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8/7/2019 S and Fe Cycle
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biogeochemical cycles
Movement(transfer,storage,and exchange)
of material through the living and non living
component of biosphere in cyclic manner. Chemicals that circulates through
life(bio)and earth again and again.
All livng organism get matter from thebiosphere components i.e
lithosphere,hydrosphere and atmosphere
material must have been used over and over
in the for mation of new generation of
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Biogeochemical cycle
A)gaseous cycle:in this the reservoir for the
elements is in the atmosphere orhydrosphere and the biochemical used fortransformation or circulation are biotic
/abiotic components are gaseous in nature.
4 most abundant elements in the living
system H,C,N,O have predominantly gaseous
cycle.
Gaseous ccle such N AND Chave capacitu to
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b) Sedimentary cycle:material involves is non
gaseous in nature reservoir for the element in
the sediments of earth.-it involves element like
phosphrous,sulphur,potassium and calcium.
-elements like phosphrous and sulphur tend tobe easily distributed bcoz large portion of
nutrients is in inactive or immobile reservoir
in earth crust.
Slow and less prefect systems in that elements
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Sulfur Cycle
SO4-2
H2S
S
0 SO4
-2
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Global sulphur cycle
S is the tenth most abundant element in earths crust.
Essential element for biological organisms and make upapp. 1% of dry wt. of a bacterial cell.
Valence states: +6 (SO42-) to -2 (sulfides)
Original pool: Pyrite, FeS2
Cells contain sulphur in reduced or sulfide form ( incompounds like amino acids- cysteine & methionine,vitamins,hormones and coenzymes) and in oxidizedstate( glucose sulfate, choline sulfate, phenolic sulfate
and the ATP sulfate compounds).
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sulfur reservoirs
Largest reservoir in Earths crust-
Inert elemental Sulfur deposits, sulfur,metal precipitatessuch as pyrite (FeS2) and gypsum (CaSO4).
Sulfur associated with buried fossil fuels. Second large reservoir- sulfur found in ocean
2 recent practices causing disturbance in global sulphurreservoirs-
1. Strip mining causes acid mine drainage by exposinglarge area of metal sulfide ore to the atmosphere.
2. Burning of fossil fuelsSO2 emission intoatmosphereAcid Rain
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Global sulfur reservoirs
Sulfur Reservoir Metric tons sulfur Actively cycled
Atmosphere
SO2/ H2S 1.4 *106 Yes
OceanBiomass 1.5*108 Yes
Soluble inorg. ion(SO42-) 1.2*1015 Slow
Land
Living biomass 8.5*109 Yes
Organic matter 1.6*1010 Yes
Earths crust 1.8*1016 No
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Driving forces:microbial
transformation Assi ilat ry s lfat
cti a lf ri ralizati
lf r xi ati
lf r r cti R -H
S0
SO42-
S0
H2
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Assimilatory sulfate
reduction Primary soluble form of inorganic sulfur found in soil is
sulfate.
Plants and most microorganisms incorporate reduced
sulfur (sulfide) into amino acids or other sulfur requiringmolecules, they take up sulfur in oxidized sulfate formand then reduce it internally.
SO42- R- SH
Most commonly, the amino acid serine is used to removesulfide as it is reduced, forming the sulfur containingamino acid cysteine.
Occurs under aerobic or anaerobic conditions.
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Sulfur mineralization
The release of sulfur from organic forms.
Enzyme sulfhydrylase can remove sulfide from cysteine.
cysteine serine + H2S
In Marine Environment,
DMSP degradationDMS
H2S/ DMS UV SO42- H2O H2SO4
After death, bacterial decomposition of plants and animal
proteinsH2S
By fungi, actinomycetes and bacteria (heterotroph- Proteus
vulgaris)
Fossil fuels containing S compounds combustion SO2 +H2O
H2
SO3
Acid Rain
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Sulfur oxidation
Group S conversion abitatRequirements
abitat Genera
Obligate orfacultative
chemo-autotrophs
H2SS0
S0SO42-
S2O32-SO42-
H2S- O2Interface
Mud, hotsprings,
miningsurfaces, acid
minedrainage, soil
Acidithiobacillus,
Sulfobacillus,Thiomicrospira
, Beggiatoa,Thermothrix
Anaerobicphototrophs
H2SS0
S0SO42-
Anaerobic,H2S, Light
Shallowwater,
anaerobicsediments,meta orhypolimnion,
anaerobicwater
Chlorobium,Thiopedia,
Rhodopseudomonas
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Chemoautotrophic S oxidation-
Aerobic process but most sulfur oxidizers are microaerophilic.
In Aerobic neutral to alkaline soil, some heterotrophs oxidizesulfur but obtain no energy.
This process may result in formation of acid mine drainage.
This process can be used in metal recovery.
Photoautotrophic SOxidation-
It is an anaerobic process that is limited to the purple and greensulfur bacteria.
These bacteria fix C using light energy, but instead of oxidizingwater to oxygen, they use oxidation of sulfide to sulfur.
CO2 + H2SS0 + Fixed Carbon
It is responsible for a very small portion of total photosyntheticactivity.
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Sulfur reduction
S Reduction
Dissimilatoryreduction
S Respiration
Sulfatereduction
AssimilatorySulfate Redution
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Dissimilatory Pathways-Use an inorganic form of S as a terminal electron acceptor (TEA)
S0 as TEA: Desulfuromonas acetooxidans grows on small C compounds
such as acetate, ethanol and propanol.
CH3COOH + 2H2O + 4S0 2CO2 + 4S
2- + 8H+
SO42- as TEA :
Important environmental process.
Sulfate reducing bacteria are found in anaerobic sediments ofaquatic environment, water saturated soils and animal
intestines. Examples are: Desulfobacter, Desulfotomaculum, Desulfosarcina
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Use H2 as electron donor. ( 4H2 + SO42-S2- + 4H2O)
SRB obtain C from low molecular weight compounds such as
acetate or methanol.
4CH3OH + 3SO42- 4CO2 + 3S
2- + 8H2O
So, SRB are chemoheterotrophic organisms.
End product of sulfate reduction is H2
S which is responsible forcorrosion of underground metal pipes.
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Sulfur Cycle
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The global sulfur cycle depends on
the activities of metabolically and
phylogenetically diverse micro -
organisms, most of which reside inthe ocean.
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Marine sulfur cycle
Ocean is large source of aerosols (sea salts) that contains SO42-
. Most of the flux is re-deposited in the ocean in
precipitation and dry-fall
Dimethyl-sulfid (CH3)2S or DMS is the major biogenic gasesemitted from sea
annual flux is about 15
mean residence time about 1-2 days - most of S fromDMS is also re-deposited in the ocean
The net transport of S from sea to land is about 20x1012 g S/yr. Ocean
receives a net input of S.
Major marine sinks: metallic sulfides precipitated at hydroMajor marine sinks: metallic sulfides precipitated at hydro--thermalthermal
vents,vents, biogenic pyrites,biogenic pyrites, the formation of organic sulfur.
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DimethylsulfideDimethylsulfide (CH(CH33))22S orS orDMSDMS is the major one of biogenic gases emitted from seaDMS is the major one of biogenic gases emitted from sea
is produced during decomposition ofis produced during decomposition of dimethyldimethyl--sulfonpropionatesulfonpropionate
(DMSP) from dying phytoplankton(DMSP) from dying phytoplankton
mean residence time is about 1mean residence time is about 1--2 days2 days -- most of S from DMS ismost of S from DMS isalso realso re--deposited in the oceandeposited in the ocean
only small fraction lost into the atmosphereonly small fraction lost into the atmosphere
oxidation of DMS to sulfate aerosols increases the abundance ofoxidation of DMS to sulfate aerosols increases the abundance ofcloud condensation nucleicloud condensation nuclei pp to greater cloudinessto greater cloudiness
clouds over sea reflect incoming sunlightclouds over sea reflect incoming sunlightpp global coolingglobal cooling
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yrite Formation in Sediments
H2S
BACTERIA
FeS
BACTERIA
S0
BACTERIA
FeS2
PYRITE
SO42-
ORGANICMATTER
FeMINERALS
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references
Environmental Microbiology Pepper, Gerba,
Maier
Fundamentals of Microbiology - Jeffrey C.Pommerville
Internet