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Chapter 22Lecture Outline
Microbes and the Global Environment
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 2
Biogeochemical Cycles All living organism elements flow in cycles
Rate of cycling varies Biomass vs. organic Environment: atmospheric, land, or ocean
Lack of necessary elements limits growth IronPhosphorusFixed nitrogenMicronutrients
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 3
Biogeochemical Cycles Elements move from large sources to sinks
Reservoirs provide both Ocean important for carbon, nitrogen Land important for sulfur
Oxidation state governs element reactivityNitrogen gas plentiful, fixed nitrogen rare
Measure elements in atmosphere viaChemical reactionsRadioactivity measurements
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 4
Carbon Cycle
Aerobic carbon cyclingPhotosynthesis fixes CO2 into biomass
Produces O2 and organic carbon compounds
Lithotrophs also reduce CO2 to biomass
Respiration returns CO2 to atmosphere Net gain of O2, loss of CO2 in photic zone
Major reservoir is oceanAtmospheric reservoir
is much smaller
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 5
Carbon Cycle
Anaerobic carbon cyclingLower cycling rate than aerobic cycles
Less iron, and less redox potential than oxygen
Subsurface environment Soil, benthos, rock
Fermentation, lithotrophic respiration Incomplete breakdown of biomass carbon Formation of peat, oil, gas
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 6
Carbon Cycle Human activity accelerates CO2 release
Ocean absorbs most CO2
Increased photosynthesis absorbs CO2
Forests, ocean environments
Atmospheric CO2 levels risingRole of newly
discovered microbesunclear
E.g., annamox bacteria
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 7
Nitrogen Cycle Multiple oxidation
states of NitrogenMore than for any
other biological molecule
Prokaryotes crucial for nitrogen conversionOnly natural nitrogen fixers
Haber process doubled biological fixation
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 8
The “Nitrogen Triangle”
Both reduced and oxidized N used for biomass
NITRIFICATION
ATMOSPHERIC N2
REDUCEDNITROGEN
OXIDIZEDNITROGEN
FIXATION DENITRIFICATION
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 9
Nitrogen Cycle—N2 Fixation N2 NH3 NH4
+
NH4+ is rapidly assimilated into amino acids
Catalyzed by nitrogenaseOnly works anaerobicallyOccurs in all ecosystems
Klebsiella, Clostridium, Pseudomonas in soil
Rhizobium within legumes Cyanobacteria in oceans,
freshwater
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 10
Nitrogen Cycle—Nitrification NH4
+ NO2- NO3
-
Oxidation of NH4+ provides electrons, energy
In soil, one species oxidizes NH4+ to NO2
- Nitrosomas
2nd species oxidizes NO2- to NO3
-
Nitrobacter
Excessive fertilizer use causes nitrate runoffEutrophication of streamsDanger to water supplies
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 11
Nitrogen Cycle—Denitrification NO3
- NO2- NO N2O N2
Dissimilatory nitrate reduction Nitrate is anaerobic electron acceptor
N2O (nitrous oxide) buildup if much NO3- present
Prevalent in hypoxic ocean waters Greenhouse gas
In some environments, NO3- NH4
+ Anaerobic sludge, cow rumen H2 gas available as electron donor
Other Geochemical Cycles
Sulfur Phosphate Iron and other metals
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 12
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 13
Hydrologic Cycle Water precipitates from
atmosphereWater vapor evaporates
from land, ocean Water flowing over ground picks up nutrients
Carbon, nitrogen runoff allows respirationRespiring microbes deplete O2 in water
BOD = Biochemical Oxygen Demand
High BOD anoxic runoff hypoxic coasts fish die-offs
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 14
Wastewater Treatment Natural treatment
Wetlands filter water Slow water passage Bacteria in wetland denitrify water
Municipal treatmentReduce nutrients to
reduce BOD Allow microbes to grow,
digest nutrients Aerate to restore
oxygen levels
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 15
Municipal Wastewater Treatment Preliminary, primary treatments
Remove solid debris, sediment Secondary treatment
Microbial treatment to eliminate organic content Anaerobic treatment by methanogens
Release CH4, recover gas as fuel
Aerobic treatment Zooglia, Flavobacterium, Pseudomonas, Nocardia Ciliates, amoebas, nemaotdes, rotifers
Possible tertiary treatment to kill pathogens Release into river
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 16
Concept QuizCarbon is oxidized from biomass to CO2 by the process of
a. Respiration
b. Photosynthesis
c. Lithotrophy
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 17
Concept QuizNitrification is the process by which
a. N2 gas is converted to NH4+
b. NH4+ is oxidized to NO3
-
c. NO3- is reduced to N2O