Individual Flagellar Waveform Affects Collective Behavior of XXXX .

@entity72161 @entity2060
Bioconvection is a form of collective motion that occurs spontaneously in the suspension of swimming microorganisms. In a previous study, we quantitatively described the "pattern transition," a phase transition phenomenon that so far has exclusively been observed in bioconvection of the unicellular green alga @entity2060 . We suggested that the transition could be induced by changes in the balance between the gravitational and shear-induced torques, both of which act to determine the orientation of the organism in the shear flow. As both of the torques should be affected by the geometry of the @entity2060 cell, alteration in the flagellar waveform might change the extent of torque generation by altering overall geometry of the cell. Based on this working hypothesis, we examined bioconvection behavior of two flagellar mutants of @entity2060 , ida1 and @entity72161 , making reference to the wild type. Flagella of ida1 beat with an abnormal waveform, while flagella of @entity72161 show a normal waveform but lower beat frequency. As a result, both mutants had swimming speed of less than 50% of the wild type. ida1 formed bioconvection patterns with smaller spacing than those of wild type and @entity72161 . Two-axis view revealed the periodic movement of the settling blobs of ida1, while @entity72161 showed qualitatively similar behavior to that of wild type. Unexpectedly, ida1 showed stronger negative gravitaxis than did wild type, while @entity72161 showed relatively weak gravitaxis. These findings suggest that flagellar waveform, not swimming speed or beat frequency, strongly affect bioconvection behavior in @entity2060 .
