HighlightsAFM measured the equivalent diameters of LDL (∼22.7 nm) and HDL (∼14.4 nm) in PBS.AFM detected the mean Young’s moduli of LDL (∼0.39 GPa) and HDL (∼0.47 GPa) in PBS.AFM detected the mean adhesive forces of LDL (∼0.19 nN) and HDL (∼0.15 nN) in PBS.AFM detected much larger sizes of Young’s moduli and adhesive forces of LDL/HDL in air.
Summary:The rigidity/stiffness is an important biomechanical property of bacteria and potentially correlated with many bacterial activities. While the rigidity or fluidity of the bacterial membrane has been extensively studied, the contributions of different bacterial substructures to the bacterial rigidity are less investigated. Here, we utilized four Escherichia coli (E. coli) strains with different membrane lipid compositions and three antibacterial drugs (EDTA, lysozyme, and streptomycin) to specifically alter bacterial substructures. By using atomic force microscopy (AFM), we found that the average height and Young's modulus of phosphatidylethanolamine (PE)-deficient E. coli strains were larger than those of PE þ strains and that EDTA, EDTA plus lysozyme instead of lysozyme alone, and streptomycin all caused significant decreases in height and Young's modulus of the four E. coli strains. Our data imply that membrane lipid composition, the integrated outer membrane, the cell wall, and the cytoplasmic content are all responsible for bacterial rigidity but to different extents. SCANNING 38:70-79, 2016.
The nonionic detergent extraction at 4 °C and the cholesterol-depletion-induced lipid raft disruption are the two widely used experimental strategies for lipid raft research. However, the effects of raft disruption and/or cold treatment on the ultrastructural and mechanical properties of cells are still unclear. Here, we evaluated the effects of raft disruption and/or cold (4 °C) treatment on these properties of living human umbilical vein endothelial cells (HUVECs). At first, the cholesterol-depletion-induced raft disruption was visualized by confocal microscopy and atomic force microscopy (AFM) in combination with fluorescent quantum dots. Next, the cold-induced cell contraction and the formation of end-branched filopodia were observed by confocal microscopy and AFM. Then, the cell-surface ultrastructures were imaged by AFM, and the data showed that raft disruption and cold treatment induced opposite effects on cell-surface roughness (a significant decrease and a significant increase, respectively). Moreover, the cell-surface mechanical properties (stiffness and adhesion force) of raft-disrupted- and/or cold-treated HUVECs were measured by the force measurement function of AFM. We found that raft disruption and cold treatment induced parallel effects on cell stiffness (increase) or adhesion force (decrease) and that the combination of the two treatments caused dramatically strengthened effects. Finally, raft disruption was found to significantly impair cell migration as previously reported, whereas temporary cold treatment only caused a slight but nonsignificant decrease in cell migration performed at physiological temperature. Although the mechanisms for causing these results might be complicated and more in-depth studies will be needed, our data may provide important information for better understanding the effects of raft disruption or cold treatment on cells and the two strategies for lipid raft research.
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