2002 Fiscal Year Final Research Report Summary
Study on the bacterial locomotion mechanism
| Project/Area Number |
13650056
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied physics, general
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| Research Institution | Toin University of Yokohama |
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Principal Investigator |
KUDO Seishi Toin University of Yokohama, Faculty of Engineering, Professor, 工学部, 教授 (70308550)
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| Co-Investigator(Kenkyū-buntansha) |
MAGARIYAMA Yukio National Food Research Institute, Food Engineering Division, Senior researcher, 食品総合研究所, 主任研究官
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| Project Period (FY) |
2001 – 2002
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| Keywords | bacteria / flagella / laser dark-field microscopy / hydrodynamic force / polymer solution |
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| Research Abstract |
Many bacteria have cell bodies about 1.5 μm long and thin helical flagellar filaments that are 5 - 10 μm in length and 30 nm in diameter. Bacteria swim by rotating their flagellar filaments, which act as screw propellers.
Bacterial swimming speed is sometimes known to increase with viscosity. This phenomenon is peculiar to bacterial motion. Berg and Turner (1979) indicated that the phenomenon was caused by a loose, quasi-rigid network formed by polymer molecules that were added to increase viscosity. We mathematically developed their concept by introducing two apparent viscosities and obtained results similar to the experimental data reported before. Addition of polymer improved the propulsion efficiency, which surpasses the decline in flagellar rotation rate, and the swimming speed increased with viscosity.
Flagellar filaments consist of protein called flagellin. If flagella change their shapes largely, the efficiency of propulsion will change significantly. It is presumed that flagella have elasticity like hard spring, though they possibly expand and contract during rotation. We developed an experimental method to observe the flagellar shape during swimming by using laser dark-field microscopy. The flagellar pitch of Vibrio alginolyticus was observed to decrease when a cell swam forward, while it was observed to increase when a cell swam backward. The change was about 3 % when a cell swam forward or backward at the speed of 100 μm/s, respectively. On the contrary, the significant change in radius was not observed within the experimental error. The deformation in flagellar helix observed was considered to only slightly influence the propulsion efficiency because the change in the ratio of swimming speed to flagellar rotation rate (v-f ratio) that corresponds to the propulsion efficiency was estimated to change by only a few percent.
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