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We characterize the taxis enhancement of swimming bacteria by collective migration without apparent clustering. We confine a dilute Salmonella suspension in a shallow channel and evaluate the thermotaxis response to local heating and diffusion. By combining cell tracking analysis and numerical simulation based on simple modeling, we show that the alignment interaction suppresses orientation fluctuation, strengthens migration bias, and also prevents the dispersion of accumulated population. The results show a prominent example of how a collective motion of active matter implements a biological function.

The giant acceleration (GA) of diffusion is a universal phenomenon predicted by the theoretical analysis given by Reimann et al. [Phys. Rev. Lett. 87, 010602 (2001)]. Here we apply the theory of the GA of diffusion to a single-molecule experiment on a rotary motor protein, F1, which is a component of F0F1, adenosine triphosphate synthase. We discuss the energetic properties of F1 and identify a high energy barrier of the rotary potential to be 20kBT, with the condition that the adenosine diphosphates are tightly bound to the F1 catalytic sites. To conclude, the GA of diffusion is useful for measuring energy barriers in nonequilibrium and single-molecule experiments. [ABSTRACT FROM AUTHOR]