The importance of surface-active metabolites (biosurfactants) in bacterial social behaviours

在自然生态系统中，细菌以微生物群落的形式存在，利用细胞间相互作用和交流的复杂系统来适应不断变化的环境条件。细菌作为社会有机体的概念正在深刻地改变我们对微生物学的看法。******生物膜是细菌在自然环境中首选的生长方式，也是微生物群落研究得最好的例子，它帮助细菌在不利条件下生存。生物膜在生物技术和医学领域的重要性日益明显。******“群体运动”，鞭毛细菌的一种鲜为人知的社会行为，被认为与多细胞活动中涉及的基因和机制的鉴定有关。铜绿假单胞菌是社会微生物学研究中研究最广泛的细菌种类。我们之前已经揭示了P. aeruginosa中涉及群体运动，生物膜形成和细胞间通讯的一些机制。此外，我们广泛研究了细胞外润湿剂和称为鼠李糖脂的趋化剂的产生，这是独特的群体表型所需的一种特殊细菌特征。******我们最近发现了一种混合感觉系统，它是正常蜂群运动的关键，并且独立于鼠李糖脂的产生。值得注意的是，这个感觉系统似乎参与了介导群体运动和生物膜发育的表达，特别是通过检测表面。******因为生活在表面上的细菌与群居细菌有几个共同的特征，我们假设群居运动反映了生物膜发育的基本方面。两个主要的工作假设将推动这项社会微生物学研究：(1)鼠李糖脂作为促进细菌扩散/生态系统定植的机制。我们的初步结果表明，鼠李糖脂的产生可以通过限制生长条件来促进，从而支持分散/增强新生态位的定植。(2)特定的感觉通路专门响应表面上的生长，调节群体运动所需的调节机制。******这个拟议的研究项目旨在通过研究群体运动作为一种模式微生物社会行为，进一步提高我们对细菌多细胞功能的理解。我们正在使用多方面的方法，主要基于微生物生理学功能基因组学和化学生物学的结合，来深入了解群体运动并确定其意义。知识的获得也有助于揭示控制细菌生物膜建立的途径。

In their natural ecosystems, bacteria persist as microbial communities, where they exploit elaborate systems of intercellular interaction and communication to adapt to changing environmental conditions. The concept of bacteria as social organisms is profoundly altering our views of microbiology. ******Biofilms, the preferred modes of growth of bacteria in the natural environment and the best-studied examples of microbial communities, help bacteria to survive under unfavourable conditions. The importance of biofilms in the biotechnological and medical fields is increasingly evident. ******«Swarming motility», a poorly understood social behaviour of flagellated bacteria is believed to be relevant to the identification of genes and mechanisms involved in multicellular activities. The ubiquitous and extremely versatile Pseudomonas aeruginosa is the most widely studied bacterial species in sociomicrobiology research. We have previously revealed a number of mechanisms involved in swarming motility, biofilm formation and intercellular communication in P. aeruginosa. Furthermore, we have extensively investigated the production of extracellular wetting and chemotactic agents called rhamnolipids, a special bacterial feature required for the unique swarming phenotype.******We have recently identified an hybrid sensory system that is key to normal swarming motility, and that is independent of rhamnolipid production. Significantly, this sensory system appears involved in mediating the expression of swarming motility and biofilm development specifically by detection of surfaces.******Because bacteria living on a surface share several features with swarming bacteria, we hypothesize that swarming motility reflects fundamental aspects of biofilm development. Two principal working hypotheses will drive this sociomicrobiology investigation: (1) rhamnolipids function as a mechanism promoting bacteria dispersal/ecosystem colonization. Our preliminary results suggest that production of rhamnolipids is promoted by restricting growth conditions, thus supporting the benefit of dispersion/enhanced colonization of new niches, (2) Specific sensory pathways specially responding to growth on a surface modulate the regulatory mechanisms required for swarming motility.******This proposed research project aims at further improve our understanding of the multicellular functions of bacteria through the study of swarming motility as a model microbial social behaviour. We are using a multi-faceted approach, primarily based on a combination of microbial physiology functional genomics, and chemical biology, to gain insight into swarming motility and determine its significance. Knowledge gain also contributes to reveal avenues to control the establishment of bacterial biofilms.