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Chapter 28Chapter 28Microorganisms and the Microorganisms and the

EnvironmentEnvironment

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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