Seishi Kudo

Simultaneous Measurement of Bacterial Flagellar Rotation Rate and Swimming Speed

Swimming speeds and flagellar rotation rates of individual free-swimming Vibrio alginolyticus cells were measured simultaneously by laser dark-field microscopy at 25, 30, and 35 degrees C. A roughly linear relation between swimming speed and flagellar rotation rate was observed. The ratio of swimming speed to flagellar rotation rate was 0.113 microns, which indicated that a cell progressed by 7% of pitch of flagellar helix during one flagellar rotation. At each temperature, however, swimming speed had a tendency to saturate at high flagellar rotation rate. That is, the cell with a faster-rotating flagellum did not always swim faster. To analyze the bacterial motion, we proposed a model in which the torque characteristics of the flagellar motor were considered. The model could be analytically solved, and it qualitatively explained the experimental results. The discrepancy between the experimental and the calculated ratios of swimming speed to flagellar rotation rate was about 20%. The apparent saturation in swimming speed was considered to be caused by shorter flagella that rotated faster but produced less propelling force.

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.

Thermodynamic efficiency and mechanochemical coupling of F1-ATPase.

F1-ATPase is a nanosized biological energy transducer working as part of FoF1-ATP synthase. Its rotary machinery transduces energy between chemical free energy and mechanical work and plays a central role in the cellular energy transduction by synthesizing most ATP in virtually all organisms. However, information about its energetics is limited compared to that of the reaction scheme. Actually, fundamental questions such as how efficiently F1-ATPase transduces free energy remain unanswered. Here, we demonstrated reversible rotations of isolated F1-ATPase in discrete 120° steps by precisely controlling both the external torque and the chemical potential of ATP hydrolysis as a model system of FoF1-ATP synthase. We found that the maximum work performed by F1-ATPase per 120° step is nearly equal to the thermodynamical maximum work that can be extracted from a single ATP hydrolysis under a broad range of conditions. Our results suggested a 100% free-energy transduction efficiency and a tight mechanochemical coupling of F1-ATPase.

Effect of intracellular pH on the torque-speed relationship of bacterial proton-driven flagellar motor.

Bacterial flagella responsible for motility are driven by rotary motors powered by the electrochemical potential difference of specific ions across the cytoplasmic membrane. The stator of proton-driven flagellar motor converts proton influx into mechanical work. However, the energy conversion mechanism remains unclear. Here, we show that the motor is sensitive to intracellular proton concentration for high-speed rotation at low load, which was considerably impaired by lowering intracellular pH, while zero-speed torque was not affected. The change in extracellular pH did not show any effect. These results suggest that a high intracellular proton concentration decreases the rate of proton translocation and therefore that of the mechanochemical reaction cycle of the motor but not the actual torque generation step within the cycle by the stator-rotor interactions.

Hydrostatic Pressure Effect on the Dielectric Properties of K2SeO4

Hydrostatic pressure effect on the dielectric constant e c or K 2 SeO 4 was studied. The incommensurate transition temperature T 2 lowers linearly with the slope of -7.3 ±0.2 K/kbar. The Curie temperature T 3 also decreases with pressure, but the slope denpends on pressure; the initial slope is -17.2 ±2.5 K/kbar and the slope above 0.6 kbar is -11.4 ±1.0 K/kbar. The dielectric behaviors under the pressure are qualitatively discussed based on the theoretical treatments already developed by other authors, and some problems are suggested.

Elastic Compliance Anomalies in K2SeO4

Elastic compliance coefficients of K2SeO4 have been measured as functions of temperature by the composite-bar and piezoelectric resonance methods. The components s11, s22, s33 and s44 show anomalies around the transition temperature T2(129.5 K), but only s55 exhibits an anomaly at the Curie temperature T3 (93.0 K). The origin of these anomalies is qualitatively considered, taking into account the data of other experiments seen in literature.

Birefringence and Lattice Strain in K2SeO4

Temperature dependence of birefringences and lattice strains in K 2 SeO 4 has been investigated. They exhibit anomalies at the upper transition temperature (129.5 K), whereas no anomalies are found at the Curie temperature (93 K). Experimental results are analyzed by a phenomenological theory based on the incommensurate order parameter. Spontaneous birefringences are ascribed to the coupling with the order parameter and to the photoelastic effect through the spontaneous lattice strains.

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.

X-Ray Determination of Incommensurate Superlattices in K2SeO4 and (NH4)2BeF4

Incommensurate superlattice reflections have been observed by X-ray diffractometry in K2SeO4 and (NH4)2BeF4. A simple method is proposed based on the ω-scan technique. This is free from systematic errors, and is not affected by the precision of the lattice constant determination. The incommensurate superlattice parameter of K2SeO4 measured using this procedure is in agreement with that measured using neutron scattering. The incommensurate structure of (NH4)2BeF4 is elucidated for the first time by the present method.