1 Early Life and the Diversification of Prokaryotes24 Early Life and the Diversification of Prokaryotes
2 Overview: The First CellsEarth formed 4.6 billion years ago The oldest fossil organisms are prokaryotes dating back to 3.5 billion years ago Prokaryotes are single-celled organisms in the domains Bacteria and Archaea Some of the earliest prokaryotic cells lived in dense mats that resembled stepping stones 2
3 Figure 24.1 Figure 24.1 What organisms lived on early Earth? 3
4 Prokaryotes are the most abundant organisms on Earth There are more in a handful of fertile soil than the number of people who have ever lived Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms Some prokaryotes colonize the bodies of other organisms 4
5 Figure 24.2 Figure 24.2 Bacteria that inhabit the human body 5
6 Concept 24.1: Conditions on early Earth made the origin of life possibleChemical and physical processes on early Earth may have produced very simple cells through a sequence of stages Abiotic synthesis of small organic molecules Joining of these small molecules into macromolecules Packaging of molecules into protocells, membrane-bound droplets that maintain a consistent internal chemistry Origin of self-replicating molecules 6
7 Synthesis of Organic Compounds on Early EarthEarth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, and hydrogen) As Earth cooled, water vapor condensed into oceans, and most of the hydrogen escaped into space 7
8 In the 1920s, A. I. Oparin and J. B. SIn the 1920s, A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible 8
9 Organic molecules have also been found in meteoritesHowever, the evidence is not yet convincing that the early atmosphere was in fact reducing Instead of forming in the atmosphere, the first organic compounds may have been synthesized near volcanoes or deep-sea vents Miller-Urey-type experiments demonstrate that organic molecules could have formed with various possible atmospheres Organic molecules have also been found in meteorites Video: Hydrothermal Vent Video: Tubeworms 9
10 Number of amino acids amino acids (mg) Mass ofFigure 24.3 20 200 Number of amino acids amino acids (mg) Mass of 10 100 1953 2008 1953 2008 Figure 24.3 Amino acid synthesis in a simulated volcanic eruption 10
11 Figure 24.3a Figure 24.3a Amino acid synthesis in a simulated volcanic eruption (photo) 11
12 Abiotic Synthesis of MacromoleculesRNA monomers have been produced spontaneously from simple molecules Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock 12
13 Protocells Replication and metabolism are key properties of life and may have appeared together Protocells may have been fluid-filled vesicles with a membrane-like structure In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer 13
14 Adding clay can increase the rate of vesicle formation Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment 14
15 index of vesicle numberFigure 24.4 0.4 Precursor molecules plus montmorillonite clay index of vesicle number Relative turbidity, an 0.2 Precursor molecules only 20 40 60 Time (minutes) (a) Self-assembly Vesicle boundary 1 m Figure 24.4 Features of abiotically produced vesicles 20 m (b) Reproduction (c) Absorption of RNA 15
16 index of vesicle numberFigure 24.4a 0.4 Precursor molecules plus montmorillonite clay index of vesicle number Relative turbidity, an 0.2 Precursor molecules only Figure 24.4a Features of abiotically produced vesicles (part 1: self-assembly) 20 40 60 Time (minutes) (a) Self-assembly 16
17 20 m (b) Reproduction Figure 24.4bFigure 24.4b Features of abiotically produced vesicles (part 2: reproduction) 20 m (b) Reproduction 17
18 Vesicle 1 m boundary (c) Absorption of RNA Figure 24.4cFigure 24.4c Features of abiotically produced vesicles (part 3: absorption of RNA) (c) Absorption of RNA 18
19 Self-Replicating RNA The first genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions For example, ribozymes can make complementary copies of short stretches of RNA 19
20 Natural selection has produced self-replicating RNA molecules RNA molecules that were more stable or replicated more quickly would have left the most descendant RNA molecules The early genetic material might have formed an “RNA world” 20
21 Vesicles with RNA capable of replication would have been protocells RNA could have provided the template for DNA, a more stable genetic material 21
22 Fossil Evidence of Early LifeMany of the oldest fossils are stromatolites, layered rocks that formed from the activities of prokaryotes up to 3.5 billion years ago Ancient fossils of individual prokaryotic cells have also been discovered For example, fossilized prokaryotic cells have been found in 3.4-billion-year-old rocks from Australia 22
23 Nonphotosynthetic bacteriaFigure 24.5 30 m 5 cm 10 m Stromatolites Figure 24.5 Appearance in the fossil record of early prokaryote groups Nonphotosynthetic bacteria Possible earliest appearance in fossil record Cyanobacteria 4 3 2 1 Time (billions of years ago) 23
24 Nonphotosynthetic bacteriaFigure 24.5a Stromatolites Nonphotosynthetic bacteria Possible earliest appearance in fossil record Cyanobacteria Figure 24.5a Appearance in the fossil record of early prokaryote groups (part 1: graph) 4 3 2 1 Time (billions of years ago) 24
25 30 m 3-billion-year-old fossil of a cluster of nonphotosyntheticFigure 24.5b 30 m 3-billion-year-old fossil of a cluster of nonphotosynthetic prokaryote cells Figure 24.5b Appearance in the fossil record of early prokaryote groups (part 2: nonphotosynthetic bacteria) 25
26 fossilized stromatoliteFigure 24.5c 5 cm Figure 24.5c Appearance in the fossil record of early prokaryote groups (part 3: stromatolite) 1.1-billion-year-old fossilized stromatolite 26
27 1.5-billion-year-old fossil of a cyanobacteriumFigure 24.5d 10 m Figure 24.5d Appearance in the fossil record of early prokaryote groups (part 4: cyanobacterium) 1.5-billion-year-old fossil of a cyanobacterium 27
28 The cyanobacteria that form stromatolites were the main photosynthetic organisms for over a billion years Early cyanobacteria began the release of oxygen into Earth’s atmosphere Surviving prokaryote lineages either avoided or adapted to the newly aerobic environment 28
29 Concept 24.2: Diverse structural and metabolic adaptations have evolved in prokaryotesMost prokaryotes are unicellular, although some species form colonies Most prokaryotic cells have diameters of 0.5–5 µm, much smaller than the 10–100 µm diameter of many eukaryotic cells Prokaryotic cells have a variety of shapes The three most common shapes are spheres (cocci), rods (bacilli), and spirals 29
30 1 m 1 m 3 m (a) Spherical (b) Rod-shaped (c) Spiral Figure 24.6Figure 24.6 The most common shapes of prokaryotes 1 m 1 m 3 m (a) Spherical (b) Rod-shaped (c) Spiral 30
31 1 m (a) Spherical Figure 24.6aFigure 24.6a The most common shapes of prokaryotes (part 1: spherical) 1 m (a) Spherical 31
32 1 m (b) Rod-shaped Figure 24.6bFigure 24.6b The most common shapes of prokaryotes (part 2: rod-shaped) 1 m (b) Rod-shaped 32
33 Figure 24.6c Figure 24.6c The most common shapes of prokaryotes (part 3: spiral) 3 m (c) Spiral 33
34 Cell-Surface StructuresA key feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment Eukaryote cell walls are made of cellulose or chitin Bacterial cell walls contain peptidoglycan, a network of modified sugars cross-linked by polypeptides 34
35 Archaeal cell walls contain polysaccharides and proteins but lack peptidoglycanScientists use the Gram stain to classify bacteria by cell wall composition Gram-positive bacteria have simpler walls with a large amount of peptidoglycan Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic 35
36 of lipopolysaccharideFigure 24.7 (a) Gram-positive bacteria (b) Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Peptido- glycan layer Outer membrane Cell wall Cell wall Peptidoglycan layer Plasma membrane Plasma membrane Gram-positive bacteria Gram-negative bacteria Figure 24.7 Gram staining 10 m 36
37 (a) Gram-positive bacteria Peptido- Cell glycan wall layer PlasmaFigure 24.7a (a) Gram-positive bacteria Peptido- glycan layer Cell wall Figure 24.7a Gram staining (part 1: Gram-positive) Plasma membrane 37
38 of lipopolysaccharideFigure 24.7b (b) Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Figure 24.7b Gram staining (part 2: Gram-negative) Peptidoglycan layer Plasma membrane 38
39 Gram-positive bacteria Gram-negative bacteria 10 m Figure 24.7cFigure 24.7c Gram staining (part 3: micrograph) 10 m 39
40 Many antibiotics target peptidoglycan and damage bacterial cell walls Gram-negative bacteria are more likely to be antibiotic resistant A polysaccharide or protein layer called a capsule covers many prokaryotes 40
41 Bacterial capsule Bacterial cell wall Tonsil cell 200 nm Figure 24.8Figure 24.8 Capsule 200 nm 41
42 Some bacteria develop resistant cells called endospores when they lack an essential nutrientOther bacteria have fimbriae, which allow them to stick to their substrate or other individuals in a colony Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA 42
43 Figure 24.9 Fimbriae Figure 24.9 Fimbriae 1 m 43
44 Motility In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from a stimulus Chemotaxis is the movement toward or away from a chemical stimulus 44
45 Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently 45
46 Flagellum 20 nm Filament Hook Motor Cell wall Peptidoglycan PlasmaFigure 24.10 Flagellum 20 nm Filament Hook Motor Cell wall Figure A prokaryotic flagellum Peptidoglycan layer Plasma membrane Rod 46
47 Figure 24.10a 20 nm Hook Motor Figure 24.10a A prokaryotic flagellum (TEM) 47
48 Evolutionary Origins of Bacterial FlagellaBacterial flagella are composed of a motor, hook, and filament Many of the flagella’s proteins are modified versions of proteins that perform other tasks in bacteria Flagella likely evolved as existing proteins were added to an ancestral secretory system This is an example of exaptation, where existing structures take on new functions through descent with modification 48
49 Internal Organization and DNAProkaryotic cells usually lack complex compartmentalization Some prokaryotes do have specialized membranes that perform metabolic functions These are usually infoldings of the plasma membrane 49
50 (a) Aerobic prokaryote (b) Photosynthetic prokaryoteFigure 24.11 0.2 m 1 m Respiratory membrane Thylakoid membranes Figure Specialized membranes of prokaryotes (a) Aerobic prokaryote (b) Photosynthetic prokaryote 50
51 (a) Aerobic prokaryoteFigure 24.11a 0.2 m Respiratory membrane Figure 24.11a Specialized membranes of prokaryotes (part 1: aerobic) (a) Aerobic prokaryote 51
52 (b) Photosynthetic prokaryoteFigure 24.11b 1 m Thylakoid membranes Figure 24.11b Specialized membranes of prokaryotes (part 2: photosynthetic) (b) Photosynthetic prokaryote 52
53 The prokaryotic genome has less DNA than the eukaryotic genome Most of the genome consists of a circular chromosome The chromosome is not surrounded by a membrane; it is located in the nucleoid region Some species of bacteria also have smaller rings of DNA called plasmids 53
54 Chromosome Plasmids 1 m Figure 24.12Figure A prokaryotic chromosome and plasmids 1 m 54
55 There are some differences between prokaryotes and eukaryotes in DNA replication, transcription, and translation These allow people to use some antibiotics to inhibit bacterial growth without harming themselves 55
56 Nutritional and Metabolic AdaptationsProkaryotes can be categorized by how they obtain energy and carbon Phototrophs obtain energy from light Chemotrophs obtain energy from chemicals Autotrophs require CO2 as a carbon source Heterotrophs require an organic nutrient to make organic compounds 56
57 Energy and carbon sources are combined to give four major modes of nutritionPhotoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy 57
58 Table 24.1 Table 24.1 Major nutritional modes 58
59 The Role of Oxygen in MetabolismProkaryotic metabolism varies with respect to O2 Obligate aerobes require O2 for cellular respiration Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration, in which substances other than O2 act as electron acceptors Facultative anaerobes can survive with or without O2 59
60 Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids Prokaryotes can metabolize nitrogen in a variety of ways In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) 60
61 Metabolic CooperationCooperation between prokaryotes allows them to use environmental resources they could not use as individual cells In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products 61
62 Photosynthetic cells Heterocyst 20 m Figure 24.13Figure Metabolic cooperation in a prokaryote 20 m 62
63 In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms 63
64 Reproduction Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours Key features of prokaryotic biology allow them to divide quickly They are small They reproduce by binary fission They have short generation times 64
65 Adaptations of Prokaryotes: A SummaryThe ongoing success of prokaryotes is an extraordinary example of physiological and metabolic diversification Prokaryotic diversification can be viewed as a first great wave of adaptive radiation in the evolutionary history of life 65
66 Concept 24.3: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes Prokaryotes have considerable genetic variation Three factors contribute to this genetic diversity Rapid reproduction Mutation Genetic recombination 66
67 Rapid Reproduction and MutationProkaryotes reproduce by binary fission, and offspring cells are generally identical Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population High diversity from mutations allows for rapid evolution Prokaryotes are not “primitive” but are highly evolved 67
68 Population growth rate (relative to ancestralFigure 24.14 Experiment Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium) Results 1.8 1.6 Population growth rate (relative to ancestral population) Figure Inquiry: Can prokaryotes evolve rapidly in response to environmental change? 1.4 1.2 1.0 5,000 10,000 15,000 20,000 Generation 68
69 Population growth rate (relative to ancestralFigure 24.14a Results 1.8 1.6 Population growth rate (relative to ancestral population) 1.4 1.2 Figure 24.14a Inquiry: Can prokaryotes evolve rapidly in response to environmental change? (results) 1.0 5,000 10,000 15,000 20,000 Generation 69
70 Genetic RecombinationGenetic recombination, the combining of DNA from two sources, contributes to diversity Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation Movement of genes among individuals from different species is called horizontal gene transfer 70
71 Transformation and TransductionA prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria) 71
72 Phage infects bacterial donor cell with A and B alleles.Figure Phage DNA 1 Phage infects bacterial donor cell with A and B alleles. A B Donor cell Figure Transduction (step 1) 72
73 Phage infects bacterial donor cell with A and B alleles.Figure Phage DNA 1 Phage infects bacterial donor cell with A and B alleles. A B Donor cell 2 Phage DNA is replicated and proteins synthesized. A B Figure Transduction (step 2) 73
74 Phage infects bacterial donor cell with A and B alleles.Figure Phage DNA 1 Phage infects bacterial donor cell with A and B alleles. A B Donor cell 2 Phage DNA is replicated and proteins synthesized. A B 3 Fragment of DNA with A allele is packaged within a phage capsid. A Figure Transduction (step 3) 74
75 Phage infects bacterial donor cell with A and B alleles.Figure Phage DNA 1 Phage infects bacterial donor cell with A and B alleles. A B Donor cell 2 Phage DNA is replicated and proteins synthesized. A B 3 Fragment of DNA with A allele is packaged within a phage capsid. A Crossing over Figure Transduction (step 4) 4 Phage with A allele infects bacterial recipient cell. A A− B− Recipient cell 75
76 Phage infects bacterial donor cell with A and B alleles.Figure Phage DNA 1 Phage infects bacterial donor cell with A and B alleles. A B Donor cell 2 Phage DNA is replicated and proteins synthesized. A B 3 Fragment of DNA with A allele is packaged within a phage capsid. A Crossing over Figure Transduction (step 5) 4 Phage with A allele infects bacterial recipient cell. A A− B− Recipient cell Recombinant cell 5 Incorporation of phage DNA creates recombinant cell with genotype AB. A B− 76
77 Conjugation and PlasmidsConjugation is the process where genetic material is transferred between prokaryotic cells In bacteria, the DNA transfer is one way In E. coli, the donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA 77
78 Figure 24.16 1 m Sex pilus Figure Bacterial conjugation 78
79 The F factor is a piece of DNA required for the production of pili Cells containing the F plasmid (F+) function as DNA donors during conjugation Cells without the F factor (F–) function as DNA recipients during conjugation The F factor is transferable during conjugation 79
80 F cell (donor) F− cell (recipient)Figure Bacterial chromosome F plasmid F cell (donor) Mating bridge F− cell (recipient) Bacterial chromosome 1 One strand of F cell plasmid DNA breaks at arrowhead. Figure Conjugation and transfer of an F plasmid, resulting in recombination (step 1) 80
81 F cell (donor) F− cell (recipient)Figure Bacterial chromosome F plasmid F cell (donor) Mating bridge F− cell (recipient) Bacterial chromosome 1 One strand of F cell plasmid DNA breaks at arrowhead. Figure Conjugation and transfer of an F plasmid, resulting in recombination (step 2) 2 Broken strand peels off and enters F− cell. 81
82 F cell (donor) F− cell (recipient)Figure Bacterial chromosome F plasmid F cell (donor) Mating bridge F− cell (recipient) Bacterial chromosome 1 One strand of F cell plasmid DNA breaks at arrowhead. Figure Conjugation and transfer of an F plasmid, resulting in recombination (step 3) 2 Broken strand peels off and enters F− cell. 3 Donor and recipient cells synthesize complementary DNA strands. 82
83 F cell (donor) F cell F cell F− cell (recipient)Figure Bacterial chromosome F plasmid F cell (donor) F cell Mating bridge F cell F− cell (recipient) Bacterial chromosome 1 One strand of F cell plasmid DNA breaks at arrowhead. Figure Conjugation and transfer of an F plasmid, resulting in recombination (step 4) 2 Broken strand peels off and enters F− cell. 3 Donor and recipient cells synthesize complementary DNA strands. 4 Recipient cell is now a recombinant F cell. 83
84 The F factor can also be integrated into the chromosome A cell with the F factor built into its chromosomes functions as a donor during conjugation The recipient becomes a recombinant bacterium, with DNA from two different cells 84
85 R Plasmids and Antibiotic Resistance Genes for antibiotic resistance are carried in R plasmids Antibiotics kill sensitive bacteria, but not bacteria with specific R plasmids Through natural selection, the fraction of bacteria with genes for resistance increases in a population exposed to antibiotics Antibiotic-resistant strains of bacteria are becoming more common 85
86 Concept 24.4: Prokaryotes have radiated into a diverse set of lineagesProkaryotes have radiated extensively due to diverse structural and metabolic adaptations Prokaryotes inhabit every environment known to support life 86
87 An Overview of Prokaryotic DiversityApplying molecular systematics to the investigation of prokaryotic phylogeny has produced dramatic results Molecular systematics led to the splitting of prokaryotes into bacteria and archaea Molecular systematists continue to work on the phylogeny of prokaryotes 87
88 Domain Eukarya Eukaryotes Korarchaeotes Euryarchaeotes Domain ArchaeaFigure 24.18 Domain Eukarya Eukaryotes Korarchaeotes Euryarchaeotes Domain Archaea Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Proteobacteria Chlamydias Figure A simplified phylogeny of prokaryotes Spirochetes Domain Bacteria Cyanobacteria Gram-positive bacteria 88
89 A handful of soil may contain 10,000 prokaryotic species The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes A handful of soil may contain 10,000 prokaryotic species Horizontal gene transfer between prokaryotes obscures the root of the tree of life 89
90 Bacteria Bacteria include the vast majority of prokaryotes familiar to most people Diverse nutritional types are scattered among the major groups of bacteria Video: Tubeworms 90
91 Eukarya Archaea Bacteria Figure 24.UN01Figure 24.UN01 In-text figure, bacteria mini-tree, p. 471 91
92 Alpha subgroup Beta subgroup Gamma subgroup Delta subgroupFigure 24.19a Alpha subgroup Beta subgroup Alpha Beta Gamma Proteo- bacteria Delta Epsilon 1 m 2.5 m Rhizobium (arrows) (TEM) Nitrosomonas (TEM) Gamma subgroup Delta subgroup Epsilon subgroup Figure 24.19a Exploring major groups of bacteria (part 1) 200 m 300 m 2 m Thiomargarita namibiensis (LM) Chondromyces crocatus (SEM) Helicobacter pylori (TEM) 92
93 Some are anaerobic and others aerobicProteobacteria are gram-negative bacteria including photoautotrophs, chemoautotrophs, and heterotrophs Some are anaerobic and others aerobic 93
94 Alpha Beta Gamma Proteobacteria Delta Epsilon Figure 24.19aaFigure 24.19aa Exploring major groups of bacteria (part 1a: proteobacteria tree) 94
95 Members of the subgroup alpha proteobacteria are closely associated with eukaryotic hosts in many cases Scientists hypothesize that mitochondria evolved from aerobic alpha proteobacteria through endosymbiosis Example: Rhizobium, which forms root nodules in legumes and fixes atmospheric N2 Example: Agrobacterium, which produces tumors in plants and is used in genetic engineering 95
96 Alpha subgroup Rhizobium (arrows) inside a root cell of a legume (TEM)Figure 24.19ab Alpha subgroup Rhizobium (arrows) inside a root cell of a legume (TEM) 2.5 m Figure 24.19ab Exploring major groups of bacteria (part 1b: alpha subgroup) 96
97 Members of the subgroup beta proteobacteria are nutritionally diverse Example: the soil bacterium Nitrosomonas, which converts NH4+ to NO2– 97
98 Beta subgroup Nitrosomonas (colorized TEM) 1 m Figure 24.19acFigure 24.19ac Exploring major groups of bacteria (part 1c: beta subgroup) 98
99 The subgroup gamma proteobacteria includes sulfur bacteria such as Thiomargarita namibiensis and pathogens such as Legionella, Salmonella, and Vibrio cholerae Escherichia coli resides in the intestines of many mammals and is not normally pathogenic 99
100 Gamma subgroup Thiomargarita namibiensis containing sulfur wastes (LM)Figure 24.19ad Gamma subgroup Thiomargarita namibiensis containing sulfur wastes (LM) 200 m Figure 24.19ad Exploring major groups of bacteria (part 1d: gamma subgroup) 100
101 The subgroup delta proteobacteria includes the slime-secreting myxobacteria and bdellovibrios, a bacteria that attacks other bacteria 101
102 Delta subgroup Fruiting bodies of Chondromyces crocatus,Figure 24.19ae Delta subgroup Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) 300 m Figure 24.19ae Exploring major groups of bacteria (part 1e: delta subgroup) 102
103 The subgroup epsilon proteobacteria contains many pathogens including Campylobacter, which causes blood poisoning, and Helicobacter pylori, which causes stomach ulcers 103
104 Epsilon subgroup Helicobacter pylori (colorized TEM) 2 mFigure 24.19af Epsilon subgroup Helicobacter pylori (colorized TEM) 2 m Figure 24.19af Exploring major groups of bacteria (part 1f: epsilon subgroup) 104
105 Gram-positive bacteriaFigure 24.19b Chlamydias Spirochetes Cyanobacteria 2.5 m 5 m 40 m Chlamydia (arrows) (TEM) Leptospira (TEM) Oscillatoria Gram-positive bacteria Figure 24.19b Exploring major groups of bacteria (part 2) 5 m 2 m Streptomyces (SEM) Mycoplasmas (SEM) 105
106 Chlamydias are parasites that live within animal cells Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission 106
107 Chlamydias Chlamydia (arrows) inside an animal cell (colorized TEM)Figure 24.19ba Chlamydias Chlamydia (arrows) inside an animal cell (colorized TEM) Figure 24.19ba Exploring major groups of bacteria (part 2a: chlamydias) 2.5 m 107
108 Spirochetes are helical heterotrophs Some are parasites, including Treponema pallidum, which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease 108
109 Spirochetes Leptospira, a spirochete (colorized TEM) 5 mFigure 24.19bb Spirochetes Leptospira, a spirochete (colorized TEM) Figure 24.19bb Exploring major groups of bacteria (part 2b: spirochetes) 5 m 109
110 Cyanobacteria are photoautotrophs that generate O2 Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis 110
111 Cyanobacteria Oscillatoria, a filamentous cyanobacterium 40 mFigure 24.19bc Cyanobacteria Oscillatoria, a filamentous cyanobacterium 40 m Figure 24.19bc Exploring major groups of bacteria (part 2c: cyanobacteria) 111
112 Gram-positive bacteria includeActinomycetes, which decompose soil Streptomyces, which are a source of antibiotics Bacillus anthracis, the cause of anthrax Clostridium botulinum, the cause of botulism Some Staphylococcus and Streptococcus, which can be pathogenic Mycoplasms, the smallest known cells 112
113 Gram-positive bacteriaFigure 24.19bd Gram-positive bacteria Streptomyces, the source of many antibiotics (SEM) 5 m Figure 24.19bd Exploring major groups of bacteria (part 2d: Gram-positive, Streptomyces) 113
114 Gram-positive bacteriaFigure 24.19be Gram-positive bacteria Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) 2 m Figure 24.19be Exploring major groups of bacteria (part 2e: Gram-positive, mycoplasmas) 114
115 Archaea Archaea share certain traits with bacteria and other traits with eukaryotes 115
116 Eukarya Archaea Bacteria Figure 24.UN02Figure 24.UN02 In-text figure, Archaea mini-tree, p. 471 116
117 Table 24.2 Table 24.2 A comparison of the three domains of life 117
118 Table 24.2a Table 24.2a A comparison of the three domains of life (part 1) 118
119 Table 24.2b Table 24.2b A comparison of the three domains of life (part 2) 119
120 Some archaea live in extreme environments and are called extremophiles Extreme halophiles live in highly saline environments Extreme thermophiles thrive in very hot environments Video: Cyanobacteria (Oscillatoria) 120
121 Figure 24.20 Figure Extreme thermophiles 121
122 Methanogens produce methane as a waste product Methanogens are strict anaerobes and are poisoned by O2 Methanogens live in swamps and marshes, in the guts of cattle, and near deep-sea hydrothermal vents 122
123 Figure 24.21 2 m Figure A highly thermophilic methanogen 123
124 Figure 24.21a Figure 24.21a A highly thermophilic methanogen (part 1: photo) 124
125 Figure 24.21b 2 m Figure 24.21b A highly thermophilic methanogen (part 2: micrograph) 125
126 Recent metagenomic studies have revealed many new groups of archaea Some of these may offer clues to the early evolution of life on Earth 126
127 Concept 24.5: Prokaryotes play crucial roles in the biosphereProkaryotes are so important that if they were to disappear, the prospects for any other life surviving would be dim 127
128 Chemical Recycling Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems Chemoheterotrophic prokaryotes function as decomposers, breaking down dead organisms and waste products 128
129 Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth Prokaryotes can also “immobilize” or decrease the availability of nutrients 129
130 Uptake of K by plants (mg)Figure 24.22 1.0 0.8 0.6 Uptake of K by plants (mg) 0.4 0.2 Seedlings growing in the lab Figure Impact of bacteria on soil nutrient availability No bacteria Strain 1 Strain 2 Strain 3 Soil treatment 130
131 Seedlings growing in the labFigure 24.22a Figure 24.22a Impact of bacteria on soil nutrient availability (photo) Seedlings growing in the lab 131
132 Ecological InteractionsSymbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont Prokaryotes often form symbiotic relationships with larger organisms 132
133 In mutualism, both symbiotic organisms benefit In commensalism, one organism benefits while neither harming nor helping the other in any significant way In parasitism, an organism called a parasite harms but does not kill its host Parasites that cause disease are called pathogens 133
134 Figure 24.23 Figure Mutualism: bacterial “headlights” 134
135 The ecological communities of hydrothermal vents depend on chemoautotrophic bacteria for energy135
136 Impact on Humans The best-known prokaryotes are pathogens, but many others have positive interactions with humans 136
137 Mutualistic Bacteria Human intestines are home to about 500–1,000 species of bacteria Many of these are mutualists and break down food that is undigested by our intestines 137
138 Pathogenic Bacteria Prokaryotes cause about half of all human diseasesFor example, Lyme disease is caused by a bacterium and carried by ticks 138
139 Figure 24.24 5 m Figure Lyme disease 139
140 Figure 24.24a Figure 24.24a Lyme disease (part 1: tick) 140
141 Figure 24.24b Figure 24.24b Lyme disease (part 2: rash) 141
142 Figure 24.24c Figure 24.24c Lyme disease (part 3: SEM) 5 m 142
143 Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxinsExotoxins are secreted and cause disease even if the prokaryotes that produce them are not present Endotoxins are released only when bacteria die and their cell walls break down 143
144 Horizontal gene transfer can spread genes associated with virulence For example, pathogenic strains of the normally harmless E. coli bacteria have emerged through horizontal gene transfer 144
145 Prokaryotes in Research and TechnologyExperiments using prokaryotes have led to important advances in DNA technology For example, E. coli is used in gene cloning For example, Agrobacterium tumefaciens is used to produce transgenic plants 145
146 Bacteria can now be used to make natural plastics Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment Bacteria can be engineered to produce vitamins, antibiotics, and hormones Bacteria are also being engineered to produce ethanol from waste biomass 146
147 Figure 24.25 (b) (a) Figure Products from prokaryotes 147
148 Figure 24.25a (a) Figure 24.25a Products from prokaryotes (part 1: PHA) 148
149 Figure 24.25b (b) Figure 24.25b Products from prokaryotes (part 2: E-85) 149
150 Figure 24.26 Figure Bioremediation of an oil spill 150
151 Figure 24.UN03 Figure 24.UN03 Skills exercise: making a bar graph and interpreting data 151
152 Fimbriae Cell wall Circular chromosome Capsule Sex pilus InternalFigure 24.UN04 Fimbriae Cell wall Circular chromosome Capsule Sex pilus Internal organization Figure 24.UN04 Summary of key concepts: prokaryote adaptations Flagella 152
153 Figure 24.UN05 Figure 24.UN05 Test your understanding, question 8 (mutualism) 153