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

在它们的自然生态系统中，细菌以微生物群落的形式存在，在那里它们利用复杂的细胞间相互作用和交流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的首选生长方式，也是微生物群落研究最深入的例子，有助于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。 “群居运动”是鞭毛细菌的一种鲜为人知的社会行为，人们认为这与识别参与多细胞活动的基因和机制有关。铜绿假单胞菌是目前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参与铜绿假单胞菌的群体运动、生物膜形成和细胞间通讯的一些机制。此外，我们还广泛研究了称为鼠李糖脂的细胞外润湿和化学趋化剂的生产，这是一种独特的集群表型所需的特殊细菌特征。 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，而且独立于鼠李糖脂的产生。值得注意的是，这种感觉系统似乎特别通过对表面的检测参与了成群运动和生物膜发育的表达。 由于生活在表面的细菌与成群的细菌有几个共同的特征，我们假设成群的运动性反映了生物膜发展的基本方面。两个主要的工作假说将推动这项社会微生物学研究：(1)鼠李糖脂作为一种促进细菌扩散/生态系统定植的机制发挥作用。我们的初步结果表明，限制生长条件可以促进鼠李糖脂的生产，从而支持新生态位的分散/增强定植的好处；(2)特定的感官通路特别对表面上的生长做出反应，调节集群运动所需的调节机制。 这项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的社会行为，进一步提高我们对细菌多细胞功能的理解。我们正在使用一种多方面的方法，主要基于微生物生理学、功能基因组学和化学生物学的组合，以深入了解蜂群运动并确定其意义。知识的获得也有助于揭示控制细菌生物被膜建立的途径。

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.