Cell Structure and Function in Bacteria and Archaea Chapter 3 Cell Structure and Function in Bacteria and Archaea

I. Cell Shape and Size 3.1 Cell Morphology 3.2 Cell Size and the Significance of Smallness © 2012 Pearson Education, Inc.

3.1 Cell Morphology Morphology = cell shape Major cell morphologies (Figure 3.1) Coccus (pl. cocci): spherical or ovoid Rod: cylindrical shape Spirillum: spiral shape Cells with unusual shapes Spirochetes, appendaged bacteria, and filamentous bacteria Many variations on basic morphological types © 2012 Pearson Education, Inc.

Coccus Rod Spirillum Spirochete Stalk Hypha Budding and Figure 3.1 Spirochete Coccus Stalk Hypha Rod Budding and appendaged bacteria Figure 3.1 Representative cell morphologies of prokaryotes. Spirillum Filamentous bacteria © 2012 Pearson Education, Inc. 4

3.1 Cell Morphology Morphology typically does not predict physiology, ecology, phylogeny, etc. of a prokaryotic cell Selective forces may be involved in setting the morphology Optimization for nutrient uptake (small cells and those with high surface-to-volume ratio) Swimming motility in viscous environments or near surfaces (helical or spiral-shaped cells) Gliding motility (filamentous bacteria) © 2012 Pearson Education, Inc.

3.2 Cell Size and the Significance of Smallness Size range for prokaryotes: 0.2 µm to >700 µm in diameter Most cultured rod-shaped bacteria are between 0.5 and 4.0 µm wide and <15 µm long Examples of very large prokaryotes Epulopiscium fishelsoni (Figure 3.2a) Thiomargarita namibiensis (Figure 3.2b) Size range for eukaryotic cells: 10 to >200 µm in diameter © 2012 Pearson Education, Inc.

Figure 3.2 Figure 3.2 Some very large prokaryotes. © 2012 Pearson Education, Inc. 7

3.2 Cell Size and the Significance of Smallness Surface-to-Volume Ratios, Growth Rates, and Evolution Advantages to being small (Figure 3.3) Small cells have more surface area relative to cell volume than large cells (i.e., higher S/V) support greater nutrient exchange per unit cell volume tend to grow faster than larger cells © 2012 Pearson Education, Inc.

Surface Volume Surface Volume r = 1 m = 3 = 1.5 Figure 3.3 r = 1 m r = 1 m Surface area (4r2) = 12.6 m2 3 4 Volume ( r3) = 4.2 m3 Surface = 3 Volume r = 2 m r = 2 m Surface area = 50.3 m2 Volume = 33.5 m3 Figure 3.3 Surface area and volume relationships in cells. Surface = 1.5 Volume © 2012 Pearson Education, Inc. 9

3.2 Cell Size and the Significance of Smallness Lower Limits of Cell Size Cellular organisms <0.15 µm in diameter are unlikely Open oceans tend to contain small cells (0.2–0.4 µm in diameter) © 2012 Pearson Education, Inc.

II. The Cytoplasmic Membrane and Transport 3.4 Functions of the Cytoplasmic Membrane 3.5 Transport and Transport Systems © 2012 Pearson Education, Inc.

3.3 The Cytoplasmic Membrane in Bacteria and Archaea Thin structure that surrounds the cell 6–8 nm thick Vital barrier that separates cytoplasm from environment Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products © 2012 Pearson Education, Inc.

3.3 The Cytoplasmic Membrane Composition of Membranes General structure is phospholipid bilayer (Figure 3.4) Contain both hydrophobic and hydrophilic components Can exist in many different chemical forms as a result of variation in the groups attached to the glycerol backbone Fatty acids point inward to form hydrophobic environment; hydrophilic portions remain exposed to external environment or the cytoplasm Animation: Membrane Structure © 2012 Pearson Education, Inc.

Glycerol Fatty acids Phosphate Ethanolamine Hydrophilic region Figure 3.4 Glycerol Fatty acids Phosphate Ethanolamine Hydrophilic region Hydrophobic Fatty acids region Figure 3.4 Phospholipid bilayer membrane. Hydrophilic region Glycerophosphates Fatty acids © 2012 Pearson Education, Inc. 14

3.3 The Cytoplasmic Membrane Cytoplasmic Membrane (Figure 3.5) 6–8 nm wide Embedded proteins Stabilized by hydrogen bonds and hydrophobic interactions Mg2+ and Ca2+ help stabilize membrane by forming ionic bonds with negative charges on the phospholipids Somewhat fluid © 2012 Pearson Education, Inc.

Out In Phospholipids Hydrophilic groups 6–8 nm Hydrophobic groups Figure 3.5 Out Phospholipids Hydrophilic groups 6–8 nm Hydrophobic groups In Figure 3.5 Structure of the cytoplasmic membrane. Integral membrane Phospholipid proteins molecule © 2012 Pearson Education, Inc. 16

3.3 The Cytoplasmic Membrane Membrane Proteins Outer surface of cytoplasmic membrane can interact with a variety of proteins that bind substrates or process large molecules for transport Inner surface of cytoplasmic membrane interacts with proteins involved in energy-yielding reactions and other important cellular functions © 2012 Pearson Education, Inc.

3.3 The Cytoplasmic Membrane Membrane Proteins (cont’d) Integral membrane proteins Firmly embedded in the membrane Peripheral membrane proteins One portion anchored in the membrane © 2012 Pearson Education, Inc.

3.3 The Cytoplasmic Membrane Membrane-Strengthening Agents Sterols Rigid, planar lipids found in eukaryotic membranes Strengthen and stabilize membranes Hopanoids Structurally similar to sterols Present in membranes of many Bacteria © 2012 Pearson Education, Inc.

3.3 The Cytoplasmic Membrane Archaeal Membranes Ether linkages in phospholipids of Archaea (Figure 3.6) Bacteria and Eukarya that have ester linkages in phospholipids Archaeal lipids lack fatty acids, have isoprenes instead Major lipids are glycerol diethers and tetraethers (Figure 3.7a and b) Can exist as lipid monolayers, bilayers, or mixture (Figure 3.7d and e) © 2012 Pearson Education, Inc.

Ester Ether Bacteria Archaea Eukarya Figure 3.6 Figure 3.6 General structure of lipids. Bacteria Archaea Eukarya © 2012 Pearson Education, Inc. 21

CH3 groups Isoprene unit Glycerol diether Figure 3.7a Phytanyl Figure 3.7 Major lipids of Archaea and the architecture of archaeal membranes. © 2012 Pearson Education, Inc. 22

Diglycerol tetraethers Figure 3.7b Biphytanyl Diglycerol tetraethers Figure 3.7 Major lipids of Archaea and the architecture of archaeal membranes. © 2012 Pearson Education, Inc. 23

Figure 3.7c Crenarchaeol Figure 3.7 Major lipids of Archaea and the architecture of archaeal membranes. © 2012 Pearson Education, Inc. 24

Out In Glycerophosphates Phytanyl Membrane protein Lipid bilayer Figure 3.7d Out Glycerophosphates Phytanyl Membrane protein In Figure 3.7 Major lipids of Archaea and the architecture of archaeal membranes. Lipid bilayer © 2012 Pearson Education, Inc. 25

Out In Biphytanyl Lipid monolayer Figure 3.7e Figure 3.7 Major lipids of Archaea and the architecture of archaeal membranes. Lipid monolayer © 2012 Pearson Education, Inc. 26

3.4 Functions of the Cytoplasmic Membrane Permeability Barrier (Figure 3.8) Polar and charged molecules must be transported Transport proteins accumulate solutes against the concentration gradient Protein Anchor Holds transport proteins in place Energy Conservation © 2012 Pearson Education, Inc.

Permeability barrier: Protein anchor: Energy conservation: Figure 3.8 Permeability barrier: Prevents leakage and functions as a gateway for transport of nutrients into, and wastes out of, the cell Protein anchor: Site of many proteins that participate in transport, bioenergetics, and chemotaxis Energy conservation: Site of generation and use of the proton motive force Figure 3.8 The major functions of the cytoplasmic membrane. © 2012 Pearson Education, Inc. 28

3.5 Transport and Transport Systems Carrier-Mediated Transport Systems (Figure 3.9) Show saturation effect Highly specific © 2012 Pearson Education, Inc.

Transporter saturated with substrate Figure 3.9 Transporter saturated with substrate Rate of solute entry Transport Figure 3.9 Transport versus diffusion. Simple diffusion External concentration of solute © 2012 Pearson Education, Inc. 30

3.5 Transport and Transport Systems Three major classes of transport systems in prokaryotes (Figure 3.10) Simple transport Group translocation ABC system All require energy in some form, usually proton motive force or ATP © 2012 Pearson Education, Inc.

Out In Simple transport: Driven by the energy in the proton motive Figure 3.10 In Simple transport: Driven by the energy in the proton motive force Out Transported substance Group translocation: Chemical modification of the transported substance driven by phosphoenolpyruvate 1 Figure 3.10 The three classes of transport systems. 2 ABC transporter: Periplasmic binding proteins are involved and energy comes from ATP 3 © 2012 Pearson Education, Inc. 32

3.5 Transport and Transport Systems Three transport events are possible: uniport, symport, and antiport (Figure 3.11) Uniporters transport in one direction across the membrane Symporters function as co-transporters Antiporters transport a molecule across the membrane while simultaneously transporting another molecule in the opposite direction © 2012 Pearson Education, Inc.

Out In Uniporter Antiporter Symporter Figure 3.11 Figure 3.11 Structure of membrane-spanning transporters and types of transport events. Uniporter Antiporter Symporter © 2012 Pearson Education, Inc. 34

3.5 Transport and Transport Systems Simple Transport: Lac Permease of Escherichia coli (Figure 3.12) Lactose is transported into E. coli by the simple transporter lac permease, a symporter Activity of lac permease is energy driven Other symporters, uniporters, and antiporters © 2012 Pearson Education, Inc.

Figure 3.12 Out In Figure 3.12 The lac permease of Escherichia coli and several other well-characterized simple transporters. Sulfate symporter Potassium uniporter Phosphate symporter Sodium-proton antiporter Lac permease (a symporter) © 2012 Pearson Education, Inc. 36

3.5 Transport and Transport Systems The Phosphotransferase System in E. coli (Figure 3.13) Type of group translocation: substance transported is chemically modified during transport across the membrane Best-studied system Moves glucose, fructose, and mannose Five proteins required Energy derived from phosphoenolpyruvate © 2012 Pearson Education, Inc.

Figure 3.13 Glucose Out Cytoplasmic membrane Nonspecific components Specific components Enz IIC Direction of glucose transport PE Enz HPr Enz IIa Enz IIb Pyruvate In Figure 3.13 Mechanism of the phosphotransferase system of Escherichia coli. Direction of P transfer Glucose 6–P © 2012 Pearson Education, Inc. 38

3.5 Transport and Transport Proteins ABC (ATP-Binding Cassette) Systems (Figure 3.14) >200 different systems identified in prokaryotes Often involved in uptake of organic compounds (e.g., sugars, amino acids), inorganic nutrients (e.g., sulfate, phosphate), and trace metals Typically display high substrate specificity Contain periplasmic binding proteins © 2012 Pearson Education, Inc.

Out In Periplasm Peptidoglycan Periplasmic binding protein Transported Figure 3.14 Peptidoglycan Periplasmic binding protein Periplasm Transported substance Out Membrane- spanning transporter Figure 3.14 Mechanism of an ABC transporter. ATP- hydrolyzing protein In © 2012 Pearson Education, Inc. 40

3.5 Transport and Transport Proteins Protein Export Translocases: responsible for exporting proteins through and inserting into prokaryotic membranes Sec translocase system: exports proteins and inserts integral membrane proteins into the membrane Type III secretion system: common in pathogenic bacteria; secreted protein translocated directly into host © 2012 Pearson Education, Inc.

III. Cell Walls of Prokaryotes 3.6 The Cell Wall of Bacteria: Peptidoglycan 3.7 The Outer Membrane 3.8 Cell Walls of Archaea © 2012 Pearson Education, Inc.

3.6 The Cell Wall of Bacteria: Peptidoglycan Peptidoglycan (Figure 3.16) Rigid layer that provides strength to cell wall Polysaccharide composed of N-acetylglucosamine and N-acetylmuramic acid Amino acids Lysine or diaminopimelic acid (DAP) Cross-linked differently in gram-negative bacteria and gram-positive bacteria (Figure 3.17) © 2012 Pearson Education, Inc.

Lysozyme- sensitive bond Diaminopimelic acid N-Acetylglucosamine Figure 3.16 N-Acetylglucosamine N-Acetylmuramic acid N-Acetyl group Glycan tetrapeptide Lysozyme- sensitive bond Peptide cross-links Figure 3.16 Structure of the repeating unit in peptidoglycan, the glycan tetrapeptide. L-Alanine D-Glutamic acid Diaminopimelic acid D-Alanine © 2012 Pearson Education, Inc. 44

Figure 3.17 Polysaccharide backbone Interbridge Peptides Escherichia coli (gram-negative) Staphylococcus aureus (gram-positive) Figure 3.17 Peptidoglycan in Escherichia coli and Staphylococcus aureus. Y Peptide bonds X Glycosidic bonds © 2012 Pearson Education, Inc. 45

3.6 The Cell Wall of Bacteria: Peptidoglycan Gram-Positive Cell Walls (Figure 3.18) Can contain up to 90% peptidoglycan Common to have teichoic acids (acidic substances) embedded in the cell wall Lipoteichoic acids: teichoic acids covalently bound to membrane lipids © 2012 Pearson Education, Inc.

Figure 3.18 Peptidoglycan cable Ribitol Teichoic acid Peptidoglycan Wall-associated protein Lipoteichoic acid Figure 3.18 Structure of the gram-positive bacterial cell wall. Cytoplasmic membrane © 2012 Pearson Education, Inc. 47

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 Out In Cell wall O-polysaccharide Core polysaccharide Lipid A Protein Out Lipopolysaccharide (LPS) Porin Outer membrane 8 nm Cell wall Phospholipid Peptidoglycan Periplasm Lipoprotein Figure 3.20 The gram-negative cell wall. Cytoplasmic membrane In © 2012 Pearson Education, Inc. 50

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.

Figure 3.20b Periplasm Cytoplasmic membrane Outer membrane Figure 3.20 The gram-negative cell wall. © 2012 Pearson Education, Inc. 52

3.7 The Outer Membrane Structural differences between cell walls of gram-positive and gram-negative Bacteria are responsible for differences in the Gram stain reaction © 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.

group N-Acetylglucosamine N-Acetyltalosaminuronic acid Figure 3.21 N-Acetyltalosaminuronic acid Lysozyme-insensitive N-Acetyl group N-Acetylglucosamine Figure 3.21 Pseudomurein. Peptide cross-links © 2012 Pearson Education, Inc. 55

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 Figure 3.22 The S-layer. © 2012 Pearson Education, Inc. 57

IV. Other Cell Surface Structures and Inclusions 3.10 Cell Inclusions 3.11 Gas Vesicles 3.12 Endospores © 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.

Cell Capsule Figure 3.23 Figure 3.23 Bacterial capsules. © 2012 Pearson Education, Inc. 60

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.

Flagella Fimbriae Figure 3.24 Figure 3.24 Fimbriae. © 2012 Pearson Education, Inc. 62

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.

Virus- covered pilus Figure 3.25 Figure 3.25 Pili. © 2012 Pearson Education, Inc. 64

3.10 Cell Inclusions Carbon storage polymers Poly--hydroxybutyric acid (PHB): lipid (Figure 3.26) Glycogen: glucose polymer Polyphosphates: accumulations of inorganic phosphate (Figure 3.27) Sulfur globules: composed of elemental sulfur Magnetosomes: magnetic storage inclusions (Figure 3.28) © 2012 Pearson Education, Inc.

Polyhydroxyalkanoate Figure 3.26 -carbon Figure 3.26 Poly-β-hydroxyalkanoates. Polyhydroxyalkanoate © 2012 Pearson Education, Inc. 66

Polyphosphate Sulfur Figure 3.27 Figure 3.27 Polyphosphate and sulfur storage products. Sulfur © 2012 Pearson Education, Inc. 67

Figure 3.28 Figure 3.28 Magnetotactic bacteria and magnetosomes. © 2012 Pearson Education, Inc. 68

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 3.29 Figure 3.29 Buoyant cyanobacteria. © 2012 Pearson Education, Inc. 70

Figure 3.30 Figure 3.30 Gas vesicles of the cyanobacteria Anabaena and Microcystis. © 2012 Pearson Education, Inc. 71

3.11 Gas Vesicles Molecular Structure of Gas Vesicles Gas vesicles are composed of two proteins: GvpA and GvpC (Figure 3.31) Function by decreasing cell density © 2012 Pearson Education, Inc.

Ribs GvpA GvpC Figure 3.31 Figure 3.31 Gas vesicle architecture. © 2012 Pearson Education, Inc. 73

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.

Terminal Subterminal Central spores spores spores Figure 3.32 Figure 3.32 The bacterial endospore. © 2012 Pearson Education, Inc. 75

Vegetative cell Developing spore Germination Sporulating cell Figure 3.33 Vegetative cell Developing spore Germination Sporulating cell Figure 3.33 The life cycle of an endospore-forming bacterium. Mature spore © 2012 Pearson Education, Inc. 76

3.12 Endospores Endospore Structure (Figure 3.35) Structurally complex Contains dipicolinic acid Enriched in Ca2+ Core contains small acid-soluble proteins (SASPs) © 2012 Pearson Education, Inc.

Exosporium Spore coat Core wall Cortex DNA Figure 3.35 Figure 3.35 Structure of the bacterial endospore. © 2012 Pearson Education, Inc. 78

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

Sporulation stages Vegetative cycle Figure 3.37 Coat Spore coat, Ca2 uptake, SASPs, dipicolinic acid Free endospore Maturation, cell lysis Stage VI, VII Growth Stage V Germination Cortex Vegetative cycle Sporulation stages Cell wall Cytoplasmic membrane Cell division Asymmetric cell division; commitment to sporulation, Stage I Stage IV Cortex formation Figure 3.37 Stages in endospore formation. Prespore Septum Engulfment Mother cell Stage III Stage II © 2012 Pearson Education, Inc. 80

V. Microbial Locomotion 3.13 Flagella and Motility 3.14 Gliding Motility 3.15 Microbial Taxes © 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 © 2012 Pearson Education, Inc.

Figure 3.38 Figure 3.38 Bacterial flagella. © 2012 Pearson Education, Inc. 83

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 L Filament P Flagellin MS Outer membrane (LPS) Hook L Ring Rod P Ring Periplasm Peptidoglycan Figure 3.41 Structure and function of the flagellum in gram-negative Bacteria. Rod MS Ring Basal body MS Ring Mot protein C Ring C Ring Cytoplasmic membrane Mot protein Fli proteins (motor switch) Mot protein 45 nm © 2012 Pearson Education, Inc. 85

3.13 Flagella and Motility Flagellar Synthesis Several genes are required for flagellar synthesis and motility (Figure 3.43) MS ring made first Other proteins and hook made next Filament grows from tip © 2012 Pearson Education, Inc.

Figure 3.43 Filament synthesis Late hook Hook- filament junction Outer membrane Cap Filament Early hook MS/C ring Motor (Mot) proteins P ring L ring Figure 3.43 Flagella biosynthesis. Peptidoglycan Cytoplasmic membrane © 2012 Pearson Education, Inc. 87

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.

Unidirectional flagella Figure 3.44 Tumble—flagella pushed apart (CW rotation) Bundled flagella (CCW rotation) Flagella bundled (CCW rotation) Peritrichous Reversible flagella Figure 3.44 Movement in peritrichously and polarly flagellated prokaryotes. CCW rotation CW rotation Unidirectional flagella Cell stops, reorients CW rotation CW rotation Polar © 2012 Pearson Education, Inc. 89

3.14 Gliding Motility Gliding Motility Flagella-independent motility (Figure 3.46) Slower and smoother than swimming Movement typically occurs along long axis of cell Requires surface contact Mechanisms Excretion of polysaccharide slime Type IV pili Gliding-specific proteins © 2012 Pearson Education, Inc.

In Out Surface Cytoplasmic membrane Peptidoglycan Outer membrane Figure 3.46 In Cytoplasmic membrane Peptidoglycan Outer membrane Figure 3.46 Gliding motility in Flavobacterium johnsoniae. Out Movement of outer membrane proteins Surface Movement of cell © 2012 Pearson Education, Inc. 91

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.

No attractant present: Random movement Attractant present: Figure 3.47 Tumble Attractant Tumble Run Run Figure 3.47 Chemotaxis in a peritrichously flagellated bacterium such as Escherichia coli. No attractant present: Random movement Attractant present: Directed movement © 2012 Pearson Education, Inc. 94

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.

Control Attractant Repellent Attractant Cells per tube Control Figure 3.48 Control Attractant Repellent Attractant Cells per tube Control Figure 3.48 Measuring chemotaxis using a capillary tube assay. Repellent Time © 2012 Pearson Education, Inc. 96