The 57th Annual Meeting of the Biophysical Society of Japan

This symposium welcomed seven speakers who have been working on motility and cellular sensing of various model organisms from the level of cytoplasm to multicellular collective motion.

Dr. Daisuke Nakane (Gakushuin University) is a specialist of bacterial motility over surfaces such as seen in gliding motility of Mycoplasma mobile. Describing the subject of light-controlled bacterial motility, Dr. Nakane gave a lecture on the mechanism by which cyanobacteria navigate in response to a spatial light gradient making reference to their recent results (Nakane and Nishizaka 2017). Dr. Andrew S Utada (University of Tsukuba) addresses the topic of bacterial motility and communication in the context of biofilm formation (Utada et al. 2014). His presentation described the quantification of physical/geometrical parameters used to describe filamentous bacterial elongation by time-lapse imaging of live bacteria using microfluidics. This research helps to understand the underlying mechanics of filament behavior with implications for microbial mat formation and bacterial communication. Dr. Yoshiaki Kinosita (University of Oxford) previously succeeded in directly observing the rotation of archaeal flagella called archaella (Kinosita et al. 2016). Dr. Kinosita this time presented recent results of archaellar dynamics obtained by such biophysical experiments as single-molecule measurements and fluorescent microscopy. The results of these experiments show a similarity with bacterial flagella, such as reversal of the rotational direction and turnover of torque generators. Dr. Norihiro Oyama (National Institute of Advanced Industrial Science and Technology, AIST) gave a theoretical interpretation of the intriguing phenomenon that the fluidity of bacterial cytoplasm depends on its metabolic activity: cytoplasm becomes “glassy” under conditions of suppressed metabolism (Nishizawa et al. 2017). A proposed non-equilibrium particulate model could explain the metabolism-dependent fluidization of the cytoplasm by treating the metabolic condition as one involving changes in the effective size of particles modeled as immobile proteins. It was demonstrated numerically that such immobile-type particle transitions alone can account for the experimental observations of glassy dynamics and inform upon situations involving active fluidization and changes in fragility (Oyama et al. 2019). Dr. Ken-ichi Wakabayashi (Tokyo Institute of Technology) has been addressing the mechanism of phototactic behavior of the volvocine green algae using unicellular Chlamydomonas and multicellular Volvox, showing that these two different cellular levels of organism existence display similar light-dependent behavior but possess distinct regulatory system of flagella (Ueki and Wakabayashi 2018). Dr. Wakabayashi presented their ongoing experiments in which four-celled Tetrabaena were investigated to gain evolutionary insight into volvocine phototaxis. Dr. Azusa Kage, one of the symposium organizers (and co-author of this Commentary), has been primarily investigating bioconvection observed in Chlamydomonas (Kage et al. 2013). This time, Dr. Kage noted two classes of collective swimming of Chlamydomonas uniflagellated mutant: one is two-body spinning translation caused by direct intercellular interaction via flagella, and the other is multi-body movement by indirect, hydrodynamic interaction. Detailed analysis of the observed spatial heterogeneity in collective motion revealed a scenario describing emergence of large-scale collective motion from the localized spinners. The final speaker Dr. Chika Okimura (Yamaguchi University) studies three-dimensional movement of stress fibers aligned in the wound-healing cells of fish skin keratocytes (Okimura et al. 2018). Dr. Okimura gave a detailed lecture on the structure and dynamics of stress fibers and proposed a plausible model of the migration mechanism of keratocytes.