Environmental Engineering Reference
In-Depth Information
CH Hg
(CH) Hg
Hg
2+
Cd
2+
Volatilization
Cd
2+
Cd
2+
Cd
2+
Zn
2+
Zn
2
Cu
2+
Cu
2+
Cu
2+
Cd
2+
Pb
2+
Pb
2+
Pb
2+
Pb
2+
Efflux pumps
Pb
2+
Enzymatic
detoxification
Intra cellular
sequestration
Electron transport
system
(cytochrome): Cr(VI)
Reduction
Hg
2+
Hg
0
Cu
2+
Cu
0
Metal precipitation (metal binding
proteins and precipitators)
Cd
2+
Cd
S
Cd
2+
Cd
PO
Chemotaxis
(+/-ve movement by chemical
gradient)
Reduction - metal sensitive
by altering the cellular compounds
FIGURE 16.3
Microbial. mechanisms. for. metal. resistance. and. sequestration.. (Modiied. from. Gadd,. G.M.,.
Microbiology
,.156,.609,.2010.)
with.metal-binding.proteins.(Hettiarachchi.et.al..2000),.and.(3).conversion.of.
soluble.metals.in.the.medium.to.insoluble.forms.via.interaction.with.metabo-
lites.like.exopolysaccharides..In.response.to.metal.toxicity,.many.microorgan-
isms. have. developed. unique. mechanisms. of. resistance. and. detoxiication..
These.mechanisms.may.be.intracellular.or.extracellular.and.may.be.speciic.
to.a.particular.metal.or.a.general.metal.interaction.mechanism.(Figure.16.3)..
Extracellular. molecules. produced. under. metal. stress. by. microorganisms.
may. also. provide. general. resistance. to. metals.. For. example,. siderophores,.
the.iron-complexing.low-molecular-weight.organic.compounds.produced.by.
some.microorganisms.like.cyanobacteria.in.their.habitats.with.low.iron.con-
tent,.not.only.facilitate.iron.transport.into.the.cell.but.also.interact.with.other.
metals.similar.to.iron.in.chemistry,.such.as.Al,.Cr,.and.Cu..Exploration.for.
microorganisms. with. pollutant-degradative. capabilities. is.needed. for.their.
potential.application.in.remediation.of.soils.contaminated.with.mixtures.
MicrobialDegradationofOrganicPollutants
Direct Microbial Metabolism
Roane.and.Pepper.(1997).showed.that.the.metal-resistant.population.could.
protect. the. metal-sensitive. and. organic-pollutant-degrading. population.
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