氢、磷脂酶C和AprA蛋白(一种碱性蛋白酶)的合成影响细菌毒力,同时磷酸化的GacA激活sRNA RsmY、RsmZ的转录,RsmY和RsmZ与翻译调节蛋白RsmA及RsmF结合,间接影响二者对靶标mRNA的调控,进而影响细菌毒力;铜绿假单胞菌的Ⅵ型菌毛、T3SS等急性毒力因子的表达受到RsmA/RsmF的促进,而T6SS、生物被膜等慢性毒力因子的表达则受到抑制(图 1);因此该毒力调控系统被认为在铜绿假单胞菌对宿主的侵染从急性转变为慢性的过程中发挥着关键作用[4]

图 1 GacS-GacA-RsmY/RsmZ-RsmA/RsmF毒力调控网络示意图 Figure 1 Schematic diagram of GacS-GacA-RsmY/RsmZ-RsmA/RsmF virulence control network. 双组分系统GacS/GacA由传感器激酶GacS和同源的反应调节器蛋白GacA组成,当GacS被激活,GacS与GacA之间发生磷转移,GacA被磷酸化,LadS、RetS是两个独立的传感器激酶,分别对GacS存在促进和抑制作用;磷酸化的GacA激活sRNA RsmY/Z的转录,二者与翻译调节蛋白RsmA/F结合,进而影响受RsmA/F蛋白调控的T3SS、T6SS及生物被膜等毒力因子的表达 The two-component system GacS/GacA is composed of sensor kinase GacS and homologous reaction regulator protein GacA, phosphorus transfer occurs between GacS and GacA, and GacA is phosphorylated when GacS is activated, LadS and RetS are two independent sensor kinases, which promote and inhibit GacS respectively; Phosphorylated GacA activates the transcription of sRNA RsmY/Z, which combines with the translation regulatory protein RsmA/F, thus affecting the expression of bacterial virulence factors such as T3SS, T6SS and biofilm regulated by RsmA/F protein.

NrsZ是在铜绿假单胞菌中由NtrB/NtrC双组分系统诱导产生的sRNA,其能够通过正向调节rhlA mRNA的表达调控鼠李糖脂的合成,而鼠李糖脂是与铜绿假单胞菌的集群运动密切相关的毒力因子[20]。PesA是PAPI-1毒力岛所转录的sRNA,能够与编码杀伤蛋白S3A和免疫蛋白S3I的pyoS3A、pyoS3I mRNA结合并诱导二者表达,从而正向调节铜绿假单胞菌外毒素绿脓菌素S3的表达,利用囊性纤维化的人类支气管上皮细胞进行感染实验,发现感染ΔpesA突变株的细胞存活率明显高于感染野生型菌株的细胞[21]

sRNA AmiL是在铜绿假单胞菌中新发现的一种群体感应调节sRNA,其对铜绿假单胞菌的多种毒力均有不同程度的影响,包括绿脓菌素的合成、生物被膜形成、溶血活性等,研究发现AmiL能够靶向抑制PhzC蛋白(绿脓菌素合成途径中的关键蛋白)的表达,从而抑制绿脓菌素的合成;实验结果显示,ΔamiL突变株的绿脓菌素表达水平相较于野生型提高了近60%,而amiL过表达菌株的绿脓菌素表达水平则下降了约30%[22]

2.1.3 霍乱弧菌

霍乱弧菌(Vibrio cholera)是人类急性传染病“霍乱”的病原体,患者感染后将出现剧烈的呕吐、腹泻,并在极短的时间内死亡。在霍乱弧菌中,sRNA Qrr1、Qrr2、Qrr3和Qrr4的转录受到群体感应系统的调节,低密度条件下Qrr1-4的转录被磷酸化的LuxO激活后,能够在伴侣蛋白Hfq的协助下激活低密度关键调控元件AphA的表达,并抑制高密度关键调控元件LuxR的翻译,以调控霍乱弧菌的毒力[23]。最近的研究发现,另一种新型sRNA VqmR同样通过霍乱弧菌群体感应系统影响其毒力。当细胞密度不断增加时,自诱导物3, 5-二甲基吡-2-醇(3, 5-dimethylpyrazin-2-ol, DPO)不断累积,激活VqmR的转录进而抑制AphA蛋白的合成,从而抑制霍乱弧菌毒力基因的表达[24]

sRNA VrrA被证明是霍乱弧菌外膜蛋白A (Outer membrane protein A, OmpA)的合成抑制因子,其能够与ompA mRNA的核糖体结合位点配对来抑制OmpA蛋白的翻译;通过抑制OmpA的合成,VrrA能够正向调控外膜囊泡(outer-membrane vesicles, OMVs)的释放,而越来越多地研究表明OMVs的形成和释放与毒力因子传递途径相关,同时VrrA还能够通过调控定殖因子毒素共调菌毛(toxin co-regulated pilus, Tcp)的合成来影响霍乱弧菌的肠内定殖能力;此外,研究还发现VrrA在伴侣蛋白Hfq的协助下,下调了核糖体相关抑制蛋白Vrp的表达,这有助于霍乱弧菌在寡营养条件下的生存[25]。另一sRNA CoaA被证实能够靶向结合编码Tcp负调控因子的tcpI mRNA以抑制其翻译,从而提高霍乱弧菌的肠内定殖能力,霍乱弧菌ΔcoaR突变株的小肠内定殖能力相较于野生型菌株有所下降[26]

2.1.4 金黄色葡萄球菌

金黄色葡萄球菌(Staphylococcus aureus)是一种常见的致病微生物,能够引起人与动物的多种疾病。在金黄色葡萄球菌中,sRNA RNAⅢ能够调控多个毒力相关基因的表达。其5ʹ端与呈折叠状态的hla mRNA (α-溶血素编码mRNA)结合时,能够暴露其核糖体结合位点,从而激活α-溶血素的表达;其3ʹ端能够与靶标mRNA (如spa mRNA、rot mRNA)的核糖体结合位点结合,抑制靶标mRNA的翻译,并与RNase Ⅲ共同作用诱导靶标mRNA降解(图 2),其中spa mRNA编码金黄色葡萄球菌的主要黏附蛋白A;而rot mRNA编码毒素抑制调控蛋白Rot,RNA Ⅲ可通过抑制Rot蛋白合成间接激活多种外毒素的转录[27]

图 2 RNAⅢ结合靶标mRNA示意图 Figure 2 Schematic diagram of RNAⅢ binding target mRNA. RNAⅢ与不同的mRNA结合调控其对应蛋白的表达,文中提供了进一步的阐述 RNAⅢ combines with different mRNA to regulate the expression of its corresponding protein, further explanation is provided in the text.

Autolysin (ATL)蛋白是金黄色葡萄球菌的主要自溶素,作为重要的毒力因子之一参与了对宿主细胞的黏附和侵袭,与金黄色葡萄球菌的致病性密切相关;sRNA SprC能够与atl mRNA结合以阻止核糖体就位,从而抑制ATL蛋白的合成,研究表明金黄色葡萄球菌ΔsprC突变株的ATL蛋白表达水平相较于野生型菌株有所提高,但宿主的单核细胞和巨噬细胞对突变株的吞噬作用也相应增强,猜测该sRNA的表达有利于细菌与宿主共生[28]

透明质酸裂解酶A (hyaluronate lyase A, HysA)和胞外丝氨酸蛋白酶D (serine proteaselike protein D, SplD)是金黄色葡萄球菌重要的毒力因子,二者均在其侵袭宿主细胞的过程中发挥着重要的作用;sRNA RsaF对HysA和SplD蛋白的表达具有正向调节作用,实验结果显示,ΔrsaF突变株中hysA mRNA转录水平下调了80%–99.9%,HysA酶活性下降了80%–90%,并促进了其生物膜的形成,splD mRNA转录水平下调了20%,同时通过酶谱分析发现多种蛋白酶的活性均有所降低;相反地,RsaF的过表达则导致hysA mRNA水平和透明质酸裂解酶活性上调了2–4倍,而且hysAsplD mRNA在rsaF+回补株中的稳定性均有所增强[29]

α型酚溶性调节蛋白(phenol-soluble modulin alpha, PSM-α)是金黄色葡萄球菌能够产生的最强的细菌毒素之一,可引起包括红细胞、白细胞在内的多种细胞发生裂解,刺激炎症反应的发生,并促进生物膜的形成[30]。sRNA Teg41是由金黄色葡萄球菌中编码PSM-α基因座中的片段转录而来的一种sRNA,研究发现Teg41的过表达提高了PSM-α的表达水平及溶血能力,而在敲除了Teg41的3ʹ端24个碱基之后,鼠脓肿感染模型中金黄色葡萄球菌溶血活性和毒力均减弱,这种减弱在对Teg41进行回补后得到恢复[30]。表明Teg41可促进PSM-α的表达,随着对Teg41产生与作用机制的进一步深入研究,相信Teg41可能将成为抗金黄色葡萄球菌感染的新作用靶点。

2.2 sRNA调控细菌宿主基因表达影响毒力

外膜囊泡(OMVs)是由细菌外膜分泌的球状囊泡,由脂质、蛋白质和脂多糖(lipopolysaccharide, LPS)构成,OMVs介导的宿主免疫应答是宿主和病原菌相互作用的一种重要机制[31]。研究发现多种革兰氏阴性菌的OMVs中存在大量sRNAs,并且OMVs能够保护其中的sRNAs不被RNA酶破坏,其中部分sRNAs能够通过调控宿主基因的表达影响病原菌毒力[31]。例如,存在于支气管上皮细胞黏液层中的铜绿假单胞菌通过分泌OMVs将sRNA-52320递送到宿主细胞中,sRNA-52320通过靶向LPS/MAPK信号通路中的多个基因,抑制宿主对细菌感染的免疫反应,减少IL-8分泌和中性粒细胞向小鼠肺部的迁移,有助于铜绿假单胞菌在免疫受损个体中建立慢性肺部感染;伴放线放线杆菌(Actinobacillus actinomycetemcomitans)通过OMVs分泌的sRNAs可以穿过血脑屏障,激活巨噬细胞中的NF-κB信号通路来刺激TNF-α产生,从而促进大脑促炎细胞因子的分泌;尿路致病性大肠杆菌OMVs中的sRNAs被转移到膀胱上皮细胞,可抑制LPS诱导的IL-1α分泌[32-34]。类似地,单增李斯特菌(Listeria monocytogenes) OMVs中的sRNA Rli32被发现能够刺激骨髓源性巨噬细胞产生IFN-β,从而促进病原菌在细胞内的增殖[35]

3 sRNA对细菌抗生素耐药性的调控作用

大量研究表明细菌可利用sRNA进行转录后调控以应答抗生素压力,这些sRNA可通过不同的作用机制来影响细菌的抗生素耐药性[36]

3.1 通过调控细胞壁膜的合成与修饰影响细菌耐药性

sRNA GlmY/GlmZ能够通过参与大肠杆菌中葡萄糖胺-6-磷酸合成酶(glucosamine-6-phosphate synthase, GlmS)的合成通路,进而调节LPS及肽聚糖的合成;GlmZ在伴侣蛋白Hfq的协助下与glmS mRNA结合,暴露出glmS核糖体结合位点,从而促进其翻译表达,RapZ蛋白可与GlmZ结合,并诱导RNase E降解GlmZ,而GlmY与GlmZ结构类似,同样能够与RapZ结合;当菌体内的葡萄糖胺-6-磷酸(glucosamine-6-phosphate, GlcN6P)水平降低时,GlmY得到积累并与RapZ竞争性结合使得GlmZ的降解被抑制,从而促进glmS mRNA的翻译,使得GlcN6P不断被合成,当菌体GlcN6P水平提高时GlmY的积累被抑制,此时RapZ与GlmZ结合,GlcN6P的合成受到抑制(图 3);这种调节机制为大肠杆菌提供了针对相关抗生素的保护作用,抗生素引起的GlcN6P表达水平下降促进了sRNA GlmY的积累,最终促进GlmS的表达使得GlcN6P表达水平回调,进而克服抗生素对菌体的生长抑制[37]

图 3 GlmY/Z-GlmS系统调节细胞膜合成机制示意图 Figure 3 Schematic diagram of GlmY/Z system regulating cell membrane synthesis. sRNA GlmY/GlmZ通过参与大肠杆菌中GlmS的合成通路调节LPS及肽聚糖的合成,文中提供了进一步的阐述 sRNA GlmY/GlmZ regulates the synthesis of LPS and peptidoglycan by participating in the synthesis pathway of GlmS in Escherichia coli, further explanation is provided in the text.

除直接调控细胞壁膜的合成外,sRNA还能通过修饰细菌LPS成分影响细菌耐药性。EptB是大肠杆菌的一种LPS修饰酶,能够降低LPS中脂质A的负电荷,从而减弱LPS对带有正电荷的多粘菌素的亲和力,进而产生耐药性[38]。sRNA分子MgrR能够抑制eptB mRNA的翻译,从而提高LPS负电荷,使得大肠杆菌对多黏菌素类抗生素的敏感性提高,实验表明ΔmgrR突变株的多黏菌素抗性是野生型的近10倍[39]。此外,铜绿假单胞菌中的sRNA Sr006的过表达明显提高类脂A脱酰基酶PagL的水平,从而降低铜绿假单胞菌对多黏菌素类抗生素的敏感性[40]

3.2 通过调控药物的摄取与外排影响细菌耐药性

大肠杆菌中的cycA mRNA编码抗生素d-环丝氨酸的转运蛋白,而sRNA GcvB能在伴侣蛋白协助下与之结合并抑制其翻译,从而降低细菌对d-环丝氨酸的敏感性[41]。类似地,OprD蛋白是铜绿假单胞菌负责碳青霉烯类抗生素摄取的主要孔蛋白,sRNA Sr0161能够靶向oprD mRNA而抑制其翻译,使细菌对碳青霉烯类抗生素耐药[40]。sRNA也可通过控制细菌对药物的外排影响细菌耐药性。由MdtE、MdtF及TolC蛋白共同组成的MdtEF-TolC系统是大肠杆菌重要的多药外排泵之一,sRNA DsrA可以通过激活大肠杆菌中的MdtE和MdtF蛋白编码基因的表达,而sRNA SdsR与tolC mRNA核糖体结合位点上游配对抑制其表达,从而改变大肠杆菌对新生霉素的耐药性[42-44]

3.3 通过改变细菌遗传信息影响细菌耐药性

大肠杆菌sRNA SdsR的表达受到RpoS (一般压力应答σ因子)介导的细菌致突变修复(一类以引入突变为代价的DNA损伤修复)的调控,SdsR被激活后能够通过抑制错配修复蛋白MutS的合成,致使突变在细胞内不断地积累,使细菌获得耐药变异的可能性增加[45]。同时,研究发现某些sRNA在环境压力下能够促进细菌的致突变修复,例如sRNA GcvB能够通过维持大肠杆菌的膜完整性降低细胞内的RpoE (膜压力应答σ因子)水平,而RpoE在高水平下会抑制RpoS的调控作用(图 4),因此GcvB通过抑制大肠杆菌中RpoE的表达间接促进了RpoS介导的致突变修复[46]

图 4 GcvB、SdsR参与大肠杆菌遗传信息改变机制示意图 Figure 4 Schematic diagram of GcvB and SdsR participating in genetic information change of Escherichia coli. sRNA GcvB通过维持膜完整性使得RpoE蛋白的表达水平下降,进而使得RpoS蛋白的表达水平上升;除激活sRNA SdsR抑制错配修复外,RpoS蛋白还能够促进DNA聚合酶Ⅳ的表达,凭借DNA聚合酶Ⅳ参与修复时易出错的特性间接促进大肠杆菌的突变 sRNA GcvB reduces the expression level of RpoE protein by maintaining membrane integrity, thus increasing the expression level of RpoS protein; In addition to activating sRNA SdsR to inhibit the mismatch repair of Escherichia coli, RpoS protein can also promote the expression of DNA polymerase Ⅳ, and indirectly promote the mutation of Escherichia coli by virtue of the error-prone nature of DNA polymerase Ⅳ in repair.
4 总结与展望

现有文献表明,sRNA在细菌的毒力基因调控网络中发挥着关键作用,其通过多种作用机制在转录后水平对靶标基因进行调节,从而有效地调控细菌毒力。然而目前的研究主要集中在sRNA分子对细菌自身基因的表达影响上,对于其在病原菌-宿主作用过程中的作用研究较少。此外,细菌sRNA分子进入到宿主细胞后如何维持其稳定性继而发挥作用是值得深入探索的问题。现有研究发现sRNA分子也可以通过细胞壁膜、药物进入及排出系统、改变DNA遗传信息等方面影响细菌抗生素耐药性。然而,相关研究主要集中在sRNA对细菌固有耐药性方面的调控作用,而对于获得性耐药性的研究较少,这些水平转移耐药基因不受sRNA调控的原因尚不清楚。此外,细菌在抗生素应激过程中sRNA-mRNA互作网络的变化情况解析尚不全面。相信随着sRNA互作组分析、Term-Seq、RNase作用位点分析等相关技术的进步,对于sRNA如何参与调控网络以控制病原微生物致病性及抗生素耐药性的认识将不断提高,致病菌防治手段的开发也将更加有的放矢。

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