A tale of two motilities: adaptive biomechanical systems in complex, changing environments

Abstract

Natural environments are heterogeneous and can fluctuate with time. As such, biomechanical systems from proteins to whole organisms have developed strategies to deal with considerable spatial and temporal variability. Understanding the physics behind these strategies is important both in an evolutionary context and for the development of bioinspired systems. I will discuss two (quite different!) broadly successful locomotive modes: flagellated motility in bacteria and interfacial locomotion in geckos. (1) A bacterium's life can be complicated: it must swim through fluids of varying viscosity as well as interact with surfaces and other bacteria. We characterized the mechanosensitive adaptation in bacterial flagella that facilitates these transitions by using magnetic tweezers to manipulate external torque on the bacterial flagellar motor. Our model for the dynamics of load-dependent assembly in the flagellar motor illustrates how this nanomachine allows bacteria to adapt to changes in their surroundings. (2) Animals that live in areas with periodic flooding must deal with seasonal fluctuations in their habitats. In the field, we showed that tropical geckos can run across the water’s surface as fast as they can on land. In the lab, we showed that these geckos use both surface slapping and surface tension, as well as take advantage of their superhydrophobic skin, to transition between terrestrial and semi-aquatic locomotion.