铜绿假单胞菌胞外多糖和鼠李糖脂交互调控的分子机理

Biofilms are defined as surface-associated communities of microorganisms. They are prevalent in environmental and clinical settings. Bacteria within biofilms are usually embedded within an extracellular polymeric substance matrix, which confers a critical property of the biofilm resistance phenotype. Pseudomonas aeruginosa can readily form biofilms on a variety of surfaces and has become a model organism for biofilm research. Exopolysaccharide and rhamnolipid are two kinds of key extracellular matrix components in P. aeruginosa biofilms, which contribute to the biofilm formation. Yet it is still not clear how P. aeruginosa coordinates the synthesis of exopolysaccharide and rhamnolipid. Recently, we found that when exopolysaccharide over-produced in P. aeruginosa, the swarming motility reduced and rhamnolipid production decreased. In order to further investigate the link between exopolysaccharide and rhamnolipid, we will focus on the following three questions: .1) Does exopolysaccharide compete with rhamnolipid for synthesis substances or does exopolysaccharide and rhamnolipid regulate each other’s synthesis at the level of transcription or translation? .2) Is exopolysaccharide relative to quorum sensing system which can regulates rhamnolipid production? .3) Is the links between exopolysaccharide and rhamnolipid and quorum sensing system consistent in different P. aeruginosa strains? ..The study will be helpful to develop strategies to control biofilm-related complications in natural and clinical settings. On the other hand, rhamnolipid is one of the most promising biosurfactants and understanding its synthesis and regulation will also be beneficial for the construction of high-producing rhamnolipid industrial strains by using metabolic engineering.

生物被膜(Biofilm)是微生物依附于载体表面形成的微群落膜性聚合物，由于胞外多聚基质的保护，生物被膜内的细菌具有更强的环境适应性。胞外多糖和鼠李糖脂是铜绿假单胞菌合成的两种胞外多聚物，在生物被膜形成过程中各有贡献。铜绿假单胞菌如何协调这两种胞外多聚物的合成尚不清楚。申请者初步研究发现，胞外多糖大量合成时，菌体“群集”运动减弱，鼠李糖脂的合成量下降。本项目拟在此基础上进一步阐明以下问题：1）胞外多糖和鼠李糖脂之间是否会竞争底物或是调控彼此的转录或翻译；2）胞外多糖与调控鼠李糖脂的群体感应系统是否也存在交互的调控；3）胞外多糖与鼠李糖脂、群体感应系统的关系在不同假单胞菌菌株中是否一致。此研究，一方面有助于阐明生物被膜形成的分子机理，为控制生物被膜带来的各种问题提供理论依据和解决办法；另一方面，鼠李糖脂也是一种应用广泛的优良表面活性剂，其调控途径的阐明将有助于应用代谢工程进一步提高其产量。

生物被膜是微生物在自然界存在的一种常见状态，生物被膜内的细菌由于生物被膜中胞外多聚基质，尤其是胞外多糖的保护，从而具有更强的环境抗逆性，包括对各种抗生素的处理。胞外多糖和鼠李糖脂是铜绿假单胞菌合成的两种胞外多聚物，二者均控制生物被膜的形成，但是，二者是否有相互联系或者协调控制铜绿假单胞菌生物被膜的形成仍旧未知。本项目分别控制菌体胞外多糖和鼠李糖脂的合成，然后检测另一种产物的合成情况，结果发现，胞外多糖产量高的时候，鼠李糖脂的合成量就少，同时，与之相关的swarming运动和生物被膜的形成都发生相应的改变。进一步研究发现，二者的糖前体AlgC蛋白如果表达量多的时候，二者合成量均提高。同时，群体感应基因也会通过影响鼠李糖脂的合成而影响胞外多糖的产量进而影响生物被膜的形成。因此，本研究首次将影响生物被膜形成的两个重要因子，群体感应和胞外多糖联系在一起。因此，文章在微生物权威期刊《Applied and Environmental Microbiology》发表之后，立即被主编选为亮点文章，随后被国际生物医学领域具有高影响力的重要学术论文评估机构“Faculty of 1000”推荐阅读。

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