Figure 3.18 Peptidoglycan cable Ribitol Wall-associated protein Teichoic acid Peptidoglycan Lipoteichoic acid Cytoplasmic membrane © 2012 Pearson Education, Inc.

3.6 The Cell Wall of Bacteria: Peptidoglycan Prokaryotes That Lack Cell Walls –Mycoplasmas Group of pathogenic bacteria –Thermoplasma Species of Archaea © 2012 Pearson Education, Inc.

3.7 The Outer Membrane Total cell wall contains ~10% peptidoglycan (Figure 3.20a) Most of cell wall composed of outer membrane (aka lipopolysaccharide [LPS] layer) –LPS consists of core polysaccharide and O-polysaccharide –LPS replaces most of phospholipids in outer half of outer membrane –Endotoxin: the toxic component of LPS © 2012 Pearson Education, Inc.

Figure 3.20a O-polysaccharide Peptidoglycan Core polysaccharide Lipid A Protein Porin Out 8 nm Phospholipid Lipopolysaccharide (LPS) Lipoprotein In Outer membrane Periplasm Cytoplasmic membrane Cell wall © 2012 Pearson Education, Inc.

3.7 The Outer Membrane Porins: channels for movement of hydrophilic low- molecular weight substances (Figure 3.20b) Periplasm: space located between cytoplasmic and outer membranes –~15 nm wide –Contents have gel-like consistency –Houses many proteins © 2012 Pearson Education, Inc.

3.8 Cell Walls of Archaea No peptidoglycan Typically no outer membrane Pseudomurein –Polysaccharide similar to peptidoglycan (Figure 3.21) –Composed of N-acetylglucosamine and N- acetyltalosaminuronic acid –Found in cell walls of certain methanogenic Archaea Cell walls of some Archaea lack pseudomurein © 2012 Pearson Education, Inc.

Figure 3.21 Lysozyme-insensitive N-Acetylglucosamine N-Acetyltalosaminuronic acid N-Acetyl group Peptide cross-links © 2012 Pearson Education, Inc.

3.8 Cell Walls of Archaea S-Layers –Most common cell wall type among Archaea –Consist of protein or glycoprotein –Paracrystalline structure (Figure 3.22) © 2012 Pearson Education, Inc.

Figure 3.22 © 2012 Pearson Education, Inc.

3.9 Cell Surface Structures Capsules and Slime Layers –Polysaccharide layers (Figure 3.23) May be thick or thin, rigid or flexible –Assist in attachment to surfaces –Protect against phagocytosis –Resist desiccation © 2012 Pearson Education, Inc.

Figure 3.23 Cell Capsule © 2012 Pearson Education, Inc.

3.9 Cell Surface Structures Fimbriae –Filamentous protein structures (Figure 3.24) –Enable organisms to stick to surfaces or form pellicles © 2012 Pearson Education, Inc.

Figure 3.24 Flagella Fimbriae © 2012 Pearson Education, Inc.

3.9 Cell Surface Structures Pili –Filamentous protein structures (Figure 3.25) –Typically longer than fimbriae –Assist in surface attachment –Facilitate genetic exchange between cells (conjugation) –Type IV pili involved in twitching motility © 2012 Pearson Education, Inc.

Figure 3.25 Virus- covered pilus © 2012 Pearson Education, Inc.

Figure 3.26  -carbon Polyhydroxyalkanoate © 2012 Pearson Education, Inc.

Figure 3.27 Polyphosphate Sulfur © 2012 Pearson Education, Inc.

Figure 3.28 © 2012 Pearson Education, Inc.

3.11 Gas Vesicles Gas Vesicles –Confer buoyancy in planktonic cells (Figure 3.29) –Spindle-shaped, gas-filled structures made of protein (Figure 3.30) –Gas vesicle impermeable to water © 2012 Pearson Education, Inc.

Figure 3.31 Ribs GvpA GvpC © 2012 Pearson Education, Inc.

3.12 Endospores Endospores –Highly differentiated cells resistant to heat, harsh chemicals, and radiation (Figure 3.32) –“Dormant” stage of bacterial life cycle (Figure 3.33) –Ideal for dispersal via wind, water, or animal gut –Only present in some gram-positive bacteria © 2012 Pearson Education, Inc.

Figure 3.32 Terminal spores Subterminal spores Central spores © 2012 Pearson Education, Inc.

Figure 3.33 Vegetative cell Developing spore Sporulating cell Mature spore © 2012 Pearson Education, Inc.

3.12 Endospores Endospore Structure (Figure 3.35) –Structurally complex –Contains dipicolinic acid –Enriched in Ca 2+ –Core contains small acid-soluble proteins (SASPs) © 2012 Pearson Education, Inc.

Figure 3.35 Exosporium Spore coat Core wall Cortex DNA © 2012 Pearson Education, Inc.

3.12 Endospores The Sporulation Process –Complex series of events (Figure 3.37) –Genetically directed © 2012 Pearson Education, Inc.

Figure 3.37 Free endospore Stage VI, VII Stage V Coat Stage IV Stage III Stage II Mother cell Prespore Septum Sporulation stages Cortex Cell wall Cytoplasmic membrane Vegetative cycle Maturation, cell lysis Cell division Germination Growth Engulfment Asymmetric cell division; commitment to sporulation, Stage I Spore coat, Ca 2  uptake, SASPs, dipicolinic acid Cortex formation © 2012 Pearson Education, Inc.

3.13 Flagella and Motility Flagellum (pl. flagella): structure that assists in swimming –Different arrangements: peritrichous, polar, lophotrichous (Figure 3.38) –Helical in shape Animation: The Prokaryotic Flagellum Animation: The Prokaryotic Flagellum © 2012 Pearson Education, Inc.

Figure 3.38 © 2012 Pearson Education, Inc.

3.13 Flagella and Motility Flagellar Structure –Consists of several components (Figure 3.41) –Filament composed of flagellin –Move by rotation © 2012 Pearson Education, Inc.

Figure 3.41 Rod C Ring MS Ring Mot protein Mot protein Fli proteins (motor switch) 45 nm Cytoplasmic membrane Basal body Rod C Ring MS Ring P Ring Periplasm Peptidoglycan L Ring Hook Outer membrane (LPS) Flagellin Filament MS L P 15—20 nm © 2012 Pearson Education, Inc.

3.13 Flagella and Motility Flagella increase or decrease rotational speed in relation to strength of the proton motive force Differences in swimming motions (Figure 3.44) –Peritrichously flagellated cells move slowly in a straight line –Polarly flagellated cells move more rapidly and typically spin around © 2012 Pearson Education, Inc.

Figure 3.44 Polar Peritrichous CW rotation CCW rotation Unidirectional flagella Cell stops, reorients Reversible flagella Bundled flagella (CCW rotation) Tumble—flagella pushed apart (CW rotation) Flagella bundled (CCW rotation) CW rotation © 2012 Pearson Education, Inc.

3.15 Microbial Taxes Taxis: directed movement in response to chemical or physical gradients –Chemotaxis: response to chemicals –Phototaxis: response to light –Aerotaxis: response to oxygen –Osmotaxis: response to ionic strength –Hydrotaxis: response to water © 2012 Pearson Education, Inc.

3.15 Microbial Taxes Chemotaxis –Best studied in E. coli –Bacteria respond to temporal, not spatial, difference in chemical concentration –“Run and tumble” behavior (Figure 3.47) –Attractants and receptors sensed by chemoreceptors © 2012 Pearson Education, Inc.

Figure 3.47 No attractant present: Random movement Attractant present: Directed movement Tumble Run Tumble Run Attractant © 2012 Pearson Education, Inc.

3.15 Microbial Taxes  Measuring Chemotaxis (Figure 3.48)  Measured by inserting a capillary tube containing an attractant or a repellent in a medium of motile bacteria  Can also be seen under a microscope © 2012 Pearson Education, Inc.

Figure 3.48 Time Repellent Control Attractant Repellent Control Attractant Cells per tube © 2012 Pearson Education, Inc.