Gram-Positive Cell Wall & Archaea Cell Walls (PDF)

Overview of the gram-positive cell wall: up to 90 percent peptidoglycan and peptidoglycan “cables” are formed. common to have teichoic acids (acidic substances) covalently bound to peptidoglycan bind divalent metal ions (e.g., Ca+2 and Mg+2) prior to...

Overview of the gram-positive cell wall: up to 90 percent peptidoglycan and peptidoglycan “cables” are formed. common to have teichoic acids (acidic substances) covalently bound to peptidoglycan bind divalent metal ions (e.g., Ca+2 and Mg+2) prior to transport lipoteichoic acids: teichoic acids covalently bound to membrane lipids https://www.touristjapan.com/japanese-chopstick-etiquette/  Archaeal Cell Walls No peptidoglycan, but has Pseudomurein (Pseudopeptidoglycan): found in cell walls of certain methanogenic Archaea polysaccharide similar to peptidoglycan (Figure 2.15) composed of N-acetylglucosamine (in peptidoglycan) and N- acetyltalosaminuronic acid (different, replaces N-acetylmuramic acid) β-1,3 glycosidic bonds instead of β-1,4 amino acids all L-stereoisomer cannot be destroyed by lysozyme and penicillin Spot the differences comparing to Figure 2.10?  Cell walls of some Archaea lack pseudomurein. contain other polysaccharide polymers S-Layers (Figure 2.16) most common cell wall type consist of protein or glycoprotein paracrystalline structure in many organisms, S-layers present in addition to other cell wall components, usually polysaccharides always outermost layer https://digital.wwnorton.com/ebooks/epub/microbio4/OEBPS/images/sfmb4e_1903.jpg  Paracrystalline structure of glycoprotein subunits The S-layer. Transmission electron micrograph of an S- layer fragment showing its paracrystalline nature. Shown is the S-layer from Aquaspirillum (Bacteria); this S-layer shows hexagonal symmetry common in S- layers of Archaea. Schematic illustration of the supramolecular architecture of the major classes of prokaryotic cell envelopes containing surface (S) layers. S- layers in archaea with glycoprotein lattices as exclusive wall component are composed either of mushroom-like subunits with pillar-like, hydrophobic trans-membrane domains (a), or lipid-modified glycoprotein subunits (b). Individual S-layers can be composed of glycoproteins possessing both types of membrane anchoring mechanisms. Few archaea possess a rigid wall layer (e.g. pseudomurein in methanogenic organisms) as intermediate layer between the plasma membrane and the S-layer (c). In Gram-positive bacteria (d) the S- layer (glyco)proteins are bound to the rigid peptidoglycan-containing layer via secondary cell wall polymers. In Gram-negative bacteria (e) the S-layer is closely associated with the lipopolysaccharide of the outer membrane. Sleytr et al. 2014  Cell Surface Structures Capsules and slime layers not considered part of cell wall because these do not confer significant structural strength polysaccharide layers (Figure 2.17) may be thick or thin, rigid or flexible capsule: if tightly attached, tight matrix; visible if treated with India ink slime layer: loosely attached, easily deformed (e.g., Leuconostoc) Functions assist in attachment to surfaces role in development and maintenance of biofilms virulence factors: protect against phagocytosis prevent dehydration/desiccation  Disease Example: Streptococcus pneumoniae pneumococcus Elongated gram-positive cocci arranged in pairs (diplococci) and short chains; encapsulated; fastidious growth; cell wall includes teichoic acid rich in phosphorylcholine (C polysaccharide), which is required for the activity of an autolytic enzyme, amidase. https://www.pinterest.com/pin/405394403938075967/  Commonly colonized in healthy people, more common in children and adult living with children. All colonies undergo autolysis with aging—that is, the central portion of the colony dissolves, leaving a dimpled appearance. autolysis  Pneumococcal disease Respiratory track diseases usually occurs when natural defense system is weakened. And can occur following other diseases e.g. influenza viral infection. Pneumococcal pneumonia (lung infection) is the most common serious form of pneumococcal disease. Symptoms include: Fever and chills Cough Rapid breathing or difficulty breathing Chest pain  Disease mechanism Virulent strains of S. pneumoniae are covered with a complex polysaccharide capsule. The capsular polysaccharides have been used for the serologic classification of strains; currently, 90 serotypes are recognized. Purified capsular polysaccharides from the most commonly isolated serotypes are used in a polyvalent vaccine. http://www.thelancet.com/  Polyvalent pneumococcus vaccine Prevnar (PCV7) and Prevnar 13 (PCV13): the bacterial capsule sugars - capsular polysaccharides from 7 or 13 serotypes, are linked to CRM197, a nontoxic recombinant variant of diphtheria toxin. http://www.hkpf.org.hk/ A blockbuster vaccine: Prevnar 13: sale of $5.95 billion in 2020 Highest among all vaccines http://www.scmp.com/ vaccineresistancemovement.org (except covid-19 vaccines)  Salmonella enterica Fimbriae filamentous protein structures (Figures 2.18 and 2.19) ~2–10 nm wide Fimbriae enable organisms to stick to surfaces or form pellicles (thin sheets of pellicles cells on a liquid surface). Identification of genes essential for pellicle formation in Acinetobacter baumannii, BMC Microbiology  Pili Pili are typically longer, and fewer (1 or a few) found per cell than fimbriae. Conjugative/sex pili facilitate genetic exchange between cells (conjugation). Type IV pili adhere to host tissues (mediate bacterial virulence) and support twitching motility (e.g., Pseudomonas and Moraxella).