Download Environmental Microbiology

2016/2/19
PowerPoint® Lecture
Presentations prepared by
Bradley W. Christian,
McLennan Community
College
CHAPTER
27
Environmental
Microbiology
© 2016 Pearson Education, Ltd.
© 2016 Pearson Education, Ltd.
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Microbial Diversity and Habitats
• Microbial populations are diverse
• Take advantage of any niches in their environment
• Compete with other organisms
• Extremophiles live in extreme conditions (pH,
temperature, salinity)
• Most are members of the Archaea
• Have extremozymes that make growth possible
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Symbiosis
• Close association between two unlike organisms
that is beneficial to one or both of them
• Symbiosis between animals and microbes
• Ruminants (such as sheep and cows) and digestive
bacteria in the rumen
• Mycorrhizae: relationship between plant roots and
fungi that extend the root surface area
• Endomycorrhizae
• Ectomycorrhizae
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Figure 27.1 Mycorrhizae and their considerable commercial value.
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Soil Microbiology and Biogeochemical Cycles
• Millions of bacteria per gram of soil
• Most cannot be cultured
• Largest populations in the top few centimeters
• Biogeochemical cycles
• Elements are oxidized and reduced by microorganisms
to meet their metabolic needs
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The Carbon Cycle
• Photoautotrophs fix CO2 into organic matter using
energy from sunlight
• Chemoheterotrophs use organic matter for energy
• Energy and CO2 are released via respiration; cycle
repeats
• Decomposers oxidize organic compounds from
dead plants and animals
• Global warming releases CO2 into atmosphere
from burning fossil fuels
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Figure 27.2 The carbon cycle.
Burning
KEY
CO2 in atmosphere
Fixation
Respiration
Plants, algae,
cyanobacteria
Plant
respiration
Animal
respiration
Photosynthetic
fixation
Wood and
fossil fuels
Plants
CH4 +CO2
Animals
Dissolved
CO2
Decomposition
Soil and
water microbes
Fossil
fuels
Dead
organisms
Aquatic
bacteria
Photosynthetic
fixation
Plants, algae,
cyanobacteria
Dead organisms,
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The Nitrogen Cycle
• Nitrogen is required to make proteins and nucleic
acids
• N2 makes up 80% of the atmosphere
• Must be fixed into organic compounds by
microorganisms
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Figure 27.3 The nitrogen cycle.
KEY
Ammonification
Fixation
Nitrification
Denitrification
Free nitrogen gas
(N2) in atmosphere
(N2)
Decomposition
Nonsymbiotic
Azotobacter,
Beijerinckia,
cyanobacteria,
Clostridium
Leguminous
plants
Protein
from
dead cells
Industrial
fixation as
fertilizer
Fixation
(N2O)
Denitrifying bacteria
(Pseudomonas,
Bacillus licheniformis,
Paracoccus
denitrificans,
and others)
Decay organisms
(aerobic and
anaerobic bacteria
and fungi)
Nitrites
(NO2–)
Denitrification
Symbiotic
Rhizobium,
Bradyrhizobium
Assimilation
Ammonification
Ammonia
(NH3)
Nitrosomonas
Nitrites
(NO3–)
Nitrites
(NO2–)
Nitrification
Nitrobacter
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The Nitrogen Cycle
• Microbial decomposition breaks down proteins into
amino acids
• Deamination: amino groups removed and converted to
ammonia (NH3)
• Ammonification: release of ammonia by bacteria and
fungi
• Ammonia becomes ammonium ions (NH4+) in water
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The Nitrogen Cycle
• Nitrification: oxidation of ammonium ions to
produce nitrate
• Nitrate used by plants for protein synthesis
• Conducted by autotrophic nitrifying bacteria
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The Nitrogen Cycle
• Denitrification: nitrate used as an electron
acceptor by microbes in the absence of oxygen
• Produces nitrogen gas (lost to the atmosphere)
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The Nitrogen Cycle
• Nitrogen fixation: bacterial process that converts
nitrogen gas to ammonia
• Uses nitrogenase enzyme
• Free-living nitrogen-fixing bacteria
• Found in rhizosphere
•
•
•
•
Azotobacter
Beijerinckia
Clostridium pasteurianum
Cyanobacteria: contain heterocysts that provide
anaerobic conditions for fixation
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The Nitrogen Cycle
• Symbiotic nitrogen-fixing bacteria
• Adapted to leguminous plants
• Form root nodules
• Rhizobium
• Bradyrhizobium
• Frankia
• Lichens
• Combination of fungus and algae or cyanobacteria
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Figure 27.4 The formation of a root nodule.
Pea plant
Root
hairs
Root
Nodules
Rhizobia attach
to root hair.
Rhizobia
Enlarged root cells
form a nodule.
Infection
thread
Bacteroids
Bacteria change into
bacteroids; packed root
cells enlarge.
An infection thread is formed,
through which bacteria enter
root cells.
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Figure 27.5 The Azolla–cyanobacteria symbiosis.
Heterocysts
Cyanobacteria
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The Sulfur Cycle
• Hydrogen sulfide (H2S) forms under anaerobic
conditions
• Source of energy for autotrophic bacteria
• Converted to elemental sulfur granules and sulfates
(SO42–)
• Beggiatoa: use light for energy; H2S reduces CO2
• Plants incorporate sulfates into amino acids
• Dissimilation: protein decomposition releases
H2S into the sulfur cycle
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Figure 27.6 The sulfur cycle.
Burning of
fossil
fuels
KEY
H2SO3
SO2
H2S
Dissimilation
Volatile
sulfur
emissions
SO42–
Assimilation by plants
and bacteria
Acidithiobacillus
Anaerobic
respiration
Elemental
sulfur
H2S
S0
Reduction by
Desulfovibrio
Oxidation
Excretion
Plant
decay
Solution,
plant
uptake
Assimilation
Microbial
oxidation
SH sulfhydryl
groups of proteins
Decomposition
by microbes
(dissimilation)
Purple
and green
bacteria
S0
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Life without Sunshine
• Primary producers in the dark
• Conducted by chemoautotrophic bacteria
• Occur in deep-sea vents and within rocks
• Endoliths: bacteria in rocks
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The Phosphorous Cycle
• Phosphorus changes from soluble to insoluble
forms and organic to inorganic forms
• Exists primarily as phosphate ions (PO43–)
• Related to pH
• Acidithiobacillus: produces acid that solubilizes phosphate
in rocks
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The Degradation of Synthetic Chemicals in Soil
and Water
• Natural organic matter is easily degraded by
microbes
• Xenobiotics are resistant to degradation
• Made of chemicals that do not naturally occur in nature
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The Degradation of Synthetic Chemicals in Soil
and Water
• Bioremediation
• Use of microbes to detoxify or degrade pollutants
• Enhanced by nitrogen and phosphorus fertilizer
• Bioaugmentation
• Addition of specific microbes to degrade a pollutant
• Composting
• Arranging organic waste to promote microbial
degradation by thermophiles
• Convert plant remains into the equivalent of natural
humus
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Figure 27.7 Bioremediation of an oil spill in Alaska.
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Figure 27.8 Composting municipal wastes.
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Aquatic Microbiology and Sewage Treatment
• Aquatic microbiology: study of microorganisms
and activities in natural waters
• Large numbers of microorganisms in water
indicate high nutrient levels
• Many bacteria have appendages and holdfasts to
attach to aquatic surfaces
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Freshwater Microbiota
• Littoral zone
• Along the shore; rooted vegetation
• Limnetic zone
• Surface of open water away from the shore
• Photosynthetic algae
• Profundal zone
• Deeper water under the limnetic zone; low oxygen
• Anaerobic purple and green photosynthetic bacteria
• Benthic zone
• Bottom sediment; no light or oxygen
• Desulfovibrio; methane-producing bacteria
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Seawater Microbiota
• Phytoplankton abundant in the top 100 meters
• Photosynthetic cyanobacteria fix carbon and nitrogen
• Prochlorococcus
• Synechococcus
• Trichodesmium
• Archaea dominate below 100 meters
• Crenarchaeota
• Large populations of Archaea in seafloor
sediments
• 1/3 of all life on the planet
• Produce methane gas
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Seawater Microbiota
• Bioluminescence
• Luminescent bacteria form symbiotic relationships with
benthic-dwelling fish
• Aids in attracting and capturing prey
• Luciferase enzyme works in the electron transport chain
to help emit electron energy as a photon of light
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Figure 27.9 Bioluminescent bacteria as light organs in fish.
Luminous
organ
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The Role of Microorganisms in Water Quality
• The transmission of infectious diseases
• Microbes are filtered from water that percolates into
groundwater
• Some pathogens are transmitted to humans in drinking
and recreational water from feces
• Typhoid fever
• Cholera
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The Role of Microorganisms in Water Quality
• Chemical pollution
• Chemicals that enter water are often resistant to
biodegradation
• Eutrophication: overabundance of nutrients in lakes
and streams
• Excessive nitrogen and phosphorus cause algal blooms
• Dead algae and cyanobacteria are degraded by bacteria,
depleting oxygen
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Figure 27.10 A red tide.
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Water Purity Tests
• Indicator organisms
• Used to detect fecal contamination of water
• Coliforms
• Aerobic or facultatively anaerobic, gram-negative,
non–endospore-forming rods
• Ferment lactose with acid and gas within 48 hours, at
35C
• Predominantly Escherichia coli
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Water Purity Tests
• Presence of coliforms determined by:
• Most probable number (MPN) method
• Membrane filtration method
• Media containing ONPG and MUG
• Limitations to using coliforms as indicator
organisms
• Growth in biofilms
• Viruses and protozoans resistant to chemical
disinfection
• Giardia intestinalis
• Cryptosporidium
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Water Treatment
• Coagulation and filtration
• Particulates in raw water settle out
• Flocculation: removal of colloidal materials, bacteria,
and viruses by adding alum
• Filtration: passing water through fine sand or coal;
microorganisms adsorb to sand particles
• Disinfection
• Chlorination
• Ozone treatment
• UV light
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Figure 27.11 The steps involved in water treatment in a typical municipal water purification plant.
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Sewage (Wastewater) Treatment
• Primary sewage treatment
• Removal of solids
• Sludge collects in sedimentation tanks
• Biochemical oxygen demand (BOD)
• Measure of the biodegradable organic matter in water
• Primary treatment removes 25–35% of BOD
• Determined by the amount of oxygen required by
bacteria to metabolize organic matter
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Sewage (Wastewater) Treatment
• Secondary sewage treatment
• Activated sludge system
• Air passes through the effluent from primary treatment
• Contains aerobic sewage-metabolizing microbes
• Removes 75–95% of BOD
• Trickling filters
• Sewage sprayed over rocks or plastic, forming biofilm of
aerobic microbes
• Removes 80–85% of BOD
• Rotating biological contactor
• Rotation of disks aerates wastewater
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Figure 27.12 The stages in typical sewage treatment.
PRIMARY TREATMENT
Sewage is
screened, skimmed,
and ground.
Solid matter
settles out.
SECONDARY TREATMENT
(biological oxidation)
DISINFECTION
AND RELEASE
Primary effluent
undergoes aeration;
microorganisms
oxidize organic
Trickling filter
matter.
Effluent is disinfected
by chlorination and
released.
Primary
effluent
Chlorinator
Sewage
Effluent
Primary
sedimentation
tank
or
Activated
sludge system
Primary sludge
Secondary
effluent
Settling tank
Secondary sludge
from settling tank
KEY
Physical
processes
Anaerobic sludge
digester
Sludge
effluent
Sludge effluent
is dried.
Remaining sludge
is digested anaerobically,
producing methane.
Sludge is
removed and
disposed of
in landfill or
agricultural
land.
Microbial
processes
Chemical
processes
Drying bed
SLUDGE DIGESTION
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Figure 27.13 An activated sludge system of secondary sewage treatment.
Primary sewage
effluent
Aeration tank
Settling tank
Clear
effluent
Air
Activated
sludge
return
Excess
secondary
sludge
To
sludge
digestion
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Figure 27.14 A trickling filter of secondary sewage treatment.
Rotating spray arm
for incoming sewage
Rock bed or plastic
honeycomb
Sewage wastes
Effluent (enters settling
tank to remove sludge
before discharge)
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Sewage (Wastewater) Treatment
• Disinfection and release
• Sewage is disinfected by chlorination before release
• Sludge digestion
• Additional treatment of sludge from primary
sedimentation tanks
• Occurs in anaerobic sludge digesters
• Anaerobic bacteria degrade organic solids into methane
and carbon dioxide
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Figure 27.15 Sludge digestion.
Gas outlet
Sludge
inlet
Methane gas
Scum layer
Supernatant
Scum removal
Supernatant
removal
Actively digesting sludge
Stabilized sludge
Sludge outlet
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Sewage (Wastewater) Treatment
• Septic tank
• Device used for primary treatment of sewage from areas
with low population density
• Effluent from the holding tank is piped into a drainage
field
• Decomposed by soil microorganisms
• Oxidation ponds
• First stage: settles sludge
• Second stage: effluent pumped into a system of shallow
ponds
• Grows algae that produce oxygen for aerobic
decomposition
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Figure 27.16 A septic tank system.
Access
manhole
House
sewer
line
Septic
tank
Leaching
field
Distribution
box
Perforated
pipes
Overall plan. Most soluble organic matter is
disposed of by percolation into the soil.
Access manhole
inlet
Outlet
Sludge
A section of a septic tank
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Sewage (Wastewater) Treatment
• Tertiary sewage treatment
• Removal of remaining BOD, nitrogen, and phosphorus
• Physical and chemical treatment
• Chlorination
• Water is drinkable after treatment
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