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Bacteria
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The boundary of the bacterial cell is referred to as the cell envelope, it includes the cell wall, one lipid bilayer membrane and, in Gram-negative bacteria, a lipid bilayer outside of the cell wall. These layers contain a variety of components, some of which control the transport of nutrients, including ions, in and out of the cell and also provide protection from changes in osmotic pressure. In addition, some envelop components, e.g., pili, serve as sites for attachment to host cells.
Structure and function of skin
Published in Roger L. McMullen, Antioxidants and the Skin, 2018
In addition to and following the series of events described thus far in the stratum granulosum, there are several more steps leading to the ultimate transformation of the keratinocyte to a cornified cell. First, the disintegration of ribosomes, mitochondria, and nuclei. In addition to these events, the plasma membrane is no longer able to survive and is replaced by a thick cornified cell envelope. Construction of the cell envelope takes place inside the boundaries of the plasma membrane. Two key proteins in the fabrication of the cell envelope include loricrin, derived from the keratohyalin granules, and involucrin from the cytoplasm. The contents of the cell envelope consist of these two proteins as well as a variety of other proteins, such as small proline-rich proteins, elafin, and envoplakin. The cell envelope is reinforced by epsilon-(gamma-glutamyl)lysine isopeptide cross-links, which are induced by transglutaminases. The resulting membrane is insoluble and impenetrable to polar substances. There are three known transglutaminases, expressed in the stratum granulosum, which carry out distinct functions.
Symptom flowcharts and testing guidelines
Published in Sarah Bekaert, Alison White, Integrated Contraceptive and Sexual Healthcare, 2018
Sarah Bekaert, Alison White, Kathy French, Kevin Miles
Following solvent treatment, only Gram-positive cells remain stained, possibly because of their thick cell wall, which is not permeable to solvent. After the staining procedure, cells are treated with a counterstain, e.g. a red acidic dye such as safranin or acid fuchsin, in order to make Gram-negative (decolourised) cells visible. Counterstained Gram-negative cells appear red, and Gram-positive cells remain blue. Although the cell walls of Gram-negative and Gram-positive bacteria are similar in chemical composition, the cell wall of Gram-negative bacteria has a thin layer between an outer lipid-containing cell envelope and the inner cell membrane. This means that within the staining process, the cell wall loses the crystal violet colour during the use of the alcohol in the decolourisation process and takes on the red stain at the end part of the staining process. The Gram-positive cell wall is much thicker, and retains the crystal violet stain even through the decolourisation process.
Destruction of Pseudomonas aeruginosa pre-formed biofilms by cationic polymer micelles bearing silver nanoparticles
Published in Biofouling, 2020
Tsvetelina Paunova-Krasteva, Emi Haladjova, Petar Petrov, Aleksander Forys, Barbara Trzebicka, Tanya Topouzova-Hristova, Stoyanka R. Stoitsova
The SEM images of an AgNO3-treated biofilm showed that the structural effects were somehow stratified. The outward layer was composed of vesiculated material, interpreted as the outcome of blebbing of the bacterial cells. The layer situated closer to the substratum was composed of cells with apparently less altered morphology and clearer outlines. However, fusions between individual cells again indicated cell envelope collapse. The cell-to-cell differences within the AgNO3-treated biofilm showed the variable response of individual cells to the treatments. In the literature, different mechanisms for Ag+-induced alterations in bacteria are mentioned. The cell envelope is the first-line target, and responds by loss of cell membrane integrity and lysis of the peptidoglycan (Ishida 2018; Tambosi et al. 2018). Other possible affects due to Ag+ would include free radical formation, ribosome destabilization, interaction with sulfur-containing proteins, intercalation between DNA bases and cell death (Chen et al. 2014; Franci et al. 2015; Rajivgandhi et al. 2019; Singh, Paknikar et al. 2019). While the cell envelope integrity is subjected to rapid damage, this damage would not necessarily be related to morphological changes visible at the SEM level (Randall et al. 2013). However, while the present SEM images revealed variable cell surface alterations under the action of AgNO3, the CLSM observation showed red fluorescence throughout the biofilm, which indicated that practically all the bacteria had substantial disruption of the permeability barrier of the surface envelope.
Yeast-inspired drug delivery: biotechnology meets bioengineering and synthetic biology
Published in Expert Opinion on Drug Delivery, 2019
Chinnu Sabu, Panakkal Mufeedha, Kannissery Pramod
Yeast cells are 2–3 µm ovoid or ellipsoidal structures covered by a thick cell wall. Saccharomyces is a Latin word which means sugar fungus, and cerevisiae is derived from two Latin words ceres and vise which means grain and strength. Cell envelope constitutes 15% of the total cell volume and is responsible for regulating the osmotic and permeability characteristics of the cell. The cytosol is further enveloped by a plasma membrane, periplasmic space, and the cell wall. Yeast cell wall which constitutes 25% of the total dry mass of cell is a rigid structure with a thickness of 200 nm. The four major macromolecules that constitute the cell wall are highly glycosylated glycoprotein or mannoproteins, two types of β-glucans and chitin. The cell wall constitution varies in accordance with growth condition of the cell. Spheroplasts or naked cells are formed by removing cell wall by reaction with a lytic enzyme in presence of osmotic stabilizers without causing any harm. They are susceptible to intergeneric and intrageneric cell fusions [8].
Molecular regulation of adhesion and biofilm formation in high and low biofilm producers of Bacillus licheniformis using RNA-Seq
Published in Biofouling, 2019
Faizan Ahmed Sadiq, Steve Flint, Hafiz Arbab Sakandar, GuoQing He
Increased peptidoglycan biosynthesis in biofilms may be related to the persistence of the cell wall. It is known that the cell envelope is a highly active component of bacterial cells in biofilms and plays an important role in biofilm development, resistance and sustainment (Resch et al. 2005; Bucher et al. 2015). Increased peptidoglycan biosynthesis has been reported in the biofilms formed by G. vaginalis (Castro et al. 2017), P. aeruginosa (El Zoeiby et al. 2001) and S. aureus (Resch et al. 2005). In the current study, it was found the ATP-binding cassette (ABC) transporters pathway was significantly enriched in the high biofilm forming strain only. This result shows that biofilm cells may be involved in transporting more solutes and small molecules compared to planktonic cells. An abundance of genes involved in ABS transporters has been reported in G. vaginalis (Castro et al. 2017), E. coli (Schembri et al. 2003), Desulfovibrio vulgaris (Clark et al. 2012) and biofilms formed by many other species. ABC transporter proteins have previously been reported to have a function in stress response in Streptococcus mutans (Nagayama et al. 2014). Increased amino sugar and nucleotide sugar metabolism in the high biofilm former indicates the role of amino sugars and nucleotide sugars (uracil-diphosphate glucose; UDP-glucose) in the biofilm matrix. Nucleotide sugars are important substrates for the enzyme glucosyltransferases (Gantt et al. 2013) which play an important role in polysaccharide synthesis (Li J and Wang 2012; Ren et al. 2016). It is important to mention that biofilm samples were obtained from 24 h biofilms in which bacterial cells may still be constructing biofilms thereby requiring more energy. For future studies, it will be equally important to study the metabolism of biofilm formation in B. licheniformis after 24 h.