Transcript Chapter 33
Chapter 33: Bacteria Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-1 Prokaryotes • Bacteria are prokaryotes • Characteristics – – – – single-celled semi-rigid wall around plasma membrane no membrane-bound organelles genetic material free in cytoplasm Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-2 The first life • Bacteria were the earliest forms of life on Earth – oldest fossils of bacteria are 3.5 billion years old • Early forms existed under conditions hostile to most modern living organisms – anaerobic atmosphere with H2, NH3, H2S – high levels of UV radiation • Descendants of early bacteria now found in hot, hypersaline or anoxic areas that resemble ancient earth Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-3 Early photosynthetic bacteria • • • Evolution of photosynthesis allowed bacteria to fix carbon Early photosynthetic pathways were anoxygenic (did not produce oxygen) Subsequent evolution of oxygenic photosynthesis (2.5 billion years ago) produced enough O2 to change composition of atmosphere Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-4 Classifying bacteria • Biochemical, physiological and immunological characteristics are used as a rapid method of identifying and classifying bacteria – – – – – – – – staining reactions cell shape cell grouping presence of special structures growth medium antibiotic resistance DNA sequences immunological tests Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-5 Super kingdoms • • Prokaryotes are divided into two groups on the basis of biochemical characteristics Super kingdom Bacteria – formerly called Eubacteria (‘true bacteria’) • Super kingdom Archaea – formerly called Archaeobacteria (‘ancient bacteria’) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-6 Fig. 33.3: Evolutionary relationships Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-7 Super kingdom Bacteria • Diverse metabolic pathways have allowed Bacteria to use most materials as sources of energy – only some plastics and organochlorine compounds are resistant to bacteria • Characteristics – – – – peptidoglycan is major cell wall polymer membrane lipids are esters protein synthesis disrupted by streptomycin some nitrifying and photosynthetic species Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-8 Bacteria • Cyanobacteria are also known as ‘blue-green algae’ – blue phycobilins (a water-soluble pigment) gives them the characteristic blue-green colour, which is obvious when they form dense mats or blooms in shallow waters • Under poor conditions, endospores form inside bacteria (such as Clostridium and Bacillus) – endospores are resistant to high temperatures, radiation and chemicals – many species of endospore-forming bacteria are important pathogenic agents Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-9 Archaea • Many Archaea occur in extreme environments, including deep sea volcanic vents and thermal pools – halophiles (hypersaline) – acidophiles (low ph) – thermophiles (high temperatures) • Characteristics – – – – peptidoglycan is not major cell wall polymer membrane lipids are ethers protein synthesis disrupted by diphtheria toxin no nitrifying or photosynthetic species Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-10 Abundance • Bacteria populations are very large and dense • Human skin harbours c. 100 000 cells/cm-1 – clustered distribution in moist, bacteria-friendly areas – suite of species varies from person to person • Human faecal material contains c. 100 000 000 000 cells/gm-1 – high diversity of bacteria in colon Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-11 Metabolic diversity • Energy source – phototrophs use radiant (light) energy – chemotrophs use chemical energy • Carbon source – autotrophs synthesise organic compounds from inorganic carbon – heterotrophs use organic compounds as energy source • Four nutritional types – – – – chemoautotrophs chemoheterotrophs photoautotrophs photoheterotrophs Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-12 Autotrophs • Photoautotrophs – photosynthetic bacteria: cyanobacteria, purple bacteria and green bacteria – use light energy to reduce CO2 – reductant may be H2O, H2S, H2 • Chemoautotrophs – nitrifying bacteria, methanogenic bacteria, iron-oxidising bacteria and others – use chemical energy (NH4+, NO2-, H2S, S, Fe3+) to reduce CO2 – reductant may be H2O, H2 Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-13 Fig. 33.8 b + c: Cellular metabolic categories Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-14 Heterotrophs • Photoheterotrophs – anaerobically-growing purple bacteria and green bacteria – use light energy to reduce CH2O – reductant may be CH2O, H2S, S, H2 • Chemoheterotrophs – many bacteria (also animals and fungi) – CH2O is reductant and provides energy Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-15 Fig. 33.8 d + a: Cellular metabolic categories Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-16 Anaerobic bacteria • Anaerobic pathways use compounds other than O2 as terminal oxidants CH2O + NO3- CO2 + N2 or SO42-, HCO3-, Fe3+ or fumarate or S, CH4, Fe2+ or succinate Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-17 Nitrogen cycle • Nitrogen-fixing bacteria (cyanobacteria, plant symbiotes, Clostridium, others) are the only organisms capable of fixing molecular nitrogen N2 + 8H+ + 6e- 2NH4+ • • Reaction is sensitive to molecular oxygen and other oxidants, so occurs in a highly reducing or anaerobic environment Ammonium ion is used to form glutamine and glutamate (amino acids) in bacterial cell (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-18 Nitrogen cycle (cont.) • Nitrifying bacteria oxidise ammonium to nitrite (Nitrosomonas) and nitrate (Nitrobacter) – transform fixed nitrogen from nitrogen fixers or decomposing organisms • Denitrifying bacteria (Pseudomonas, anaerobic bacteria) use nitrite and nitrate as terminal electron receptors – produce gaseous nitrous oxide and molecular nitrogen – nitrogen is no longer available for other organisms, except nitrogen-fixing organisms Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-19 Fig. 33.9a: Nitrogen cycle Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-20 Bacterial fermentation • • Fermentation (anaerobic energy metabolism) produces a range of end products, many of which are used in agriculture and food and alcohol production Lactic acid – Lactobacillus, Lactococcus and other bacteria are used in the production of yoghurt and milk • Ethanol – Bacteria decarboxylate pyruvate to form acetate, which is then reduced to ethanol Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-21 Methanogens • Chemoautotrophic methanogens use hydrogen and carbon dioxide to produce methane 4H2 + CO2 CH4 + 2H2O or acetate or formate • Methanogens occur in anaerobic environments, such as animal intestines, waterlogged soils and mud Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-22 Genetic systems • • Bacteria reproduce asexually by fission (cell division) Genetic variation in bacteria is due to – mutation – mixing genetic material between different cells transformation conjugation transduction Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-23 Transformation • • • Bacteria may take free DNA molecules into their cells DNA recognised as foreign may be broken down DNA similar to the bacterium’s DNA may – recombine with the chromosomal or plasmid DNA – become a plasmid • This process of taking up free DNA and making it part of the cell is transformation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-24 Conjugation • • • DNA may be transferred directly between bacteria via plasmids in the process of conjugation A plasmid may pass a copy of itself from one cell to another Once in a new cell, a plasmid may – establish itself as an independent plasmid in the cell – combine with another plasmid – combine with the chromosomal DNA Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-25 Transduction • • • Bacteriophages (viruses that live in bacterial cells) integrate their DNA into the host’s chromosomal DNA Temperate (non-virulent) phages become virulent under certain conditions, rupturing the cell and releasing virions (phage particles) A virion may inadvertently carry the original host’s DNA into another cell, where it may recombine or integrate with the new host’s DNA Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-26 Plasmids and phages • • Plasmids and phages are abundant in bacterial populations Gene transfer often confers new properties on host bacteria – – – – – – antibiotic resistance antibiotic synthesis toxin synthesis production of tissue-damaging enzymes gall-production in plants resistance to phage attack Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 33-27