Environmental Engineering Reference
In-Depth Information
from. metal. toxicity.. However,. this. study. suggested. staggered. approach.
wherein.48.h.time.must.be.allowed.for.metal.detoxiication.to.occur.before.
organic. degradation. could. be. observed.. The. viability. of. the. population.
that. degrades. organic. pollutant. decreased. when. it. was. added. to. the. sys-
tem.prior.to.metal.detoxiication..There.are.two.widely.observed.processes.
for.microbial.detoxiication.of.environmental.pollutants:.(1).many.microor-
ganisms. are. capable. of. degrading. a. variety. of. organic. pollutants,. and. (2).
a. number. of. metal-resistant. microorganisms. are. known. to. detoxify. met-
als,.such.as.Cd,.Hg,.Pb,.Zn,.and.Se.(Roane.et.al..2001)..Exploring.these.two.
processes. further. by. involving. two. different. organisms. (dual. bioaugmen-
tation). or. one. organism. (metal-resistant. and. PAH-degrading). could. be. the.
viable. bioremediation. approach. for. soils. contaminated. with. both. PAHs.
and. metals.. The. dual-bioaugmentation. approach. involves. coinoculating. a.
metal-detoxifying/resistant. organism. and. an. organic-pollutant-degrading.
organism.that.cooperatively.functions.to.remediate.both.metal.and.organic.
pollutants.in.a.mixed.contaminated.system.(Roane.et.al..2001)..This.can.be.
achieved.only.by.directing.future.research.toward.isolating.and.character-
izing.specialized.microorganisms.with.abilities.of.both.metal.detoxiication.
and.degradation.of.organic.pollutant.
Pepper.et.al..(2002).reported.that.in.mixed.contaminated.soils,.cell.bioaug-
mentation.that.allows.immediate.degradation.of.the.organic.pollutant.may.
be. the. viable. technique.. The. study. of. Roane. et. al.. (2001). on. augmentation.
reported.the.potential.of.Cd-resistant.microorganisms.to.reduce.soluble.Cd.
levels.and.to.enhance.degradation.of.2,4-dichlorophenoxyacetic.acid.(2,4-D)..
Pseudomonas
. sp.. strain. H1. and.
Bacillus
. sp.. strain. H9. possessing. plasmid-
dependent.intracellular.mechanism.for.Cd.detoxiication.reduced.soluble.Cd.
levels.by.36%..Both.
Arthrobacter
.strain.D9.and.
Pseudomonas
.strain.I1.produced.
an.extracellular.polymer.layer.that.bound.and.reduced.soluble.Cd.levels.by.
22%.and.11%,.respectively..Although.none.of.the.Cd-resistant.isolates.could.
degrade.2,4-D,.results.of.dual-bioaugmentation.studies.conducted.with.both.
the.pure.cultures.in.laboratory.soil.microcosms.showed.that.each.of.the.four.
Cd-resistant.isolates.supported.complete.degradation.of.500.mg.of.2,4-D.by.
the. Cd-sensitive. 2,4-D-degrading.
Ralstonia eutropha
. JMP134.. Degradation.
occurred.in.the.presence.of.Cd.up.to.24.mg.in.pure.cultures.and.up.to.60.mg.
in.amended.soil.microcosms.
Degradation by Metal-Resistant Microorganisms
The. presence. of. multiple. contaminants. may. provide. a. more. restricted.
niche. because. microbes.must. tolerate.both. metals.and.toxic. hydrocarbons..
Consequently,.metals.and.hydrocarbons.impose.selection.pressure.for.spe-
ciic.microbial.types..These.stresses.may.cause.a.reduced.phylogenetic.diver-
sity.due.to.the.elimination.of.some.microbes.or.the.enrichment.of.particularly.
successful. ecotypes.. The. surviving. bacterial. strains. in. soils. contaminated.
with.PAHs.and.metals.for.long.term,.as.in.the.case.of.former.MGP.sites.and.
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