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CAMPBELL BIOLOGY IN FOCUS URRY • CAIN • WASSERMAN • MINORSKY • REECE 24 Early Life and the Diversification of Prokaryotes Mr. Karns SECOND EDITION The First Cells Earth 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; others were free-floating individual cells © 2016 Pearson Figure 24.1 © 2016 Pearson Education, Inc. Prokaryotes are the most abundant organisms on Earth They thrive in most environments, including places too acidic, salty, cold, or hot for most other organisms Some prokaryotes colonize the bodies of other organisms © 2016 Pearson Education, Inc. Figure 24.2 © 2016 Pearson Education, Inc. Concept 24.1: Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into macromolecules 3. Packaging of molecules into protocells, membranebound droplets that maintain a consistent internal chemistry 4. Origin of self-replicating molecules © 2016 Pearson Synthesis of Organic Compounds on Early Earth Earth’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 © 2016 Pearson In 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 © 2016 Pearson Education, Inc. Some evidence suggests that the early atmosphere was neither reducing nor oxidizing The first organic compounds may have been synthesized in areas with reducing conditions such as volcanoes or deep-sea vents Amino acids can form spontaneously in conditions simulating volcanic eruptions © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. 20 10 0 1953 2008 Mass of amino acids (mg) Number of amino acids Figure 24.3 200 100 0 1953 2008 Figure 24.3-1 © 2016 Pearson Education, Inc. The first organic molecules may have been brought to Earth in meteorites For example, the Murchison meteorite contained several key organic molecules © 2016 Pearson Education, Inc. Abiotic Synthesis of Macromolecules RNA monomers have been produced spontaneously from simple molecules Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock Amino acid polymers may have functioned as weak catalysts for chemical reactions on early Earth © 2016 Pearson Protocells Replication and metabolism are key properties of life and may have appeared together in early protocells 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 © 2016 Pearson Adding clay can increase the rate of vesicle formation Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment © 2016 Pearson Education, Inc. Relative turbidity, an Index of vesicle number Figure 24.4 0.4 Precursor molecules plus montmorillonite clay Precursor molecules only 0.2 0 0 20 40 Time (minutes) 60 (a) Self-assembly Vesicle boundary 1 mm 20 mm (b) Reproduction © 2016 Pearson Education, Inc. (c) Absorption of RNA Relative turbidity, an Index of vesicle number Figure 24.4-1 0.4 Precursor molecules plus montmorillonite clay Precursor molecules only 0.2 0 0 (a) Self-assembly © 2016 Pearson Education, Inc. 20 40 Time (minutes) 60 Figure 24.4-2 20 mm (b) Reproduction © 2016 Pearson Education, Inc. Figure 24.4-3 Vesicle boundary 1 mm (c) Absorption of RNA © 2016 Pearson Education, Inc. 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 © 2016 Pearson 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” © 2016 Pearson Education, Inc. Vesicles with self-replicating, catalytic RNA would have been able to produce daughter protocells with properties similar to those of their parent RNA may have provided the template for DNA, a more stable genetic material © 2016 Pearson Education, Inc. Fossil Evidence of Early Life Many 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 © 2016 Pearson 5 cm 30 mm Figure 24.5 10 mm Stromatolites Nonphotosynthetic bacteria Possible earliest appearance in fossil record 4 © 2016 Pearson Education, Inc. Cyanobacteria 3 1 2 Time (billions of years ago) 0 Figure 24.5-1 Stromatolites Nonphotosynthetic bacteria Possible earliest appearance in fossil record 4 © 2016 Pearson Education, Inc. Cyanobacteria 3 2 1 Time (billions of years ago) 0 30 mm Figure 24.5-2 3-billion-year-old fossil of a cluster of nonphotosynthetic prokaryotes © 2016 Pearson Education, Inc. 5 cm Figure 24.5-3 1.1-billion-year-old fossilized stromatolite © 2016 Pearson Education, Inc. Figure 24.5-4 10 mm 1.5-billion-year-old fossil of a cyanobacterium © 2016 Pearson Education, Inc. 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 © 2016 Pearson Education, Inc. Concept 24.2: Diverse structural and metabolic adaptations have evolved in prokaryotes Most 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 © 2016 Pearson (a) Spherical © 2016 Pearson Education, Inc. (b) Rod-shaped 3 mm 1 mm 1 mm Figure 24.6 (c) Spiral 1 mm Figure 24.6-1 (a) Spherical © 2016 Pearson Education, Inc. 1 mm Figure 24.6-2 (b) Rod-shaped © 2016 Pearson Education, Inc. 3 mm Figure 24.6-3 (c) Spiral © 2016 Pearson Education, Inc. Cell-Surface Structures Prokaryotes have cell walls, which maintain cell shape, protect the cell, and prevent 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 Archaeal cell walls contain polysaccharides and proteins but lack peptidoglycan © 2016 Pearson Scientists 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 © 2016 Pearson Education, Inc. Figure 24.7 (a) Gram-positive bacteria (b) Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Cell wall Peptidoglycan layer Plasma membrane Outer membrane Cell wall Peptidoglycan layer Plasma membrane Gram-positive bacteria Gram-negative bacteria 10 mm © 2016 Pearson Education, Inc. Figure 24.7-1 (a) Gram-positive bacteria Cell wall Peptidoglycan layer Plasma membrane © 2016 Pearson Education, Inc. Figure 24.7-2 (b) Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Peptidoglycan layer Plasma membrane © 2016 Pearson Education, Inc. Figure 24.7-3 Gram-positive bacteria Gram-negative bacteria 10 mm © 2016 Pearson Education, Inc. 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 and allows them to adhere to the substrate or each other © 2016 Pearson Education, Inc. Figure 24.8 Bacterial cell wall Bacterial capsule Tonsil cell 200 nm © 2016 Pearson Education, Inc. Some bacteria develop resistant cells called endospores when they lack water or essential nutrients Some prokaryotes stick to the substrate or each other using hairlike appendages called fimbriae Pili (or sex pili) are longer than fimbriae and allow prokaryotes to exchange DNA © 2016 Pearson Education, Inc. Figure 24.9 Fimbriae 1 mm © 2016 Pearson Education, Inc. Motility In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from a stimulus For example, some prokaryotes exhibit chemotaxis, movement toward or away from a chemical stimulus © 2016 Pearson Many prokaryotes have flagella to facilitate movement Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently © 2016 Pearson Education, Inc. Figure 24.10 Flagellum Filament Hook Motor Cell wall Plasma membrane © 2016 Pearson Education, Inc. Rod Peptidoglycan layer 20 nm Figure 24.10-1 20 nm Hook Motor © 2016 Pearson Education, Inc. Evolutionary Origins of Bacterial Flagella Bacterial 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 © 2016 Pearson Internal Organization and DNA The cells of prokaryotes are structurally simpler than those of eukaryotes Prokaryotic cells lack complex compartmentalization Some prokaryotes do have specialized membranes that perform metabolic functions These are usually infoldings of the plasma membrane © 2016 Pearson Figure 24.11 1 mm 0.2 mm Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote © 2016 Pearson Education, Inc. (b) Photosynthetic prokaryote Figure 24.11-1 0.2 mm Respiratory membrane (a) Aerobic prokaryote © 2016 Pearson Education, Inc. Figure 24.11-2 1 mm Thylakoid membranes (b) Photosynthetic prokaryote © 2016 Pearson Education, Inc. The prokaryotic genome has less DNA than the eukaryotic genome Most of the genome consists of a single circular chromosome The genetic material is not enclosed inside a membrane; it is located in the nucleoid region Some species of bacteria also have smaller rings of DNA called plasmids © 2016 Pearson Education, Inc. Figure 24.12 Chromosome Plasmids 1 mm © 2016 Pearson Education, Inc. 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 © 2016 Pearson Education, Inc. Nutritional and Metabolic Adaptations Prokaryotes 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 obtain carbon from organic nutrients © 2016 Pearson Energy and carbon sources are combined to give four major modes of nutrition Photoautotrophy Chemoautotrophy Photoheterotrophy Chemoheterotrophy © 2016 Pearson Education, Inc. Table 24.1 © 2016 Pearson Education, Inc. The Role of Oxygen in Metabolism Prokaryotic 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 use O2 if it is available, but can survive without it © 2016 Pearson Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids in all organisms Prokaryotes can metabolize nitrogen in a variety of ways In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) © 2016 Pearson Metabolic Cooperation Some prokaryotic cells cooperate to make use of otherwise unavailable resources In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocysts (or heterocytes) exchange metabolic products Cooperation is necessary because the oxygen produced by photosynthesis disrupts nitrogen fixation © 2016 Pearson Figure 24.13 Photosynthetic cells Heterocyst 20 mm © 2016 Pearson Education, Inc. Metabolic cooperation between different prokaryotic species occurs in surface-coating colonies called biofilms © 2016 Pearson Education, Inc. Reproduction Many prokaryotes reproduce rapidly by binary fission, a process by which one cell divides into two Key features of prokaryotic biology allow them to divide quickly They are small They reproduce by binary fission They have short generation times © 2016 Pearson Adaptations of Prokaryotes: A Summary The ongoing success of prokaryotes is primarily the result of physiological and metabolic diversification Metabolic diversification of prokaryotes was the first great wave of adaptive radiation in the history of life © 2016 Pearson 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 © 2016 Pearson Rapid Reproduction and Mutation Prokaryotes 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 genetic diversity allows for rapid evolution Prokaryotes are not “primitive” but are highly evolved © 2016 Pearson Figure 24.14 Experiment Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium) Population growth rate (relative to ancestral population) Results 1.8 1.6 1.4 1.2 1.0 0 5,000 10,000 15,000 Generation 20,000 Data from V. S. Cooper and R. E. Lenski, The population genetics of ecological specialization in evolving Escherichia coli populations, Nature 407:736–739 (2000). © 2016 Pearson Education, Inc. Figure 24.14-1 Experiment Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) © 2016 Pearson Education, Inc. New tube (9.9 mL growth medium) Figure 24.14-2 Population growth rate (relative to ancestral population) Results 1.8 1.6 1.4 1.2 1.0 0 5,000 15,000 10,000 Generation 20,000 Data from V. S. Cooper and R. E. Lenski, The population genetics of ecological specialization in evolving Escherichia coli populations, Nature 407:736–739 (2000). © 2016 Pearson Education, Inc. Genetic Recombination Genetic 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 © 2016 Pearson Transformation and Transduction Some prokaryotic cells can take up and incorporate foreign DNA from the surrounding environment in a process called transformation Transduction is the movement of genes between prokaryotic cells by phages (viruses that infect bacteria) © 2016 Pearson Figure 24.15-s1 Phage DNA Phage infects bacterial donor cell with A+ and B+ alleles. A+ B+ Donor cell © 2016 Pearson Education, Inc. Figure 24.15-s2 Phage DNA Phage infects bacterial donor cell with A+ and B+ alleles. A+ B+ Donor cell Phage DNA is replicated and proteins synthesized. © 2016 Pearson Education, Inc. A+ B+ Figure 24.15-s3 Phage DNA Phage infects bacterial donor cell with A+ and B+ alleles. A+ B+ Donor cell Phage DNA is replicated and proteins synthesized. Fragment of DNA with A+ allele is packaged within a phage capsid. © 2016 Pearson Education, Inc. A+ B+ A+ Figure 24.15-s4 Phage DNA Phage infects bacterial donor cell with A+ and B+ alleles. A+ B+ Donor cell Phage DNA is replicated and proteins synthesized. A+ B+ Fragment of DNA with A+ allele is packaged within a phage capsid. A+ Phage with allele infects bacterial recipient cell. A+ Crossing over A+ A- B- Recipient cell © 2016 Pearson Education, Inc. Figure 24.15-s5 Phage DNA Phage infects bacterial donor cell with A+ and B+ alleles. A+ B+ Donor cell Phage DNA is replicated and proteins synthesized. A+ B+ Fragment of DNA with A+ allele is packaged within a phage capsid. A+ A+ Crossing over Phage with allele infects bacterial recipient cell. Incorporation of phage DNA creates recombinant with genotype A+B-. © 2016 Pearson Education, Inc. A+ A- B- Recipient cell Recombinant cell A+ B– Conjugation and Plasmids Conjugation is a process by which genetic material is transferred directly between prokaryotic cells In bacteria, the DNA transfer is one way For example, in E. coli, the donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA © 2016 Pearson Figure 24.16 1 mm Pilus © 2016 Pearson Education, Inc. The F factor is a piece of DNA required for the production of pili It may be present in a plasmid or the chromosome 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 transferred during conjugation © 2016 Pearson Education, Inc. Figure 24.17-s1 F plasmid Bacterial chromosome F+ cell (donor) Mating bridge F– cell (recipient) Bacterial chromosome One strand of F+ cell plasmid DNA breaks at arrowhead. © 2016 Pearson Education, Inc. Figure 24.17-s2 F plasmid Bacterial chromosome F+ cell (donor) Mating bridge F– cell (recipient) Bacterial chromosome One strand of F+ cell plasmid DNA breaks at arrowhead. © 2016 Pearson Education, Inc. Broken strand peels off and enters F– cell. Figure 24.17-s3 F plasmid Bacterial chromosome F+ cell (donor) Mating bridge F– cell (recipient) Bacterial chromosome One strand of F+ cell plasmid DNA breaks at arrowhead. © 2016 Pearson Education, Inc. Broken strand peels off and enters F– cell. Donor and recipient cells synthesize complementary DNA strands. Figure 24.17-s4 F plasmid Bacterial chromosome F+ cell (donor) F+ cell Mating bridge F– cell (recipient) F+ cell Bacterial chromosome One strand of F+ cell plasmid DNA breaks at arrowhead. © 2016 Pearson Education, Inc. Broken strand peels off and enters F– cell. Donor and recipient cells synthesize complementary DNA strands. Recipient cell is now a recombinant F+ cell. 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 © 2016 Pearson Education, Inc. R Plasmids and Antibiotic Resistance Genes for antibiotic resistance are often 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 © 2016 Pearson Education, Inc. Concept 24.4: Prokaryotes have radiated into a diverse set of lineages Prokaryotes have radiated extensively due to diverse structural and metabolic adaptations Prokaryotes inhabit every environment known to support life © 2016 Pearson An Overview of Prokaryotic Diversity The application of molecular systematics has led to dramatic revisions of the prokaryote phylogeny For example, the use of molecular systematics led to the splitting of prokaryotes into Bacteria and Archaea © 2016 Pearson Figure 24.18 Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Domain Archaea Korarchaeotes Domain Eukarya Eukaryotes Proteobacteria Spirochetes Cyanobacteria Gram-positive bacteria © 2016 Pearson Education, Inc. Domain Bacteria Chlamydias The use of rapid sequencing techniques, such as polymerase chain reaction (PCR), adds new branches to the tree of life each year Only a tiny fraction of prokaryote diversity has been identified and described thus far © 2016 Pearson Education, Inc. Horizontal gene transfer has played a key role in the evolution of prokaryotes Such gene transfers obscure the phylogenetic relationships among prokaryote lineages © 2016 Pearson Education, Inc. Bacteria Bacteria include the vast majority of prokaryotes familiar to most people Every major mode of nutrition and metabolism is represented among bacteria A wide diversity of nutritional modes can be found even within small taxonomic groups © 2016 Pearson Video: Tubeworms © 2016 Pearson Education, Inc. Figure 24.UN01 Eukarya Archaea Bacteria © 2016 Pearson Education, Inc. Proteobacteria is a clade of gram-negative bacteria with diverse metabolic and nutritional modes It has been divided into five subgroups (alpha, beta, gamma, delta, and epsilon proteobacteria) based on molecular relationships © 2016 Pearson Education, Inc. Figure 24.19-1 Alpha subgroup Thiomargarita namibiensis (LM) © 2016 Pearson Education, Inc. Delta subgroup 200 mm Gamma subgroup Chondromyces crocatus (SEM) 1 mm Nitrosomonas (TEM) Epsilon subgroup 2 mm Rhizobium (arrows) (TEM) 2.5 mm Proteobacteria 300 mm Alpha Beta Gamma Delta Epsilon Beta subgroup Helicobacter pylori (TEM) Figure 24.19-1a Alpha Beta Gamma Delta Epsilon © 2016 Pearson Education, Inc. Proteobacteria Many species in the subgroup alpha proteobacteria are closely associated with eukaryotic hosts For example, Rhizobium forms root nodules in legumes and fixes atmospheric N2 Scientists use Agrobacterium to transfer foreign DNA into crop plants Aerobic alpha proteobacteria may have given rise to mitochondria through endosymbiosis © 2016 Pearson Education, Inc. Figure 24.19-1b Alpha subgroup 2.5 mm Rhizobium (arrows) inside a root cell of a legume (TEM) © 2016 Pearson Education, Inc. Members of the subgroup beta proteobacteria have diverse nutritional modes For example, Nitrosomonas participates in soil nitrification by oxidizing ammonium (NH4+) and producing nitrite (NO2–) © 2016 Pearson Education, Inc. Figure 24.19-1c Beta subgroup 1 mm Nitrosomonas (colorized TEM) © 2016 Pearson Education, Inc. The subgroup gamma proteobacteria includes autotrophs and heterotrophs For example, Thiomargarita namibiensis is an autotroph that obtains energy from H2S Some heterotrophic members of this group are pathogenic For example, Salmonella causes food poisoning, and Vibrio cholerae causes cholera Escherichia coli is a common heterotrophic gamma proteobacteria that is not normally pathogenic © 2016 Pearson Education, Inc. Figure 24.19-1d Gamma subgroup 200 mm Thiomargarita namibiensis containing sulfur wastes (LM) © 2016 Pearson Education, Inc. The subgroup delta proteobacteria includes the slime-secreting myxobacteria and bdellovibrios, a bacteria that attacks other bacteria © 2016 Pearson Education, Inc. Figure 24.19-1e Delta subgroup 300 mm Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) © 2016 Pearson Education, Inc. Most species in the subgroup epsilon proteobacteria are pathogenic For example, Helicobacter pylori causes stomach ulcers © 2016 Pearson Education, Inc. Figure 24.19-1f Epsilon subgroup 2 mm Helicobacter pylori (colorized TEM) © 2016 Pearson Education, Inc. Chlamydias are disease-causing parasites that can only live within animal host cells For example, Chlamydia trachomatis causes blindness and the sexually transmitted disease, nongonococcal urethritis © 2016 Pearson Education, Inc. Figure 24.19-2a Chlamydias 2.5 mm Chlamydia (arrows) inside an animal cell (colorized TEM) © 2016 Pearson Education, Inc. Spirochetes are helical gram-negative heterotrophs Many species are free-living, but some are parasitic For example, Treponema pallidum causes syphilis, and Borrelia burgdorferi causes Lyme disease © 2016 Pearson Education, Inc. Figure 24.19-2b Spirochetes 5 mm Leptospira, a spirochete (colorized TEM) © 2016 Pearson Education, Inc. Cyanobacteria are gram-negative photoautotrophs that generate O2 through plantlike photosynthesis Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis Cyanobacteria are common members of the phytoplankton in marine and freshwater communities © 2016 Pearson Education, Inc. Figure 24.19-2c Cyanobacteria 40 mm Oscillatoria, a filamentous cyanobacterium © 2016 Pearson Education, Inc. Gram-positive bacteria include Actinomycetes, many of which are soil decomposers Streptomyces, which are a source of antibiotics Bacillus anthracis, the cause of anthrax Clostridium botulinum, the cause of botulism Staphylococcus and Streptococcus, which can be pathogenic Mycoplasmas, which are the smallest known cells and the only bacteria lacking a cell wall © 2016 Pearson Education, Inc. Figure 24.19-2d Gram-positive bacteria 5 mm Streptomyces, the source of many antibiotics (SEM) © 2016 Pearson Education, Inc. Figure 24.19-2e Gram-positive bacteria 2 mm Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) © 2016 Pearson Education, Inc. Figure 24.19-2 Chlamydia (arrows) (TEM) Cyanobacteria 5 mm Leptospira (TEM) Oscillatoria © 2016 Pearson Education, Inc. 2 mm 5 mm Gram-positive bacteria Streptomyces (SEM) 40 mm Spirochetes 2.5 mm Chlamydias Mycoplasmas (SEM) Archaea Archaea share some traits in common with bacteria and others with eukaryotes © 2016 Pearson Figure 24.UN02 Eukarya Archaea Bacteria © 2016 Pearson Education, Inc. Table 24.2-1 © 2016 Pearson Education, Inc. Table 24.2-2 © 2016 Pearson Education, Inc. Some archaea live in extreme environments and are called extremophiles Extreme halophiles either tolerate or require a highly saline environment For example, members of the genus Halobacterium cannot survive if salinity drops below 9% © 2016 Pearson Education, Inc. Video: Cyanobacteria (Oscillatoria) © 2016 Pearson Education, Inc. Extreme thermophiles thrive in very hot environments For example, members of the genus Sulfolobus live in hot springs with temperatures up to 90°C Many archaea live in more moderate environments © 2016 Pearson Education, Inc. Figure 24.20 © 2016 Pearson Education, Inc. Methanogens are strict anaerobes that produce methane as a waste product Methanogens live in swamps and marshes, in the guts of cattle, and near deep-sea hydrothermal vents © 2016 Pearson Education, Inc. Figure 24.21 2 mm © 2016 Pearson Education, Inc. Figure 24.21-1 © 2016 Pearson Education, Inc. Figure 24.21-2 2 mm © 2016 Pearson Education, Inc. Recent metagenomic studies have revealed many new groups of archaea Some of these may offer clues to the early evolution of life on Earth © 2016 Pearson Education, Inc. Concept 24.5: Prokaryotes play crucial roles in the biosphere The role of prokaryotes in the biosphere is essential to the survival of many other species © 2016 Pearson Chemical Recycling Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems For example, some chemoheterotrophic prokaryotes are decomposers, organisms that break down dead organic materials and release mineral nutrients © 2016 Pearson Some prokaryotes can convert molecules into forms that can be taken up by other organisms For example, some species can fix atmospheric nitrogen (N2) into forms available to plants Prokaryotes can also “immobilize” or decrease the availability of plant nutrients © 2016 Pearson Education, Inc. Uptake of K+ by plants (mg) Figure 24.22 1.0 0.8 0.6 0.4 0.2 Seedlings growing in the lab 0 No Strain 1 Strain 2 Strain 3 bacteria Soil treatment © 2016 Pearson Education, Inc. Figure 24.22-1 Seedlings growing in the lab © 2016 Pearson Education, Inc. Ecological Interactions Symbiosis 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 These symbiotic relationships increase the fitness of one or both organisms © 2016 Pearson In mutualism, both 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 © 2016 Pearson Education, Inc. Figure 24.23 © 2016 Pearson Education, Inc. The ecological communities of hydrothermal vents depend on chemoautotrophic bacteria for energy © 2016 Pearson Education, Inc. Impact on Humans The best-known prokaryotes are pathogens, but many others have positive interactions with humans © 2016 Pearson 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 © 2016 Pearson Pathogenic Bacteria Prokaryotes cause about half of all human diseases For example, Lyme disease is caused by a bacterium carried by ticks © 2016 Pearson Figure 24.24 5 mm © 2016 Pearson Education, Inc. Figure 24.24-1 © 2016 Pearson Education, Inc. Figure 24.24-2 © 2016 Pearson Education, Inc. Figure 24.24-3 5 mm © 2016 Pearson Education, Inc. Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins Exotoxins 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 © 2016 Pearson Education, Inc. 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 © 2016 Pearson Education, Inc. Prokaryotes in Research and Technology Experiments using prokaryotes have led to important advances in DNA technology For example, E. coli is used in gene cloning, and the DNA polymerase from Pyrococcus furiosus is used in the PCR technique © 2016 Pearson Experimental treatment of human cells with the prokaryotic CRISPR-Cas9 system has shown promising results for the treatment of HIV © 2016 Pearson Education, Inc. Figure 24.25 (a) Control cells © 2016 Pearson Education, Inc. (b) Experimental cells Figure 24.25-1 (a) Control cells © 2016 Pearson Education, Inc. Figure 24.25-2 (b) Experimental cells © 2016 Pearson Education, Inc. Some bacteria can be used to make natural, biodegradable plastics Others have been engineered to produce ethanol from plant sources and agricultural and municipal wastes © 2016 Pearson Education, Inc. Figure 24.26 (b) (a) © 2016 Pearson Education, Inc. Figure 24.26-1 (a) © 2016 Pearson Education, Inc. Figure 24.26-2 (b) © 2016 Pearson Education, Inc. Prokaryotes are also used in bioremediation, the use of organisms to remove pollutants from the environment © 2016 Pearson Education, Inc. Figure 24.27 © 2016 Pearson Education, Inc. Figure 24.UN03-1 © 2016 Pearson Education, Inc. Figure 24.UN03-2 © 2016 Pearson Education, Inc. Figure 24.UN04 Fimbriae Cell wall Circular chromosome Capsule Pilus Internal organization Flagella © 2016 Pearson Education, Inc. Figure 24.UN05 © 2016 Pearson Education, Inc. Figure 24.UN06 © 2016 Pearson Education, Inc. Figure 24.UN06-1 © 2016 Pearson Education, Inc. Figure 24.UN06-2 © 2016 Pearson Education, Inc.