  Cooperative motion in biological microswimmers is crucial for their survival
as it facilitates adhesion to surfaces, formation of hierarchical colonies,
efficient motion, and enhanced access to nutrients. Synthetic microswimmers
currently lack truly cooperative behavior that originates from activity-induced
interactions. Here, we demonstrate that catalytic microswimmers show a variety
of cooperative behaviors along one-dimensional paths. We show that their speed
increases with the number of swimmers, while the activity induces a preferred
distance between swimmers. Using a minimal model, we ascribe this behavior to
an effective activity-induced potential that stems from a competition between
chemical and hydrodynamic coupling. These interactions further induce active
self-assembly into trains as well as compact chains that can elongate,
break-up, become immobilized and remobilized. We identify the crucial role that
environment morphology and swimmer directionality play on these highly dynamic
chain behaviors. These activity-induced interactions open the door towards
exploiting cooperation for increasing the efficiency of, as well as provide
temporal and spatial control over, microswimmer motion, thereby enabling them
to perform intricate tasks inside complex environments.
