The Biosynthesis of Anisotropic Nanoparticles - Bionanotechnology: Global Prospects - page 182

inorganic.nanomaterials,.either.intracellularly.or.extracellularly..Some.well-known.exam-
ples.include.the.synthesis.of.magnetic.nanoparticles.by.magnetotactic.bacteria, 5 .siliceous.
materials.produced.by.diatoms, 6 .and.production.of.gypsum.and.calcium.carbonate.layers.
by.S-layer.bacteria. 7 .In.addition,.the.interactions.between.microorganisms.and.metals.have.
been.well.documented, 8 .and.the.ability.of.microorganisms.to.extract.and.accumulate.met-
als.is.already.employed.in.biotechnological.processes.such.as.bioleaching.and.bioremedia-
tion,.and.it.is.well.known.that.microorganisms.such.as.bacteria,.yeast,.and.fungi.play.an.
important.role.in.remediation.of.toxic.metals.through.reduction.of.the.metal.ions. 9
Even. though. the. biological. generation. of. anisotropic. nanoparticles. could. be. demon-
strated,.the.development.of.reliable.approaches.for.stable.production.of.nanoparticles.of.
different.materials,.and.understanding.the.detailed.mechanisms.involved.in.controlling.
the.shape.of.the.nanoparticles,.are.still.a.challenge..A.brief.overview.of.the.current.research.
on. the. use. of. biological. systems. as. biofactories. for. the. synthesis. of. metal. nanoparticles.
is.provided.in.this.chapter..The.production.of.nanoparticles.using.bacteria,.fungi,.yeast,.
actinomycetes,. and. biotemplates,. the. potential. to. manipulate. key. reaction. conditions. to.
achieve.controlled.size.and.shape.of.the.particles,.and.progress.on.gaining.a.better.under-
standing.of.the.biological.mechanisms.involved.in.the.process.will.be.reviewed.
9.2 BiosynthesisofNanoparticles
A.wealth.of.different.microbes.have.been.evaluated.for.their.ability.to.produce.anisotropic.
nanoparticles..A.brief.selection.of.some.of.these.organisms.and.the.characteristics.of.the.
particles.produced.will.be.discussed.
9.2.1 Bacterial Production of Nanomaterials
Several. bacterial. species. have. been. successfully. used. for. intracellular. and. extracellular.
synthesis.of.nanoparticles..In.early.studies,.Beveridge 10 .demonstrated.the.formation.of.gold.
particles.of.nanoscale.dimensions.inside.the.cell.walls.of. Bacillus subtilis .after.exposure.to.
Au 3+ .ions.under.ambient.temperature.and.pressure.conditions..More.recently,.the.synthe-
sis.of.gold.nanoplates.by. Rhodopseudomonas capsulata .was.demonstrated.by.He.et.al. 11 .The.
group.also.demonstrated.the.extracellular.production.of.gold.nanowires.(50-60 nm).with.
a.network.structure.after.exposure.of.cell-free.extract.of. R. capsulata .to.gold. 12 .Further.pro-
cess.developments.include.the.extracellular.synthesis.of.gold.nanoparticles.(15-30.nm).by,.
e.g.,. Pseudomonas aeroginosa , 13 .as.well.as.the.use.of.bacterial.cell.supernatant.for.the.reduc-
tion.of.gold.ions,.resulting.in.extracellular.biosynthesis.of.gold.nanoparticles. 14 .This.could.
be.an.advantage.from.a.process.point.of.view,.since.it.will.eliminate.the.complex.process.
of.harvesting.and.recovery.of.the.particles.
Although.silver.is.toxic.to.most.microorganisms,.Klaus.et.al. 15 .reported.on.a.metal-accu-
mulating.bacterium,. Pseudomonas stutzeri .AG259,.capable.of.producing.silver-based.single.
crystals.in.the.size.range.of.a.few.nanometers.up.to.200.nm..Growing.these.bacteria.in.a.
solution. of. AgNO 3 . resulted. in. the. reduction. of. the. Ag + . ions. and. the. formation. of. silver.
nanoparticles.of.well-deined.size.and.distinct.morphology.within.the.periplasmic.space.
of.the.bacteria.