Week 4 Lectures November 2001

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Week 4 LecturesNovember 2001
Microbial Ecology and Geochemical Cycles
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This Weeks Lecture

• Microbial Ecology
• Importance of Oxic/Anoxic Environment
• Geochemical Cycles
• Applications

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Microbial Ecology

• Understand the biodiversity of microorganisms and
  how different metabolically diverse organisms
  interact
• Monitor the activities of microorganisms and
  their impact on ecosystems

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Important Terms

• Environment everything surrounding microorganism
  including the physical, biological, and chemical
  factors that act on the organism
• Populations of individual microbial species
• Guilds are metabolically related populations
• The microbial community is made up of guilds

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Guilds and Communities

• Community 1
• Photic zone
• algae
• cyanobacter

• Community 2 Oxic Zone
• Chemoorganoheterotrophs
• Chemolithoautotrophs
• Guild 1 nitrifiers
• Guild 2 sulfur oxidizing bacteria

• Community 3 Anoxic Zone
• Chemoorganoheterotrophs
• Guild 3 denitrifiers
• Guild 4 sulfate reducers
• Guild 5 fermenters
• Chemolithoautotrophs
• Guild 6 methanogens
• Guild 7 sulfate reducers

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Microbial Habitats and the Oxic/Anoxic Interface

• Oxygen clearly plays an important role in
  determining the range of microbial mediated
  reactions that occur in any environment
• It is important to understand the relationships
  between these two environments and the factors
  that lead to the formation of both

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Oxygen Relationships in Lake Ecosystems
Epilimnion oxygen concentration relatively
uniform and may be as higher as near saturation

Oxic

Thermocline zone of sharp temperature gradient
that separates the epilimnion and hypolimnion

Hypolimnion zone of unmixed water having low
oxygen content
Anoxic
Sediments
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Oxygen Relationships in Surface Waters (Streams
and Rivers)
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Oxygen Relationships in Groundwater

• Groundwater constituents that consume oxygen
  include
• dissolved organic carbon (plant exudates, etc.
• methane
• inorganics
• reduced nitrogen
• reduced iron
• Typically oxygen concentrations decrease with
  travel distance

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Terrestrial Ecosystems
O horizon layer of undecomposed plant material
A horizon surface soil high in organic matter
and high microbial activity
B horizon subsoil minerals and humus leached
from A horizon accumulate, little organic matter
C horizon soil base with low microbial activity
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Interrelationship Between Moisture Content and
Oxygenation in Soils

• Soils that retain water tend to be more
  susceptible to anaerobic conditions
• Clays and silts

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Microenvironments Using Soil as an Example
Distance, mm
Distance, mm
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Geochemical Cycles

• oxidation/reduction reactions that describe the
  changes in an element as it passes through an
  ecosystem
• geochemical cycles then are of interest for
  elements that undergo oxidation/reduction
  reactions (C, S, N, Fe, and others)
• as shown before, oxygen plays a key role in
  metabolic reactions and is a major consideration
  in the description of geochemical cycles

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Carbon Geochemical Cycle
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Nitrogen Geochemical Cycle
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Sulfur Geochemical Cycle