Abstract
Cells are complex biochemical systems whose behaviors emerge from interactions among myriad molecular components. Computation is often invoked as a general framework for navigating this cellular complexity. However, it is unclear how cells might embody computational processes such that the theories of computation, including finite-state machine models, could be productively applied. Here, we demonstrate finite-state-machine-like processing embodied in cells using the walking behavior of Euplotes eurystomus, a ciliate that walks across surfaces using fourteen motile appendages (cirri). We found that cellular walking entails regulated transitions among a discrete set of gait states. The set of observed transitions decomposes into a small group of high-probability, temporally irreversible transitions and a large group of low-probability, time-symmetric transitions, thus revealing stereotypy in the sequential patterns of state transitions. Simulations and experiments suggest that the sequential logic of the gait is functionally important. Taken together, these findings implicate a finite-state-machine-like process. Cirri are connected by microtubule bundles (fibers), and we found that the dynamics of cirri involved in different state transitions are associated with the structure of the fiber system. Perturbative experiments revealed that the fibers mediate gait coordination, suggesting a mechanical basis of gait control.
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•Euplotes eurystomus is a cell that walks with 14 leg-like appendages called cirri•The walking gait involves complex, partially stereotyped patterns of cirral activity•Sequential patterns defining gait coordination are necessary for proper motility•Gait coordination is mediated by an internal system of bundled microtubules
Larson et al. analyze the motility of the unicellular organism Euplotes eurystomus, which uses leg-like appendages called cirri to walk across surfaces. Walking involves an unusual gait with elements of variability and stereotypy in patterns of cirral activity. Gait coordination is mediated by an internal system of bundled microtubules.