Hydrodynamically Assisted Bacterial Chemotaxis

流体动力学辅助细菌趋化作用

• 批准号: 1066193
• 负责人: Donald Koch
• 金额: $ 31.02万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2014-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1066193&HistoricalAwards=false
• 关键词: Hydrodynamically; Assisted; Bacterial; Chemotaxis

1066193 PI: KochCommon bacterial species such as E. coli and B. subtilis swim through fluids at low Reynolds numbers propelled from behind by a flagella bundle. The flagella bundle unravels at times leading to cell tumbling. This run and tumble motion becomes biased in the presence of a chemical attractant gradient such as a nutrient or a chemical signal released by other cells. The cells tumble less frequently when swimming up the chemical gradient leading to a mean chemotactic cell velocity. This biased motion also leads to a net orientation of the cells and an anisotropy of the active stresses the cells exert on the fluid as they swim. Thus, a bacterial suspension viewed as a continuum living fluid has the unusual feature of developing anisotropic stresses due to chemical gradients. This project explores the ways in which these chemically induced hydrodynamic stresses and the resulting hydrodynamic flows aid or hinder suspensions of bacteria as they use chemotaxis to seek nutrients or respond to cell-cell chemical signaling.Intellectual Merit: Linear stability analyses and computational solutions of the nonlinear behavior of ensemble averaged equations of motion for bacteria suspensions are used to predict the macroscopic hydrodynamic flows induced by chemotactic bacteria. Complementary experiments include visualization of the motion of fluorescent bacterial cells and tracer colloidal beads and measurement of the bacteria cell concentration. A bacteria suspension in a microfluidic well subjected to a linear chemo-attractant gradient provides a simple case with a time-independent base state. In this system a dilute bacteria suspension develops a steady concentration that is an exponential function of position in the chemo-gradient direction due to the competition of the chemotactic velocity and the diffusion due to their run-and-tumble motion. However, the chemical-gradient induced active stresses are expected to induce convection above a critical bacteria concentration. Experimental measurements will test the critical concentration predicted by linear stability analysis and the convective patterns obtained from numerical solutions. The dispersal of bacteria into a chemical attractant is studied for two parallel fluid streams which carry bacteria and attractant in a microchannel. A quasi-steady stability analysis and a dynamic solution of the equations of motion will be used to predict the conditions leading to formation of waves at the bacteria-attractant interface in both the presence and absence of an imposed pressure-driven flow. When bacteria release chemical signals that attract other bacteria, they form patterns including rings and spherical clusters with high cell concentrations. Similarity solutions have been developed based on chemotaxis and diffusion that predict the development of singularities in the concentration field. This project considers the role of active hydrodynamic stresses in this clustering phenomenon. Broader Impacts: The possibility that collective hydrodynamic motions alter important bacteria behaviors involving search for nutrients and assembly due to chemical signals could have a broad impact in the field of microbiology. This topic also provides a good setting in which to introduce students to the nonlinear dynamics of coupled reaction-convection-diffusion in an interesting biological setting. A web site and summer research opportunity targeted toward high school students will be developed to explore pattern formation due to chemical signaling among bacteria.

1066193 PI：Koch 大肠杆菌和枯草芽孢杆菌等常见细菌在鞭毛束的推动下以低雷诺数在液体中游动。 鞭毛束有时会散开，导致细胞翻滚。 在存在化学引诱剂梯度（例如营养物或其他细胞释放的化学信号）的情况下，这种奔跑和翻滚运动会变得有偏差。 当细胞沿着化学梯度游动时，翻滚的频率会降低，从而导致平均趋化细胞速度。 这种偏向运动还导致细胞的净方向以及细胞在游动时施加在流体上的主动应力的各向异性。 因此，被视为连续体活液的细菌悬浮液具有由于化学梯度而产生各向异性应力的不寻常特征。 该项目探讨了这些化学诱导的流体动力应力以及由此产生的流体动力流动如何帮助或阻碍细菌的悬浮，因为细菌利用趋化性来寻求营养或对细胞间的化学信号作出反应。智力优点：线性稳定性分析和计算解决方案细菌悬浮液整体平均运动方程的非线性行为用于预测趋化细菌引起的宏观流体动力流动。 补充实验包括荧光细菌细胞和示踪胶体珠运动的可视化以及细菌细胞浓度的测量。 微流体孔中的细菌悬浮液经受线性化学引诱剂梯度，提供了具有与时间无关的基础状态的简单情况。 在该系统中，由于趋化速度的竞争以及由于它们的运行和翻滚运动而导致的扩散，稀释的细菌悬浮液形成稳定的浓度，该浓度是化学梯度方向上的位置的指数函数。 然而，化学梯度引起的主动应力预计会引起超过临界细菌浓度的对流。 实验测量将测试线性稳定性分析预测的临界浓度和从数值解获得的对流模式。研究了在微通道中携带细菌和引诱剂的两条平行流体流的细菌向化学引诱剂的分散。准稳态稳定性分析和运动方程的动态解将用于预测在存在和不存在施加压力驱动流的情况下导致细菌-引诱剂界面处形成波的条件。当细菌释放吸引其他细菌的化学信号时，它们会形成包括高细胞浓度的环和球形簇在内的图案。 相似性解决方案是基于趋化性和扩散而开发的，可预测浓度场中奇点的发展。 该项目考虑了主动水动力应力在这种聚集现象中的作用。 更广泛的影响：集体流体动力学运动可能会改变重要的细菌行为，包括由于化学信号而寻找营养物质和组装，这可能会对微生物学领域产生广泛的影响。 本主题还提供了一个良好的环境，向学生介绍有趣的生物环境中反应-对流-扩散耦合的非线性动力学。 将开发一个针对高中生的网站和夏季研究机会，以探索细菌之间化学信号传导的模式形成。