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：Kochcommon细菌种类，例如大肠杆菌和枯草芽孢杆菌，在低雷诺的液体中游泳，由鞭毛束从后面推动。 鞭毛束有时会导致细胞翻滚。 这种运行和滚筒运动在存在化学吸引力梯度（例如养分或其他细胞释放的化学信号）的情况下变得有偏见。 在游泳的化学梯度导致平均趋化细胞速度的化学梯度时，细胞会降低。 这种偏见的运动还导致细胞的净方向和活性应力的各向异性在游泳时施加在液体上。 因此，一种被视为连续活液的细菌悬浮液具有由于化学梯度引起的各向异性应激的异常特征。 该项目探讨了这些化学诱导的流体动力应激以及所得的流体动力流动的帮助或阻碍细菌的悬浮液，因为它们使用趋化性寻求营养或响应细胞细胞 - 细胞 - 细胞 - 细胞化学信号的功绩。趋化细菌诱导的流量。 互补实验包括可视化荧光细菌细胞和示踪剂胶体珠的运动以及细菌细胞浓度的测量。 经受线性化学吸引梯度的微流体中的细菌悬浮液提供了一个简单的情况，具有与时间无关的碱态。 在该系统中，由于趋化速度的竞争和由于其奔跑和摔倒的运动而导致的扩散，稀释细菌悬浮液会形成稳定的浓度，这是化学梯度方向上位置的指数函数。 然而，预期化学梯度诱导的活性应力将在临界细菌浓度以上引起对流。 实验测量将测试通过线性稳定性分析预测的临界浓度和从数值溶液中获得的对流模式。研究细菌将细菌分散到化学吸引剂中，用于两种平行的液体，这些流液在微通道中携带细菌和吸引剂。在存在和不存在施加的压力驱动流动的情况下，将使用准稳定的稳定性分析和动态方程的动态解来预测导致细菌吸引界面波形成波的条件。当细菌释放吸引其他细菌的化学信号时，它们会形成包括环和高细胞浓度的球形簇在内的模式。 基于趋化性和扩散性的相似性解决方案，这些溶液预测了浓度场中奇异性的发展。 该项目认为活跃的流体动力应力在这种聚类现象中的作用。 更广泛的影响：集体水动力运动改变了重要的细菌行为，涉及搜索营养和由于化学信号引起的组装，可能会对微生物学领域产生广泛的影响。 该主题还提供了一个良好的环境，可以在有趣的生物环境中向学生介绍耦合反应接触扩散的非线性动态。 将开发针对高中生的网站和夏季研究机会，以探索由于细菌之间的化学信号而导致的模式形成。