Modeling biological synchronization

Synchronized oscillatory processes in populations of living cells can arise in two ways. In one type of transition, individual cells oscillate out of synchrony at low number density and gradually synchronize as their density is increased. In another type, cells exhibit no oscillations at low density, but above a threshold density they suddenly begin oscillating in synchrony. Biological systems’ complexity makes understanding the transition mechanisms a challenge. But now, researchers led by Kenneth Showalter of West Virginia University have observed transitions of both types in a simpler nonbiological system. They used a version of the oscillating Belousov-Zhabotinsky reaction based on the catalyst ferroin, which they loaded onto porous particles 200 µm in diameter. When the particles were suspended in a reagent solution, the reaction on each particle oscillated at its own frequency, which could be monitored as the ferroin changed in color. Stirring the solution caused chemicals to be exchanged between each particle and the surrounding solution; as a result, the particles’ oscillation cycles could influence one another and thereby synchronize, as shown in the time-sequence images in the figure. When the researchers stirred the solution slowly, they observed synchronization of the first, gradual type. When they stirred more quickly, the transition was of the second, sudden type. The researchers explain their results using a kinetic model of the reaction and species exchange, which may aid in the understanding of biological synchronization. (A. F. Taylor et al., Science 323, 614, 2009 .) — Johanna L. Miller