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

该奖项研究薄膜的形成和生长，薄膜是聚集在液体界面上的膜状细菌群落。在许多环境中都会发现薄膜，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/水界面形成的膜具有不同的性质和形成动力学，例如，它们的形状随着时间的推移经历复杂的变化，并且受到氧气可用性的强烈影响。微重力实验为研究薄膜生长的两个未被探索的方面提供了一个独特的机会：(1)重力驱动机制在细菌和界面附近氧气运输中的作用，以及(2)球形界面上的生长。研究球状界面上的膜层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运输机制，可以控制薄膜用于食物保存、感染控制和环境修复等目的。国际空间站上将使用环形剪切液滴模块进行实验，该模块可以部署厘米级的液滴，受表面张力的限制。微重力下的液滴可用作无容器反应器，用于研究气/液界面现象。薄膜形成的两个方面将被研究：(1)在短时间(2-6小时)内，在没有重力驱动的对流和沉积的情况下，细菌和氧气向界面的初始传输，以及(2)在长时间尺度上(48小时)球形液滴界面上的薄膜的形态发生。数值模拟将补充实验，以破译负责膜形态形成的特定运输过程的个体贡献。通过比较微重力实验和地面对照的结果，可以区分重力对薄膜形成的影响。微重力对固体表面的细菌生物膜有显著的影响，预计微重力对弹性流体界面的膜生长将产生更大的影响。探索这种影响将使人们能够有价值地深入了解导致膜最初粘连、生长和增殖的机制。该奖项还将描述液滴空气/水界面的薄膜形态发生，重点是由于界面不稳定性和生长产生的压应力而发生的平面外屈曲转变。具有近似球形边界的三维曲线形状上的膜动力学可以作为一个模型系统，模拟在软的生物材料中观察到的自然转变。由于微重力能够部署厘米级的液滴，该奖项将是第一个观察到球形界面上的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智力优势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.