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