Basic Microbiology
Philip A. Geis in Cosmetic Microbiology, 2020
Free-living bacteria require protection against osmotic stresses. Osmotic stress is encountered when bacteria enter hypotonic or hypertonic environments depending on the concentration of solutes within the cell. This can lead water to cross the plasma membrane by osmosis in an attempt to normalize solute concentrations across the membrane. Excess gain of water can cause the bacteria to lyse or explode due to cellular swelling whereas excess loss of water can cause membrane rupture by excessive shrinkage (plasmolysis). Most bacteria utilize a carbohydrate-based cell wall in order to provide resistance to osmotic forces. The basis of the cell wall is a macromolecular complex unique to bacteria called “peptidoglycan” or murein (Figure 1.4). The basic repeating structure of peptidoglycan is a disaccharide comprising N-acetylglucosamine (NAG) linked to N-acetylmuramic acid (NAM). This disaccharide is repeated hundreds of times to build long carbohydrate chains that are linked together by short peptides (called stem peptides) that contain unusual amino acids, some not found in proteins. These long chains appear to be wound into helices first and then cross-linked to other helices to form the peptidoglycan structure (2). The peptidoglycan is attached firmly to the cell membrane by lipoproteins. Although bacteria have proteins that determine the overall morphology of the cell, the peptidoglycan reinforces that morphology.
Hugo de Vries (1848–1935)
Krishna Dronamraju in A Century of Geneticists, 2018
Pursuing physiological studies at Leiden, de Vries earned his doctorate in plant physiology in 1870 but felt stifled by the university, where conditions for experimental work were crude and where there was open hostility to Darwinism. He therefore decided to continue his education in Germany, first at Heidelberg (1870) and then at Würzburg (1871), with Julius Sachs. Sachs took a great interest in de Vries’ career, helping him refine his experimental techniques and nominating him for several important posts over the next few years. Sachs was a strong proponent of experimentation. Under his guidance, de Vries began a series of detailed studies of osmosis, plasmolysis, and the effects of salt solutions on plant cells. He carried out these experiments at Würzburg, then at Amsterdam while teaching in a gymnasium (1871–1877), and finally at the University of Amsterdam, where he was appointed lecturer in plant physiology in 1877 and professor in 1881; he remained in Amsterdam until his retirement in 1918 and later moved to the village of Lunteren.
Environmental and Cytotoxicity Risks of Graphene Family Nanomaterials
Suresh C. Pillai, Yvonne Lang in Toxicity of Nanomaterials, 2019
GONS and quantum dots also proved toxic to the model green alga C. vulgaris. Ouyang et al. (Ouyang et al., 2015) studied the possible synergistic envelopment–internalization effects of the GO-derived nanostructures using metabolomics. Larger GONS intensively entrapped single-celled C. vulgaris, which in turn reduced cell permeability. In contrast, smaller GO quantum dots (GOQD) stimulated intense shrinkage of C. vulgaris cell’s plasma membrane and improved cell permeability via remarkable internalization reactions such as plasmolysis, GFN uptake and increased oxidative stress, in addition to the inhibition of cell division and chlorophyll biosynthesis. The phytotoxicity of rGO in microalgae S. obliquus also inhibited chlorophyll a and b levels which suppressed microalgae growth (Du et al., 2016b).
Cellular biogenesis of metal nanoparticles by water velvet (Azolla pinnata): different fates of the uptake Fe3+ and Ni2+ to transform into nanoparticles
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2021
Ratima Janthima, Sineenat Siri
Figure 6 shows the representative TEM images of vascular cells of A. pinnata roots exposed to Fe(NO3)3 and both Fe(NO3)3 and Ni(NO3)2. With Fe(NO3)3 exposure, FeNPs were observed near the cell wall of the metaxylem and in paramural bodies of pericycle cells. With both metal treatments, FeNPs also localized near the cell membrane of pericycle cells. The plasmolysis was also observed. It was likely due to the osmosis of water to the outside of the cell in a hypertonic environment. The average diameter of FeNPs in vascular cells was 18.53 ± 10.24 nm, which their diameters ranged from 4.47 to 52.86 nm.
Vision of bacterial ghosts as drug carriers mandates accepting the effect of cell membrane on drug loading
Published in Drug Development and Industrial Pharmacy, 2020
Fars K. Alanazi, Abdulaziz A. Alsuwyeh, Nazrul Haq, Mounir M. Salem-Bekhit, Abdullah Al-Dhfyan, Faiyaz Shakeel
Based on these results, the higher loading efficiency was achieved at tonicity of 0.9%. However, since no considerably difference between 0.9% and 0.7% were observed, tonicity 0.7% was preferred and selected to avoid bacterial raptured or plasmolysis at 0.9% tonicity in presence of High DOX concentration (10 mg/mL). When, cells are placed in high tonicity environments, plasmolysis occurs due to reductions in cytoplasmic volume because of water loss by osmosis. The thin peptidoglycan layer of Gram-negative microorganisms is anchored to the cytoplasmic membrane and can be distended by plasmolysis or even ruptured when plasmolysis is more extreme [28].
Detrimental effect of UV-B radiation on growth, photosynthetic pigments, metabolites and ultrastructure of some cyanobacteria and freshwater chlorophyta
Published in International Journal of Radiation Biology, 2021
Mostafa M. El-Sheekh, Eman A. Alwaleed, Aml Ibrahim, Hani Saber
The TEM observation of M. aeruginosa before UV-B radiation exposure exhibited that, control cells showed normal spherical cells, cell wall and membrane combined closely, and internal structure were distributed in the cytoplasm. By exposure to 3 h of UV-B, the cell boundary blurred. In some cells, cellular content became disorganized, and many gas vacuoles emerged, indicating the loss of cell inclusion and damage of the cell. In severe cases, after 7 h of exposure, cell wall and membrane appeared thickened, destroyed, and plasmolysis began to appear (Figure 6).