Chemotaxis of cargo-carrying self-propelled particles

Active particles with their characteristic feature of self-propulsion are regarded as the simplest models for motility in living systems. The accumulation of active particles in low activity regions has led to the general belief that chemotaxis requires additional features and at least a minimal ability to process information and to control motion. We show that self-propelled particles display chemotaxis and move into regions of higher activity, if the particles perform work on passive objects, or cargo, to which they are bound. The origin of this cooperative chemotaxis is the exploration of the activity gradient by the active particle when bound to a load. We theoretically capture the most relevant features of these active-passive dimers, and predict the crossover between anti-chemotactic and chemotactic behaviour. Moreover we show that connecting active particles in chains is sufficient to obtain the crossover from anti-chemotaxis to chemotaxis with increasing chain length. The observed transition is of significance to proto-forms of life enabling them to locate a source of nutrients even in the absence of any supporting sensomotoric apparatus.