High-speed video reveals how algae swim
EU-funded scientists have discovered how individual algal cells change direction while swimming. The scientists used high-speed cinematography to study the motion of the flagella, hair-like appendages that the cells use to propel themselves through the water, in the algal species Chlamydomonas reinhardtii. The study, published in the journal Science, was supported in part by the CYCLOSIS ('The biophysics of cytoplasmic streaming in Chara corallina') project, which was financed through the People programme of the Seventh Framework Programme (FP7). The findings are important because flagella are found in many organisms, and in fact they are almost identical to the cilia found on cells in the human body. The coordination of cilia or flagella is key to many important processes, including movement, sensing, development, and the transport of fluid in the respiratory system. However, the way these structures control locomotion is poorly understood. In this latest piece of research, the scientists found that the algae have two distinct 'gears'. Most of the time, the two flagella of the cell beat synchronously, so that the cells look like they are swimming breaststroke. During this time, the cells swim in a straight line. However, every few seconds, the flagella beat asynchronously, triggering a sharp change in direction. A mathematical analysis of the beating motion reveals that the two flagella are 'coupled oscillators', which synchronise their motion in a similar way to the flashing of fireflies or a 'Mexican wave' in a sports stadium. According to the researchers, the coupling arises from the fluid flows created by the beating flagella. The study represents the first direct proof that synchronisation is caused by hydrodynamic interactions. 'These results indicate that flagellar synchronisation is a much more complex problem than had been appreciated, and involves a delicate interplay of cellular regulation, hydrodynamics, and biochemical noise,' commented Professor Raymond Goldstein of the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge in the UK. In a related article, Roman Stocker and William Durham of the Massachusetts Institute of Technology (MIT) in the US speculate that C. reinhardtii's 'run and tumble' motion may help it to evade predators.
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