8/7/2019 ROLE OF MICRO-ORGANISMS

1/23

ROLE OF MICRO-ORGANISMS

INSULPHUR CYCLE

By

Geethu chellappan1 sem M.tech

8/7/2019 ROLE OF MICRO-ORGANISMS

2/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

3/23

RESERVOIRS OF SULPHUR

In Valence states: -2 (sulfides) to +6 (SO42-)

Sulfate -most stable

Reservoirs

Deep oceanic rocks

Sediments

Freshwater

Ice

Atmosphere

Sea

8/7/2019 ROLE OF MICRO-ORGANISMS

4/23

8/7/2019 ROLE OF MICRO-ORGANISMS

5/23

SULPHUR CYCLE

SHOWING THE ROLE OF

MICROORGANISMS

8/7/2019 ROLE OF MICRO-ORGANISMS

6/23

8/7/2019 ROLE OF MICRO-ORGANISMS

7/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

8/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

9/23

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.

8/7/2019 ROLE OF MICRO-ORGANISMS

10/23

sulphur is Released into the environment to

form H2S

Reaction

CH2SH CH3

cysteine desulfuraseCHNH2 + H2O C=O + H2S + NH3

COOH COOH

cysteine pyruvic

acid

8/7/2019 ROLE OF MICRO-ORGANISMS

11/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

12/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

13/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

14/23

8/7/2019 ROLE OF MICRO-ORGANISMS

15/23

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.

8/7/2019 ROLE OF MICRO-ORGANISMS

16/23

8/7/2019 ROLE OF MICRO-ORGANISMS

17/23

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)

8/7/2019 ROLE OF MICRO-ORGANISMS

18/23

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.

8/7/2019 ROLE OF MICRO-ORGANISMS

19/23

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.

8/7/2019 ROLE OF MICRO-ORGANISMS

20/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

21/23

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

8/7/2019 ROLE OF MICRO-ORGANISMS

22/23

8/7/2019 ROLE OF MICRO-ORGANISMS

23/23

THANK U