Figure 3 18 Peptidoglycan cable Ribitol Wallassociated protein

3. 6 The Cell Wall of Bacteria: Peptidoglycan • Prokaryotes That Lack Cell Walls

3. 7 The Outer Membrane • Total cell wall contains ~10% peptidoglycan (Figure 3. 20 a) • 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. 20 a O-polysaccharide Core polysaccharide Lipid A Protein Out Lipopolysaccharide (LPS) Porin Cell wall 8 nm Outer membrane Periplasm Cytoplasmic membrane © 2012 Pearson Education, Inc. Peptidoglycan Phospholipid Lipoprotein In

3. 7 The Outer Membrane • Porins: channels for movement of hydrophilic lowmolecular weight substances (Figure 3. 20 b) • 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 Nacetyltalosaminuronic acid – Found in cell walls of certain methanogenic Archaea • Cell walls of some Archaea lack pseudomurein © 2012 Pearson Education, Inc.

Figure 3. 21 N-Acetyltalosaminuronic acid Lysozyme-insensitive N-Acetylglucosamine Peptide cross-links © 2012 Pearson Education, Inc.

3. 8 Cell Walls of Archaea • S-Layers – Most common cell wall type

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)

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 Viruscovered 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 Gvp. A Gvp. C © 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 © 2012 Pearson Education, Inc. Subterminal spores Central spores

Figure 3. 33 Vegetative cell Developing spore Sporulating cell Mature spore © 2012 Pearson

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,

3. 12 Endospores • The Sporulation Process – Complex series of events (Figure 3.

Figure 3. 37 Coat Maturation, cell lysis Free endospore Growth Spore coat, Ca 2 uptake, SASPs, dipicolinic acid Stage VI, VII Germination Stage V Cortex Sporulation stages Vegetative cycle Cell division Cell wall Cytoplasmic membrane Asymmetric cell division; commitment to sporulation, Stage I Cortex formation Prespore Septum Engulfment Mother cell Stage II © 2012 Pearson Education, Inc. Stage III Stage IV

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 © 2012 Pearson Education, Inc.

Figure 3. 38 © 2012 Pearson Education, Inc.

3. 13 Flagella and Motility • Flagellar Structure – Consists of several components (Figure

Figure 3. 41 15— 20 nm L P Filament Flagellin MS Hook Outer membrane (LPS) L Ring Rod P Ring Periplasm Peptidoglycan Rod MS Ring Basal body C Ring Cytoplasmic membrane Mot protein C Ring Fli proteins Mot protein (motor switch) 45 nm © 2012 Pearson Education, Inc. MS Ring Mot protein

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

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 Tumble Run No attractant present: Random movement © 2012 Pearson Education,

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.