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Silicon-Based Nanoscale Probes for Biological Cells
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Youjin Lee, Andrew W.Phillips, Bozhi Tian
It is perhaps instructive to consider interactions of cells with highly anisotropic topographical features as a form of mechanical stimulation. Bianxiao Cui’s group and others have looked at the effect of such topography on intracellular signaling. Cells naturally contain mechanisms to sense and alter membrane curvature. These processes are relevant for cellular processes involving vesicle formation and fusion, like endocytosis and exocystosis. As Cui’s group describes what they call the curvature hypothesis, the same proteins involved in endogenous curvature-recognizing mechanisms are activated by artificial sources of curvature; namely, inward deformations of the cell membrane around anisotropic materials. Further, mechanical stimulation of the nucleus by anisotropic structures can also affect gene expression (Lou et al. 2018).
Geometry of Purple Membranes in Aqueous Medium
Published in Stoyl P. Stoylov, Maria V. Stoimenova, Molecular and Colloidal Electro-Optics, 2016
The reasons for the deformation remain hypothetical. In Refs. [75,76] curvature change in electric field is explained by an inverse flexoelectric effect connected with the asymmetry of charged lipids in the two monolayers of the membrane. Membrane curvature is changed because of an electric‐field induced flip‐flop of lipid molecules from one monolayer to the other. But here this mechanism looks hardly probable as PM lipids are associated with bR macromolecules, which makes them not readily mobile.
Effect of photocatalysis (TiO2/UVA) on the inactivation and inhibition of Pseudomonas aeruginosa virulence factors expression
Published in Environmental Technology, 2021
Faouzi Achouri, Myriam Ben Said, Mohamed Ali Wahab, Latifa Bousselmi, Serge Corbel, Raphaël Schneider, Ahmed Ghrabi
The photocatalytic effects of (TiO2/UVA) on the morphology of the bacterial cell were examined by atomic force microscopy (AFM). The morphological changes over the treatment period are presented in Figure 2. According to Figure 2(a), the cells before irradiation had a cylindrical shape, however, after 15 min of irradiation Figure 2(b), obvious morphological changes of the membrane were recognized by an increase in the membrane curvature. Indeed, under stressful conditions, the morphological changes in bacterial shape are considered as a strategy to protect bacteria against stress and to minimize the bactericidal effect of photocatalytic treatment on their biological activities [32]. When increasing photocatalytic treatment to 30 min, the morphological changes were more accentuated by the change of the cell wall components concentrations, and the disorganization in the outermost layer of the cell reflected by the appearance of grooves on the cell surface owing probably to the change in the concentrations of extracellular polymeric substances (EPS) or the release of cytoplasm (Figure 2(c)). The cell damages were more apparent and severe after 60 min of photocatalysis treatment (Figure 2(d)) highlighted by a complete disappearance of the cylindrical shape of the cells, suggesting a complete decomposition of dead cells. These observations are in agreement with our previous study [33] indicating that after photocatalytic treatment the majority of cells displayed morphological alterations with a concomitant cell size reduction which increased in a time-dependent manner. The present results are also in accordance with previous reports indicating that the cell envelope is the primary target of the ROS generated during photocatalysis [26]. Such morphological changes were also observed by Kiwi and Nadtochenko, who had also quantified the cellular components degradation and in particular the phenomena of lipid peroxidation in E. coli strain by Fourier-transform infrared spectroscopy FTIR and AFM, demonstrating a membrane fluidity inevitably leading to bacterial lysis [34,35]. Furthermore, Thabet et al. highlighted the released of various compounds after photocatalytic treatment [36]. They have demonstrated that the membrane permeability would lead firstly to the release of small molecules such as ortho-nitrophenyl β-D-galactopyranoside, followed by the release of compounds of larger sizes like β-galactosidase [36]. Similarly, rapid release of potassium ions would induce a decrease in cell viability [37].