The Effects of Physical Forces on Bacteria Growth

细菌是地球上数量最多、变化最多的生命形式。细菌可以在人类以及对食物供应和环境重要的动物和植物中引起疾病。然而，细菌也可以是有益的（益生菌），并用于工业上的药品生产。控制细菌数量对于预防疾病和工业环境中的质量控制是必要的。抗生素是用来杀死细菌的，但是新抗生素的开发还没有跟上医药和工业的需要。大多数抗生素通过引起细胞壁的机械故障（破裂）导致细胞死亡来杀死细菌。这项工作的研究目标是确定细菌的生理变化如何响应物理力，并确定细菌细胞壁抵抗物理力的能力。这项工作的教育目标是举办一个为期一周的关于生物材料力学特性的讲习班，对象是来自传统上代表性不足群体的高中生，并为在机构内和国家一级扩大代表性不足群体成员参与科学的其他活动作出贡献。目前提出了两种假说来解释参与细胞壁合成的细胞内蛋白的定位和迁移：a)参与细胞壁合成的细胞内蛋白受局部细胞壁曲率的引导；b)细胞壁合成蛋白被定向到细胞壁应力/应变增加的位置。这项工作使用基于微流体的机械测试方法解决了这个问题，该方法可以在不改变细胞壁曲率的情况下修改机械应力/应变。该方法的新颖之处在于，当施加机械负荷时，它可以观察活细菌中的细胞内蛋白质，并且不需要改变细菌生理条件（改变渗透压，丝状生长等）。本工作的研究目标是：1)确定与细胞壁合成相关的蛋白质（MreB蛋白）的机械应变、细胞壁生长区域和亚细胞运动之间的关系；2)确定细菌细胞壁在施加载荷时的整个机械应变场。

Bacteria are the most populous and variable form of life on Earth. Bacteria can cause disease in humans as well as in animals and plants important to the food supply and the environment. However, bacteria can also be beneficial (probiotics) and are used industrially in the production of pharmaceuticals. Controlling bacterial populations is necessary to prevent disease and for quality control in industrial settings. Antibiotics are used to kill bacteria, but the development of new antibiotics has not kept up with needs in medicine and industry. Most antibiotics kill bacteria by causing mechanical failure (rupture) of the cell wall leading to cell death. The research goal of this work is to determine how bacterial physiology changes in response to physical forces and to determine how well the bacterial cell wall resists physical forces. The educational objectives of the work are to lead a week-long workshop on the mechanical properties of biological materials targeted to high-school students from traditionally under-represented groups and contribute to other activities to broaden participation in science by members of under-represented groups within the institution and at the national level.Two hypotheses have been presented to explain the location and migration of intracellular proteins involved in cell wall synthesis: a) intracellular proteins involved in cell wall synthesis are directed by local cell wall curvature; and b) that cell wall synthesis proteins are directed to locations of increased cell wall stress/strain. This work addresses this question using a microfluidics-based mechanical testing approach that can modify mechanical stress/strain without large changes in cell wall curvature. The approach is novel in that it makes it possible to observe intracellular proteins in live bacteria while mechanical loading is being applied and does not require conditions of altered bacterial physiology (altered osmolality, filamentous growth, etc.). The research goals of this work are to: 1) Determine the relationship between mechanical strain, regions of cell wall growth and subcellular movement of a protein associated with cell wall synthesis (the MreB protein); and 2) Determine the entire mechanical strain field in the bacterial cell wall while load is applied.