Karmakar, R.; Karanam, A. R.; Tang, M.-H.; Rappel, W.-J.

When cells of the social amoeba Dictyostelium discoideum are starved of nutrients they start to synthesize and secrete the chemical messenger and chemoattractant cyclic Adenosine Mono Phosphate (cAMP). This signal is relayed by other cells, resulting in the establishment of periodic waves. The cells aggregate through chemotaxis towards the center of these waves. We investigated the chemotactic response of individual cells to repeated exposure to waves of cAMP generated by a microfluidic device. When the period of the waves is short, the chemotactic ability of the cells was found to increase upon exposure to more waves, suggesting the development of a longer-term memory. This effect was not significant for longer wave periods. We show that the experimental results are consistent with a model that includes a slowly rising and decaying component that is activated by the temporal gradient of cAMP concentration. The observed enhancement in chemotaxis is relevant to populations in the wild: once sustained, periodic waves of the chemoattractant are established, it is beneficial to cells to improve their chemotactic ability in order to reach the aggregation center sooner.