Chapter 28
Microorganisms and the
Environment
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Soil Environments
• Mineralization
– Organic material converted to inorganic form
• Availability of oxygen
– Soil fertility
• Adequate supply of inorganic molecules
• Bacteria and Fungi
– diverse population
– break down plant and animal remains
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Soil Environments
• Symbiosis
– mycorrhizae
• soil fungi and roots of plants
• acquire nutrient for plant
– rhizosphere
• area of soil surrounding root
• specific microorganisms
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Water Environments
• Extent of microorganisms in water
– Almost all aqueous environments
– Differences between bodies of water
• Nutrients
– Nutrient poor
• Oceans
– Phytoplankton
• Freshwater
– Clarity and color
– Too much nutrient—eutrophic
• Pathogens
– Freshwater is reservoir
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Air Environments
• No growth in air
• Passengers of aerosols
– Cough
– Sneeze
– Talk
– Agitation of water
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Nitrogen Cycle
• Nitrogen exists in many forms
– nitrogen gas in atmosphere
• converted to ammonia
– Nitrogen fixation
• by bacteria
• nonsymbiotic
– Cyanobacteria
• symbiotic
–
–
–
–
root hairs
infection thread
root nodules
bacteroids
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Nitrogen Cycle
– Nitrification
• ammonia
oxidized to
nitrate ion
– by nitrifying
bacteria
– Denitrification
• only
prokayrotes
• supply
nitrogen to
atmosphere
Figure 28.7
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Carbon Cycle
• Carbon dioxide to
organic compounds to
carbon dioxide
– Photosynthesis
• conversion of CO2 to
glucose
– Respiration and
combustion
• organic compounds to
CO2.
– Earth’s CO2 is increasing
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Carbon Cycle
Figure 28.9
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Phosphorus Cycle
• Phosphorus to inorganic phosphate to
organic phosphate and back.
– Differs from nitrogen and carbon cycles
• No gaseous phase
• phosphorus neither oxidized or reduced
– ecological importance
• phosphates often limiting nutrient
– increase in phosphates results in eutrophication
• removal from sewage important
– bacteria convert to polyphosphate granules
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Phosphorous Cycle
Figure 28.11
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Sulfur Cycle
• Reducing sulfate ion to hydrogen sulfide gas
– sulfate-reducing bacteria
• nutrient
• terminal electron acceptor
• sulfate rich anaerobic environments
– mud flats
• Reoxidizing to sulfate
– sulfur-oxidizing bacteria
– nonoxygenic phototrophic bacteria
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Sulfur Cycle
Figure 28.12
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Wastewater treatment
• Sewage treatment
– reduce the biochemical oxygen demand
(BOD)
– Primary treatment
• solid material is sedimented
Figure 28.13
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Wastewater treatment
– Secondary treatment
• liquid from primary
• biological treatment
– aeration
– trickling filter
– oxygen added
• bacteria mineralize sewage
– floc: mixture of slime and
bacteria
• activated sludge--used to
inoculate next batch
Figure 28.14
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Wastewater treatment
• Septic tanks
– sludge settles
– effluent piped into
leach field
Figure 28.15
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Drinking Water: Treatment
• Treatment
– filtration
• beds of sand
• diatomaceous earth
– activated charcoal
– disinfection
• chlorine
• ozone
Fig 28.16
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Drinking Water: Testing
• Test for coliforms
– indicator organisms
– more practical than testing for pathogens
• Two methods
– Most probable number (MPN)
– Membrane filter (MF)
• Safe levels
– 1 coliform/100 ml
• tested frequently
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Most Probable Number (MPN)
• Presumptive test
– lactose and gas production
• Confirmed test
– plated on EMB agar
• Completed test
– growth in lactose broth and slants.
Fig 28.17
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Membrane Filter (MF)
• 100 ml water
– filtered
– filter is placed on surface of a
media which identifies coliform
bacteria
– incubation
– coliform colonies are counted
Fig 28.17
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