role of micro-organisms
TRANSCRIPT
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ROLE OF MICRO-ORGANISMS
INSULPHUR CYCLE
By
Geethu chellappan1 sem M.tech
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SULPHUR
It is an essential element for life
Sulphur makes up about 1% of the dry
weight of organisms as
Constituents of protein (primarily the S-
containing amino acids, cysteine and
methionine), in coenzymes (e.g.,
coenzyme A, biotin, thiamine),in the formof iron-sulfur clusters in metalloproteins,
and in bridging ligands
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RESERVOIRS OF SULPHUR
In Valence states: -2 (sulfides) to +6 (SO42-)
Sulfate -most stable
Reservoirs
Deep oceanic rocks
Sediments
Freshwater
Ice
Atmosphere
Sea
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SULPHUR CYCLE
SHOWING THE ROLE OF
MICROORGANISMS
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Sulphur enters the atmosphere as H2S
and SO2by combustion of fossil fuels,
volcanic eruptions ,by decompostion oforganic materials and from surface of
oceans
H2S also oxidies into SO2 by certain
phtoplanktons this SO2 is carried back toearth as H2SO4 in rain water
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Oxidation of sulphur
Sulphur (elemental form )cannot beutilized by plants or animals
Oxidation of sulphur to sulphates is done
by the bacterial genus Thiobacillus, thegenus Thiomicrospira, and the genus
Sulfolobus
Example Thiobacillus thiooxidans Reaction
2S+2H2O+3O2 2H2SO4
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Assimilative Sulfate Reduction
(Desulfuration) The sulfate is reduced to organic groupsby plants animals , fungi and variousprokaryotes. It occurs anaerobically as
well as aerobically Degradtion of protiens liberates aminoacids some of which contain sulphur
This sulphur is released from aminoacids
by enzymatic activity of manyheterotrophic bacteria
Example Proteus vulgaris.
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sulphur is Released into the environment to
form H2S
Reaction
CH2SH CH3
cysteine desulfuraseCHNH2 + H2O C=O + H2S + NH3
COOH COOH
cysteine pyruvic
acid
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Reduction of Sulfate into Sulfide
Sulphates also be reduced to hydrogen
sulphide by soil microorganism
Example genera Desulfovibrio andDesulfotomaculum
Reaction
4H2+CaSO4 H2S + Ca(OH2) + 2H2O
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Oxidization of H2
S Hydrogen sulphide resulting from sulphate
reduction and aminoacid decompostion isoxidized to elemental sulphur by
photosynthetic sulphur bacteria example Chromatium and chlorobium
Reaction
lightCO2 +2H2S (CH2O)x + H2O + 2S
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Marine sulphur cycle
Oceans in the form of dissolved sulfate
and sedimentary minerals
Weathering and leaching of rocks and
sediments are its main sources to theocean.
Dimethyl-sulfid (CH3)2S or DMS is the
major biogenic gases emitted from sea
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Photic Zone
Assimilatory uptake of sulfate by phytoplankton(both eukaryotic algae and prokaryoticcyanobacteria)
Most is assimilated into methionine and
cysteine. Methionine is converted by some phytoplankton
into dimethylsulfoniopropionate (DMSP) ahighly stable and soluble form of reduced sulfur.
DMSP synthesis by marine photoautotrophsaccounts for about 50 x 1012moles of sulfur peryear.
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Some phytoplankton that produce DMSP have
enzymesDMSP-lyase, that cleave DMSP into
Dimethylsulfide (CHDimethylsulfide (CH33))22S (S (DMS)and acrylic acid
prymesiophytes ,dinoflagellates and bloom
forming taxa e.g. Emiliania, and Alexandrium
Because of Demethylation pathway that doesnot produce DMS, Bacteria from diverse
lineages produce DMS in limited amounts
Instead, this pathway results in formation of
methiolpropionate and, subsequently,methanethiol(CH3SH; MeSH)
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DMS emissions from the surface ocean to theatmosphere range from 0.5 to 1.0x1012molesper year
Once it is transferred to the atmosphere thegaseous DMS is oxidized to tropospheric sulfateaerosols and these particulate aerosols act ascloud condensation nuclei (CCN), attractingmolecules of water. Water vapor condenses onthese CCN particles, forming the water dropletsthat make up clouds.
Clouds affect the Earths radiation balance andthereby greatly influence its temperature andclimate.
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continental margin sediments
As soon as organic material settles on the
seafloor, oxygen is rapidly exhausted and
sulfate is used as an electron acceptor by
sulfate-reducing prokaryotes (SRP) to
oxidize organic material
As a result of this anaerobic respiration,
large amounts of foul-smelling sulfide areproduced.
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Some of the energy in the original organic
matter is conserved in the sulfide, and it
can be released by a special group ofbacteria
The large, vacuolated sulfur bacteria of the
genera Beggiatoa, Thioploca, and
Thiomargarita can oxidize sulphide even
when oxygen is absent by using nitrate as
eletron acceptor
They can play an important role inphosphorous cycling
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Deep-Sea Hydrothermal Vents
They are highly productive ecosystems At deep-sea hydrothermal vents, sulfate
precipitates out of seawater as anhydrite(CaSO4) at temperatures above 150C
H2S is produced geothermally within theoceanic crust as a result of rock-sea waterinteractions at high temperatures
The H2S contained in the ensuing reduced
hydrothermal fluids is utilized in energy-yieldingreactions by free-living and symbiotic sulfur-oxidizing microbes
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THANK U