When illuminated by near-UV light, titanium dioxide (TiO2) exhibits excellent bactericidal activity. However, there exist some different mechanisms for cell killing via photocatalysis. In the present study, the photocatalytically bactericidal mechanism of TiO2 thin films was investigated by atomic force microscopy (AFM) in conjugation with some other techniques. The decomposition process of the cell wall and the cell membrane was directly observed by AFM for the first time. The resultant change in cell permeability was confirmed by potassium ion (K+) leakage. Quantum dots (QDs) were designed originally as a probe to examine the cell permeability for macromolecules. The corresponding bactericidal activity of TiO2 thin films was examined by cell viability assay. These results suggested that the cell death was caused by the decomposition of the cell wall and the cell membrane and the resultant leakage of intracellular molecules.
Extremely halophilic archaea are a diverse group of prokaryotes that inhabit highly saline environments. H. salinarum, a species of archaebacteria, is a photosynthetic bacteria that can survive in 4 M NaCl solutions. When the concentration of Na + is low, the cell wall will break apart and the cell will be lysed. 1 To date, the reason why H. salinarum requires a high concentration of sodium ions for growth has not been fully explained. Archaebacteria have a different morphology than other prokaryotes, such as E. coli. 2,3 As is known, the functions of the cells are related to the structure of the cell membrane. Thus, investigations of the structure of the H. salinarum surface are quite significant. Atomic force microscopy (AFM) is a nondestructive imaging technique with nanometer resolution. Since its introduction in 1986, AFM has been used more extensively in the field of life sciences. [4][5][6] AFM images can reveal the surface ultrastructure of living microbial cells with unprecedented resolution. [7][8][9] AFM can be operated in several operational modes, including contact, tapping and MAC modes. 10In the MAC mode, an alternating magnetic field, generated by a solenoid placed under the sample, is used to directly drive a magnetically coated cantilever to enable a stable operation. The advantages of the MAC mode are high resolution and easy operation in fluids for in situ studies, and little harm to soft biological samples due to intermittent contact.For AFM imaging, samples must be immobilized on a substrate. A variety of methods have been used to immobilize cells for AFM imaging, including trapping living cells in filtrate films, placing cells in agar, or immobilizing cells onto a surface such as mica or glass. 4 In microbiology, the heat-fixation method is widely used for immobilizing bacterial cells onto glass slides for observing cell morphology by optical microscopy. For low-resolution observations with an optical microscope, it seems that this method does not affect the cell morphology. However, the effect of this method on the ultrastructure of the cell morphology has not been examined.Herein, the effect of the heat-fixation method on cell morphology studied by MAC mode atomic force microscopy is reported. Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) were investigated, respectively, as representatives of Gram-negative bacteria and Gram-positive bacteria. The heatfixation method was then employed to prepare H. salinarum samples for AFM study.Details of the ultrastructural morphology of H. salinarum surface were obtained by MAC mode AFM. ExperimentalCulture of bacteria E. coli JM109 and B. subtilis DB104 were grown in LuriaBertani (LB). H. salinarum R1 was grown in a medium containing 0.25% lactalbumin hydrolysate, 0.2% yeast extract, 25% NaCl and 3% magnesium chloride heptahydrate at pH 7.0. The three species of bacteria were cultured at 37˚C with shaking and harvested in the late exponential phase of growth. Bacteria were centrifuged at 5000 rpm for 4 min, and the wet pellets were r...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.