DISSERTATION RESEARCH: Structured groups and the evolution of cooperation in pathogenic bacterial biofilms

细菌通常被认为是最简单的生物，但这种观点正迅速被对细菌非常复杂的行为和社会生活的认识所取代。我们现在知道，自然界中的大多数细菌都存在于被称为生物膜的大规模三维群落中，这通常被比作“微生物城市”。其他人甚至认为生物膜最类似于多细胞组织，就像那些构成植物和动物的组织一样。无论是哪种情况，我们现在都知道细菌通过使用化学信号进行交流，协同迁移以构建多细胞结构，并付出代谢“代价”来产生一系列共享的有益分子。最后一种形式的合作似乎特别难以解释：如果自私的类型可以在不付出代价的情况下获得所有相同的好处，为什么进化会青睐合作类型？这个问题有三种可能的答案：1)也许产生有益分子的细胞本身比不产生有益分子的“搭便车”邻居受益更多；2)因为细菌繁殖是克隆的，生物膜中的“邻居”往往是克隆的伴侣，这意味着合作者倾向于在合作者周围，而搭便车者则靠近搭便车者；或者3)拥有更多合作者的整个生物膜将比拥有更多搭便车者的生物膜为全球人口贡献更多的后代。拟议中的实验将使用三维荧光显微镜精确测量人类病原体铜绿假单胞菌中的合作者和搭便车者之间的竞争，以绘制每种类型在生长的生物膜中的传播。这些实验将加强William Driscoll与遗传学家Leland和Elizabeth Pierson之间建立的跨学科合作，并极大地加强William Driscoll和一名本科生助理在微生物学和共聚焦显微镜方法方面的培训。最后，这些重要实验的结果将在2011年的国际科学会议“进化”上发表，并发表在同行评议的科学杂志上。

Bacteria are often thought to be the very simplest organisms, but this view is being quickly replaced by an appreciation for the very complex behavior and social lives of bacteria. We now know that most bacteria in nature exist in massive, three-dimensional communities called biofilms, which are often likened to 'microbial cities'. Others even suggest that biofilms are most similar to multicellular tissues, like those that make up plants and animals. In either case, we now know that bacteria communicate through the use of chemical signals, migrate in concert to build multicellular structures, and pay a metabolic 'cost' to produce an array of shared, beneficial molecules. This last form of cooperation seems especially challenging to explain: why would evolution favor a cooperative type, if a selfish type can get all of the same benefits without paying a cost? There could be three possible answers to this question: 1) perhaps a cell that produces a beneficial molecule can itself benefit more than a 'free rider' neighbor who does not, 2) because bacterial reproduction is clonal, 'neighbors' in biofilms tend to be clone-mates, which means cooperators will tend to be around cooperators while free riders are near free riders, or 3) entire biofilms with more cooperators will contribute more offspring to the global population than biofilms with more free riders. The proposed experiments will precisely measure competition between cooperators and free riders in the human pathogen Pseudomonas aeruginosa using three-dimensional fluorescent microscopy to map the spread of each type in a growing biofilm. These experiments will strengthen an established, interdisciplinary collaboration between William Driscoll and the geneticists Leland and Elizabeth Pierson and greatly enhance the training of William Driscoll and an undergraduate assistant in methods in microbiology and confocal microscopy. Finally, the results of these important experiments will be presented at the international scientific conference Evolution in 2011 and published in a peer-reviewed scientific journal.