14
Bacterial Cellulose
studying.cellulose.biosynthesis,.for.the.reasons.mentioned.earlier,.and.until.
the.1990s.only.a.few.other.bacteria.were.known.to.produce.cellulose.(Ross.
et al..1991)..In.this.group.of.other.bacteria,.cellulose.production.was.analyzed.
in.some.detail.in.Agrobacterium tumefaciens,.where.cellulose.was.suggested.
to. play. a. role. in. the. infection. of. plants. (Matthysse. 1983).. However,. soon.
after.the.identification.of.the.gene.for.cellulose.synthase.and.other.genes.in.
the. bacterial. cellulose-synthesizing. operon. in. G. xylinus,. these. genes. were.
identified. in. other. bacteria,. suggesting. that. these. bacteria. have. the. potential.to.synthesize.cellulose..Interestingly,.one.of.the.first.organisms.in.which.
these.genes.were.identified.through.analysis.of.the.partial.genome.sequence.
was.E. coli.(Sofia.et.al..1994)..We.were.not.completely.surprised.by.this.discovery,. as. we. had. detected. c-di-GMP-activated. in. vitro. cellulose. synthase.
activity. in. permeabilized. cells. and. crude. membrane. fraction. from. certain.
strains. of. E. coli. (Saxena. and. Brown. 2002). even. before. cellulose. synthesis.
was.. demonstrated.in.this.bacterium.(Zogaj.et.al..2001)..Although.genes.for.
. cellulose. synthesis. were. identified. in. A. tumefaciens. by. complementation.
of. Cel − mutants. (Matthysse. et. al.. 1995),. in. most. other. bacteria. these. genes.
have. been. identified. from. analysis. of. the. genome. sequences. (Nobles. and.
Brown.2007;.Römling.2007;.Valla.et.al..2009)..Using.the.BcsA.sequence.from.
G. xylinus,. and. the. homologous. sequences. from. A. tumefaciens. and. Nostoc,.
as.the.query.in.a.BLAST.search,.homologous.sequences.were.identified.in.
cyanobacteria,. Firmicutes,. Planctomycetes,. Aquificae,. and. proteobacteria.
belonging.to.the.α,.β,.γ,.and.δ.subdivisions.(Valla.et.al..2009)..The.presence.
of. the. cellulose. synthase. sequence. in. all. these. groups. suggests. that. this.
sequence.likely.predates.the.divergence.of.these.groups.(Nobles.and.Brown.
2007)..Although.it.has.not.been.possible.to.study.the.evolution.of.cellulose.
synthesis. in. bacteria. using. the. cellulose. synthase. sequences,. relationships.
between. different. bacteria. have. been. established. by. analyzing. the. organization. of. genes. for. cellulose. synthesis. and. grouping. them. into. four. gene.
c . lusters.(Nobles.and.Brown.2007)..Group.I.gene.clusters.are.present.in.the.
α,. β,. and. γ. subdivisions. of. proteobacteria,. and. this. cluster. represents. the.
organization. of. cellulose-synthesizing. genes. associated. with. the. cellulose.
synthase.gene.that.is.observed.in.G. xylinus.and.E. coli.(Figure 1.1).
Even. as. the. ability. to. synthesize. cellulose. is. being. recognized. in. many.
more.bacterial.species.based.on.genome.sequences,.identification.of.cellulose-.
producing. bacteria. from. natural. habitats. should. be. pursued. more. vigorously.. An. example. of. this. endeavor. is. the. identification. of. Asaia bogorensis .
as. a. novel. cellulose. producer. (Kumagai. et. al.. 2011).. This. bacterium. produces. a. pellicle. with. ultrafine. cellulose. fibers. and. has. an. organization. of.
genes. for. cellulose. synthesis. that. is. similar. to. that. observed. in. G. xylinus,.
albeit.with.a.yhjQ.gene.upstream.of.the.bcsAB.gene..Although.the.amount.
of. cellulose. . produced. by. this. bacterium. is. less. than. what. is. produced. by.
strains.of.G. xylinus,.it.is.much.more.than.what.is.known.to.be.produced.by.
the.other.cellulose-producing.bacteria,.and.so.not.only.does.this.bacterium.
offer.a.new.system.to.study.cellulose.biosynthesis,.it.is.also.a.source.of.BNC.
Bacterial Cellulose
studying.cellulose.biosynthesis,.for.the.reasons.mentioned.earlier,.and.until.
the.1990s.only.a.few.other.bacteria.were.known.to.produce.cellulose.(Ross.
et al..1991)..In.this.group.of.other.bacteria,.cellulose.production.was.analyzed.
in.some.detail.in.Agrobacterium tumefaciens,.where.cellulose.was.suggested.
to. play. a. role. in. the. infection. of. plants. (Matthysse. 1983).. However,. soon.
after.the.identification.of.the.gene.for.cellulose.synthase.and.other.genes.in.
the. bacterial. cellulose-synthesizing. operon. in. G. xylinus,. these. genes. were.
identified. in. other. bacteria,. suggesting. that. these. bacteria. have. the. potential.to.synthesize.cellulose..Interestingly,.one.of.the.first.organisms.in.which.
these.genes.were.identified.through.analysis.of.the.partial.genome.sequence.
was.E. coli.(Sofia.et.al..1994)..We.were.not.completely.surprised.by.this.discovery,. as. we. had. detected. c-di-GMP-activated. in. vitro. cellulose. synthase.
activity. in. permeabilized. cells. and. crude. membrane. fraction. from. certain.
strains. of. E. coli. (Saxena. and. Brown. 2002). even. before. cellulose. synthesis.
was.. demonstrated.in.this.bacterium.(Zogaj.et.al..2001)..Although.genes.for.
. cellulose. synthesis. were. identified. in. A. tumefaciens. by. complementation.
of. Cel − mutants. (Matthysse. et. al.. 1995),. in. most. other. bacteria. these. genes.
have. been. identified. from. analysis. of. the. genome. sequences. (Nobles. and.
Brown.2007;.Römling.2007;.Valla.et.al..2009)..Using.the.BcsA.sequence.from.
G. xylinus,. and. the. homologous. sequences. from. A. tumefaciens. and. Nostoc,.
as.the.query.in.a.BLAST.search,.homologous.sequences.were.identified.in.
cyanobacteria,. Firmicutes,. Planctomycetes,. Aquificae,. and. proteobacteria.
belonging.to.the.α,.β,.γ,.and.δ.subdivisions.(Valla.et.al..2009)..The.presence.
of. the. cellulose. synthase. sequence. in. all. these. groups. suggests. that. this.
sequence.likely.predates.the.divergence.of.these.groups.(Nobles.and.Brown.
2007)..Although.it.has.not.been.possible.to.study.the.evolution.of.cellulose.
synthesis. in. bacteria. using. the. cellulose. synthase. sequences,. relationships.
between. different. bacteria. have. been. established. by. analyzing. the. organization. of. genes. for. cellulose. synthesis. and. grouping. them. into. four. gene.
c . lusters.(Nobles.and.Brown.2007)..Group.I.gene.clusters.are.present.in.the.
α,. β,. and. γ. subdivisions. of. proteobacteria,. and. this. cluster. represents. the.
organization. of. cellulose-synthesizing. genes. associated. with. the. cellulose.
synthase.gene.that.is.observed.in.G. xylinus.and.E. coli.(Figure 1.1).
Even. as. the. ability. to. synthesize. cellulose. is. being. recognized. in. many.
more.bacterial.species.based.on.genome.sequences,.identification.of.cellulose-.
producing. bacteria. from. natural. habitats. should. be. pursued. more. vigorously.. An. example. of. this. endeavor. is. the. identification. of. Asaia bogorensis .
as. a. novel. cellulose. producer. (Kumagai. et. al.. 2011).. This. bacterium. produces. a. pellicle. with. ultrafine. cellulose. fibers. and. has. an. organization. of.
genes. for. cellulose. synthesis. that. is. similar. to. that. observed. in. G. xylinus,.
albeit.with.a.yhjQ.gene.upstream.of.the.bcsAB.gene..Although.the.amount.
of. cellulose. . produced. by. this. bacterium. is. less. than. what. is. produced. by.
strains.of.G. xylinus,.it.is.much.more.than.what.is.known.to.be.produced.by.
the.other.cellulose-producing.bacteria,.and.so.not.only.does.this.bacterium.
offer.a.new.system.to.study.cellulose.biosynthesis,.it.is.also.a.source.of.BNC.