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Surrounding Fluid (surrounding + fluid)
Selected AbstractsProtists with different feeding modes change biofilm morphologyFEMS MICROBIOLOGY ECOLOGY, Issue 2 2009Anne Böhme Abstract The effect of Dexiostoma (filter feeder), Vannella, Chilodonella (raptorial feeders), Spumella, and Neobodo (direct interception feeders) on the morphology of multispecies bacterial biofilms was investigated in small flow cells. The filter feeder Dexiostoma campylum did not alter biofilm volume and porosity but stimulated the formation of larger microcolonies compared with ungrazed biofilms. In contrast, the raptorial feeder Vannella sp. efficiently grazed bacteria from the biofilm surface, leading to smaller microcolonies and lower maximal and basal layer thickness compared with ungrazed biofilms. Microcolony formation was not stimulated in the presence of the sessile Spumella sp. Chilodonella uncinata rasped bacteria from the outer surface leading to mushroom-shaped microcolonies. In the presence of C. uncinata and Spumella sp., the biofilm volume was 2.5,6.3 times lower compared with ungrazed biofilms. However, the biofilm porosity and the ratio of biofilm surface area to biofilm volume were 1.5,3.7 and 1.2,1.8 times higher, respectively. Thus, exchange of nutrients and gases between the biofilm and its surrounding fluid should also be improved in deeper biofilm layers, hence accelerating microbial growth. [source] A viscous vortex particle method for deforming bodies with application to biolocomotionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009Li Jeany Zhang Abstract Bio-inspired mechanics of locomotion generally consist of the interaction of flexible structures with the surrounding fluid to generate propulsive forces. In this work, we extend, for the first time, the viscous vortex particle method (VVPM) to continuously deforming two-dimensional bodies. The VVPM is a high-fidelity Navier,Stokes computational method that captures the fluid motion through evolution of vorticity-bearing computational particles. The kinematics of the deforming body surface are accounted for via a surface integral in the Biot,Savart velocity. The spurious slip velocity in each time step is removed by computing an equivalent vortex sheet and allowing it to flux to adjacent particles; hence, no-slip boundary conditions are enforced. Particles of both uniform and variable size are utilized, and their relative merits are considered. The placement of this method in the larger class of immersed boundary methods is explored. Validation of the method is carried out on the problem of a periodically deforming circular cylinder immersed in a stagnant fluid, for which an analytical solution exists when the deformations are small. We show that the computed vorticity and velocity of this motion are both in excellent agreement with the analytical solution. Finally, we explore the fluid dynamics of a simple fish-like shape undergoing undulatory motion when immersed in a uniform free stream, to demonstrate the application of the method to investigations of biomorphic locomotion. Copyright © 2008 John Wiley & Sons, Ltd. [source] Mouse spermatozoa contain a nuclease that is activated by pretreatment with EGTA and subsequent calcium incubationJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 5 2008Segal M. Boaz Abstract We demonstrated that mouse spermatozoa cleave their DNA into ,50 kb loop-sized fragments with topoisomerase IIB when treated with MnCl2 and CaCl2 in a process we term sperm chromatin fragmentation (SCF). SCF can be reversed by EDTA. A nuclease then further degrades the DNA in a process we term sperm DNA degradation (SDD). MnCl2 alone could elicit this activity, but CaCl2 had no effect. Here, we demonstrate the existence of a nuclease in the vas deferens that can be activated by ethylene glycol tetraacetic acid (EGTA) to digest the sperm DNA by SDD. Spermatozoa were extracted with salt and dithiothreitol to remove protamines and then incubated with EGTA. Next, the EGTA was removed and divalent cations were added. We found that Mn2+, Ca2+, or Zn2+ could each activate SDD in spermatozoa but Mg2+ could not. When the reaction was slowed by incubation on ice, EGTA pretreatment followed by incubation in Ca2+ elicited the reversible fragmentation of sperm DNA evident in SCF. When the reactions were then incubated at 37°C they progressed to the more complete degradation of DNA by SDD. EDTA could also be used to activate the nuclease, but required a higher concentration than EGTA. This EGTA-activatable nuclease activity was found in each fraction of the vas deferens plasma: in the spermatozoa, in the surrounding fluid, and in the insoluble components in the fluid. These results suggest that this sperm nuclease is regulated by a mechanism that is sensitive to EGTA, possibly by removing inhibition of a calcium binding protein. J. Cell. Biochem. 103: 1636,1645, 2008. © 2007 Wiley-Liss, Inc. [source] Online assessment of biofilm development, sloughing and forced detachment in tube reactor by means of magnetic resonance microscopyBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Michael Wagner Abstract Magnetic resonance microscopy (MRM) was successfully applied for non-invasive online monitoring of biofilm development, sloughing, and forced detachment. Biofilm cultivation was performed in a tube reactor directly placed in the MRM scanner. Based on the differences in relaxation time of free and bound protons, the distributed water signal was allocated to the bulk and the biofilm phase. The velocity of the flowing water in the tube reactor was measured in all three directions (x, y, and z) at spatial resolutions of 78,µm. From the velocity data, maps of flow gradients (shear rates) were derived. The experiments showed that a more compact biofilm structure is sloughed off in total with nearly no biomass left on the substratum. Continued biofilm cultivation resulted in filamentous biofilm structures, which did not show any sloughing. Experiments at higher Reynolds numbers were performed in order to force biofilm detachment. Continuous measuring of proton velocity and biomass was used to characterize the different stages of biofilm development. The measurements revealed that biofilms are able to resist extremely high local shear stress being raised up to factor of 20 compared to the mean local shear stress acting on the complete biofilm surface. The maximum local shear stress of single biofilm structures exposed to flow was found to be on average seven times higher compared to the mean local shear stress of the entire biofilm surface. MRM was able to visualize and quantify the development of biofilms and interaction of biofilms with the surrounding fluid at the meso-scale. It is suggested that detachment and sloughing depends on both internal and external structural parameters. Biotechnol. Bioeng. 2010;107: 172,181. © 2010 Wiley Periodicals, Inc. [source] | ||||||||||