It is a well known fact that in nature many animals exhibit collective behaviours to move more efficiently and save energy. For example, birds fly in flocks when they migrate, fish swim together when they feed, and cyclists ride in a close group during a race to dramatically reduce drag. However, little is known about what happens when we consider collective behaviour in the microscopic world of bacteria. In particular, whether collective swimming is also the most efficient way of moving at the micro-scales, where viscous effects are dominant, is a question that until recently had no answer.

 The mystery has been solved by Dr. Ishikawa and his group, who investigated the collective swimming of bacteria. By measuring the three-dimensional velocity field, they discovered that by moving together bacteria can swim three times as fast, and that the mass transport in the suspension can be considerably improved.

 Surprisingly, to achieve this enormous increase in speed, the bacteria used only a tiny amount of additional energy. The study was the first to discover that also for microorganisms collective swimming is the most energy-efficient way of moving and of absorbing oxygen and nutrients in nature.

More information  (Japanese) 

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Associate Professor Takuji Ishikawa

Graduate School of Engineering, Tohoku University

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