Yukio Magariyama

Dielectrophoretic measurement of bacterial motor characteristics

Novel methods of the bacterial motor characteristic measurement using AC field effects in a microfabricated electrode system are presented. Two methods are developed in this paper. One is the measurement of the external force-to-velocity characteristics (F-v) of swimming bacteria. Electrostatic orientation of bacteria parallel to the field lines is used to guide the bacterial locomotion along a line. dielectrophoresis is used to apply external force both forwards or backwards to the swimming bacteria, and by measuring the velocity of the locomotion, the F-v curve is obtained. The other is the measurement of torque-to-speed characteristics (T- omega ) of the motor. Electrorotation is used to apply external torque to the tethered cells, and by changing the applied torque to the tethered cells, and by changing the applied torque and measuring the rotation speed, T- omega curves obtained.<<ETX>>

A mathematical explanation of an increase in Bacterial swimming speed with viscosity in linear-polymer solutions

Bacterial swimming speed is sometimes known to increase with viscosity. This phenomenon is peculiar to bacterial motion. Berg and Turner (Nature. 278:349-351, 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.

Direct Measurement of Helical Cell Motion of the Spirochete Leptospira

Leptospira are spirochete bacteria distinguished by a short-pitch coiled body and intracellular flagella. Leptospira cells swim in liquid with an asymmetric morphology of the cell body; the anterior end has a long-pitch spiral shape (S-end) and the posterior end is hook-shaped (H-end). Although the S-end and the coiled cell body called the protoplasmic cylinder are thought to be responsible for propulsion together, most observations on the motion mechanism have remained qualitative. In this study, we analyzed the swimming speed and rotation rate of the S-end, protoplasmic cylinder, and H-end of individual Leptospira cells by one-sided dark-field microscopy. At various viscosities of media containing different concentrations of Ficoll, the rotation rate of the S-end and protoplasmic cylinder showed a clear correlation with the swimming speed, suggesting that these two helical parts play a central role in the motion of Leptospira. In contrast, the H-end rotation rate was unstable and showed much less correlation with the swimming speed. Forces produced by the rotation of the S-end and protoplasmic cylinder showed that these two helical parts contribute to propulsion at nearly equal magnitude. Torque generated by each part, also obtained from experimental motion parameters, indicated that the flagellar motor can generate torque >4000 pN nm, twice as large as that of Escherichia coli. Furthermore, the S-end torque was found to show a markedly larger fluctuation than the protoplasmic cylinder torque, suggesting that the unstable H-end rotation might be mechanically related to changes in the S-end rotation rate for torque balance of the entire cell. Variations in torque at the anterior and posterior ends of the Leptospira cell body could be transmitted from one end to the other through the cell body to coordinate the morphological transformations of the two ends for a rapid change in the swimming direction.

Ethnic Fermented Foods and Alcoholic Beverages of Japan

Japanese traditional fermented foods are centerpieces of taste of Washoku cuisine which was added to UNESCO’s Intangible Cultural Heritage list in 2013. Miso is fermented soybean paste. It is used for every day’s miso soup and as a seasoning in many kinds of cooking. Shoyu – soy sauce – is a liquid-type seasoning made of soybeans, wheat, koji, and salt water. Natto is soybeans fermented with Bacillus, with sticky but tasty γ-polyglutamic acid. Su is a traditional vinegar of cereal or fruit. Rice vinegar which is usually made directly from rice and rice koji is the most popular in Japan. Tsukemono is pickled vegetables, of which the traditional one is fermented with lactic acid bacteria. Tsukemono is usually served daily as a side dish with boiled rice. A variety of fermented seafoods, salted type (gyoshyo, shiokara, kusaya), pickled type (nare-zushi, nuka-zuke), and molded type (fushi) are also developed. The last one “fushi” is an indispensable ingredient in Japanese cuisine. Two kinds of alcoholic beverages, famous sake (rice wine) and shochu (spirits), are also important gifts of fermentation. The outline, including information of microbes, preparation methods and functionality and health benefits, of these traditional fermented foods and beverages popular in Japan are introduced.

Measurement of the Brownian motion of tobacco mosaic virus

There are some cases where the swimming speed of a bacterial cell in a polymer solution increases with the viscosity. This phenomenon is not yet explained by the traditional theories, and such phenomena never appear under macroscopic conditions. We showed it could be explained by the hypothesis in which the anisotropic effect of polymer was introduced into a traditional theory. To evaluate the hypothesis, it is necessary to measure the hydrodynamic force acting on an ultra small needle in both the directions parallel and perpendicular to its axis. Tobacco mosaic virus (TMV; needle-shaped, 18 nm in width, 400 nm in length) is a suitable sample for this purpose. It is, however, very difficult to measure TMV Brownian motion and estimate the force acting on it because TMV can not be observed by typical optical microscopy. In this paper, we introduce our recent study about the measurement of TMV Brownian motion.

Asymmetric Swimming Motion of Singly Flagellated Bacteria near a Rigid Surface

This paper gives an overview of consecutive studies on the asymmetrical motion of Vibrio alginolyticus cells, which possess a single polar flagellum. Inertial forces are negligible because of the cell size and the motion is expected to be symmetrical. However, asymmetrical characteristics between forward and backward motions were observed. The asymmetry observed in trajectory, swimming speed, and residence time appears only when a cell swims close to a surface. In backward motion, a cell traces circular path, while in forward motion the cell moves in a straight line. The backward swimming speed is faster than the forward speed. Backward swimming cells tend to stay close to a surface longer than forward swimming cells do. An explanation for these asymmetrical characteristics is given based on the results of boundary element analyses of creeping flow around a cell model that consists of a cell body and a rotating flagellum. According to the explanation, the attitude of a cell relative to a surface produces the asymmetry. The studies presented here indicate that the fluid-dynamic interaction between bacterial cells and a surface produces the unexpected asymmetrical motion. This asymmetry may help cells search for preferable states on a surface or to attach to the surface.

An Engineering Perspective on Swimming Bacteria:High-Speed Flagellar Motor, Intelligent Flagellar Filaments, and Skillful Swimming in Viscous Environments

Many bacteria swim by rotating their helical flagellar filaments which are driven by flagellar motors embedded in the cell membranes. In mechanical engineering, bacterial swimming is an interesting subtopic of robotics and nano-mechanics since countless nano-machines made of bio-molecules are packed into 1 µm cells. In this paper, we present three exceptionally interesting facts about swimming bacteria, which have been known for the past decade. First, a flagellar motor rotates extremely fast (the maximum recorded is 1,700 rps). This information produces many new questions regarding, for example, the torque generation mechanism and the wear. The second fact concerns the flagellar filament as an intelligent material. It is sufficiently rigid for a use as a propeller and yet can change its helical form to relax the stress when an excessive force acts on it. The mechanism is now being explored at an atomic level. The last fact is that bacterial cells sometimes swim well in viscous environments. This phenomenon contradicts common knowledge but could be explained by a new hypothesis in which the effect of the polymer network on the bacterial motion was expressed mathematically. We were impressed by the acumen of bacteria. (Review)

Changes in stiffness of yeast cells during cell cycle by passability through micromachined channel arrays

Possibility of cell sorting by cellular deformability was examined using yeast cells and previously described microchannel arrays. Cells harvested at every hour during incubation were washed and suspended in sorbitol solution at a concentration of O.D. 0.3. An aliquot of each suspension was caused to flow through the microchannel concentration of O.D. 0.3. An aliquot of each suspension was caused to flow through the microchannel arrays by applying 20 cmH2O suction. Cells at two hours of incubation could not enter into the microchannels, while cells at 4-5 hours of incubation could enter into the microchannels despite their larger size due to budding than the preceding ones and some few cells were observed to pass through 8 micrometers width microchannels. The number of cells that could enter into the microchannels decreased at 7-8 hours and re-increased at 9- 10 hours, but the synchronism in this second cycle appeared to decrease. Protoplasts prepared by treatment with zymolyase from cells at 4-5 hours of incubation showed no appreciable resistance to the microchannel passage.