Biological Engineering Program, Faculty of Engineering, King Mongkut's University of Technology Thonburi, Bangkok, Thailand.
Division of Biotechnology, School of Bioresources and Technology, King Mongkut's University of Technology Thonburi, Bangkok, Thailand.
PLoS One. 2018 May 10;13(5):e0196383. doi: 10.1371/journal.pone.0196383. eCollection 2018.
Morphological transformations in primitive organisms have long been observed; however, its biomechanical roles are largely unexplored. In this study, we investigate the structural advantages of dimorphism in Arthrospira platensis, a filamentous multicellular cyanobacterium. We report that helical trichomes, the default shape, have a higher persistence length (Lp), indicating a higher resistance to bending or a large value of flexural rigidity (kf), the product of the local cell stiffness (E) and the moment of inertia of the trichomes' cross-section (I). Through Atomic Force Microscopy (AFM), we determined that the E of straight and helical trichomes were the same. In contrast, our computational model shows that I is greatly dependent on helical radii, implying that trichome morphology is the major contributor to kf variation. According to our estimation, increasing the helical radii alone can increase kf by 2 orders of magnitude. We also observe that straight trichomes have improved gliding ability, due to its structure and lower kf. Our study shows that dimorphism provides mechanical adjustability to the organism and may allow it to thrive in different environmental conditions. The higher kf provides helical trichomes a better nutrient uptake through advection in aquatic environments. On the other hand, the lower kf improves the gliding ability of straight trichomes in aquatic environments, enabling it to chemotactically relocate to more favorable territories when it encounters certain environmental stresses. When more optimal conditions are encountered, straight trichomes can revert to their original helical form. Our study is one of the first to highlight the biomechanical role of an overall-shape transformation in cyanobacteria.
原始生物的形态转变早已被观察到，但它的生物力学作用在很大程度上尚未被探索。在这项研究中，我们研究了蓝藻 Arthrospira platensis 中二态性的结构优势，这是一种丝状多细胞蓝藻。我们报告说，螺旋状的发状毛（trichomes）是默认形状，具有更高的持久长度（Lp），这表明它更能抵抗弯曲或具有较大的弯曲刚度（kf），即局部细胞刚度（E）和发状毛横截面的惯性矩（I）的乘积。通过原子力显微镜（AFM），我们确定了直的和螺旋状的发状毛的 E 是相同的。相比之下，我们的计算模型表明 I 很大程度上取决于螺旋半径，这意味着发状毛形态是 kf 变化的主要贡献者。根据我们的估计，仅增加螺旋半径就可以使 kf 增加 2 个数量级。我们还观察到，由于其结构和较低的 kf，直的发状毛具有更好的滑行能力。我们的研究表明，二态性为生物体提供了机械可调节性，使其能够在不同的环境条件下茁壮成长。较高的 kf 使螺旋状发状毛在水生环境中通过平流更好地吸收营养。另一方面，较低的 kf 提高了直的发状毛在水生环境中的滑行能力，使其在遇到某些环境压力时能够向更有利的区域进行趋化运动。当遇到更优的条件时，直的发状毛可以恢复到原来的螺旋状。我们的研究是首次强调蓝藻整体形状转变的生物力学作用的研究之一。
