Pressure-Ineduced Activation of the Swimming Motility of Magnetotactic Bacterium

Abstract

The marine bacterium MO-1 cell has a flagellar apparatus with two lophotrichous bundles. Each apparatus is a tight bundle of seven flagellar filaments in a sheath [1]. The unique motility machinery is sensitive to environmental factors including physical and chemical conditions. Here, we performed a motility assay of marine bacterium MO-1 at high-pressure. In general, application of pressure could change the structure and function of motility machineries [2]. We enclosed MO-1 cells in a high-pressure chamber for optical microscopy [3]. At ambient pressure condition (0.1 MPa), most cells did not show any directional motions. When pressure was increased to 80 MPa, many cells started to swim in solution. The fraction of swimming cells drastically increased with time, and reached to a peak of ∼70 %, and then gradually decreased. The translational speed of the swimming cells at the peak was about 50 µm s−1, which was almost half of the speed of swimming cells at 0.1 MPa. The speed also gradually decreased with time. The pressure-induced activation of cell motility occurred remarkably in the limited pressure region of 60-100 MPa. High-speed video microscopy revealed that MO-1 cells swim constantly in a helical trajectory at high-pressure conditions. But, the pitch in a helical motion at 80 MPa was about 2 times larger than that at 0.1 MPa. This result indicated that the flagellar motion induced by high pressure is slightly different from that under normal pressure. The detailed mechanism would be revealed by monitoring the motion of individual sheaths. [1] Ruan J., T. Kato, …, K. Namba. 2012. Proc. Natl. Acad. Sci.USA.109:20643-8. [2] Nishiyama M. 2017. Biophys Chem., DOI: 10.1016/j.bpc.2017.03.010. [3] Nishiyama M., and Y. Arai. 2017. Methods Mol Biol. 1593:175-184. doi: 10.1007/978-1-4939-6927-2_13.