Transcript Justus von Leibig (1803

Week 4 Lectures
November 2001
Microbial Ecology and
Geochemical Cycles
This Week’s Lecture

Microbial Ecology

Importance of Oxic/Anoxic Environment

Geochemical Cycles

Applications
Microbial Ecology

Understand the biodiversity of
microorganisms and how different
metabolically diverse organisms interact

Monitor the activities of microorganisms
and their impact on ecosystems
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
Guilds and Communities
Community 1
 Photic zone


algae
cyanobacter
Community 2: Oxic Zone

Oxic
Anoxic
Sediments

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
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
Oxygen Relationships in Lake Ecosystems
Oxic
Anoxic
Sediments
{
Epilimnion: oxygen concentration relatively
uniform and may be as higher as near
saturation
{
{
Thermocline: zone of sharp temperature
gradient that separates the epilimnion and
hypolimnion
Hypolimnion: zone of unmixed water
having low oxygen content
Dissolved Oxygen mg/L
Oxygen Relationships in Surface Waters
(Streams and Rivers)
Wastewater Discharge
Low Dissolved Oxygen
Distance Downstream
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
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
Interrelationship Between Moisture
Content and Oxygenation in Soils

Soils that retain
water tend to be
more
susceptible to
anaerobic
conditions

Clays and silts
Distance, mm
Microenvironments
Using Soil as an Example
Distance, mm
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
Carbon
Geochemical
Cycle
Nitrogen Geochemical Cycle
Sulfur Geochemical Cycle
Coupling of Sulfur and Carbon
Cycles: Concrete Corrosion
S=
SO4 + H+
acid
Aerobic sulfur oxidation
in crown where
condensation occurs
Aerobic
atmosphere
sewage with organics
H 2S
H 2S
anaerobic sulfate reduction
SO4
S=
Summary by Example: Pipe Corrosion

organics in sewage are used as energy
source to convert SO4 to S= by sulfate
reducers (chemoorganoheterotrophs)

S= in equilibrium with dissolved H2S

Dissolved H2S in equilibrium with
gaseous H2S
Example Continued


Gaseous H2S dissolves into condensate
at crown of sewer pipe and is used as
energy source by sulfide oxidizers
(chemolithoautotrophs)
As H2S metabolized, acid is produced
which dissolves concrete crown causing
pipe to collapse
Coupling of Carbon and Mercury
Cycles: Mercury Cycling
oxidized in
atmosphere
Coupling of Sulfur and Iron Cycles:
Acid Mine Drainage




Significant problem in areas where coal
has been mined
What happens?
Why does it only happen after mining is
started?
Where does the yellow and reddish
stain in contaminated streams come
from?
Acid Mine Drainage: Sulfur
Oxidation and the Propogation
Cycle for Iron
Most coal contains some pyrite
Pyrite has the formula of FeS2
When exposed to oxygen,
pyrite undergoes the
following slow spontaneous
reaction which may be also
biologically catalyzed
FeS2 + 3 O2 + H2O  Fe3+ + 2 S042- +
2H+
Acid Mine Drainage: Now what
happens?
FeS2 + 3 O2 + H2O  Fe2+ + 2 S042- +
2H+
Under acidic conditions, ferrous iron (Fe2+) is then
oxidized biologically to ferric iron (Fe3+) . This
reaction does not proceed without the presence of
iron oxidizing bacteria because ferrous iron is stable
under acidic pH
Fe2+ + O2 + H+  Fe3+ +
H2O
Generation of more acid and reduced
iron
Ferric iron produced by iron oxidizing bacteria reacts with
more pyrite to form more reduced iron to accelerate the
cycle and increase acidity
FeS2 + 14 Fe3+ + H2O  15 Fe2+ + 2 S042- + 16H+
Putting it All Together
Slow spontaneous reaction that initiates process
FeS2 + 3 O2 + H2O  Fe2+ + 2 S042- +
2H+
Fe2+ +
H2O
O2 +
H+

Fe3+
+
Fe2+
Not much
O2
energy so iron
oxidizing
organisms
Fe3+
oxidize large
amounts of iron
FeS2
FeS2 + 14 Fe3+ + H2O  15 Fe2+ + 2 S042- + 16H+
note production of large
amounts of reduced iron and
acid
Answers to Questions



When does it start?
Stains?
Jarosite [HFe3(SO4)2(OH)6]