2
Bacterial Cellulose
complex. and. the. organization. of. these. complexes. in. the. bacterial.
. envelope. determines. the. nature. of. the. cellulose. product.. Interestingly,.
cellulose. production. has. not. been. demonstrated. for. a. majority. of. the.
bacteria.where.genes.for.cellulose.biosynthesis.have.been.identified,.but.
with.better.assays.it.may.be.possible.to.determine.cellulose.production.
in.these.bacteria.and.discuss.its.evolutionary.significance.
Introduction
The.polysaccharide.cellulose.is.considered.to.be.the.most.abundant.biomacromolecule,.and.one.that.is.produced.by.almost.all.groups.of.living.organisms..
In.nature,.it.is.produced.in.large.amounts.by.plants.and.algae,.where.it.is.
an. essential. component. of. the. cell. walls.. It. provides. not. only. mechanical.
strength.to.the.cell.wall.surrounding.the.cells.of.these.organisms,.but also.
contributes. to. the. direction. of. cell. growth.. In. most. other. organisms. it. is.
secreted.as.an.extracellular.product,.but.it.is.not.part.of.the.cell.envelope.and.
so.does.not.contribute.to.any.known.function.in.the.synthesizing.cells.
Cellulose.is.composed.of.β-1,4-glucan.chains.that.assemble.to.form.crystalline.and.noncrystalline.forms.depending.on.how.the.chains.are.assembled..
The.structure.of.cellulose.produced.by.living.cells.is.intimately.linked.to.its.
synthesis,.and.the.organization.and.arrangement.of.cellulose-synthesizing.
sites.on.the.cell.membrane.are.vital.to.the.parallel.assembly.of.glucan.chains.
observed. in. the. cellulose. I. allomorph. found. in. nature. (Brown. 1996).. Even.
though. crystalline. cellulose. I. is,. in. general,. the. form. of. cellulose. that. is.
assembled. by. living. cells,. the. more. stable. form. of. cellulose. is. cellulose. II,.
in. which. the. glucan. chains. are. assembled. in. an. antiparallel. arrangement..
This.form.of.cellulose.is.not.commonly.synthesized.by.cells.and.is.mostly.
obtained.by.chemical.treatment.of.native.cellulose.I.
Studies. on. the. structure,. synthesis,. and. applications. of. cellulose. have.
mostly. focused. on. plants,. as. they. are. the. main. producers. of. cellulose.. At.
the.same.time,.significant.knowledge.of.cellulose.synthesis.has.come.from.
. studies. of. bacteria,. and. bacterial. nanocellulose. (BNC). has. found. unique.
applications. in. various. industries.. Much. of. the. discussion. in. this. chapter.
will. refer. to. cellulose. synthesis. in. the. bacterium. Gluconacetobacter xylinus.
for. reasons—the. amount. and. form. of. cellulose. produced,. visualization.
of. . cellulose-synthesizing. sites,. and. identification. of. genes. and. proteins.
involved.in.cellulose.synthesis—that.make.this.bacterium.a.unique.organism. for. understanding. the. mechanism. of. biosynthesis. of. cellulose.. In. the.
last. few. years,. interest. in. cellulose. biosynthesis. in. other. bacteria. has. also.
increased,.mainly.because.of.the.identification.of.genes.for.cellulose.biosynthesis.from.genome.sequencing.of.these.bacteria..Although.many.of.these.
studies.have.provided.interesting.insights.into.the.organization.of.genes.for.
Bacterial Cellulose
complex. and. the. organization. of. these. complexes. in. the. bacterial.
. envelope. determines. the. nature. of. the. cellulose. product.. Interestingly,.
cellulose. production. has. not. been. demonstrated. for. a. majority. of. the.
bacteria.where.genes.for.cellulose.biosynthesis.have.been.identified,.but.
with.better.assays.it.may.be.possible.to.determine.cellulose.production.
in.these.bacteria.and.discuss.its.evolutionary.significance.
Introduction
The.polysaccharide.cellulose.is.considered.to.be.the.most.abundant.biomacromolecule,.and.one.that.is.produced.by.almost.all.groups.of.living.organisms..
In.nature,.it.is.produced.in.large.amounts.by.plants.and.algae,.where.it.is.
an. essential. component. of. the. cell. walls.. It. provides. not. only. mechanical.
strength.to.the.cell.wall.surrounding.the.cells.of.these.organisms,.but also.
contributes. to. the. direction. of. cell. growth.. In. most. other. organisms. it. is.
secreted.as.an.extracellular.product,.but.it.is.not.part.of.the.cell.envelope.and.
so.does.not.contribute.to.any.known.function.in.the.synthesizing.cells.
Cellulose.is.composed.of.β-1,4-glucan.chains.that.assemble.to.form.crystalline.and.noncrystalline.forms.depending.on.how.the.chains.are.assembled..
The.structure.of.cellulose.produced.by.living.cells.is.intimately.linked.to.its.
synthesis,.and.the.organization.and.arrangement.of.cellulose-synthesizing.
sites.on.the.cell.membrane.are.vital.to.the.parallel.assembly.of.glucan.chains.
observed. in. the. cellulose. I. allomorph. found. in. nature. (Brown. 1996).. Even.
though. crystalline. cellulose. I. is,. in. general,. the. form. of. cellulose. that. is.
assembled. by. living. cells,. the. more. stable. form. of. cellulose. is. cellulose. II,.
in. which. the. glucan. chains. are. assembled. in. an. antiparallel. arrangement..
This.form.of.cellulose.is.not.commonly.synthesized.by.cells.and.is.mostly.
obtained.by.chemical.treatment.of.native.cellulose.I.
Studies. on. the. structure,. synthesis,. and. applications. of. cellulose. have.
mostly. focused. on. plants,. as. they. are. the. main. producers. of. cellulose.. At.
the.same.time,.significant.knowledge.of.cellulose.synthesis.has.come.from.
. studies. of. bacteria,. and. bacterial. nanocellulose. (BNC). has. found. unique.
applications. in. various. industries.. Much. of. the. discussion. in. this. chapter.
will. refer. to. cellulose. synthesis. in. the. bacterium. Gluconacetobacter xylinus.
for. reasons—the. amount. and. form. of. cellulose. produced,. visualization.
of. . cellulose-synthesizing. sites,. and. identification. of. genes. and. proteins.
involved.in.cellulose.synthesis—that.make.this.bacterium.a.unique.organism. for. understanding. the. mechanism. of. biosynthesis. of. cellulose.. In. the.
last. few. years,. interest. in. cellulose. biosynthesis. in. other. bacteria. has. also.
increased,.mainly.because.of.the.identification.of.genes.for.cellulose.biosynthesis.from.genome.sequencing.of.these.bacteria..Although.many.of.these.
studies.have.provided.interesting.insights.into.the.organization.of.genes.for.