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

该奖项研究薄膜的形成和生长，薄膜是在液体界面积累的膜状细菌群落。薄膜存在于许多环境中，并导致食物腐败，医院感染和环境污染。在空气/水界面处形成的膜与在固体界面上形成的生物膜相比表现出不同的性质和形成动力学，例如，它们的形状随时间发生复杂的变化，并受到氧气可用性的强烈影响。微重力实验提供了一个独特的机会来研究薄膜生长的两个未探索的方面：（1）重力驱动机制在界面附近的细菌和氧气运输中的作用，以及（2）在球形界面处的生长。研究球形界面处的薄膜生长模式可以深入了解软生物材料的行为，这对组织工程和生物材料具有重要价值。通过了解薄膜生长的传输机制，薄膜可以被控制用于食品保存，感染控制和环境修复等目的。实验将使用国际空间站上的环剪切滴模块进行，该模块可以部署受表面张力约束的厘米级液滴。微重力下的液滴可用作研究气/液界面现象的无容器反应器。将研究薄膜形成的两个方面：（1）在没有重力驱动的对流和沉降的情况下，细菌和氧气在短时间尺度（2-6小时）内初始运输到界面，以及（2）在长时间尺度（48小时）内球形液滴界面处薄膜的形态发生。数值模拟将补充实验，以破译负责表膜形态发生的特定运输过程的个人贡献。通过将微重力实验的结果与地面控制的结果进行比较，可以区分重力对薄膜形成的影响。已知微重力显著影响固体表面处的细菌生物膜，并且预期微重力将对弹性流体界面处的薄膜生长施加甚至更大的影响。探索这种影响将使有价值的见解机制负责的初始粘附，生长和增殖的薄膜。该奖项还将表征薄膜形态发生在下降的空气/水界面，专注于面外屈曲过渡，发生由于界面不稳定性和生长产生的压缩应力。具有近似球形边界的三维弯曲形状上的膜动力学可以作为模拟在软的生活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，因此该奖项将是第一个观察球形界面处薄膜形态发生的奖项。该奖项反映了NSF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.