A macroscopic scale model of bacterial flagellar bundling

Escherichia coli and other bacteria use rotating helical filaments to swim. Each cell typically has about four filaments, which bundle or disperse depending on the sense of motor rotation. To study the bundling process, we built a macroscopic scale model consisting of stepper-motor-driven polymer helices in a tank filled with a high-viscosity silicone oil. The Reynolds number, the ratio of viscous to elastic stresses, and the helix geometry of our experimental model approximately match the corresponding quantities of the full scale E. coli cells. We analyze digital video images of the rotating helices to show that the initial rate of bundling is proportional to the motor frequency and is independent of the characteristic relaxation time of the filament. We also determine which combinations of helix handedness and sense of motor rotation lead to bundling.Comment: 6 pages, 4 figures (3 in color). A supporting movie is published at the PNAS websit

Swimming Efficiency of Bacterium Escherichia Coli

We use in vivo measurements of swimming bacteria in an optical trap to determine fundamental properties of bacterial propulsion. In particular, we determine the propulsion matrix, which relates the angular velocity of the flagellum to the torques and forces propelling the bacterium. From the propulsion matrix dynamical properties such as forces, torques, swimming speed and power can be obtained from measurements of the angular velocity of the motor. We find significant heterogeneities among different individuals even though all bacteria started from a single colony. The propulsive efficiency, defined as the ratio of the propulsive power output to the rotary power input provided by the motors, is found to be 0.2%.Comment: 6 page

Predicting Broccoli Development: I. Development Is Predominantly Determined By Temperature Rather Than Photoperiod

Predictive models of broccoli (Brassica oleracea L. var. italica Plenck) ontogeny will aid farmers who need to forecast changes in crop maturity arising from variable climatic conditions so that their forward marketing arrangements can match their anticipated supply. The objective of this study was to quantify the temperature and photoperiod responses of development in a sub-tropical environment from emergence to floral initiation (EFI), and from floral initiation to harvest maturity (FIHM). Three cultivars, ('Fiesta', 'Greenbelt' and 'Marathon') were sown on eight dates from 11 March to 22 May 1997 and grown under natural and extended (16 h) photoperiods at Gatton College, south-east Queensland, under non-limiting conditions of water and nutrient supply. Climatic data, dates of emergence, floral initiation and harvest maturity were obtained. The estimated base (Tbase) and optimum (Topt) temperatures of 0 and 20 degrees C, respectively were consistent across cultivars, but thermal time requirements were cultivar specific. Differences in thermal time between cultivars during FIHM were small and of little practical importance, but differences in thermal time during EFI were large. Sensitivity to photoperiod and solar radiation was low in the three cultivars used. When the thermal time models were tested on independent data for five cultivars ('Fiesta', 'Greenbelt', 'Marathon', 'CMS Liberty' and 'Triathlon') grown as commercial crops over two years, they adequately predicted floral initiation and harvest maturity

The role of body rotation in bacterial flagellar bundling

In bacterial chemotaxis, E. coli cells drift up chemical gradients by a series of runs and tumbles. Runs are periods of directed swimming, and tumbles are abrupt changes in swimming direction. Near the beginning of each run, the rotating helical flagellar filaments which propel the cell form a bundle. Using resistive-force theory, we show that the counter-rotation of the cell body necessary for torque balance is sufficient to wrap the filaments into a bundle, even in the absence of the swirling flows produced by each individual filament

Electron Diffraction at Low Temperature II. : Radial Distribution Analysis of Metastable Structure of Metal Films Prepared by Low Temperature Condensation

Electron diffraction patterns of films of bismuth and gallium prepared at 4.2°K show diffuse halos characteristic of an amorphous state (Fujime, 1966). If the state of atomic aggregate of these films is amorphous, they will be examples of amorphous superconductors. In order to decide whether the films of bismuth and gallium prepared by low temperature condensation are in an amorphous state or consist of very fine crystallites, the radial distribution analysis has been carried out for these films. The results of this analysis lead, after some consideration, to the conclusion that the state of atomic aggregate of these films is certainly amorphous

Electron Diffraction at Low Temperature II. : Radial Distribution Analysis of Metastable Structure of Metal Films Prepared by Low Temperature Condensation

Electron diffraction patterns of films of bismuth and gallium prepared at 4.2°K show diffuse halos characteristic of an amorphous state (Fujime, 1966). If the state of atomic aggregate of these films is amorphous, they will be examples of amorphous superconductors. In order to decide whether the films of bismuth and gallium prepared by low temperature condensation are in an amorphous state or consist of very fine crystallites, the radial distribution analysis has been carried out for these films. The results of this analysis lead, after some consideration, to the conclusion that the state of atomic aggregate of these films is certainly amorphous

Electron Diffraction at Low Temperature III. : Radial Distribution Analysis of Metastable Structure of Metal Films Prepared by Low Temperature Condensation

Electron diffraction patterns of films of Pb-12%Bi and beryllium prepared at 4.2°K show diffuse halos characteristic of amorphous state (Fujime, 1966). If the state of atomic aggregate of these films is amorphous, they will be examples of amorphous superconductors. In order to decide whether the films of Pb-12%Bi and beryllium prepared by the low temperature condensation are in an amorphous state or consist of very fine crystallites, the radial distribution analysis has been carried out for these films. The results of analysis lead to the conclusion that the state of atomic aggregate of these films is certainly amorphous

Electron Diffraction at Low Temperature : I. Apparatus and Preliminary Results

An electron diffraction apparatus has been constructed for studies at low-temperature down to 4.2°K. In this apparatus, a specimen holder is attached to a bottom of a small cryostat, into which liquid helium is poured from a storage vessel through a transfer tube. The specimen temperature is controlled mainly by adjusting the flowing quantity of liquid helium and sometimes by the operation of a small electrical heater. The construction and characteristics of the apparatus are presented. Preliminary results on bismuth, gallium, Pb-12%Bi and beryllium films prepared by the low temperature condensation are also described. The present results on bismuth and gallium are different in some respects from those of a previous researcher. Correspondence between change of a state of atomic aggregate and anomalies of electrical resistance are confirmed in the cases of Pb-12%Bi and beryllium films prepared by low temperature condensation

The Intensity of Satellite Reflections in Electron Diffraction Patterns from Evaporated Alloy Films with CuAu II Type Superstructure

In order to elucidate the origin of satellite reflections flanking the direct spot in the electron diffraction pattern of a single crystal evaporated film with CuAu II type superlattice, the peak as well as integrated intensities have been measured as functions of the wavelength of electrons corresponding to the accelerating voltage from 75 to 280KV. It has been revealed that the intensity of the satellite in question relative to a fundamental reflection consists of two parts, a major part which depends on the wavelength in such a way as predicted by the theory of multiple reflection, and the other minor part which is independent of the wavelength. The existence of the latter part shows that the reflection is not a forbidden one and, therefore, a lattice modulation accompanies the regular anti-phase structure. Fourier potential due to this lattice modulation, V_s, is estimated to be in the order of one tenth the magnitude of V_ Some consideration concerning the nature of the modulation is given by comparing the results of electron and X-ray diffraction studies