1. Chapter 22 Lecture Outline
Microbes and the Global Environment

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
Iron
Phosphorus
Fixed nitrogen
Micronutrients
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 reactivity
Nitrogen gas plentiful, fixed nitrogen rare
Measure elements in atmosphere via
Chemical reactions
Radioactivity measurements
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

4. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Carbon Cycle
Major reservoir is ocean
Atmospheric reservoir is much smaller
Aerobic carbon cycling
Photosynthesis 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
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

5. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Carbon Cycle
Anaerobic carbon cycling
Lower 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. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Carbon Cycle
Human activity accelerates CO2 release
Ocean absorbs most CO2
Increased photosynthesis absorbs CO2
Forests, ocean environments
Atmospheric CO2 levels rising
Role of newly discovered microbes unclear
E.g., annamox bacteria
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

7. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Nitrogen Cycle
Multiple oxidation states of Nitrogen
More than for any other biological molecule
Prokaryotes crucial for nitrogen conversion
Only natural nitrogen fixers
Haber process doubled biological fixation
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

8. The “Nitrogen Triangle”
ATMOSPHERIC N2
DENITRIFICATION
FIXATION
REDUCED
NITROGEN
OXIDIZED
NITROGEN
NITRIFICATION
Both reduced and oxidized N used for biomass
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 nitrogenase
Only works anaerobically
Occurs 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 runoff
Eutrophication of streams
Danger 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
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

12. Other Geochemical Cycles
Sulfur
Phosphate
Iron and other metals
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

13. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Hydrologic Cycle
Water precipitates from atmosphere
Water vapor evaporates from land, ocean
Water flowing over ground picks up nutrients
Carbon, nitrogen runoff allows respiration
Respiring 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. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Wastewater Treatment
Natural treatment
Wetlands filter water
Slow water passage
Bacteria in wetland denitrify water
Municipal treatment
Reduce 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. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
Carbon is oxidized from biomass to CO2 by the process of
Respiration
Photosynthesis
Lithotrophy
Answer: A
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

17. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
Nitrification is the process by which
N2 gas is converted to NH4+
NH4+ is oxidized to NO3-
NO3- is reduced to N2O
Answer: B
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.