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Chapter 27 Bacteria and Archaea 細菌與古生菌 PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Masters of Adaptation • Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms Ò 無所不在的原核生物 • Most prokaryotes are microscopic, but what they lack in size they make up for in numbers • There are more in a handful of fertile soil than the number of people who have ever lived Ò 型態微小卻以量取勝 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 1 Overview: Masters of Adaptation • Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms Ò 無所不在的原核生物 http://www.usatourist.com/slideshows/yellowstone/images/Hot%20Spring.jpg http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01347fd5dfb2970c-500wi Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • They have an astonishing genetic diversity • Prokaryotes are divided into two domains: bacteria and archaea Ò 原核生物: a. bacteria 細菌 b. archaea 古生菌 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 2 Fig. 27-1 Concept 27.1: Structural and functional adaptations contribute to prokaryotic success • Most prokaryotes are unicellular, although some species form colonies Ò 絕大多數為單細胞 Ò 部分則形成聚落/菌落 • Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells Ò 型態小於許多真核生物的細胞 • Prokaryotic cells have a variety of shapes Ò 具有多樣化的外形 • The three most common shapes are spheres (cocci), rods (bacilli), and spirals a. 球狀 b. 桿狀 c. 螺旋狀 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 3 Fig. 27-2 2 µm 1 µm (a) Spherical (cocci) (b) Rod-shaped (bacilli) Cell-Surface Structures 5 µm (c) Spiral / 細胞表面的構造 • An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment Ò 維持型態 / 保護 / 抵抗低張環境 • Eukaryote cell walls are made of cellulose or chitin • Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides Ò 細菌細胞壁組成為胜肽聚醣/肽聚醣 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 4 • Archaea contain polysaccharides and proteins but lack peptidoglycan Ò古生菌細胞壁則為多醣與蛋白質 • Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram-negative groups based on cell wall composition Ò 革蘭氏染色 / G(+) and G(-) • Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings http://pathmicro.med.sc.edu/fox/gram-st.jpg 5 • Many antibiotics target peptidoglycan and damage bacterial cell walls Ò 抗生素的作用標的 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-3 G(+) G(-) Carbohydrate portion of lipopolysaccharide Peptidoglycan Cell wall layer Cell wall Outer membrane Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Grampositive bacteria (a) Gram-positive: peptidoglycan traps crystal violet. Gramnegative bacteria 20 µm (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. 6 Fig. 27-3a G(+) http://faculty.ircc.edu/faculty/tfischer/micro%20resources.htm Fig. 27-3b Carbohydrate portion of lipopolysaccharide Outer membrane Cell wall Peptidoglycan layer Plasma membrane G(-) Protein (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. 7 G(-) http://faculty.ircc.edu/faculty/tfischer/micro%20resources.htm http://faculty.ircc.edu/faculty/tfischer/images/cell%20wall%20comparisons.jpg 8 http://faculty.ircc.edu/faculty/tfischer/images/gramstain.jpg http://www.personal.psu.edu/faculty/j/e/jel5/biofilms/graminstr.jpg Fig. 27-3c Grampositive bacteria Gramnegative bacteria 20 µm 9 • A polysaccharide or protein layer called a capsule covers many prokaryotes Ò 莢膜 -- 由多醣或蛋白質組成 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-4 200 nm Capsule 10 • Some prokaryotes have fimbriae (also called attachment pili), which allow them to stick to their substrate or other individuals in a colony • Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA Ò 緣毛 / 附著菌毛 Ò 性菌毛 / 線毛 –- 較長 / 具有交換DNA功能 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-5 Fimbriae 200 nm 11 Motility Ò 移動性 • Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella Ò 藉由鞭毛擺動移動/運動 • In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-6 Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane 12 Fig. 27-6a Filament Cell wall Hook Basal apparatus Plasma membrane Fig. 27-6b 50 nm Prokaryotic flagellum (TEM) 13 Internal and Genomic Organization Ò 內部構造 • Prokaryotic cells usually lack complex compartmentalization Ò 缺少複雜分隔 • Some prokaryotes do have specialized membranes that perform metabolic functions Ò 針對代謝功能特化出的內膜系統 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-7 1 µm 0.2 µm Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote Ò好氧菌 (b) Photosynthetic prokaryote Ò光合成細菌 14 Fig. 27-7a 0.2 µm Respiratory membrane (a) Aerobic prokaryote Fig. 27-7b 1 µm Thylakoid membranes (b) Photosynthetic prokaryote 15 • The prokaryotic genome has less DNA than the eukaryotic genome Ò 與真核生物相比較少DNA的基因體 • Most of the genome consists of a circular chromosome Ò 環狀的染色體 • Some species of bacteria also have smaller rings of DNA called plasmids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-8 Chromosome Plasmids 1 µm 16 • The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region Ò 不具包覆基因體的核 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Reproduction and Adaptation Ò 增殖與適應 • Prokaryotes reproduce quickly by binary fission and can divide every 1–3 hours Ò 典型增殖為二分裂 • Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries Ò 內孢子 –- 惡劣環境下的休眠狀態 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 17 Fig. 27-9 Endospore 0.3 µm • Prokaryotes can evolve rapidly because of their short generation times Ò 原核生物快速演進的原因 –- 極短的世代時間 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 18 Fig. 27-10 EXPERIMENT Daily serial transfer 0.1 mL (population sample) New tube (9.9 mL growth medium) Old tube (discarded after transfer) RESULTS Fitness relative to ancestor 1.8 1.6 1.4 1.2 1.0 0 5,000 10,000 15,000 Generation 20,000 Fig. 27-10a EXPERIMENT Daily serial transfer 0.1 mL (population sample) Old tube (discarded after transfer) New tube (9.9 mL growth medium) 19 Fig. 27-10b RESULTS Fitness relative to ancestor 1.8 1.6 1.4 1.2 1.0 0 5,000 10,000 15,000 Generation 20,000 Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes Ò 增殖 / 變異 / 遺傳多樣性 • Prokaryotes have considerable genetic variation • Three factors contribute to this genetic diversity: Ò 促成高度遺傳變異的主要原因: – Rapid reproduction Ò 快速增殖 / 累代 – Mutation Ò 易受誘導產生突變 – Genetic recombination Ò 基因 / 遺傳重組 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 20 Rapid Reproduction and Mutation • Prokaryotes reproduce by binary fission, and offspring cells are generally identical Ò 二分裂增殖 • Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population Ò 數量龐大的累代 • High diversity from mutations allows for rapid evolution Ò 突變產生的明顯變異 –- 迅速演化 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Genetic Recombination Ò 基因重組 • Additional diversity arises from genetic recombination • Prokaryotic DNA from different individuals can be brought together by: a. transformation b. transduction c. conjugation 轉型作用 轉導作用 接合增殖 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 21 Transformation and Transduction • A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation Ò 由外界獲得 • Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria) Ò 發生於兩菌體間 / 藉由噬菌體傳遞 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-11-1 Phage DNA A+ B+ A+ B+ Donor cell 22 Fig. 27-11-2 Phage DNA A+ B+ A+ B+ Donor cell A+ Fig. 27-11-3 Phage DNA A+ B+ A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell 23 Fig. 27-11-4 Phage DNA A+ B+ A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell A+ B– Recombinant cell Conjugation and Plasmids Ò 接合作用與質體 • Conjugation is the process where genetic material is transferred between bacterial cells Ò 遺傳物質在兩菌體間的交流 • Sex pili allow cells to connect and pull together for DNA transfer Ò 性菌毛的聯通 • A piece of DNA called the F factor is required for the production of sex pili • The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 24 Fig. 27-12 Sex pilus 1 µm The F Factor as a Plasmid • Cells containing the F plasmid function as DNA donors during conjugation Ò DNA的供應者 • Cells without the F factor function as DNA recipients during conjugation • The F factor is transferable during conjugation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 25 Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Hfr cell A+ A+ A+ A+ F factor F– cell A– Recombinant F– bacterium A– A– A+ A+ A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome Fig. 27-13-1 F plasmid Bacterial chromosome F+ cell Mating bridge F– cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid 26 Fig. 27-13-2 F plasmid Bacterial chromosome F+ cell Mating bridge F– cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Fig. 27-13-3 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell Bacterial chromosome F+ cell (a) Conjugation and transfer of an F plasmid 27 The F Factor in 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 • It is assumed that horizontal gene transfer is also important in archaea Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-13-4 Hfr cell A+ A+ A+ F factor F– cell A– A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome 28 Fig. 27-13-5 Hfr cell A+ A+ A+ A+ F factor A– F– cell A– A+ A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome Fig. 27-13-6 Hfr cell A+ A+ F factor F– cell A+ A+ A– Recombinant F– bacterium A– A– A+ A+ A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome 29 R Plasmids and Antibiotic Resistance • R plasmids carry genes for antibiotic resistance Ò 攜帶具有抗生素抗藥性之基因 • Antibiotics select for bacteria with genes that are resistant to the antibiotics • Antibiotic resistant strains of bacteria are becoming more common Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 27.3: Diverse nutritional and metabolic adaptations have evolved in prokaryotes • 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 • These factors can be combined to give the four major modes of nutrition: photoautotrophy, chemoautotrophy, photoheterotrophy, and chemoheterotrophy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 30 Table 27-1 The Role of Oxygen in Metabolism • Prokaryotic metabolism varies with respect to O2: – Obligate aerobes require O2 for cellular respiration Ò 絕對好氧性 – Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration Ò 絕對厭氧性 – Facultative anaerobes can survive with or without O2 Ò 兼性厭氧性 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 31 Nitrogen Metabolism Ò 氮代謝 • Prokaryotes can metabolize nitrogen in a variety of ways • In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) Ò 固氮反應 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Metabolic Cooperation Ò 共生性代謝 • Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells Ò 無法以單一細胞利用環境資源 • In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocytes exchange metabolic products Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 32 Fig. 27-14 Photosynthetic cells Heterocyte 20 µm • In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms Ò 細菌薄層 / 生物膜 http://www2.binghamton.edu/biology/faculty/davies/images/biofilm.jpg Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 33 1 µm Fig. 27-15 Concept 27.4: Molecular systematics is illuminating prokaryotic phylogeny • Until the late 20th century, systematists based prokaryotic taxonomy on phenotypic criteria • Applying molecular systematics to the investigation of prokaryotic phylogeny has produced dramatic results Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 34 Lessons from Molecular Systematics • Molecular systematics is leading to a phylogenetic classification of prokaryotes • It allows systematists to identify major new clades Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-16 Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Domain Archaea Korarcheotes Domain Eukarya Eukaryotes Proteobacteria Spirochetes Cyanobacteria Domain Bacteria Chlamydias Gram-positive bacteria 35 • The use of polymerase chain reaction (PCR) has allowed for more rapid sequencing of prokaryote genomes • A handful of soil many contain 10,000 prokaryotic species • Horizontal gene transfer between prokaryotes obscures the root of the tree of life Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Archaea • Archaea share certain traits with bacteria and other traits with eukaryotes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 36 Fig. 27-UN1 Eukarya Archaea Bacteria Table 27-2 37 • Some archaea live in extreme environments and are called extremophiles • Extreme halophiles live in highly saline environments • Extreme thermophiles thrive in very hot environments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-17 38 • Methanogens live in swamps and marshes and produce methane as a waste product • Methanogens are strict anaerobes and are poisoned by O2 • In recent years, genetic prospecting has revealed many new groups of archaea • Some of these may offer clues to the early evolution of life on Earth Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bacteria • Bacteria include the vast majority of prokaryotes of which most people are aware • Diverse nutritional types are scattered among the major groups of bacteria Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 39 Fig. 27-UN2 Eukarya Archaea Bacteria Proteobacteria • These gram-negative bacteria include photoautotrophs, chemoautotrophs, and heterotrophs • Some are anaerobic, and others aerobic Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 40 Fig. 27-18a Subgroup: Alpha Proteobacteria Alpha Beta Gamma Proteobacteria 2.5 µm Delta Epsilon Rhizobium (arrows) inside a root cell of a legume (TEM) Subgroup: Beta Proteobacteria 0.5 µm 1 µm Subgroup: Gamma Proteobacteria Thiomargarita namibiensis containing sulfur wastes (LM) Nitrosomonas (colorized TEM) Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Subgroup: Epsilon Proteobacteria B. bacteriophorus Bdellovibrio bacteriophorus attacking a larger bacterium (colorized TEM) 2 µm 5 µm 10 µm Subgroup: Delta Proteobacteria Helicobacter pylori (colorized TEM) Fig. 27-18b Alpha Beta Gamma Proteobacteria Delta Epsilon 41 Subgroup: Alpha Proteobacteria • Many species are closely associated with eukaryotic hosts • Scientists hypothesize that mitochondria evolved from aerobic alpha proteobacteria through endosymbiosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 42 2.5 µm Fig. 27-18c Rhizobium (arrows) inside a root cell of a legume (TEM) Subgroup: Beta Proteobacteria • Example: the soil bacterium Nitrosomonas, which converts NH4+ to NO2– Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 43 1 µm Fig. 27-18d Nitrosomonas (colorized TEM) Subgroup: Gamma Proteobacteria • Examples include sulfur bacteria such as Chromatium and pathogens such as Legionella, Salmonella, and Vibrio cholerae • Escherichia coli resides in the intestines of many mammals and is not normally pathogenic Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 44 0.5 µm Fig. 27-18e Thiomargarita namibiensis containing sulfur wastes (LM) Subgroup: Delta Proteobacteria • Example: the slime-secreting myxobacteria Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 45 10 µm Fig. 27-18f Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Fig. 27-18g 5 µm B. bacteriophorus Bdellovibrio bacteriophorus attacking a larger bacterium (colorized TEM) 46 Subgroup: Epsilon Proteobacteria • This group contains many pathogens including Campylobacter, which causes blood poisoning, and Helicobacter pylori, which causes stomach ulcers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 2 µm Fig. 27-18h Helicobacter pylori (colorized TEM) 47 Chlamydias / 衣原體 • These bacteria are parasites that live within animal cells • Chlamydia trachomatis causes blindness and nongonococcal urethritis by sexual transmission Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-18i CHLAMYDIAS Chlamydia (arrows) inside an animal cell (colorized TEM) 5 µm 2.5 µm SPIROCHETES Leptospira, a spirochete (colorized TEM) Two species of Oscillatoria, filamentous cyanobacteria (LM) 1 µm GRAM-POSITIVE BACTERIA 5 µm 50 µm CYANOBACTERIA Streptomyces, the source of many antibiotics (colorized SEM) Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) 48 2.5 µm Fig. 27-18j Chlamydia (arrows) inside an animal cell (colorized TEM) Spirochetes / 螺旋體 • These bacteria are helical heterotrophs • Some, such as Treponema pallidum, which causes syphilis, and Borrelia burgdorferi, which causes Lyme disease, are parasites Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 49 5 µm Fig. 27-18k Leptospira, a spirochete (colorized TEM) Cyanobacteria / 藍綠菌 • These are photoautotrophs that generate O2 • Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 50 50 µm Fig. 27-18l Two species of Oscillatoria, filamentous cyanobacteria (LM) Gram-Positive Bacteria • Gram-positive bacteria include – Actinomycetes, which decompose soil – Bacillus anthracis, the cause of anthrax / 炭疽 – Clostridium botulinum, the cause of botulism – Some Staphylococcus and Streptococcus, which can be pathogenic – Mycoplasms, the smallest known cells / 類菌質體 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 51 5 µm Fig. 27-18m Streptomyces, the source of many antibiotics (colorized SEM) 1 µm Fig. 27-18n Hundreds of mycoplasmas covering a human fibroblast cell (colorized SEM) 52 Concept 27.5: Prokaryotes play crucial roles in the biosphere • Prokaryotes are so important to the biosphere that if they were to disappear the prospects for any other life surviving would be dim Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Chemical Cycling • 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 corpses, dead vegetation, and waste products • Nitrogen-fixing prokaryotes add usable nitrogen to the environment Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 53 • Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth • Prokaryotes can also “immobilize” or decrease the availability of nutrients Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Uptake of K by plants (mg) Fig. 27-19 1.0 0.8 0.6 0.4 0.2 0 No Strain 1 Strain 2 Strain 3 bacteria Soil treatment 54 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 55 Fig. 27-20 Concept 27.6: Prokaryotes have both harmful and beneficial impacts on humans • Some prokaryotes are human pathogens, but others have positive interactions with humans Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 56 Pathogenic Prokaryotes • Prokaryotes cause about half of all human diseases • Lyme disease is an example Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 27-21 5 µm 57 Fig. 27-21a Deer tick Fig. 27-21b 5 µm Borrelia burgdorferi (SEM) 58 Fig. 27-21c Lyme disease rash • Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins • Exotoxins 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 • Many pathogenic bacteria are potential weapons of bioterrorism Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 59 Prokaryotes in Research and Technology • Experiments using prokaryotes have led to important advances in DNA technology • Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Some other uses of prokaryotes: – Recovery of metals from ores – Synthesis of vitamins – Production of antibiotics, hormones, and other products Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 60 Fig. 27-22 (b) (c) (a) Fig. 27-22a (a) 61 Fig. 27-22b (b) Fig. 27-22c (c) 62 Fig. 27-UN3 Fimbriae Cell wall Circular chromosome Capsule Sex pilus Internal organization Flagella Fig. 27-UN4 63 Fig. 27-UN5 You should now be able to: 1. Distinguish between the cell walls of grampositive and gram-negative bacteria 2. State the function of the following features: capsule, fimbriae, sex pilus, nucleoid, plasmid, and endospore 3. Explain how R plasmids confer antibiotic resistance on bacteria Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 64 4. Distinguish among the following sets of terms: photoautotrophs, chemoautotrophs, photoheterotrophs, and chemoheterotrophs; obligate aerobe, facultative anaerobe, and obligate anaerobe; mutualism, commensalism, and parasitism; exotoxins and endotoxins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 65
