Li Yung-Hua, Tang Nan, Aspiras Marcelo B, Lau Peter C Y, Lee Janet H, Ellen Richard P, Cvitkovitch Dennis G
Dental Research Institute, University of Toronto, 124 Edward Street, Toronto, Ontario, Canada M5G 1G6.
J Bacteriol. 2002 May;184(10):2699-708. doi: 10.1128/JB.184.10.2699-2708.2002.
In a previous study, a quorum-sensing signaling system essential for genetic competence in Streptococcus mutans was identified, characterized, and found to function optimally in biofilms (Li et al., J. Bacteriol. 183:897-908, 2001). Here, we demonstrate that this system also plays a role in the ability of S. mutans to initiate biofilm formation. To test this hypothesis, S. mutans wild-type strain NG8 and its knockout mutants defective in comC, comD, comE, and comX, as well as a comCDE deletion mutant, were assayed for their ability to initiate biofilm formation. The spatial distribution and architecture of the biofilms were examined by scanning electron microscopy and confocal scanning laser microscopy. The results showed that inactivation of any of the individual genes under study resulted in the formation of an abnormal biofilm. The comC mutant, unable to produce or secrete a competence-stimulating peptide (CSP), formed biofilms with altered architecture, whereas the comD and comE mutants, which were defective in sensing and responding to the CSP, formed biofilms with reduced biomass. Exogenous addition of the CSP and complementation with a plasmid containing the wild-type comC gene into the cultures restored the wild-type biofilm architecture of comC mutants but showed no effect on the comD, comE, or comX mutant biofilms. The fact that biofilms formed by comC mutants differed from the comD, comE, and comX mutant biofilms suggested that multiple signal transduction pathways were affected by CSP. Addition of synthetic CSP into the culture medium or introduction of the wild-type comC gene on a shuttle vector into the comCDE deletion mutant partially restored the wild-type biofilm architecture and further supported this idea. We conclude that the quorum-sensing signaling system essential for genetic competence in S. mutans is important for the formation of biofilms by this gram-positive organism.
在之前的一项研究中，已鉴定、表征了变形链球菌遗传感受态所必需的群体感应信号系统，并发现其在生物膜中功能最佳（Li等人，《细菌学杂志》183:897 - 908，2001年）。在此，我们证明该系统在变形链球菌启动生物膜形成的能力中也发挥作用。为了验证这一假设，对变形链球菌野生型菌株NG8及其在comC、comD、comE和comX中存在缺陷的敲除突变体，以及一个comCDE缺失突变体，进行了启动生物膜形成能力的检测。通过扫描电子显微镜和共聚焦扫描激光显微镜检查生物膜的空间分布和结构。结果表明，所研究的任何一个单独基因的失活都会导致异常生物膜的形成。无法产生或分泌感受态刺激肽（CSP）的comC突变体形成的生物膜结构改变，而在感知和响应CSP方面存在缺陷的comD和comE突变体形成的生物膜生物量减少。向培养物中外源添加CSP以及用含有野生型comC基因的质粒进行互补，可恢复comC突变体的野生型生物膜结构，但对comD、comE或comX突变体生物膜无影响。comC突变体形成的生物膜与comD、comE和comX突变体生物膜不同这一事实表明，多个信号转导途径受CSP影响。向培养基中添加合成CSP或将穿梭载体上的野生型comC基因导入comCDE缺失突变体，部分恢复了野生型生物膜结构，并进一步支持了这一观点。我们得出结论，变形链球菌遗传感受态所必需的群体感应信号系统对这种革兰氏阳性菌形成生物膜很重要。
