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Title: Environmental Microbiology 8: Nitrogen Cycle and Sulfur Cycle
Description: These notes describe the nitrogen cycle, the sulfur cycle, and the microbes involved in these cycles. This set of notes was taken from a class lecture of a 3rd year course.
Description: These notes describe the nitrogen cycle, the sulfur cycle, and the microbes involved in these cycles. This set of notes was taken from a class lecture of a 3rd year course.
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Nitrogen Cycle and Sulfur Cycle
N2 Fixation by Free-Living Bacteria
a
...
Anaerobic bacterial species: Clostridium
N2 Fixation by Symbiotic Bacteria
- Symbiosis with legume crops e
...
Gram, lentil, beans
- Symbiosis with non-legume crops: Alder tree infected with Actinomycetes Frankia sp
...
Primary soluble form of inorganic sulfur found in soil is sulfate
2
...
They take up sulfur in the oxidized sulfate form and then reduce it internally… It is called
“assimilatory sulfate reduction”
4
...
It occurs both in
aerobic and anaerobic conditions
Sulfur Oxidation
-
It is an important process in sulfur cycle
In the presence of oxygen (O2), reduced sulfur compounds can support the growth of
chemoautotrophs bacteria under aerobic conditions
Examples of bacteria
- Thiomicrospira
- Beggiatoa
- Thermatrix
- These bacteria are commonly found in hot springs, mining surfaces and soils
Photoautotrophic Bacteria:
- Chlorobium
- Thiopedia
-
Rhodopseudomonas
These bacteria oxidize sulfur under aerobic conditions
The photoautotrophic oxidation of sulfur is brought about by green and purple sulfur bacteria
These bacteria fix CO2 using light energy, but instead of oxidizing water to oxygen, they use
oxidation of sulfide to sulfates
Sulfur Reduction
It occurs in three ways:
a
...
Sulfur respiration
c
...
Terminal electron acceptor (TEA)
b
...
Dissimilatory sulfur reduction
In both the pathways, reduction of sulfur occurs under aerobic conditions
Dimethyl Sulfide (CH3)2S
Emissions from phytoplankton
Occurs over oceans
Sulfur dioxide (SO2)
Emission
- Industry example: power plants
Volcanoes
Sulfuric acid (H2SO4)
Principal uses include:
- Ore processing
- Fertilizer processing
- Oil refining
Ammonium Sulfate (NH4)2SO4
Made when ammonia reacts with H2SO4
Uses:
- Fertilizer
- Agricultural spray
- Aids for water soluble pesticides
The Forms of Sulfur
Valences
Oxidation
Reduction
Forms
-2
Lowest
Highest
Sulfides
0
Elemental sulfur
+2
Hyposulfites
+4
Sulfites
+6
Thiobacillus
Highest
Lowest
Sulfates
-
Strictly aerobic
Gram-negative
Rod shaped
Largely flagellated
Non-spore forming
Best growth at 25-35 C
Obligate autotrophs
Grow best at neutral pH
(Some spp
...
thiooxidans
S0
O2
T
...
denitrificans
S0, S2O3
NO3-
T
Title: Environmental Microbiology 8: Nitrogen Cycle and Sulfur Cycle
Description: These notes describe the nitrogen cycle, the sulfur cycle, and the microbes involved in these cycles. This set of notes was taken from a class lecture of a 3rd year course.
Description: These notes describe the nitrogen cycle, the sulfur cycle, and the microbes involved in these cycles. This set of notes was taken from a class lecture of a 3rd year course.