LM2 - 1 Lecture overview Size and shape of microbes used in...

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Unformatted text preview: 1 Lecture overview Size and shape of microbes used in classification Envelopes (includes cytoplasmic/plasma membranes, cell walls, outer membranes, S-layers) Prokaryotic appendages (flagella and pili) Cytoplasmic structures (nucleoid, ribosomes, cytoskeleton inclusions and endospores) 2 Shapes of some prokaryotes (Fig. 3.1) Shapes: cocci (spherical); bacilli (rod-like); vibrios (comma- shaped); spirilla (spirals) or spirochete (cork-screw); pleomorphic Cells can stick together after dividing to form pairs (diplo), tetrads, chains (strepto), grape-like clusters (staphylo), filaments Names of microbes often reflect shape, type of growth Sizes range from 0.05 m diameter to lengths of > 500 m E coli is a typical bacillus at 1 x 3 m Some cell shapes from text (Fig. 3.2) (a) Vibrio cholerae (vibrio, SEM) (b) Rhodospirillum rubrum (spirilla, phase contrast) (c) Leptospira interrogans (spirochete) (d) Actinomyces (filamentous, SEM) (e) Hyphomicrobium (buds) (f) Haloquadratum walsbyi (square Archaea) 3 4 Parts of bacterial envelope of Gram-positive vs. Gram-negative bacteria (Fig. 3.17) Microbial envelope contains plasma membrane (AKA cytoplasmic membrane; PM or CM); cell wall (CW) made of murein (a type of peptidoglycan) and sometimes an S-layer Gram-negative bacteria have also an outer membrane (OM) and periplasmic space (space between CM and OM) OM may be considered part of cell wall by some authors 5 The bacterial plasma membrane (Figs. 3.5-3.7) Basic structure is phospholipid bilayer with integrated hopanoids (act as fluidity buffer; bottom, right) and proteins Lipid composition depends on microbe and its environment Fluidity of the CM is critical and is determined by the level of saturation of the fatty acids at a given temperature the greater the number of double-bonds, the more fluid the membrane 6 Bacterial cell wall: Structure of murein (Figs. 3.18, 3.20) Murein: consists of layers, each layer comprised of alternating NAG and NAM (lysozyme-sensitive linkage) Each NAM has an attached short peptide that may be X-linked to another NAM short peptide on an adjacent layer (by transpeptidase) Gram-positive bacteria: X-link of D-Ala is to gly interbridge, then the bridge is X-linked to L-Lys; walls have many layers (20-80 nm) Gram- negative bacteria: No interbridges, use DAP (diaminopimelic acid) linked to D-Ala and have fewer layers (2-7 nm) 7 Gram-positive cell wall features (Figs. 3.23, 3.24) Special structures called teichoic acids (right) are covalently attached to cell wall (or lipotechoic acids, attached to CM)...
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LM2 - 1 Lecture overview Size and shape of microbes used in...

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