The importance of surface-active metabolites (biosurfactants) in cooperative 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。认识到细菌通常作为多细胞群体，为微生物的生物学和生态学提供了关键的见解，并应引导我们的研究工作更好地理解有组织的微生物群落的涌现特性。事实上，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。“群体运动”是鞭毛细菌的一种鲜为人知的社会行为。铜绿假单胞菌无处不在，用途广泛，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中涉及群体运动和细胞间通讯的一些机制。此外，我们广泛研究了称为鼠李糖脂的细胞外表面活性剂的生产，这是独特的群体表型所需的一种特殊细菌特征。鼠李糖脂是一种具有表面活性的单糖和双糖两亲性糖脂，已知已有60多年，是研究得最好的生物表面活性剂之一。这些分子由各种细菌产生，最著名的是铜绿假单胞菌和一些伯克霍尔德菌，这些分子仍然有许多秘密和希望。其他几种细菌也会产生表面活性分子。细菌释放表面活性分子的确切原因尚不清楚，人们提出了许多假设。有趣的是，我们目前正在发现涉及生物表面活性剂的不同细菌物种之间令人惊讶的相互作用，例如揭示这些表面活性分子可以作为可共享的“公共产品”，为混合社区提供新特性。这种方法也表明，以前不知道群集或产生表面活性剂的细菌在与其他微生物物种相互作用时可以表达新的表型。由于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微生物合作社会生活的基本方面。我们将使用蜂群作为微生物合作行为的模型。推动这一社会微生物学研究的主要工作假设是，生物表面活性剂是作为微生物表面生长生命的介质产生的。我们将研究与其他细菌物种的相互作用如何调节这些表面活性分子的产生。细菌通常以多细胞组织和群体的形式存在。然而，我们对这些生物的大部分知识主要是在单个细胞水平上，或者作为纯培养物。这里提出的研究将增强我们对细菌作为多细胞群落生活的新特性的理解。

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 recognition that bacteria typically act as multicellular groups is providing key insights into the biology and ecology of microorganisms and should lead our research efforts to better understand the emergent properties of organized microbial communities. Indeed, the concept of bacteria as social organisms is profoundly altering our views of microbiology. «Swarming motility» is a poorly understood social behaviour of flagellated bacteria. The ubiquitous and 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, and intercellular communication in P. aeruginosa. Furthermore, we have extensively investigated the production of extracellular surface-active agents called rhamnolipids, a special bacterial feature required for the unique swarming phenotype. Known for more than 60 years and among the best studied biosurfactants, rhamnolipids comprise a diverse group of mono- and di-sugar amphiphilic glycolipids with surface-active properties. Produced by various bacteria, the best known being Pseudomonas aeruginosa and a few Burkholderia species, these molecules still hold many secrets and promises. Several other bacterial species also produce surface-active molecules. The exact reason why bacteria release surface-active molecules is still unclear, and many hypotheses have been proposed. Interestingly, we are currently finding surprising interactions between different bacterial species involving biosurfactants, for instance revealing that these surface-active molecules can act as shareable «public goods» providing emerging properties to mixed communities. Such approach is also suggesting that bacteria not previously known to swarm or produce surfactant can express new phenotypes when interacting with other microbial species. Because bacteria living on a surface share several features with swarming bacteria, we hypothesize that swarming motility reflects fundamental aspects of the cooperative social life of microbes. We will use swarming as a a model microbial cooperative behaviour. The principal working hypothesis that will drive this sociomicrobiology investigation is that biosurfactants are produced as mediators of microbial surface growth life. We will investigate how interactions with other bacterial species might modulate the production of these surface-active molecules. Bacteria typically live as multicellular organizations and communities. However, most of our knowledge on these organisms is mostly at the individual cell level, or as pure cultures. The research proposed here will enhance our understanding of the emergent properties of bacteria living as multicellular communities.