3
Biosynthesis of Bacterial Cellulose
cellulose.biosynthesis.in.these.bacteria,.in.general.they.have.not.contributed.
much.toward.understanding.the.general.mechanism.of.cellulose.biosynthesis..One.of.the.reasons.is.that.it.is.not.known.whether.a.majority.of.these.
bacteria.produce.cellulose,.if.any.at.all,.while.others.that.do.produce.cellulose.do.it.in.very.small.amounts..However,.cellulose.biosynthesis.has.been.
studied.in.Escherichia coli.and.Salmonella.to.a.considerable.extent,.as.cellulose.
is.a.component.of.the.biofilm.in.many.strains.of.these.bacteria,.and.many.of.
these.studies.have.provided.details.of.the.genes.and.proteins.involved.in.the.
turnover. of. c-di-GMP,. the. activator. of. the. polymerizing. enzyme. cellulose.
synthase.(Römling.2007).
Gluconacetobacter xylinus is a Unique
Cellulose-Producing Bacterium
G. xylinus.is.a.Gram-negative,.α-proteobacteria.that.is.grouped.with.the.. acetic.
acid.bacteria..Known.as.Acetobacter xylinum.for.many.years,.this.bacterium.
has.undergone.name.changes.in.the.last.few.years,.so.much.so.that.the.common. laboratory. strain. ATCC. 23769,. a. strain. with. a. completely. sequenced.
genome,.is.now.classified.as.Gluconacetobacter hansenii.(Iyer.et.al..2010).
G. xylinus.is.found.in.nature.on.rotting.fruits.and.a.variety.of.niches.that.
have.fixed.carbon.in.the.form.of.sugars.or.alcohol..It.is.a.strict.aerobe,.and.
so.in.many.cases.it.is.present.at.the.air–medium.interface.where.its.presence.
can.be.detected.readily.if.it.produces.a.cellulose.film.or.pellicle..The production.of.cellulose.characterizes.this.bacterium.both.in.liquid.medium,.where.it.
produces.a.thick.pellicle.on.the.air–liquid.interface,.and.isolated.cells.where.
a. cellulose. ribbon. can. be. clearly. seen. attached. to. the. long. side. of. the. cell..
G. xylinus.is.a.rod-shaped.bacterium.without.a.flagellum,.and.although.it.is.
nonmotile,.cell.movement.can.be.observed.microscopically.in.some.strains.
during.the.formation.of.the.cellulose.ribbon.
In. shaking. cultures. of. G. xylinus,. cellulose. is. produced. as. spherical. or.
star-shaped. structures. in. place. of. the. matlike. pellicle. that. is. produced. in.
stationary.cultures..In.addition,.the.amount.of.cellulose.produced.in.shaking.
cultures.is.less.than.what.is.produced.in.stationary.cultures..Another.feature.
observed. in. shaking. cultures. is. the. presence,. at. a. much. higher. . frequency,.
of.cells.that.do.not.produce.a.cellulose.pellicle.(Valla.et.al..2009)..The.presence.of.these.cells.in.large.numbers.makes.the.culture.medium.turbid..These.
cells. produce. smooth. colonies. on. agar. plates. compared. to. rough. colonies.
that. are. produced. by. cells. that. form. a. pellicle. in. stationary. cultures.. The.
smooth. colony–producing. cells. have. commonly. been. referred. to. as. spontaneous. Cel − . mutants,. although. analysis. of. many. of. these. spontaneous.
mutants.has.revealed.that.they.produce.relatively.small.amounts.of.cellulose.
II.and.have.almost.wild-type.cellulose.synthase.activity.(Roberts.et.al..1989)..
Biosynthesis of Bacterial Cellulose
cellulose.biosynthesis.in.these.bacteria,.in.general.they.have.not.contributed.
much.toward.understanding.the.general.mechanism.of.cellulose.biosynthesis..One.of.the.reasons.is.that.it.is.not.known.whether.a.majority.of.these.
bacteria.produce.cellulose,.if.any.at.all,.while.others.that.do.produce.cellulose.do.it.in.very.small.amounts..However,.cellulose.biosynthesis.has.been.
studied.in.Escherichia coli.and.Salmonella.to.a.considerable.extent,.as.cellulose.
is.a.component.of.the.biofilm.in.many.strains.of.these.bacteria,.and.many.of.
these.studies.have.provided.details.of.the.genes.and.proteins.involved.in.the.
turnover. of. c-di-GMP,. the. activator. of. the. polymerizing. enzyme. cellulose.
synthase.(Römling.2007).
Gluconacetobacter xylinus is a Unique
Cellulose-Producing Bacterium
G. xylinus.is.a.Gram-negative,.α-proteobacteria.that.is.grouped.with.the.. acetic.
acid.bacteria..Known.as.Acetobacter xylinum.for.many.years,.this.bacterium.
has.undergone.name.changes.in.the.last.few.years,.so.much.so.that.the.common. laboratory. strain. ATCC. 23769,. a. strain. with. a. completely. sequenced.
genome,.is.now.classified.as.Gluconacetobacter hansenii.(Iyer.et.al..2010).
G. xylinus.is.found.in.nature.on.rotting.fruits.and.a.variety.of.niches.that.
have.fixed.carbon.in.the.form.of.sugars.or.alcohol..It.is.a.strict.aerobe,.and.
so.in.many.cases.it.is.present.at.the.air–medium.interface.where.its.presence.
can.be.detected.readily.if.it.produces.a.cellulose.film.or.pellicle..The production.of.cellulose.characterizes.this.bacterium.both.in.liquid.medium,.where.it.
produces.a.thick.pellicle.on.the.air–liquid.interface,.and.isolated.cells.where.
a. cellulose. ribbon. can. be. clearly. seen. attached. to. the. long. side. of. the. cell..
G. xylinus.is.a.rod-shaped.bacterium.without.a.flagellum,.and.although.it.is.
nonmotile,.cell.movement.can.be.observed.microscopically.in.some.strains.
during.the.formation.of.the.cellulose.ribbon.
In. shaking. cultures. of. G. xylinus,. cellulose. is. produced. as. spherical. or.
star-shaped. structures. in. place. of. the. matlike. pellicle. that. is. produced. in.
stationary.cultures..In.addition,.the.amount.of.cellulose.produced.in.shaking.
cultures.is.less.than.what.is.produced.in.stationary.cultures..Another.feature.
observed. in. shaking. cultures. is. the. presence,. at. a. much. higher. . frequency,.
of.cells.that.do.not.produce.a.cellulose.pellicle.(Valla.et.al..2009)..The.presence.of.these.cells.in.large.numbers.makes.the.culture.medium.turbid..These.
cells. produce. smooth. colonies. on. agar. plates. compared. to. rough. colonies.
that. are. produced. by. cells. that. form. a. pellicle. in. stationary. cultures.. The.
smooth. colony–producing. cells. have. commonly. been. referred. to. as. spontaneous. Cel − . mutants,. although. analysis. of. many. of. these. spontaneous.
mutants.has.revealed.that.they.produce.relatively.small.amounts.of.cellulose.
II.and.have.almost.wild-type.cellulose.synthase.activity.(Roberts.et.al..1989)..