ISS: The Influence of Microgravity on Bacterial Transport and Pellicle Morphogenesis

该奖项研究了膜的形成和生长，膜是在液体界面积聚的膜状细菌群落。在许多环境中都可以发现薄膜，它们会导致食物变质、医院感染和环境污染。与在固体界面上形成的生物膜相比，在空气/水界面上形成的膜具有不同的特性和形成动力学，例如，它们随着时间的推移会发生复杂的形状变化，并受到氧气可用性的强烈影响。微重力下的实验提供了一个独特的机会来研究膜生长的两个未被探索的方面：(1)重力驱动机制在界面附近细菌和氧气运输的作用，以及(2)在球形界面上的生长。研究球形界面上的膜生长模式可以深入了解软体生物材料的行为，这对组织工程和生物材料具有重要价值。通过了解膜生长背后的运输机制，可以控制膜的目的，如食品保存，感染控制和环境修复。实验将使用国际空间站上的环形剪切液滴模块进行，该模块可以部署受表面张力约束的厘米级液滴。微重力下的液滴可以用作无容器反应器，用于研究空气/液体界面的现象。研究人员将研究膜层形成的两个方面：(1)在短时间尺度（2-6小时）内，在没有重力驱动的对流和沉降的情况下，细菌和氧气向界面的初始运输；(2)在长时间尺度（48小时）内，在球形液滴界面上的膜层形态发生。数值模拟将补充实验，以破译负责薄膜形态发生的特定运输过程的个人贡献。通过比较微重力实验和地面控制的结果，可以区分重力对膜形成的影响。已知微重力会显著影响固体表面的细菌生物膜，预计微重力将对弹性流体界面的膜膜生长产生更大的影响。探索这种影响将使有价值的见解机制负责最初的粘附，生长和增殖的膜。该合同还将描述水滴空气/水界面的膜膜形态，重点研究由于界面不稳定和生长产生的压应力而发生的面外屈曲转变。具有近似球形边界的三维弯曲形状的膜膜动力学可以作为模拟软质生物材料中观察到的自然过渡的模型系统。由于微重力使厘米级液滴的部署成为可能，该奖项将首次观察到球形界面上的膜层形态发生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award investigates the formation and growth of pellicles, which are membrane-like bacterial communities that accumulate at liquid interfaces. Pellicles are found in many settings and contribute to food spoilage, hospital infections, and environmental contamination. Pellicles formed at air/water interfaces exhibit distinct properties and formation dynamics compared to biofilms formed on solid interfaces, e.g., they undergo complex changes in shape over time and are strongly influenced by oxygen availability. Experiments in microgravity provide a unique opportunity to investigate two unexplored aspects of pellicle growth: (1) the role of gravity-driven mechanisms for bacteria and oxygen transport near an interface, and (2) growth at a spherical interface. Studying pellicle growth patterns at spherical interfaces can yield insights into how soft living materials behave, which is valuable for tissue engineering and biomaterials. By understanding the transport mechanisms underlying pellicle growth, pellicles can be controlled for purposes such as food preservation, infection control, and environmental remediation.Experiments will be conducted using the Ring Shear Drop module aboard the International Space Station, which enables deployment of centimeter-scale drops constrained by surface tension. Drops in microgravity can be used as container-less reactors for studying phenomena at air/liquid interfaces. Two facets of pellicle formation will be investigated: (1) initial transport of bacteria and oxygen to the interface in the absence of gravity-driven convection and sedimentation over short timescales (2-6 hours), and (2) morphogenesis of pellicles at a spherical drop interface over long timescales (48 hours). Numerical modeling will supplement experiments to decipher the individual contributions of specific transport processes responsible for pellicle morphogenesis. By comparing results from microgravity experiments to Earth-based controls, the effects of gravity on pellicle formation can be distinguished. Microgravity is known to significantly affect bacterial biofilms at solid surfaces, and it is expected that microgravity will exert an even greater influence on pellicle growth at elastic fluid interfaces. Exploring this influence will enable valuable insights into mechanisms responsible for initial adhesion, growth, and proliferation of pellicles. This award will also characterize pellicle morphogenesis at the drop air/water interface, focusing on the out-of-plane buckling transitions that occur due to interfacial instabilities and compressive stresses generated by growth. Pellicle dynamics on three-dimensional curved shapes with approximately spherical boundaries can serve as a model system that mimics natural transitions observed in soft living materials. Because microgravity enables deployment of centimeter scale droplets, this award will be the first to observe pellicle morphogenesis at spherical interfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.