Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages – archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes – wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.

中文翻译：

---

推进纳米机器：古细菌，鞭毛和纤毛的融合进化。

与大型真核生物中飞行和视力的反复趋同收敛相呼应，推进性游泳运动已经在生命的三个领域中的微生物中独立地演化。丝状附肢–古细菌中的古细菌，细菌中的鞭毛和真核生物中的纤毛–挥动，鞭打或旋转以推动微生物，克服扩散并实现新环境的定殖。这三种推进式纳米机器的实现方式是截然不同的：古细菌和鞭毛旋转，纤毛跳动或波动；鞭毛和纤毛聚集在它们的顶端，而古细菌聚集在它们的基部。古细菌和纤毛使用ATP促进运动，而鞭毛则使用离子动力。这些根本的差异反映出发展分子机器所需的修补，在这种情况下，迭代地选择了在适当情况下存在的机器来实现新功能，并且其起源反映在它们所产生的机制中。当代的同源性表明古细菌是从非旋转菌毛演变而来的，鞭毛是从非旋转附肢或分泌系统进化而来的，纤毛是从被动的感觉结构进化而来的。在这里，我们将对三种不同解决方案的结构，组装，机理和同源性进行回顾，以此作为基础，以更好地了解推进式纳米机器如何独立地进行三次进化，并突出分子进化的原理。和纤毛来自被动的感觉结构。在这里，我们将对这三种不同解决方案的结构，组装，机理和同源性进行回顾，以此作为基础，以更好地了解推进式纳米机器如何独立地进行三次进化并突出分子进化的原理。和纤毛来自被动的感觉结构。在这里，我们将对这三种不同解决方案的结构，组装，机理和同源性进行回顾，以此作为基础，以更好地了解推进式纳米机器如何独立地进行三次进化并突出分子进化的原理。