Figure 2.3
25
Effect of Cultivation on BNC Biomaterials
10% O 2
50% O 2
Cell
Division
Fibril
Branch
700 µm
200 µm
(a)
(b)
Figure 2.3
(a). The. branching. of. cellulose. formed. by. the. cell. division. of. G. xylinus.. Adapted. from.
Yamanaka.et.al..(1989)..(b).The.effect.of.oxygen.tension.on.the.branching.of.cellulose.in.the.
cellulose.. network.formed.during.cell.division..Adapted.from.Watanabe.and.Yamanaka.(1985).
produced.is.lower.than.for.cellulose.produced.in.a.static.. culture..The.decrease.
in.DP.can.be.due.to.an.increase.in.the.activity.of.endoglucanases.in.agitated.
cultures.(Czaja.et.al..2004)..Previous.studies.have.shown.that.endoglucanases.
can.have.an.effect.on.decreased.DP.in.the.long.term.(Tahara.et.al..1997a,.1997b)..
Okajima.et.al..(1991).explained.the.phenomena.of.decreased.DP.as.a.function.of.
cultivation.time.and.generation.time.of.the.bacteria,.not.an.effect.of.enzymes.
The.pH.is.also.an.important.factor.for.cellulose.production.and.should.be.controlled.and.regulated.during.cultivation.of.G. xylinus..The.pH.outside.the.bacteria.affects.the.structure.and.permeability.of.the.bacteria.cell.membrane,.which.
can.have.an.effect.on.cellulose.production.and.network.formation..Verschuren.
et.al..(2000).demonstrated.that.an.optimal.pH.for.BNC.production.is.between.
pH.4.and.5,.which.is.in.accordance.with.Noro.et.al..(2004),.who.describe.that.
pH.4.5.is.optimal.for.BNC.production..A.cultivation.pH.below.3.5.results.in.
no.production.of.cellulose.and.the.proliferation.of.the.bacteria.is.negatively.
affected.(Embuscado.et.al..1994)..However,.the.bacteria.has.been.shown.to.be.
able.to.recover.from.exposure.to.low.pH.following.8 days.in.optimal.growth.
conditions.(i.e.,.in.this.case.a.higher.pH;.pH.4–5).(Embuscado.et.al..1994).
The.cellulose.network.production.is.also.affected.by.the.production.of.watersoluble.polysaccharides.such.as.acetan.(Figure 2.4A).and.levan.(Figure 2.4B)..
Depending.on.which.carbon.substrate.is.used—glucose,.fructose,.or.sucrose—
different.amounts.of.water-soluble.polysaccharides.are.produced..No.levan.is.
produced.in.fructose-.and.glucose-based.media,.and.in.a.sucrose-based.media,.
levan. is. produced. in. a. smaller. amount. than. acetan.. The. greatest. amount. of.
water-soluble.polysaccharides.produced.has.been.observed.when.G. xylinus.is.
25
Effect of Cultivation on BNC Biomaterials
10% O 2
50% O 2
Cell
Division
Fibril
Branch
700 µm
200 µm
(a)
(b)
Figure 2.3
(a). The. branching. of. cellulose. formed. by. the. cell. division. of. G. xylinus.. Adapted. from.
Yamanaka.et.al..(1989)..(b).The.effect.of.oxygen.tension.on.the.branching.of.cellulose.in.the.
cellulose.. network.formed.during.cell.division..Adapted.from.Watanabe.and.Yamanaka.(1985).
produced.is.lower.than.for.cellulose.produced.in.a.static.. culture..The.decrease.
in.DP.can.be.due.to.an.increase.in.the.activity.of.endoglucanases.in.agitated.
cultures.(Czaja.et.al..2004)..Previous.studies.have.shown.that.endoglucanases.
can.have.an.effect.on.decreased.DP.in.the.long.term.(Tahara.et.al..1997a,.1997b)..
Okajima.et.al..(1991).explained.the.phenomena.of.decreased.DP.as.a.function.of.
cultivation.time.and.generation.time.of.the.bacteria,.not.an.effect.of.enzymes.
The.pH.is.also.an.important.factor.for.cellulose.production.and.should.be.controlled.and.regulated.during.cultivation.of.G. xylinus..The.pH.outside.the.bacteria.affects.the.structure.and.permeability.of.the.bacteria.cell.membrane,.which.
can.have.an.effect.on.cellulose.production.and.network.formation..Verschuren.
et.al..(2000).demonstrated.that.an.optimal.pH.for.BNC.production.is.between.
pH.4.and.5,.which.is.in.accordance.with.Noro.et.al..(2004),.who.describe.that.
pH.4.5.is.optimal.for.BNC.production..A.cultivation.pH.below.3.5.results.in.
no.production.of.cellulose.and.the.proliferation.of.the.bacteria.is.negatively.
affected.(Embuscado.et.al..1994)..However,.the.bacteria.has.been.shown.to.be.
able.to.recover.from.exposure.to.low.pH.following.8 days.in.optimal.growth.
conditions.(i.e.,.in.this.case.a.higher.pH;.pH.4–5).(Embuscado.et.al..1994).
The.cellulose.network.production.is.also.affected.by.the.production.of.watersoluble.polysaccharides.such.as.acetan.(Figure 2.4A).and.levan.(Figure 2.4B)..
Depending.on.which.carbon.substrate.is.used—glucose,.fructose,.or.sucrose—
different.amounts.of.water-soluble.polysaccharides.are.produced..No.levan.is.
produced.in.fructose-.and.glucose-based.media,.and.in.a.sucrose-based.media,.
levan. is. produced. in. a. smaller. amount. than. acetan.. The. greatest. amount. of.
water-soluble.polysaccharides.produced.has.been.observed.when.G. xylinus.is.