Uncovering how bacteria move
Nagoya University, Graduate School of Science
Professor Michio Homma[About my research]
By what mechanism do bacteria move?
In my laboratory, we are studying the energy conversion mechanism of the flagellum, alocomotor organ, in bacteria (some are called harmful bugs), which can be easily analyzed by themolecular level. We also investigate how bacteria sense and process extracellular information,and then understand comprehensively how the flagellar motor is controlled in the system.
Bacterial motor energy conversion
The bacterial flagellum is structurally and functionally quite different from the flagellum of
spermatozoa (conventionally written in Chinese characters to distinguish it from the bacterialflagellum), which is the locomotor organ possessed by animals.

Animal flagella use ATP as theenergy source for their whipping motion. In contrast, bacterial flagella have motor at the basewhich is buried in cytoplasmic membrane and is rotated by the flow of ions from the outside to
the inside of the membrane.
electric motor engine.

Think of it as the difference between a gasoline engine and an

The influx of ions (hydrogen and sodium ions) directly generates therotational motion (Fig. 1). The motor is connected to the flagellar fiber or filament, which isseveral times longer than the length of the bacterial cell, as a screw and generates propulsive force
by passively rotating filament. This is equivalent to a 160-cm tall person turning a 4-meter stringat 1700 revolutions per second, the speed comparable to the engine of an F1 car. The flagellar
motor is a supramolecular complex made of many proteins (the supramolecule means a moleculewith special abilities) and contains sub-structures such as a motor-protein complex converting
ionic energy into mechanical energy, a switch complex controlling the direction of motor rotation,and others.
Electric motors convert the flow of electric current into magnetic force and the attraction andrepulsion made from magnetic force cause the motor to rotate. On the other hand, what happens
to rotate the biological motor by ion flow? To answer this very question, we are analyzing theoverall structure of that motor or energy converter of the main parts in the flagella (Fig. 2).
Although we have not yet reached a sufficient resolution enough to investigate the principles ofthe energy transduction, we are beginning to understand the molecular details of the motor.

Copyright © Ohsumi Frontier Science Foundation. All Rights Reserved.

The Mystery of the One Hair on the HeadBacteria do not move haphazardly when they are swimming. For example, they swim to use
their flagella toward where they want to go to find amino acids, such as serine, that serve as asource of nutrients. Many proteins are localized in the cell; each performs its function in thecorrect number and at the right place. For example, chemotaxis receptors, one of the sensory
organs of bacteria, are localized in large clusters at the poles of the cell and serve as sensors toreceive information from the outside world. Based on the information from these chemotaxis
receptors, bacteria can move to a better environment using flagella, pili, and other motile organs.
These locomotory organs are not randomly produced everywhere. Their number and position
are appropriately regulated by the genes flhF and flhG which are shown to control the single polar
flagellum of Vibrio. It is known that the proteins produced by these two genes are enzymes withthe activity to degrade essential molecules in the living body, such as guanosine triphosphate(GTP) and adenosine triphosphate (ATP). However, it is unclear how that activity is used todetermine the location. The mechanism by which a single hair grows on the head of the bacterialcell is also unclear.
By our research as described above, we believe that it may lead to the elucidation of newprinciples in microscopic energy conversion, which may help solve the world's energy problems.
However, even if they are not immediately applicable, our current greatest motivation why we aredoing research is that, in front of us, there is something that we can not understand.

Copyright © Ohsumi Frontier Science Foundation. All Rights Reserved.

Figure 1: Vibrio flagellar motor. (A) Electron micrograph ofVibrio cell. The Vibrio cell has a single flagellum at the edgeor pole of the cell, which rotates like a screw to swim. (B)Schematic model of the motor part. The engine (flagellarmotor), that generates the rotational force and is embeddedin the membrane (outer and inner membrane), resides at thebase of the flagellum. The rotary motor is made of a statorand a rotor. It also consists of a bearing that supports therotation of the rotor, a hook that acts as a free joint for screw,
and a filament that functions like a screw. Several stators
are placed around the rotor, and when sodium ions (Na+)
flow through the stators, they interact with the rotor toproduce the rotational force.

Figure 2: (A) Cross-section of a Vibrio flagellar basal body which was quickly frozen. The imagesof the flagellar basal body part taken by electron microscopy were superimposed to construct a
three-dimensional image, and its cross-section is shown. (B) The surface rendered image ofthree-dimensionally reconstructed Vibrio flagellar motor created from cryo-electron
tomographic images.

Copyright © Ohsumi Frontier Science Foundation. All Rights Reserved.