33-1Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Chapter 33: Bacteria
33-2Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Prokaryotes• Bacteria are prokaryotes• Characteristics
– single-celled– semi-rigid wall around plasma membrane– no membrane-bound organelles– genetic material free in cytoplasm
33-3Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-4Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-5Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-6Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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’)
33-7Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Fig. 33.3: Evolutionary relationships
33-8Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-9Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-10Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-11Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-12Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-13Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-14Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Fig. 33.8 b + c: Cellular metabolic categories
33-15Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-16Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Fig. 33.8 d + a: Cellular metabolic categories
33-17Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-18Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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.)
33-19Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-20Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Fig. 33.9a: Nitrogen cycle
33-21Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-22Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
Methanogens• Chemoautotrophic methanogens use hydrogen
and carbon dioxide to produce methane
4H2 + CO2 CH4 + 2H2O
• Methanogens occur in anaerobic environments, such as animal intestines, waterlogged soils and mud
or acetate or formate
33-23Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-24Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-25Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-26Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
33-27Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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
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