微生物学通报  2021, Vol. 48 Issue (5): 1800−1809

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文章信息

沈紫竹, 李昱龙, 孙志敏, 樊奔, 赵银娟
SHEN Zizhu, LI Yulong, SUN Zhimin, FAN Ben, ZHAO Yinjuan
细菌生物被膜分散及分子调控机制研究进展
Bacterial biofilm dispersion and molecular regulation mechanism: a review
微生物学通报, 2021, 48(5): 1800-1809
Microbiology China, 2021, 48(5): 1800-1809
DOI: 10.13344/j.microbiol.china.200829

文章历史

收稿日期: 2020-08-15
接受日期: 2020-10-31
网络首发日期: 2020-12-28
细菌生物被膜分散及分子调控机制研究进展
沈紫竹1,2 , 李昱龙1,2 , 孙志敏1,2 , 樊奔1,2 , 赵银娟1,2     
1. 南京林业大学林学院    江苏  南京    210037;
2. 南方现代林业协同创新中心    江苏  南京    210037
摘要: 生物被膜分散(Biofilm Dispersal)是生物被膜发展后期细菌响应营养物、低浓度的一氧化氮、D-氨基酸、自诱导肽(Autoinducing Peptide,AIP)、酰基高丝氨酸内酯(Acyl Homoserine Lactones,AHL)、腺苷三磷酸(Adenosine Triphosphate,ATP)等信号变化而做出的一种程序性反应,有利于细菌从恶劣的生物被膜内部环境中脱离出来寻找新的定殖位点。此外,由生物被膜引起的细菌短暂的抗生素耐受性在分散过程中会恢复正常水平,这有助于治疗由致病菌引起的难治愈的生物被膜相关疾病。目前生物被膜分散的相关研究正处于起步阶段,本文希望通过综述生物被膜分散现象、信号分子及调控机制,可以更好地了解细菌生物被膜分散对于防控病原微生物和应用有益微生物的重要意义。
关键词: 生物被膜    分散    分子机制    信号分子    
Bacterial biofilm dispersion and molecular regulation mechanism: a review
SHEN Zizhu1,2 , LI Yulong1,2 , SUN Zhimin1,2 , FAN Ben1,2 , ZHAO Yinjuan1,2     
1. College of Forestry, Nanjing Forestry University, Nanjing, Jiangsu 210037, China;
2. Collaborative Innovation Center of Sustainable Forestry in Southern China, Nanjing, Jiangsu 210037, China
Abstract: Biofilm dispersal is a programmed response of bacteria in the late development of biofilm to signal changes such as nutrients, low concentration of nitric oxide, D-amino acid, autoinducing peptide (AIP), acyl homoserine lactone (AHL), and adenosine triphosphate (ATP), which is conducive to the bacteria to break away from the harsh internal environment of biofilm to find new colonization sites. In addition, the transient antibiotic resistance of bacteria caused by biofilm returns to normal levels during dispersion, which helps to treat refractory biofilm-related diseases caused by pathogenic bacteria. At present, the research on biofilm dispersion is at an initial stage. In this paper, we hope that by summarizing the phenomenon, signaling molecules and regulatory mechanisms of biofilm dispersion, we can better understand the important significance of bacterial biofilm dispersion for the prevention and control of pathogenic microorganisms and the application of beneficial microorganisms.
Keywords: biofilm    dispersion    molecular mechanism    signal molecule    

生物被膜(Biofilm)是一类有组织的细菌群体[1]。细菌通过鞭毛等结构附着在生物体或非生物体表面,并包埋在胞外多糖、胞外蛋白等保护性细胞外聚合物基质中,形成具有稳健三维结构的生物被膜[2-3]。病原菌的传播和感染的恶化都与生物被膜的形成有关[4-5],例如金黄色葡萄球菌(Staphylococcus aureus)以生物被膜的形式存在于骨骼、心脏瓣膜等部位会引起难以根治的骨髓炎、心内膜炎等慢性疾病[6-7]。一些细菌感染性疾病难以治疗的主要原因之一是生物被膜基质不仅能帮助细菌更好地储藏营养物质和水分,而且还能显著降低抗生素渗透速率[8]。同时,生物被膜中较高的细胞密度增加了基因水平转移的可能性,使耐药性增强菌株出现的可能性也随之增高[5]。这些原因使得利用抗生素杀死细菌的成效显著下降。与可遗传的抗生素抗性机制(如外排泵、抗生素修饰酶等)不同的是,生物被膜的抗生素耐受性是一种短暂的状态。当细菌脱离生物被膜转变为浮游状态时,细菌恢复正常的抗生素敏感性[7]。因此,使细菌从生物被膜状态转变为浮游状态是抗生素治疗的关键[9]

生物被膜生长的最后阶段,生物被膜中部分细胞会主动从生物被膜中游离出来,并寻找新的定殖位点,即生物被膜分散(Biofilm Dispersal)[10-11]。这是生物被膜中细菌为应对环境压力的一个有效措施,同时也为抗生素治疗提供了合适时机。相较于最近几十年在生物被膜形成阶段深入透彻的研究,生物被膜分散的研究还处于起步阶段,然而已有很多科研工作者致力于相关研究。因此,我们通过对生物被膜分散的现象、信号分子及调控机制作一个综合论述,以期更深入地了解细菌生物被膜的分散机制,为生物被膜分散在人类疾病治疗、植物病害防控及有益微生物在自然状态下的动态定殖及促生机理提供理论依据。

1 生物被膜分散简介

细菌以生物被膜的形式存在有利于其抵抗外界环境压力。自然状态下,生物被膜会经历4个阶段,分别为附着、菌落形成、生物被膜成熟及生物被膜脱落[10, 12-13](图 1)。生物被膜形成初期,细菌通过范德华力、静电作用力等和鞭毛等结构吸附在基底上[11]。此时,生物被膜中少量细胞会受到物理因素(粘附力[14]等)或化学因素(顺式-2-癸烯酸[15]、一氧化氮[16]等)的影响直接离开基底重新回到环境中去,称之为解吸(Desorption)[17]。之后,生物被膜继续发展到一定程度时,由于维持生物被膜结构稳定性的外力失去平衡,细胞与聚合物会以分离(Detachment)的方式从生物被膜边缘脱离[17]。除外力外,外源添加的物质(如分散素B、高碘酸盐、脱氧核糖核酸酶、海藻酸裂解酶等)也会影响生物被膜分离的速度与程度[17]。随着成熟生物被膜的逐渐老化,生物被膜内部细胞缺乏生长必需的营养,同时大量积累的废物和毒素严重威胁到细菌自身的生存[18-19]。为了应对这种压力,少量细胞会以分散(Dispersion)的方式离开生物被膜,并寻找新的定殖位点(图 1)。值得注意的是,解吸与分离是细菌受到外力因素被动地从生物被膜中离开的过程,而分散则是细菌感知外界环境并对此做出反应的主动过程。

图 1 生物被膜发展过程 Figure 1 Biofilm development process 注:生物被膜的形成分为4个阶段:附着(包括可逆附着和不可逆附着)、菌落形成、生物被膜成熟、生物被膜老化。在此过程中,生物被膜中细菌以多种方式脱离生物被膜,包括解吸、分离与分散。解吸与分离是一种被动的过程,容易受到环境的影响。分散是一个主动的过程。在分散发生前,生物被膜内部分细胞开始出现运动的迹象,之后生物被膜壁发生破裂,细菌从中释放出来 Note: The formation of biofilm is divided into four stages: attachment (including reversible attachment and irreversible attachment), colony formation, biofilm maturation, and biofilm aging. In this process, the bacteria in the biofilm are separated from the biofilm in many ways, including desorption, separation and dispersion. Desorption and separation are a passive process and are easily affected by the environment. Dispersion is an active process. Before the dispersion occurs, some cells in the biofilm begin to show signs of movement, and then the biofilm wall ruptures and bacteria are released from it

同时,分散也是一个起始于生物被膜内部的群体行为。在分散发生之前,细菌在生物被膜内部有限空间内开始游动(Swimming)、抽动(Twitching)或漂浮(Floating)[17]。随着生物被膜继续发展到末期,内部参与分散的细菌积累到一定数量后会以游动或其他方式从生物被膜壁或菌落的裂口中释放进入外界环境,在生物被膜内留下空隙或塌陷区域[17]。虽然大多数细菌都具有参与分散的能力,但实际上只有生物被膜内特定的一小块区域发生分散,这些区域的位置会随时间发生变化[20]。然而目前还未有生物被膜分散区域变化的相关报道。值得注意的是,生物被膜最接近外界环境的细菌一般不参与分散[19]

参与分散行为的细菌在分散过程中也表现出一系列相应的生理变化,例如形成生物被膜降解酶如糖苷酶、蛋白酶和脱氧核糖核酸酶等,参与生物被膜基质形成的胞外多糖(Exopolysaccharides,EPS)、胞外蛋白、胞外DNA (Extracellular DNA,eDNA)释放或降解,鼠李糖脂的产生,生物被膜内小部分细胞发生自溶现象,生物被膜菌落表面细胞分裂能力增强,参与分散细菌的运动性发生改变,菌毛粘附性发生改变等[4, 9-10, 17, 21]。在白色念珠菌(Candida albicans)生物被膜研究过程中发现,分散细胞比浮游细胞具有更强的粘附力、毒力、生物被膜形成能力和抗生素耐受性[22]

2 生物被膜分散信号

当生存环境不利时,生物被膜分散是细胞应对环境变化时进行的一种优势选择;当细胞处于相对有利环境时,生物被膜分散对细胞的生存、繁殖也有一定的影响。生物被膜分散是细菌通过感知外界信号的变化来激发的。目前已知的是生物被膜分散会受到营养物[10, 23-24]、低浓度的一氧化氮[25-28]、D-氨基酸[29-31]、自诱导肽(Autoinducing Peptide,AIP)[32-33]、酰基高丝氨酸内酯(Acyl Homoserine Lactones,AHL)[34-36]、腺苷三磷酸(Adenosine Triphosphate,ATP)[24, 37]等信号的诱导。

2.1 营养物

营养物的突然变化会导致生物被膜分散。当营养匮乏时,为躲避不利条件,细胞从生物被膜中主动分散[10];当营养充足时,细胞更倾向于将代谢能量用于繁殖和分散[23]。Sauer等[23]证实,葡萄糖、琥珀酸、谷氨酸等多种营养物质突然增加可诱导铜绿假单胞菌(P. aeruginosa)生物被膜分散,这与分散细胞中鞭毛基因(fliC)表达的增加和菌毛基因(pilA)表达的减少有关。Huynh等[24]在研究中发现,葡萄糖缺乏情况下,铜绿假单胞菌生物被膜5 min内开始分散,2 h后达到最大值,24 h后,高达60%的原始生物量已经分散,经过蛋白质组分析显示,部分与能量代谢、应激反应和运动相关的蛋白具有差异表达。

2.2 低浓度的一氧化氮

一氧化氮(Nitric Oxide,NO)是一种双原子自由基气体分子,由于其具有亲脂性,可以快速发出细胞间信号[25],具有控制生物被膜变化的双重作用[26]。高浓度的NO可以通过化学修饰抗生素或诱导有氧呼吸来保护细菌免受抗生素诱导的氧化应激,从而增强粘附性,具有保护细胞的作用[38]。低浓度的一氧化氮,如10-9-10-12 µmol/L NO供体硝普纳(Sodium Nitroprusside,SNP)具有促进生物被膜分散的作用[27]。Barraud等[28]研究发现,用500 nmol/L SNP处理生长1 d的铜绿假单胞菌生物被膜,24 h内细菌粘附性减弱而运动性增强,最终导致细胞从表面分散。

2.3 D-氨基酸

枯草芽孢杆菌(Bacillus subtilis)、金黄色葡萄球菌在其稳定期可以产生具有分解生物被膜能力的D-氨基酸,包括D-亮氨酸(D-Leu)、D-甲硫氨酸(D-Met)、D-色氨酸(D-Trp)和D-酪氨酸(D-Tyr)等,这些D-氨基酸通过抑制epsAtapA等基因的表达,从而影响胞外多糖的产生并且对胞外蛋白具有毒性[29-30]。同时,D-氨基酸还会通过抑制淀粉样纤维操纵子yqxM-sipW-tasA中TasA蛋白的表达阻碍淀粉样纤维在细胞壁表面正确定位,从而引起生物被膜的分散[31]

2.4 自诱导肽

AIP信号是胞外信号分子之一,是一个由7-9个残基组成的肽,其利用C末端的羧酸酯和距离C末端5个位置的半胱氨酸残基形成环状硫内酯,具有决定功能的硫酯键[32]。Boles等[33]证实通过添加AIP可以触发金黄色葡萄球菌中参与生物被膜分散的Agr系统,即群体感应(Quorum Sensing,QS)调控机制中的附属基因调节(Accessory Gene Regulator,Agr)系统,导致分散所需的胞外蛋白酶增加,从而引起生物被膜分散。

2.5 酰基高丝氨酸内酯

AHL是一个高度保守的信号分子,其通过群体感应调控机制参与细菌的分散[34]。AHL信号分子的形成是由LuxI家族蛋白将酰基载体蛋白结合的脂肪酰基衍生物转移到S-腺苷甲硫氨酸(S-Adenosyl Methionine,SAM)的氨基上[35]。涉及生物被膜分散的AHL包括7, 8-顺-N-(十四烯酰基)高丝氨酸内酯、N-3-氧代十二烷酰基高丝氨酸内酯(3-oxo-C12-HSL)和N-丁酰-L-高丝氨酸内酯(C4-HSL)等[10]。铜绿假单胞菌中,C4-HSL通过调控鼠李糖脂生物合成基因rhaA的表达增加鼠李糖脂的产生,从而引起生物被膜分散[36]

2.6 腺苷三磷酸

ATP是生物体内进行细胞代谢的主要能量来源。Huynh等[24]研究发现,铜绿假单胞菌中由葡萄糖缺乏引起的分散是通过直接合成ATP和质子动力驱动合成ATP,并通过cAMP介导完成,这为浮游细胞存活提供能量基础。此外,当宿主细胞应激或受损时会分泌ATP到细胞外环境中,细胞外环境中ATP浓度的快速增加是引起生物被膜分散的一个信号[37]。有研究在核梭杆菌(Fusobacterium nucleatum)中证实,ATP可以螯合生物被膜中基本金属离子(如Ca2+、Mg2+等),使原本维持细菌生存能力和生物被膜结构稳定性所需的金属离子被剥离,最终导致细菌从生物被膜中释放[37]

3 生物被膜分散的调控机制

解吸与分离依赖于外在因素驱动表型转换,生物被膜分散更多的是依赖于自身细胞发生的生理变化与释放的信号因子共同组成的调节网络。值得注意的是,不同细菌的分散调节网络具有一定的差异性。截至目前已经明确描述了4种与生物被膜形成和分散相关的分子调节机制,分别为群体感应(Quorum Sensing,QS)和基于核苷酸第二信使信号通路的环二鸟苷酸(Cyclic Diguanylate,c-di-GMP)、四磷酸或五磷酸鸟嘌呤核苷[(p)ppGpp],以及小核糖核酸调节通路(Small RNA,sRNA)[4, 17, 39]

3.1 群体感应

群体感应在生物被膜分散过程中发挥重要作用。细菌通过分泌并积累一定浓度的体外自诱导物信号激活群体感应。铜绿假单胞菌的QS取决于3个系统,包括基于N酰化的高丝氨酸内酯(AHL)信号的LasI/LasR和RhlI/RhlR系统以及基于假单胞菌喹诺酮信号(Pseudomonas Quinolone Signal,PQS)的系统[39]。这3个系统以分层的方式进行调节,其中LasI/LasR系统位于顶部,对底部的RhlI/RhlR系统进行正向调节[39]。PQS系统则交织在LasI/LasR和RhlI/RhlR系统之间,是两者的调节剂[39]。LasI/LasR系统不参与最初的附着和生长,而是在随后的生物被膜分化过程中发挥调控作用,该系统可以正向调节酪氨酸磷酸酶TpbA的表达,从而抑制pel基因的表达,最终影响生物被膜分散。pel基因产物参与形成铜绿假单胞菌中生物被膜主要基质胞外多糖Pel[40]。此外,TpbA还能通过调节二鸟苷酸环化酶TpbB的活性降低c-di-GMP水平,从而进一步降低PEL生成,这是由于PEL合成需要c-di-GMP与c-di-GMP受体PelD结合[39, 41-42]。由AHL和PQS信号传导控制的细胞外表面活性剂鼠李糖脂在生物被膜分散中发挥重要作用[43]:鼠李糖脂具有两亲性,其可以降低细胞-细胞、细胞-基质和细胞-表面间相互作用的表面张力[10]。Boles等[44]研究发现,分泌正常浓度的鼠李糖脂对于生物被膜的正常发育至关重要。当鼠李糖脂合成基因(rhaAB)过表达时,鼠李糖脂的异常分泌会加速铜绿假单胞菌(P. aeruginosa)生物被膜分散[44]

金黄色葡萄球菌的QS取决于Agr系统,该系统可以产生并感知小分子肽AIP[33, 45]。Agr系统由膜结合蛋白(AgrB)和细菌双组分信号转导系统组成,前者修饰并输出QS肽(AgrD),后者由传感器组氨酸激酶(AgrC)及其同源反应调节因子(AgrA)组成。AgrD产生的AIP被进一步加工成为含有硫代内酯环的环形肽,接着由AgrC分泌并感应,最后激活AgrA[33, 45]。Agr系统通过下调表面粘附素纤连蛋白结合蛋白(FnBPs)和蛋白A等,在特定的环境条件下诱导蛋白质生物被膜基质分解[46-47]。Wang等[48]和Periasamy等[49]研究发现,金黄色葡萄球菌中具有类似表面活性剂特性的酚溶性调节蛋白(The Phenol-Soluble Modulins,PSMs),其转录受AgrA严格控制,作为单体存在时具有促进生物被膜分解的性能[39, 50]

3.2 c-di-GMP

c-di-GMP是细菌中最常见和最重要的第二信使之一,其参与调节细胞周期、分化和生物被膜形成、分散及细胞的运动、毒性的产生等过程[51-54]。c-di-GMP是革兰氏阴性细菌在自由活动和生物被膜之间转换的主要调节剂[4, 10]。高磷酸化水平的c-di-GMP通过c-di-GMP效应子HfsK[55]、DGC蛋白CelR[56]、c-di-GMP结合蛋白YcgR[57]等调节粘附素和基质多糖的生物合成而促进生物被膜形成,并抑制各种类型的细胞运动,而低磷酸化水平的c-di-GMP通过c-di-GMP降解蛋白BinA[58]、糖基水解酶PslG[59]等可提高细胞运动能力和eDNA产量,并降低胞外多糖产量、细胞大小和聚集,从而促进生物被膜分散[52, 60-61]。c-di-GMP的磷酸化水平由二鸟苷酸环化酶(Diguanylate Cyclases,DGCS)和磷酸二酯酶(Phosphodiesterases,PDE)共同调节,前者包含GGDEF结构域,后者含有EAL或HD-GYP结构域,其中DGCS合成c-di-GMP,而PDE降解c-di-GMP,两者相互协作动态调节c-di-GMP浓度,从而调控细菌种群行为[52, 60-61]。Basu Roy等[62]发现铜绿假单胞菌中二鸟苷酸环化酶NicD通过一个由外而内的信号传导机制来感应诱导分散的营养信号。在这个系统中,NicD与分散相关蛋白BdlA和磷酸二酯酶DipA以多蛋白复合物形式直接相互作用:NicD通过感应到营养信号后被去磷酸化,其DGCS活性增加,导致c-di-GMP水平的暂时升高。BdlA被磷酸化。磷酸化的BdlA和c-di-GMP的水平升高均导致BdlA蛋白水解。水解后的BdlA具有一定活性。具有活性的BdlA一方面激活DipA,导致c-di-GMP水平总体下降,另一方面向多蛋白复合物内募集磷酸二酯酶RbdA,使c-di-GMP水平下降,从而引起生物被膜分散[62]。恶臭假单胞菌(Pseudomonas putida)中已经确定c-di-GMP水平下降后的分散机制,分散的发生是通过周质蛋白酶LapG对高分子量粘附素LapA进行蛋白水解而实现的[63-65]。膜结合信号转导蛋白LapD感测c-di-GMP水平下降,解除对LapG的抑制,从而导致LapA裂解以及细胞表面和细胞间接触的分解,最终引发生物被膜分散[63-65] (图 2)。

图 2 恶臭假单胞菌生物被膜分散机制 Figure 2 Biofilm dispersion mechanism of Pseudomonas putida 注:RelA响应氨基酸缺乏信号或SpoT响应营养胁迫信号,促使(p)ppGpp水平以及辅助蛋白DksA和鞭毛σ因子FliA升高,刺激bifA转录,从而增加磷酸二酯酶BifA的水平,使c-di-GMP水平下降。膜结合信号转导蛋白LapD感测c-di-GMP水平下降,解除LapD对LapG的抑制,从而导致LapA裂解以及细胞表面和细胞间接触的分解,最终引发生物被膜分散 Note: RelA responds to amino acid deficiency signal or SpoT responds to nutrition stress signal, which promotes (p)ppGpp level, the accessory protein DksA and flagella sigma factor FliA to increase bifA transcription, thus increasing phosphodiesterase BifA level and decreasing c-di-GMP level. LapD senses the decrease of c-di-GMP level and releases the inhibition of LapD on LapG, which leads to the lysis of LapA and the decomposition of cell surface and cell-to-cell contact, and finally triggers the dispersion of biofilm
3.3 (p)ppGpp

细胞内GDP或GTP的衍生物四磷酸或五磷酸鸟嘌呤核苷[(p)ppGpp]是调节细菌生长和代谢的关键分子之一。在γ和β变形杆菌中,(p)ppGpp由RelA和SpoT这2种蛋白合成,前者在氨基酸饥饿状态下诱导激活,后者响应碳、铁、氧和脂肪酸等其他形式的营养胁迫,并具有(p)ppGpp水解酶活性[66]。Díaz-Salazar等[65]提出一个由碳饥饿控制的恶臭假单胞菌生物被膜分散的调控路径,其中由SpoT响应饥饿信号,促使(p)ppGpp水平以及辅助蛋白DksA和鞭毛σ因子FliA升高,刺激bifA转录,进而增加磷酸二酯酶BifA的水平,使c-di-GMP水平下降,从而引起生物被膜分散(图 2)。Dean等[67]研究发现,弗朗西斯菌属(Francisella novicida)中relA响应QS信号DSF,表达增加,使(p)ppGpp水平升高,也导致生物被膜分散。

3.4 sRNA

sRNA是一段长度为5-500 nt的非编码RNA,在原核生物和真核生物中发挥基因表达调节作用。其可与蛋白结合来改变靶区稳定性,影响蛋白-DNA相互作用,从而调节基因表达,还可以与mRNA直接反义碱基配对诱导mRNA构象的改变来调节翻译[68-69]。sRNA调控的靶点往往是基因本身,因此能够在调控网络中实现额外水平的控制[69]。现阶段,基于sRNA的信号在生物被膜分散中的作用还不清楚,但已在很多细菌中发现其可能与c-di-GMP和QS系统相关[69-70]。沙门氏菌(Salmonella)中,碳储存调节因子CsrA的激活可以抑制DGC活性并激活PDE活性,最终导致c-di-GMP水平下降[69]。CsrA是一种核糖核酸结合蛋白,其活性调节部分由2个sRNA CsrB和CsrC介导[71-72]。霍乱弧菌中,在高细胞密度下,自体诱导物(AI-1、AI-2)与其同源受体的结合会导致4个冗余sRNA (Qrr1-4)转录停止,从而促进生物被膜的分散[4]。每个Qrr在sRNA伴侣蛋白Hfq的协助下与hapR的5′-UTR碱基配对来抑制翻译[4]。HapR是一种转录因子,可间接抑制胞外多糖生物合成操纵子的表达,并改变细胞内c-di-GMP的水平[73-74]

4 结语

对于环境中的微生物来说,不论其是致病菌还是益生菌,都面临着在环境中可持续性存在的关键问题。生物被膜的形成有助于微生物通过多细胞的行为介导细胞与细胞、细胞与基质之间的连接,而且产生的细胞外基质可作为屏障为细胞的生命活动创造稳定的内环境,生物被膜中的细菌对抗生素和宿主免疫防御机制的抗性很强。然而对于单个浮游细菌个体来说,其抵抗外界环境压力的能力要低很多。生物被膜状态与浮游状态是周期性变化的过程。在转变过程中,细菌以主动或非主动的方式从生物被膜中脱离。其中,解吸与分离是在外力影响下被动从生物被膜中脱离的过程。分散则是生物被膜生命周期的自然步骤,是细菌响应外界环境改变的一种优势选择。如在生物体内,病原微生物通过分散使其从病灶扩散到新的部位,增加其感染位点而导致感染性疾病的加重。因此,从这个角度来说,生物被膜分散是需要控制和抑制的,而另一方面,分散开的病原微生物由于失去生物被膜的保护而变得容易去除和杀灭,因此,通过对生物被膜分散机制的研究,找到生物被膜分散调节网络的关键点,对解决治疗顽固性细菌感染的难题有很重要的积极意义,因而也成为医学领域新的研究热点。

事实上,与形成生物被膜的能力一样,大多数细菌都具有分散生物被膜的能力。然而现阶段对生物被膜分散的研究主要集中在铜绿假单胞菌、金黄色葡萄球菌等致病菌中,仅有少数文献以有益微生物如枯草芽孢杆菌等作为研究对象去阐述其分散机理[75]。益生菌如根际促生菌在植物根际定殖时是否也能主动通过生物被膜分散的行为达到生态位的最大占领,从而发挥其促生抗逆的效应,这些促生菌又是如何与植物发生信号方面的对话交流等,这些方面的研究尚属空白。

更值得注意的是,虽然大多数细菌都具有分散能力,但并不是所有细菌均参与分散。在生物被膜中,什么样的细菌参与了分散,它们有哪些基因参与调控,分散出的细菌是否更具有生态位的占领能力或者对外界压力更强的抗性等,也是值得关注的问题。

REFERENCES
[1]
Van Wolferen M, Orell A, Albers SV. Archaeal biofilm formation[J]. Nature Reviews Microbiology, 2018, 16(11): 699-713. DOI:10.1038/s41579-018-0058-4
[2]
Flemming HC, Wingender J. The biofilm matrix[J]. Nature Reviews Microbiology, 2010, 8(9): 623-633. DOI:10.1038/nrmicro2415
[3]
Trejo M, Douarche C, Bailleux V, Poulard C, Mariot S, Regeard C, Raspaud E. Elasticity and wrinkled morphology of Bacillus subtilis pellicles[J]. Proceedings of the National Academy of Sciences of the United States of America, 2013, 110(6): 2011-2016. DOI:10.1073/pnas.1217178110
[4]
Guilhen C, Forestier C, Balestrino D. Biofilm dispersal: multiple elaborate strategies for dissemination of bacteria with unique properties[J]. Molecular Microbiology, 2017, 105(2): 188-210. DOI:10.1111/mmi.13698
[5]
Del Pozo JL. Biofilm-related disease[J]. Expert Review of Anti-Infective Therapy, 2018, 16(1): 51-65. DOI:10.1080/14787210.2018.1417036
[6]
Fowler VG, Das AF, Lipka-Diamond J, Schuch R, Pomerantz R, Jáuregui-Peredo L, Bressler A, Evans D, Moran GJ, Rupp ME, et al. Exebacase for patients with Staphylococcus aureus bloodstream infection and endocarditis[J]. The Journal of Clinical Investigation, 2020, 130(7): 3750-3760. DOI:10.1172/JCI136577
[7]
Lister JL, Horswill AR. Staphylococcus aureus biofilms: recent developments in biofilm dispersal[J]. Frontiers in Cellular and Infection Microbiology, 2014, 4: 178.
[8]
Srinivasan S, Vladescu ID, Koehler SA, Wang XL, Mani M, Rubinstein SM. Matrix production and sporulation in Bacillus subtilis biofilms localize to propagating wave fronts[J]. Biophysical Journal, 2018, 114(6): 1490-1498. DOI:10.1016/j.bpj.2018.02.002
[9]
Verderosa AD, Totsika M, Fairfull-Smith KE. Bacterial biofilm eradication agents: a current review[J]. Frontiers in Chemistry, 2019, 7: 824. DOI:10.3389/fchem.2019.00824
[10]
Kaplan JB. Biofilm dispersal: mechanisms, clinical implications, and potential therapeutic uses[J]. Journal of Dental Research, 2010, 89(3): 205-218. DOI:10.1177/0022034509359403
[11]
Li YL, Lu YM, Han ZM, Fan B. Bacterial biofilm: composition, regulation and association with plant[J]. Microbiology China, 2017, 44(6): 1491-1499. (in Chinese)
李昱龙, 陆一鸣, 韩正敏, 樊奔. 细菌菌膜的成分、调控及其与植物的关系[J]. 微生物学通报, 2017, 44(6): 1491-1499.
[12]
Qi HY, Wang WB, Zheng Y, Zhu L, Xu XY. Mechanism of biofilm formation and analysis of influencing factors[J]. Microbiology China, 2013, 40(4): 677-685. (in Chinese)
戚韩英, 汪文斌, 郑昱, 朱亮, 徐向阳. 生物膜形成机理及影响因素探究[J]. 微生物学通报, 2013, 40(4): 677-685.
[13]
Ripa R, Shen AQ, Funari R. Detecting Escherichia coli biofilm development stages on gold and titanium by quartz crystal microbalance[J]. ACS Omega, 2020, 5(5): 2295-2302. DOI:10.1021/acsomega.9b03540
[14]
Gjermansen M, Nilsson M, Yang L, Tolker-Nielsen T. Characterization of starvation-induced dispersion in Pseudomonas putida biofilms: genetic elements and molecular mechanisms[J]. Molecular Microbiology, 2010, 75(4): 815-826. DOI:10.1111/j.1365-2958.2009.06793.x
[15]
Davies DG, Marques CNH. A fatty acid messenger is responsible for inducing dispersion in microbial biofilms[J]. Journal of Bacteriology, 2009, 191(5): 1393-1403. DOI:10.1128/JB.01214-08
[16]
Barraud N, Storey MV, Moore ZP, Webb JS, Rice SA, Kjelleberg S. Nitric oxide-mediated dispersal in single-and multi-species biofilms of clinically and industrially relevant microorganisms[J]. Microbial Biotechnology, 2009, 2(3): 370-378. DOI:10.1111/j.1751-7915.2009.00098.x
[17]
Petrova OE, Sauer K. Escaping the biofilm in more than one way: desorption, detachment or dispersion[J]. Current Opinion in Microbiology, 2016, 30: 67-78. DOI:10.1016/j.mib.2016.01.004
[18]
Zhao YJ, Yan F, Wu XQ. Deletion of ClpQY gene in Bacillus subtilis strain 3610 by homologous recombination and its effect on sporulation, biofilm formation and growth at high temperature[J]. Journal of Northeast Forestry University, 2015, 43(11): 111-115. (in Chinese)
赵银娟, 严芳, 吴小芹. 枯草芽孢杆菌3610 ClpQY基因缺失突变株的构建及其功能[J]. 东北林业大学学报, 2015, 43(11): 111-115. DOI:10.3969/j.issn.1000-5382.2015.11.023
[19]
Gozzi K, Ching C, Paruthiyil S, Zhao YJ, Godoy-Carter V, Chai YR. Bacillus subtilis utilizes the DNA damage response to manage multicellular development[J]. Npj Biofilms and Microbiomes, 2017, 3(1): 8. DOI:10.1038/s41522-017-0016-3
[20]
Skariyachan S, Sridhar VS, Packirisamy S, Kumargowda ST, Challapilli SB. Recent perspectives on the molecular basis of biofilm formation by Pseudomonas aeruginosa and approaches for treatment and biofilm dispersal[J]. Folia Microbiologica, 2018, 63(4): 413-432. DOI:10.1007/s12223-018-0585-4
[21]
Fleming D, Rumbaugh K. The consequences of biofilm dispersal on the host[J]. Scientific Reports, 2018, 8(1): 10738. DOI:10.1038/s41598-018-29121-2
[22]
Uppuluri P, Lopez-Ribot JL. Go forth and colonize: dispersal from clinically important microbial biofilms[J]. PLoS Pathogens, 2016, 12(2): e1005397. DOI:10.1371/journal.ppat.1005397
[23]
Sauer K, Cullen MC, Rickard AH, Zeef LA, Davies DG, Gilbert P. Characterization of nutrient-induced dispersion in Pseudomonas aeruginosa PAO1 biofilm[J]. Journal of Bacteriology, 2004, 186(21): 7312-7326. DOI:10.1128/JB.186.21.7312-7326.2004
[24]
Huynh TT, Mcdougald D, Klebensberger J, AL Qarni B, Barraud N, Rice SA, Kjelleberg S, Schleheck D. Glucose starvation-induced dispersal of Pseudomonas aeruginosa biofilms is cAMP and energy dependent[J]. PLoS One, 2012, 7(8): e42874. DOI:10.1371/journal.pone.0042874
[25]
Bacon B, Nisbett LM, Boon E. Bacterial haemoprotein sensors of NO: H-NOX and NosP[J]. Advances in Microbial Physiology, 2017, 70: 1-36.
[26]
Islam M, Durie I, Ramadan R, Purchase D, Marvasi M. Exploitation of nitric oxide donors to control bacterial adhesion on ready-to-eat vegetables and dispersal of pathogenic biofilm from polypropylene[J]. Journal of the Science of Food and Agriculture, 2020, 100(7): 3078-3086. DOI:10.1002/jsfa.10340
[27]
Wille J, Teirlinck E, Sass A, Van Nieuwerburgh F, Kaever V, Braeckmans K, Coenye T. Does the mode of dispersion determine the properties of dispersed Pseudomonas aeruginosa biofilm cells?[J]. International Journal of Antimicrobial Agents, 2020, 56(6): 106194. DOI:10.1016/j.ijantimicag.2020.106194
[28]
Barraud N, Hassett DJ, Hwang SH, Rice SA, Kjelleberg S, Webb JS. Involvement of nitric oxide in biofilm dispersal of Pseudomonas aeruginosa[J]. Journal of Bacteriology, 2006, 188(21): 7344-7353. DOI:10.1128/JB.00779-06
[29]
Kolodkin-Gal I, Romero D, Cao SG, Clardy J, Kolter R, Losick R. D-amino acids trigger biofilm disassembly[J]. Science, 2010, 328(5978): 627-629. DOI:10.1126/science.1188628
[30]
Hochbaum AI, Kolodkin-Gal I, Foulston L, Kolter R, Aizenberg J, Losick R. Inhibitory effects of D-amino acids on Staphylococcus aureus biofilm development[J]. Journal of Bacteriology, 2011, 193(20): 5616-5622. DOI:10.1128/JB.05534-11
[31]
She PF, Chen LH, Xu H, Wu Y. Effects of D-amino acids on disruption of bacterial biofilm[J]. Journal of Pathogen Biology, 2015, 10(4): 377-380. (in Chinese)
佘鹏飞, 陈丽华, 许欢, 伍勇. D-氨基酸在生物膜分散中的作用研究进展[J]. 中国病原生物学杂志, 2015, 10(4): 377-380.
[32]
Thoendel M, Horswill AR. Biosynthesis of peptide signals in gram-positive bacteria[J]. Advances in Applied Microbiology, 2010, 71: 91-112.
[33]
Boles BR, Horswill AR. Agr-mediated dispersal of Staphylococcus aureus biofilms[J]. PLoS Pathogens, 2008, 4(4): e1000052. DOI:10.1371/journal.ppat.1000052
[34]
Rice SA, Koh KS, Queck SY, Labbate M, Lam KW, Kjelleberg S. Biofilm formation and sloughing in Serratia marcescens are controlled by quorum sensing and nutrient cues[J]. Journal of Bacteriology, 2005, 187(10): 3477-3485. DOI:10.1128/JB.187.10.3477-3485.2005
[35]
Brackman G, Coenye T. Quorum sensing inhibitors as anti-biofilm agents[J]. Current Pharmaceutical Design, 2015, 21(1): 5-11.
[36]
Dong YH, Zhang XF, An SW, Xu JL, Zhang LH. A novel two-component system BqsS-BqsR modulates quorum sensing-dependent biofilm decay in Pseudomonas aeruginosa[J]. Communicative & Integrative Biology, 2008, 1(1): 88-96.
[37]
Ding QF, Tan KS. The danger signal extracellular ATP is an inducer of Fusobacterium nucleatum biofilm dispersal[J]. Frontiers in Cellular and Infection Microbiology, 2016, 6: 155.
[38]
Williams DE, Boon EM. Towards understanding the molecular basis of nitric oxide-regulated group behaviors in pathogenic bacteria[J]. Journal of Innate Immunity, 2019, 11(3): 205-215. DOI:10.1159/000494740
[39]
Solano C, Echeverz M, Lasa I. Biofilm dispersion and quorum sensing[J]. Current Opinion in Microbiology, 2014, 18: 96-104. DOI:10.1016/j.mib.2014.02.008
[40]
Dehbashi S, Pourmand MR, Alikhani MY, Asl SS, Arabestani MR. Coordination of las regulated virulence factors with multidrug-resistant and extensively drug-resistant in superbug strains of P. aeruginosa[J]. Molecular Biology Reports, 2020, 47(6): 4131-4143. DOI:10.1007/s11033-020-05559-4
[41]
Sakuragi Y, Kolter R. Quorum-sensing regulation of the biofilm matrix genes (pel) of Pseudomonas aeruginosa[J]. Journal of Bacteriology, 2007, 189(14): 5383-5386. DOI:10.1128/JB.00137-07
[42]
Ueda A, Wood TK. Connecting quorum sensing, c-di-GMP, pel polysaccharide, and biofilm formation in Pseudomonas aeruginosa through tyrosine phosphatase TpbA (PA3885)[J]. PLoS Pathogens, 2009, 5(6): e1000483. DOI:10.1371/journal.ppat.1000483
[43]
Thornhill SG, Mclean RJC. Use of whole-cell bioassays for screening quorum signaling, quorum interference, and biofilm dispersion[J]. Methods in Molecular Biology, 2018, 1673: 3-24.
[44]
Boles BR, Thoendel M, Singh PK. Rhamnolipids mediate detachment of Pseudomonas aeruginosa from biofilms[J]. Molecular Microbiology, 2005, 57(5): 1210-1223. DOI:10.1111/j.1365-2958.2005.04743.x
[45]
Valliammai A, Sethupathy S, Priya A, Selvaraj A, Bhaskar JP, Krishnan V, Pandian SK. 5-Dodecanolide interferes with biofilm formation and reduces the virulence of Methicillin-resistant Staphylococcus aureus (MRSA) through up regulation of agr system[J]. Scientific Reports, 2019, 9(1): 13744. DOI:10.1038/s41598-019-50207-y
[46]
O'Neill E, Pozzi C, Houston P, Humphreys H, Robinson DA, Loughman A, Foster TJ, O'Gara JP. A novel Staphylococcus aureus biofilm phenotype mediated by the fibronectin-binding proteins, FnBPA and FnBPB[J]. Journal of Bacteriology, 2008, 190(11): 3835-3850. DOI:10.1128/JB.00167-08
[47]
Le KY, Dastgheyb S, Ho TV, Otto M. Molecular determinants of staphylococcal biofilm dispersal and structuring[J]. Frontiers in Cellular and Infection Microbiology, 2014, 4: 167.
[48]
Wang R, Khan BA, Cheung GYC, Bach THL, Jameson-Lee M, Kong KF, Queck SY, Otto M. Staphylococcus epidermidis surfactant peptides promote biofilm maturation and dissemination of biofilm-associated infection in mice[J]. Journal of Clinical Investigation, 2011, 121(1): 238-248. DOI:10.1172/JCI42520
[49]
Periasamy S, Joo HS, Duong AC, Bach THL, Tan VY, Chatterjee SS, Cheung GYC, Otto M. How Staphylococcus aureus biofilms develop their characteristic structure[J]. Proceedings of the National Academy of Sciences of the United States of America, 2012, 109(4): 1281-1286. DOI:10.1073/pnas.1115006109
[50]
Schwartz K, Syed AK, Stephenson RE, Rickard AH, Boles BR. Functional amyloids composed of phenol soluble modulins stabilize Staphylococcus aureus biofilms[J]. PLoS Pathogens, 2012, 8(6): e1002744. DOI:10.1371/journal.ppat.1002744
[51]
Yu M, Chua SL. Demolishing the great wall of biofilms in Gram-negative bacteria: to disrupt or disperse?[J]. Medicinal Research Reviews, 2020, 40(3): 1103-1116. DOI:10.1002/med.21647
[52]
Römling U, Galperin MY, Gomelsky M. Cyclic di-GMP: the first 25 years of a universal bacterial second messenger[J]. Microbiology and Molecular Biology Reviews, 2013, 77(1): 1-52. DOI:10.1128/MMBR.00043-12
[53]
Römling U, Galperin MY. Discovery of the second messenger cyclic di-GMP[J]. Methods in Molecular Biology, 2017, 1657: 1-8.
[54]
Ha DG, O'Toole GA. C-di-GMP and its effects on biofilm formation and dispersion: a Pseudomonas aeruginosa review[J]. Microbiol Spectr, 2015, 3(2): MB-0003-2014.
[55]
Sprecher KS, Hug I, Nesper J, Potthoff E, Mahi MA, Sangermani M, Kaever V, Schwede T, Vorholt J, Jenal U. Cohesive properties of the Caulobacter crescentus holdfast adhesin are regulated by a novel c-di-GMP effector protein[J]. mBio, 2017, 8(2): e00294-17.
[56]
Barnhart DM, Su SC, Baccaro BE, Banta LM, Farrand SK. CelR, an ortholog of the diguanylate cyclase PleD of Caulobacter, regulates cellulose synthesis in Agrobacterium tumefaciens[J]. Applied and Environmental Microbiology, 2013, 79(23): 7188-7202. DOI:10.1128/AEM.02148-13
[57]
Nieto V, Partridge JD, Severin GB, Lai RZ, Waters CM, Parkinson JS, Harshey RM. Under elevated c-di-GMP in Escherichia coli, YcgR alters flagellar motor bias and speed sequentially, with additional negative control of the flagellar regulon via the adaptor protein RssB[J]. Journal of Bacteriology, 2019, 202(1): e00578-19.
[58]
Bassis CM, Visick KL. The cyclic-di-GMP phosphodiesterase BinA negatively regulates cellulose-containing biofilms in Vibrio fischeri[J]. Journal of Bacteriology, 2010, 192(5): 1269-1278. DOI:10.1128/JB.01048-09
[59]
Yu S, Su TT, Wu HJ, Liu SH, Wang D, Zhao TH, Jin ZJ, Du WB, Zhu MJ, Chua SL, et al. PslG, a self-produced glycosyl hydrolase, triggers biofilm disassembly by disrupting exopolysaccharide matrix[J]. Cell Research, 2015, 25(12): 1352-1367. DOI:10.1038/cr.2015.129
[60]
Ma Q, Zhang GS, Wood TK. Escherichia coli BdcA controls biofilm dispersal in Pseudomonas aeruginosa and Rhizobium meliloti[J]. BMC Research Notes, 2011, 4: 447. DOI:10.1186/1756-0500-4-447
[61]
Cai YM, Hutchin A, Craddock J, Walsh MA, Webb JS, Tews I. Differential impact on motility and biofilm dispersal of closely related phosphodiesterases in Pseudomonas aeruginosa[J]. Scientific Reports, 2020, 10(1): 6232. DOI:10.1038/s41598-020-63008-5
[62]
Basu Roy A, Sauer K. Diguanylate cyclase NicD-based signalling mechanism of nutrient-induced dispersion by Pseudomonas aeruginosa[J]. Molecular Microbiology, 2014, 94(4): 771-793. DOI:10.1111/mmi.12802
[63]
Boyd CD, O'Toole GA. Second messenger regulation of biofilm formation: breakthroughs in understanding c-di-GMP effector systems[J]. Annual Review of Cell and Developmental Biology, 2012, 28: 439-462. DOI:10.1146/annurev-cellbio-101011-155705
[64]
Tolker-Nielsen T. Biofilm development[J]. Microbiology Spectrum, 2015, 3(2): MB-0001-2014.
[65]
Díaz-Salazar C, Calero P, Espinosa-Portero R, Jiménez-Fernández A, Wirebrand L, Velasco-Domínguez MG, López-Sánchez A, Shingler V, Govantes F. The stringent response promotes biofilm dispersal in Pseudomonas putida[J]. Scientific Reports, 2017, 7(1): 18055. DOI:10.1038/s41598-017-18518-0
[66]
Gaca AO, Colomer-Winter C, Lemos JA. Many means to a common end: the intricacies of (p)ppGpp metabolism and its control of bacterial homeostasis[J]. Journal of Bacteriology, 2015, 197(7): 1146-1156. DOI:10.1128/JB.02577-14
[67]
Dean SN, Chung MC, Van Hoek ML. Burkholderia diffusible signal factor signals to Francisella novicida to disperse biofilm and increase siderophore production[J]. Applied and Environmental Microbiology, 2015, 81(20): 7057-7066. DOI:10.1128/AEM.02165-15
[68]
Gottesman S, Storz G. Bacterial small RNA regulators: versatile roles and rapidly evolving variations[J]. Cold Spring Harbor Perspectives in Biology, 2011, 3(12): a003798.
[69]
Chambers JR, Sauer K. Small RNAs and their role in biofilm formation[J]. Trends in Microbiology, 2013, 21(1): 39-49. DOI:10.1016/j.tim.2012.10.008
[70]
Fazli M, Almblad H, Rybtke ML, Givskov M, Eberl L, Tolker-Nielsen T. Regulation of biofilm formation in Pseudomonas and Burkholderia species[J]. Environmental Microbiology, 2014, 16(7): 1961-1981. DOI:10.1111/1462-2920.12448
[71]
Jonas K, Edwards AN, Simm R, Romeo T, Römling U, Melefors Ö. The RNA binding protein CsrA controls cyclic di-GMP metabolism by directly regulating the expression of GGDEF proteins[J]. Molecular Microbiology, 2008, 70(1): 236-257. DOI:10.1111/j.1365-2958.2008.06411.x
[72]
Quintieri L, Zühlke D, Fanelli F, Caputo L, Liuzzi VC, Logrieco AF, Hirschfeld C, Becher D, Riedel K. Proteomic analysis of the food spoiler Pseudomonas fluorescens ITEM 17298 reveals the antibiofilm activity of the pepsin-digested bovine lactoferrin[J]. Food Microbiology, 2019, 82: 177-193. DOI:10.1016/j.fm.2019.02.003
[73]
Bardill JP, Zhao XN, Hammer BK. The Vibrio cholerae quorum sensing response is mediated by Hfq-dependent sRNA/mRNA base pairing interactions[J]. Molecular Microbiology, 2011, 80(5): 1381-1394. DOI:10.1111/j.1365-2958.2011.07655.x
[74]
Lenz DH, Mok KC, Lilley BN, Kulkarni RV, Wingreen NS, Bassler BL. The small RNA chaperone Hfq and multiple small RNAs control quorum sensing in Vibrio harveyi and Vibrio cholerae[J]. Cell, 2004, 118(1): 69-82. DOI:10.1016/j.cell.2004.06.009
[75]
Bartolini M, Cogliati S, Vileta D, Bauman C, Rateni L, Leñini C, Argañaraz F, Francisco M, Villalba JM, Steil L, et al. Regulation of biofilm aging and dispersal in Bacillus subtilis by the alternative sigma factor SigB[J]. Journal of Bacteriology, 2018, 201(2): e00473-18.