Measuring energy consumption through space and time in an active matter system of cytoskeletal motors and filaments

Active matter systems consume energy from their environment to form organized, dynamical patterns and structures. These ordered states do not exist in the absence of an energy source. As such, a more general description of energy-driven behavior than is offered by near-equilibrium approaches is required to describe active matter. To gain insight into the energetic cost to form and maintain order, we investigate the assembly of an ordered aster from a disordered, homogeneous mixture of microtubules. This formation occurs due to optogenetically controllable cross-linking of the molecular motors that walk on the microtubules and hydrolyze ATP. Theoretical reaction-diffusion models predict a non-equilibrium ATP distribution resulting from a corresponding motor profile; we test these models via fluorescent readouts of ATP and motor concentrations in both space and time. Comparing the theoretical versus measured ATP profiles provides insight into the dynamics of structure formation and properties of the motors, such as if motors operate cooperatively. Our experiments revealed an ATP depletion gradient that is maximized at the aster core, where the concentration of the motors is highest. This work is a first step in understanding the role of energy consumption through space and time in the formation and maintenance of organization in this active matter system. More broadly, our work provides a case study towards the larger effort of developing generalized theories of non-equilibrium systems.