31
Effect of Cultivation on BNC Biomaterials
production. in. the. mutant. strain.. This. is. probably. due. to. the. presence. of.
dTDP.rhamnose.produced.by.the.enzyme..The.enzyme.can.activate.acetan.
synthesis,.which.in.turn.reduces.the.production.of.cellulose..The.same.study.
also.demonstrated.that.the.enzyme.dTDP-4-dehydrorhamnose.3,5-epimerase.
was. absent. in. wild-type. G. xylinus.. Another. mutant. of. G. xylinus,. K3,. has.
been.shown.to.produce.a.cellulose.network.that.is.less.dense.than.the.one.
produced.by.wild-type.G. xylinus..Investigations.of.the.cellulose.produced.
by. wild-type. G. xylinus. and. the. K3. mutant. were. performed. with. nuclear.
magnetic.resonance.(NMR).and.scanning.electron.microscopy.(SEM),.demonstrating.the.same.crystalline.structure..However,.the.difference.between.
the.wild-type.G. xylinus.and.the.mutant.K3.appeared.to.be.in.their.protein.
profiles.(Nguyen.et.al..2010).
Moreover,.Nguyen.et.al..(2010).noticed.that.in.some.of.their.static.cultures,.
the.produced.cellulose.pellicle.sank.to.the.bottom.of.the.culturing.flask..After.
investigations. of. the. pellicle. with. SEM,. it. was. shown. that. the. pellicle. consisted.of.a.looser.cellulose.network.as.compared.with.wild-type.G. xylinus..
Further. investigations. with. NMR. demonstrated. that. the. cellulose. network.
produced.was.cellulose.I,.which.is.the.same.type.of.cellulose.that.is.produced.
by.wild-type.G. xylinus.(Nguyen.et.al..2010).
G. xylinus.can.be.cultivated.in.static,.agitated,.or.aerated.conditions,.and.
different.strains.of.the.bacteria.are.used.depending.on.the.cultivation.conditions.. The. G. xylinus. strain. is. prone. to. spontaneously. mutate,. whereas. the.
special.strain.NQ5.of.G. xylinus.has.a.more.stable.genome.and.is.therefore.
often. preferable. in. agitated. and. aerated. bioreactors. (Brown. and. Lin. 1990;.
Saxena.et.al..1990).
As.described.earlier,.there.are.differences.between.the.wild-type.G. xylinus.
and. mutants. of. G. xylinus.. In. order. to. get. a. better. understanding. of. the.
. bacteria. and. its. cellulose. production. these. mutants. need. to. be. studied. in.
more.detail,.since.the.mutants.can.give.important.information.on.regulatory.
mechanisms.followed.by.changes.in.their.environment..Even.if.spontaneous.
mutations. easily. occur. in. G. xylinus,. natural. changes. in. their. metabolism,.
due.to.changes.in.the.environment.of.the.bacteria,.can.also.be.a.reason.for.
changing.the.appearance.of.the.produced.cellulose.
Production of Artificial Blood Vessels by
G. xylinus in Bioreactors
Synthetic. grafts. used. today,. such. as. polyester. (Dacron). and. ePTFE,. induce.
thrombosis.and.therefore.are.not.suitable.for.the.replacement.of.smaller.blood.
vessels.with.a.diameter.of.less.than.6.mm.(Nerem.and.Seliktar.2001)..Research.
into.new.novel.materials.is.thus.needed..Nanocellulose.produced.by.a.microorganism.can.be.used.as.a.biomaterial.in.surgical.applications,.such.as.tissue.