Bioremediation of heavy metals with the help of Fe(III),Sulfate AND Sulfur reducing bacteria bacteria,environmental clean up process using geobacter and desulfuromonas species.

1. KAVYA K N
SCTCE,
PAPPANAMCODE
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2. HEAVY METALS
Metals having relatively high molecular mass or high density
Can degrade soil water and air at high concentration and
leads to health issues
Chromium , Arsenic, Cadmium, Mercury ,lead etc. are
examples
Due to industrial activity, vehicle emission ,lead acid
batteries, paints, micro plastics floating in world oceans
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3. Are heavy metals good ???
 Used for enzyme catalysis, nutrient transport, protein
structure charge neutralisation, control of osmotic pressure
 Required as micronutrient to plants
 Act as a cofactor as part of prosthetic group of enzymes
What are the ill effects caused by heavy metals???
 Birth defects, skin lesions, growth retardation, disabilities
,liver and kidney disorders and even cancer
 Causes physiological and genetical changes in various lives
such as plants ,aquatics, insects, earthworm, fishes, birds,
mammals etc
 Heavy metal in industrial areas of India is much higher the
permissible limit of WHO
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4. Conventional Methods To Remove Heavy Metals From Soil
And Water
From soil
• Land filling
• Fixation
• Leaching
From water
• Precipitation / flocculation
• Microfiltration
• Electro dialysis
• Evaporation
• Solvent extraction
• Crystallization
• Reverse osmosis
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5. The need to remediate extensive metal contamination of
groundwater and soils from heavy metals is possible using
these technique
But they are very much uneconomic and less efficient
It is necessary to find out an effective method as a solution to
this It is possible from nature itself
Its Bioremediation
 Using microbes we are finding a remedy to this heavy metal
induced problems efficiently and effectively
 Bioremediation using Fe(III) ,Sulphur and Sulphate reducing
bacteria
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6.  Why reduction?
Most heavy metals become less soluble and toxic when reduced
 What happens during reduction?
It is the addition of electrons
Removal of oxygen
Oxidation charge increase on acceptance of electron
 What happens during bioremediation process?
Metals are immobilized
They become less bio available
They become less mobile
Hence less soluble and less contaminative diffusing into soil and
water
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7. DIFFERENT MECHANISMS OF BIOREMEDIATION
 Bio sorption
 Metal microbe interaction
 Bioaccumulation
 Bio mineralisation
 Biotransformation
 Bioleaching
The mechanism by which metal ion binds to the cell surface
include electrostatic interaction, Van-der Waals force,
covalent bonding, redox interaction or a combination of the
above
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8. A wide diversity of microorganisms are able to reduce Fe(III) .
Mainly the Geobacter species
Geobacteraceae
DesulforomonasGeobacter
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9.  Geobacter
 Colonize habitats with elevated metal concentrations, in sediments,
shallow aquifers, and in deep surfaces etc
 Various phylotypes isolated from pristine and metal-contaminated
sites
 Considered a kind of natural environmental clean-up bacteria and
new tools for bioremediation processes
 Various species of Geobacter have been isolated and characterized.
 These bacteria uses molecular hydrogen, lactate ,pyruvate or
acetate as electron donor
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10. Some bacteria growth is coupled with reduction of Fe(III)
Some others growth can only be supported
In others heavy metals are lethal and toxic to bacteria
Geobacter metallireducens
 Strict anaerobic bacterium
 Able to reduce various metals such as Mn(IV) or U(VI).
 Desulfuromonas acetoxidans is the closest relative
 These bacteria transfers electrons to Fe (III) and reduces them to
Fe(II)
 Membrane bound Fe (III) reductase
 Membrane bound c type cytochrome
Another method of Fe (III) reduction is extracellular transport
of electron to Fe(II) through microbial nanowires
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11. Desulfuromonas
 Desulfuromonas, a sulphur reducing bacterium
 Anaerobic, gram negative, flagellated and rod-shaped.
 It acquires its energy from sulphur respiration and completely
oxidizes acetate with sulphur reduction to carbon dioxide via
the citric acid cycle
Reduction of S produces hydrogen sulphide (H2S) which can react
with heavy metal ions to form less toxic insoluble metal sulphides
Sulphate +organic compound 𝐻2 𝑆
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12.  Able to enzymatically reduce and precipitate these heavy
metals as metal sulphides
𝐻2 𝑆 +Heavy metals Metal sulphides(insoluble)
Examples of Desulfuromonas species are
 Desulfuromonas acetoxidans
 Desulfuromonas palmitatis
 Desulfuromonas thiophila
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13. Sulfate Reducing Bacteria
 Strict anaerobic bacteria
 Redox potential less than -200mV
 Found in sites contaminated with metals,mettalloids
and pollutants which are lethal to bacteria
 The first isolated was spirullum desulfuricans
 Couple the oxidation of organic compound /hydrogen
with reduction of sulphate as electron acceptor
 Sulfate reduction leads to hydrogen sulphide formation
 Sulfate reduction using enzymatic pathway using c type
cytochrome
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14.  Desulphovibro desulphuricans can reduce U(VI) to U(IV) which is
insoluble
 Can also reduce Cr(VI) , Mo(VI),Se (VI), Tc(VIII)
 Recent studies have demonstrated that hydrogenases and other redox
proteins with negative redox potentials (like ferredoxins) can also reduce
metals. However, hydrogenases are proteins that are usually sensitive to
oxygen and are produced in low amount by bacteria
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15.  Some bacteria develop metal tolerance to high concentration of metals
inorder to make the process more efficient various new strains is being
developed using biotechnology
 Strains are collected from various contaminated sites and evaluated
their potent activity
 Biosensors are used to find contaminated sites
 The objective of the bioremediation study using microbes is to obtain
improved biological tools in a reliable and low cost manner
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16. Bioremediation 2 main groups
1.Enzymatic metal reductase activity of bacteria(direct method)
2.Usage of 𝐻2 𝑆 to reduce metals(indirect method)
Enzymatic Metal Reductase Activity Of Bacteria(direct Method)
 Direct reduction of metals would be applied to ground water
using bioreactor and could be applied to soil after excavating,
pulping/heaping or inoculation
 These techniques are very expensive and characterised by low
metal extraction efficiencies
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17. Usage Of 𝐻2 𝑆 To Reduce Metals
• Indirect reduction concept is used with insitu zone and bio
barriers using metal reducing bacteria.
• The installation of subsurface zones where the bacterial
growth will be induced by injection of substrate could be a
low cost solution
• The migrating metals would be intercepted and immobilized
by precipitation with biologically produced 𝐻2 𝑆
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