Laboratory of Cell Regulation
Group of Microbial Motility

ProfessorSeiji Kojima
Rotational mechanism of bacterial flagellar motor and numerical/positional regulation of flagellar biogenesis
▶Laboratory HP
Seiji Kojima Professor

Bacterial motility organ: the flagellum

Cell motility is a fundamental function of life, and so elucidation of the principle of motility machinery is one of the essential questions of life science. Bacteria, the unicellular organism, also use a motility machinery for their survival to escape from unfavorable environment containing hazardous substances and to move toward nutrient resources. The flagellum is used as a motility machinery in many motile bacteria, and the helical flagellar filament is rotated by a rotary motor embedded in the cell surface at its base to generate the driving force of movement.

Mechanism of the energy conversion and rotation of bacterial flagellar motor

The flagellar motor is powered by the electrochemical gradient of ions (ion motive force) across the cell membrane. This motor is the only rotating motility organ of life, and is the supramolecular nanomachine equipped with unique chemo-mechanical energy conversion mechanism. The flagellar motor can rotate at a speed of 1,000 revolutions per second in both counterclockwise and clockwise directions, and changes its rotational sense in a millisecond timescale. In addition, the motor itself can sense the environmental load and adjust its energy conversion ability. These elaborate properties of the motor may be applicable to develop a novel artificial motor devices learned from living organisms, thereby attract researchers in the engineering fields as well. Moreover, the flagellar motility is greatly involved in infection of pathogenic bacteria, so flagella are also medically relevant. However, the mechanisms of how the energy of ions across the cell membrane is converted into rotational force remains enigmatic. We study the function and structure of the stator (the energy conversion units), and rotational switching mechanism that occurs in the rotor C ring. We employ methods of molecular biology (mutational analysis), cell biology (protein localization), biochemistry (protein purification/activity measurement), biophysics (measurement of motility/rotation), and structural biology.

Control of the number and position of flagella

Our body is formed by the proper spatiotemporal control of functional molecules during development. In order to maintain normal tissues and organs, functional molecules must be placed in appropriate amounts at each position to work, and if this mechanism is impaired, it will cause illness. Therefore, placing biomolecules in appropriate amounts at function sites is a basic function of all living organisms. Even in bacteria, the number and position of flagella are strictly determined so that they can move properly in their habitat. Marine bacterium Vibrio alginolyticus has a single flagellum at cell pole, and we try to understand how this numerical and positional regulation occurs in this bacteria. From the simple organism like bacteria, we try to elucidate the mechanism of proper placement of supramolecular biomolecules, the fundamental and common function of all kingdom of life.

Fig 1. Schematic of the flagellar motor of Salmonella enterica and Vibrio alginolyticus

Fig 2. FlhF and FlhG regulate the polar flagellar placement and number.


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