Department of Bioengineering, University of California, Los Angeles, CA 90095.
Department of Microbiology, University of Washington, Seattle, WA 98195.
Nature. 2013 May 16;497(7449):388-391. doi: 10.1038/nature12155. Epub 2013 May 8.
Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities. Biofilm-forming bacteria such as the opportunistic pathogen Pseudomonas aeruginosa are phenotypically distinct from their free-swimming, planktonic counterparts. Much work has focused on factors affecting surface adhesion, and it is known that P. aeruginosa secretes the Psl exopolysaccharide, which promotes surface attachment by acting as 'molecular glue'. However, how individual surface-attached bacteria self-organize into microcolonies, the first step in communal biofilm organization, is not well understood. Here we identify a new role for Psl in early biofilm development using a massively parallel cell-tracking algorithm to extract the motility history of every cell on a newly colonized surface. By combining this technique with fluorescent Psl staining and computer simulations, we show that P. aeruginosa deposits a trail of Psl as it moves on a surface, which influences the surface motility of subsequent cells that encounter these trails and thus generates positive feedback. Both experiments and simulations indicate that the web of secreted Psl controls the distribution of surface visit frequencies, which can be approximated by a power law. This Pareto-type behaviour indicates that the bacterial community self-organizes in a manner analogous to a capitalist economic system, a 'rich-get-richer' mechanism of Psl accumulation that results in a small number of 'elite' cells becoming extremely enriched in communally produced Psl. Using engineered strains with inducible Psl production, we show that local Psl concentrations determine post-division cell fates and that high local Psl concentrations ultimately allow elite cells to serve as the founding population for initial microcolony development.
细菌生物膜是一种表面相关的、多细胞的、形态复杂的微生物群落。生物膜形成细菌，如机会致病菌铜绿假单胞菌，其表型与自由游动的浮游细菌明显不同。许多研究都集中在影响表面附着的因素上，已知铜绿假单胞菌分泌 Psl 胞外多糖，它通过充当“分子胶”来促进表面附着。然而，个体表面附着的细菌如何自我组织成微菌落，即群落生物膜组织的第一步，还不是很清楚。在这里，我们使用大规模并行细胞跟踪算法来提取新定植表面上每个细胞的运动历史，从而确定 Psl 在早期生物膜发育中的新作用。通过将这项技术与荧光 Psl 染色和计算机模拟相结合，我们表明，铜绿假单胞菌在表面移动时会沉积一条 Psl 轨迹，这会影响随后遇到这些轨迹的细胞的表面运动，从而产生正反馈。实验和模拟都表明，分泌的 Psl 网络控制着表面访问频率的分布，这种分布可以用幂律来近似。这种帕累托型行为表明，细菌群落以类似于资本主义经济体系的方式进行自我组织，即 Psl 积累的“富者愈富”机制，导致少数“精英”细胞在共同产生的 Psl 中极度富集。使用具有诱导性 Psl 产生的工程菌株，我们表明局部 Psl 浓度决定了分裂后细胞的命运，并且高局部 Psl 浓度最终允许精英细胞成为初始微菌落发育的起始种群。
