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In situ Raman spectra of aqueous K2WO4-HCl, K2WO4-HCl-NaCl, and K2WO4-CO2-NaCl solutions were collected at elevated temperature (T, 100–400°C) and constant pressure (P) of 30 MPa. The stretching vibration band of the W=O bond (v1) was analyzed to reveal the species of tungsten (W) responsible for the hydrothermal transport of W during mineralization. Results showed that monomeric tungstates with v1(W=O) bands at ~930 and 950 cm-1 are the dominant W species in weakly alkaline (room temperature, pH=7.7) to near-neutral (room temperature, pH=7.2) solutions under the investigated T‐P conditions. Overall, the stability of polymeric tungstate species with v1(W=O) bands at ~965–995 cm-1 decreases with rising temperature and was not detected at ≥300°C in moderately acidic solution (room temperature, pH=4.9). However, increased fluid acidity and salinity obviously enlarged the temperature stability field of polymeric tungstate species. In highly acidic solution (room temperature, pH=1.4), polymeric tungstates are the only stable W species even at 400°C. In the presence of 1.9 mol/kg NaCl, polymeric tungstate(s) can persist to at least 350°C in moderately acidic solution. Considering that 300–350°C is the major W-mineralizing T range and W-mineralizing fluid is generally characterized by a moderately acidic nature, we propose that, in addition to monomeric tungstates, polymeric tungstates can also be important W species in some natural geological fluids that are responsible for the mineralization of W. Future studies of the W mineralization mechanism should take this issue into account.

We have developed an electrophoretic cell suitable for single-molecule electrophoresis. The setup works for fluorescently labeled macromolecules by direct recording of their motion under an external electric field. The electrophoretic mobility of rodlike, polydisperse actin filaments (F-actin) were measured, as well as its dependence on the orientation of the filaments. A dipping effect is observed and quantitatively accounted for by the difference in hydrodynamic drag between motions along and perpendicular to the long axis of a filament. When averaged over all orientations, the mobility of F-actin in 50 mM KCl and 2 mM MgCl2 is determined to be -(8.5±0.7)×10-5 cm2/(V s). This method is also used to compare the mobility of F-actin and fd virus in a mixture of them. A reliable ratio of 1.26 is measured for fd virus to F-actin. The influence of the orientation dependent drag on electrophoretic mobility is discussed and a strategy for reliable measurement is proposed. [ABSTRACT FROM AUTHOR]

Background: Motility of flagellated bacteria depends crucially on their organelles such as flagella and pili, as well as physical properties of the external medium, such as viscosity and matrix elasticity. We studied the motility of wild-type and two mutant strains of Caulobacter crescentus swarmer cells in two different types of media: a viscous and hyperosmotic glycerol-growth medium mixture and a viscoelastic growth medium, containing polyethylene glycol or polyethylene oxide of different defined sizes. Results: For all three strains in the medium containing glycerol, we found linear drops in percentage of motile cells and decreases in speed of those that remained motile to be inversely proportional to viscosity. The majority of immobilized cells lost viability, evidenced by their membrane leakage. In the viscoelastic media, we found less loss of motility and attenuated decrease of swimming speed at shear viscosity values comparable to the viscous medium. In both types of media, we found more severe loss in percentage of motile cells of wild-type than the mutants without pili, indicating that the interference of pili with flagellated motility is aggravated by increased viscosity. However, we found no difference in swimming speed among all three strains under all test conditions for the cells that remained motile. Finally, the viscoelastic medium caused no significant change in intervals between flagellar motor switches unless the motor stalled. Conclusion: Hyperosmotic effect causes loss of motility and cell death. Addition of polymers into the cell medium also causes loss of motility due to increased shear viscosity, but the majority of immobilized bacteria remain viable. Both viscous and viscoelastic media alter the motility of flagellated bacteria without affecting the internal regulation of their motor switching behavior. [ABSTRACT FROM AUTHOR]

Background: Adhesion to surfaces facilitates many crucial functions of microbes in their natural habitats. Thus understanding the mechanism of microbial adhesion is of broad interest to the microbiology research community. Results: We report a study by fluorescence imaging and atomic force microscopy on the growth in size and thickness of the holdfast of synchronized Caulobacter crescentus cells as they attach to a glass surface. We found that the holdfast undergoes a two-stage process of spreading and thickening during its morphogenesis. The holdfast first forms a thin plate on the surface. The diameter of the holdfast plate reaches its final average value of 360 nm by the cell age of ∼ 30 min, while its thickness further increases until the age of ∼ 60 min. Our AFM analysis indicates that the holdfast is typically thicker in the middle, with gradual falloff in thickness towards the outer edge. Conclusions: We propose that the newly secreted holdfast substance is fluid-like. It has strong affinity to the surface and cures to form a plate-like holdfast capable of supporting strong and permanent adhesion. [ABSTRACT FROM AUTHOR]

We measured the distribution of a forward swimming strain of Caulobacter crescentus near a surface using a three-dimensional tracking technique based on dark field microscopy and found that the swimming bacteria accumulate heavily within a micrometer from the surface. We attribute this accumulation to frequent collisions of the swimming cells with the surface, causing them to align parallel to the surface as they continually move forward. The extent of accumulation at the steady state is accounted for by balancing alignment caused by these collisions with the rotational Brownian motion of the micrometer-sized bacteria. We performed a simulation based on this model, which reproduced the measured results. Additional simulations demonstrate the dependence of accumulation on swimming speed and cell size, showing that longer and faster cells accumulate more near a surface than shorter and slower ones do. [ABSTRACT FROM AUTHOR]

Background: Heme oxygenase-1 (HO-1), the rate-limiting enzyme for heme catabolism and iron production, its role in intracerebral hemorrhage (ICH) is controversial. The study was to investigate correlations between brain oxidative injury and HO-1 after experimental ICH. Method: Sprague-Dawley rats received intra-striatal infusions of 100 μl autologous whole blood as ICH models. HO-1 were examined by immunohistochemical and reverse transcription polymerase chain reaction (RT-PCR) analysis. Brain oxidative stress was quantitated by malondialdehyde (MDA); antioxidation were measured by copper-zinc superoxide dismutase (Cu/Zn-SOD) activity using RT-PCR assay. Results: The expression of the HO-1 upregulated and reached its peak at days 3 and 7 after ICH ( P < 0.01). There was a significant increase of MDA and a top at 3-day post-ICH ( P < 0.01); Cu/Zn-SOD was upregulated post-ICH and reached the top at day 7 ( P < 0.001); HO-1 was correlated significantly with brain MDA content at days 7 and 14 following ICH ( r = 0.435-0.501, P < 0.001) but there is no definite correlation between them on 1 to 3 days ( P > 0.05); conversely, HO-1 was correlated significantly with Cu/Zn-SOD on 1 to 3 days after ICH ( r = 0.433-0.621, P < 0.001) but there is no definite correlation between them at days 7 and 14 ( P > 0.05). Conclusions: HO-1 has both antioxidant and prooxidant properties in ICH. The early upregulation of HO-1 possibly fit with the events and be protective against oxidative stress, whereas its overexpression in the late stages may result in its dysfunction and be toxic. So it should be prudent to intervene ICH with the inhibitor/activator of HO-1. [ABSTRACT FROM AUTHOR]

Brownian motion influences bacterial swimming by randomizing displacement and direction. Here, we report that the influence of Brownian motion is amplified when it is coupled to hydrodynamic interaction. We examine swimming trajectories of the singly flagellated bacterium Caulobacter crescentus near a glass surface with total internal reflection fluorescence microscopy and observe large fluctuations over time in the distance of the cell from the solid surface caused by Brownian motion. The observation is compared with computer simulation based on analysis of relevant physical factors, including electrostatics, van der Waals force, hydrodynamics, and Brownian motion. The simulation reproduces the experimental findings and reveals contribution from fluctuations of the cell orientation beyond the resolution of present observation. Coupled with hydrodynamic interaction between the bacterium and the boundary surface, the fluctuations in distance and orientation subsequently lead to variation of the swimming speed and local radius of curvature of swimming trajectory. These results shed light on the fundamental roles of Brownian motion in microbial motility, nutrient uptake, and adhesion. [ABSTRACT FROM AUTHOR]

Bacterial chemotaxis relies on the clockwise-to-counterclockwise switching (and the reverse CCW-to-CW switching) of the flagellar motor’s rotational direction. Yet, despite its central role, the switch mechanism remains poorly understood. Here we study the switch statistics of the flagellar motor using computer simulations that combine first-passage time ideas and the property of dynamic binding of CheY-P to FliM. The simulated clockwise bias and switching frequency as a function of CheY-P concentration agree with the experimental results for E. coli. Moreover, the simulation results show a robust peak, which is present in some experimental reports, in the distribution of the time intervals of both clockwise and counterclockwise rotation. [ABSTRACT FROM AUTHOR]

The adhesion of bacteria to surfaces plays critical roles in the environment, disease, and industry. In aquatic environments, CauIobacter crescentus is one of the first colonizers of submerged surfaces. Using a micromanipulation technique, we measured the adhesion force of single C. crescentus cells attached to borosilicate substrates through their adhesive holdfast. The detachment forces measured for 14 cells ranged over 0.11 to 2.26 µN, averaging 0.59 ± 0.62 µN. Based on the calculation of stress distribution with the finite element analysis method (dividing an object into small grids and calculating relevant parameters for all of the elements), the adhesion strength between the holdfast and the substrate is >68 N/mm² in the central region of contact. To our knowledge, this strength of adhesion is the strongest ever measured for biological adhesives. [ABSTRACT FROM AUTHOR]

A Caulobacter crescentus swarmer cell is propelled by a helical flagellum, which is rotated by a motor at its base. The motor alternates between rotating in clockwise and counterclockwise directions and spends variable intervals of time in each state. We measure the distributions of these intervals for cells either free swimming or tethered to a glass slide. A peak time of around one second is observed in the distributions for both motor directions with counterclockwise intervals more sharply peaked and clockwise intervals displaying a larger tail at long times. We show that distributions of rotation intervals fit first passage time statistics for a biased random walker and the dynamic binding of CheY-P to FliM motor subunits accounts for this behavior. Our results also suggest that the presence of multiple CheY proteins in C. crescentus may be responsible for differences between its switching behavior and that of the extensively studied E. coli. [ABSTRACT FROM AUTHOR]

Bacterial flagella play key roles in surface attachment and host-bacterial interactions as well as driving motility. Here, we have investigated the ability of Caulobacter crescentus to assemble its flagellar filament from six flagellins: FljJ, FljK, FljL, FljM, FljN, and FljO. Flagellin gene deletion combinations exhibited a range of phenotypes from no motility or impaired motility to full motility. Characterization of the mutant collection showed the following: (i) that there is no strict requirement for any one of the six flagellins to assemble a filament; (ii) that there is a correlation between slower swimming speeds and shorter filament lengths in ΔfljK ΔfljM mutants; (iii) that the flagellins FljM to FljO are less stable than FljJ to FljL; and (iv) that the flagellins FljK, FljL, FljM, FljN, and FljO alone are able to assemble a filament. [ABSTRACT FROM AUTHOR]