S and Fe Cycle

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

S and Fe Cycle

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