136
Bacterial Cellulose
nascent.cellulose.with.the.nematic.ordered.chitin.template.was.not.as.strong.
as.that.with.the.NOC.template.(Kondo.et.al..2002).
In.nematic.ordered.chitin.templates,.hydrophilic.OH.groups.at.the.C6.position.of.the.glucopyranose.ring.and.relatively.hydrophobic.acetamide.groups.
at.the.C2.position.appeared.alternately.on.the.surface.because.of.the.2 1 .screw.
axis.of.the.molecular.chain,.whereas.the.NOC.template.provides.only.OH.
groups. at. the. C6. position. on. the. surface.. The. balance. of. the. two. substituents.strongly.affects.the.strength.of.the.interaction.between.the.surface.and.
secreted. cellulose. microfibrils.. When. the. contact. with. the. chitin. template.
is.not.as.strong.as.that.for.NOC,.the.biosynthesized.individual.subelementary.fibrils.(a.few.nanometers.in.width).usually.tend.to.be.self-assembled.to.
form.a.ribbon-type.nanofiber.with.a.width.of.40–60.nm..The.situation.when.
the.bacteria.secrete.cellulose.nanofibers.cannot.be.changed.without.such.a.
strong.interaction.between.the.interfaces..Accordingly,.the.rate.of.deposition.
of.the.fibrils.on.the.nematic.ordered.chitin.template.that.corresponds.to.the.
rate.of.the.bacterial.movement.did.not.change.from.the.initial.rate.without.
the.template.(both.the.moving.rates.were.2.05.μm.±.5%.at.24°C)..In.contrast,.
when.the.interaction.was.strong.enough,.as.in.the.case.of.NOC,.the.rate.of.
movement.was.much.higher.when.compared.with.movements.on.the.templates.composed.of.chitin.
To.explain.this.phenomenon.one.needs.to.determine.the.rate-determining.
step.for.both.the.production.of.fibers.and.bacterial.movements..In.a.previous.
chapter.(Tomita.and.Kondo.2009),.it.was.assumed.to.be.the.self-assembly.process. of. biosynthesized. subelementary. fibrils. for. forming. a. cellulose. nanofiber..That.is,.the.strong.interfacial.contact.with.the.template.prevented.the.
assembly. of. the. individual. subelementary. fibrils. soon. after. . biosynthesis,.
resulting.in.an.increase.in.the.rate..This.could.also.cause.the.release.of.stress.
for.the.enzymatic.synthesis.of.cellulose..As.a.result,.the.production.of.fibers.
on.the.NOC.template.increases,.as.does.the.rate.of.bacterial.movement..In.fact,.
we.previously.found.by.FE-SEM.observations.that.the.bacterial.subelementary. fibrils. extruded. by. the. synthesizing. enzymes. could. not. self-assemble.
on.the.NOC.template.to.form.cellulose.nanofibers,.later.becoming.flattened.
by.strongly.attaching.to.the.molecular.tracks.of.OH.groups.on.the.template.
surface.. This. shows. the. prevention. of. self-assembly. of. the. subelementary.
fibrils,. and,. simultaneously,. epitaxial. nanodeposition. along. the. molecular.
track.direction.on.the.surface.of.the.template.
The.unique.patterning.of.the.biodirected.nanodeposition.process.can.be.
also.observed.by.imaging.the.deposited.cellulose.nanofibers.using.FE-SEM.
correlated.with.real-time.video.analysis.using.light.microscopy.
At. first,. light. microscopic. observations. of. the. deposited. fiber. clarified.
that. adherence. to. the. molecular. tracks. occurred. every. 13.9. μm. (standard.
deviation.±0.2.μm).as.a.mean.distance.along.the.orientation.of.the.template,.
as. shown. in. Figure 6.14.. Alternating. with. this. parallel. movement,. the. cell.
“jumped. off”. the. tracks. and. detoured. every. 7.3. μm. (standard. deviation.
±0.2.μm).until.it.became.parallel.to.neighboring.tracks,.as.also.indicated.in.
Bacterial Cellulose
nascent.cellulose.with.the.nematic.ordered.chitin.template.was.not.as.strong.
as.that.with.the.NOC.template.(Kondo.et.al..2002).
In.nematic.ordered.chitin.templates,.hydrophilic.OH.groups.at.the.C6.position.of.the.glucopyranose.ring.and.relatively.hydrophobic.acetamide.groups.
at.the.C2.position.appeared.alternately.on.the.surface.because.of.the.2 1 .screw.
axis.of.the.molecular.chain,.whereas.the.NOC.template.provides.only.OH.
groups. at. the. C6. position. on. the. surface.. The. balance. of. the. two. substituents.strongly.affects.the.strength.of.the.interaction.between.the.surface.and.
secreted. cellulose. microfibrils.. When. the. contact. with. the. chitin. template.
is.not.as.strong.as.that.for.NOC,.the.biosynthesized.individual.subelementary.fibrils.(a.few.nanometers.in.width).usually.tend.to.be.self-assembled.to.
form.a.ribbon-type.nanofiber.with.a.width.of.40–60.nm..The.situation.when.
the.bacteria.secrete.cellulose.nanofibers.cannot.be.changed.without.such.a.
strong.interaction.between.the.interfaces..Accordingly,.the.rate.of.deposition.
of.the.fibrils.on.the.nematic.ordered.chitin.template.that.corresponds.to.the.
rate.of.the.bacterial.movement.did.not.change.from.the.initial.rate.without.
the.template.(both.the.moving.rates.were.2.05.μm.±.5%.at.24°C)..In.contrast,.
when.the.interaction.was.strong.enough,.as.in.the.case.of.NOC,.the.rate.of.
movement.was.much.higher.when.compared.with.movements.on.the.templates.composed.of.chitin.
To.explain.this.phenomenon.one.needs.to.determine.the.rate-determining.
step.for.both.the.production.of.fibers.and.bacterial.movements..In.a.previous.
chapter.(Tomita.and.Kondo.2009),.it.was.assumed.to.be.the.self-assembly.process. of. biosynthesized. subelementary. fibrils. for. forming. a. cellulose. nanofiber..That.is,.the.strong.interfacial.contact.with.the.template.prevented.the.
assembly. of. the. individual. subelementary. fibrils. soon. after. . biosynthesis,.
resulting.in.an.increase.in.the.rate..This.could.also.cause.the.release.of.stress.
for.the.enzymatic.synthesis.of.cellulose..As.a.result,.the.production.of.fibers.
on.the.NOC.template.increases,.as.does.the.rate.of.bacterial.movement..In.fact,.
we.previously.found.by.FE-SEM.observations.that.the.bacterial.subelementary. fibrils. extruded. by. the. synthesizing. enzymes. could. not. self-assemble.
on.the.NOC.template.to.form.cellulose.nanofibers,.later.becoming.flattened.
by.strongly.attaching.to.the.molecular.tracks.of.OH.groups.on.the.template.
surface.. This. shows. the. prevention. of. self-assembly. of. the. subelementary.
fibrils,. and,. simultaneously,. epitaxial. nanodeposition. along. the. molecular.
track.direction.on.the.surface.of.the.template.
The.unique.patterning.of.the.biodirected.nanodeposition.process.can.be.
also.observed.by.imaging.the.deposited.cellulose.nanofibers.using.FE-SEM.
correlated.with.real-time.video.analysis.using.light.microscopy.
At. first,. light. microscopic. observations. of. the. deposited. fiber. clarified.
that. adherence. to. the. molecular. tracks. occurred. every. 13.9. μm. (standard.
deviation.±0.2.μm).as.a.mean.distance.along.the.orientation.of.the.template,.
as. shown. in. Figure 6.14.. Alternating. with. this. parallel. movement,. the. cell.
“jumped. off”. the. tracks. and. detoured. every. 7.3. μm. (standard. deviation.
±0.2.μm).until.it.became.parallel.to.neighboring.tracks,.as.also.indicated.in.