98
Bacterial Cellulose
2007). The.biodegradation.of.cellulose.has.been.widely.investigated.(Sannino.
et.al..2009). BNC.is.not.enzymatically.degradable.in.the.animal.and.human.
body.because.of.the.absence.of.hydrolases.that.attack.the.β(1–4).linkage;.as.
a.consequence,.biodegradability.has.become.an.essential.limiting.factor.for.
some.BNC.applications.as.a.scaffold.in.tissue.engineering.(Li.et.al..2009).
Aiming.at.the.production.of.an.in.vivo.degradable.polysaccharide,.while.
exhibiting. both. chitin-. and. cellulose-like. properties,. attempts. have. been.
made.to.incorporate.N-acetylglucosamine.(GlcNAc).residues.into.BC..Ogawa.
et. al.. (1992). characterized. the. enzymatic. susceptibility. of. BNC. containing.
N-acetylglucosamine.residues.for.cellulase,.lysozyme,.and.chitinase.hydrolysis..The.results.showed.that.modified.BNC.possesses.high.susceptibility.
for. lysozyme. (proportional. to. the. GlcNAc. content). and. cellulase,. but. only.
slight. susceptibility. for. chitinase.. The. random. distribution. of. GlcNAc. residues. on. modified. BNC. is. responsible. for. the. higher. lysozyme. reactivity. ..
This. approach. was. also. studied. by. Shirai. et. al.. (1994),. who. described. a.
G. xylinus strain.adapted.to.a.medium.containing.GlcNAc.that.was.used.to.
prepare.a.novel.cellulosic.polysaccharide.containing.residual.GlcNAc..The.
amino.sugar.content.in.the.pellicles. was.measured.after. cultivation. of.the.
bacteria.in.the.presence.of.various.ammonium.salts..Ammonium.chloride.
seems.to.be.the.best.additive.to.enhance.GlcNAc.incorporation,.under.rotatory.and.aerobic.conditions..The.maximum.amount.of.N-acetylglucosamine.
(GlcNAc).incorporation.was.found.to.be.4%.(on.a.molar.basis).and.the.resulting. . polysaccharide. was. lysozyme. susceptible.. The. acceleration. of. GlcNAc.
incorporation.in.the.presence.of.ammonium.salts.seems.to.be.due.to.a.shift.
in.the.aminotransferase.equilibrium.in.the.presence.of.a.high.concentration.
of.ammonium.ion.
The.production.of.similar.polysaccharides.was.obtained.by.incubation.of.
G. xylinus in. a. modified. Hestrin–Schramm. medium. containing. lysozymesusceptible. phosphoryl. chitin. (P-chitin). and. D-glucose. (Shirai. et. al.. 1997)..
Analysis.of.the.culture.medium.by.high-performance.liquid.chromatography.
(HPLC).showed.that.the.P-chitin.is.depolymerized.to.monomeric.and.oligomeric. residues. during. the. incubation,. and. these. were. utilized. as. a. carbon. .
source. by. the. bacteria.. Furthermore,. monomeric. GlcNAc. 6-phosphate. was.
also. found. to. enhance. the. incorporation. of. GlcNAc. residues. into. the. polysaccharide..Also,.Ciechanska.(2004).obtained.a.modified.BNC.by.adding.two.
different.chitosan.forms.(chitosan.acetate.and.chitosan.lactate).to.the.culture.
medium.during.bacterial.growth..The.authors.showed.that.glucosamine.and.
N-acetylglucosamine. units. were. incorporated. into. the. cellulose. chain. following. degradation. of. chitosan. modifiers. present. in. the. nutrient. medium.
within.the.biosynthesis.process..The.modified.BNC.obtained.presented.good.
ties..Enzymatic.degradation.assays.demonstrated.that.modified.BNC.is.susceptible. to. lysozyme. degradation.. Furthermore,. modified. BNC. possesses.
bacteriostatic. activity. against. Gram-negative. and. Gram-positive. . bacteria.
and. bactericidal. activity. against. Gram-positive. bacteria.. Lee. et. al.. (2001).
Bacterial Cellulose
2007). The.biodegradation.of.cellulose.has.been.widely.investigated.(Sannino.
et.al..2009). BNC.is.not.enzymatically.degradable.in.the.animal.and.human.
body.because.of.the.absence.of.hydrolases.that.attack.the.β(1–4).linkage;.as.
a.consequence,.biodegradability.has.become.an.essential.limiting.factor.for.
some.BNC.applications.as.a.scaffold.in.tissue.engineering.(Li.et.al..2009).
Aiming.at.the.production.of.an.in.vivo.degradable.polysaccharide,.while.
exhibiting. both. chitin-. and. cellulose-like. properties,. attempts. have. been.
made.to.incorporate.N-acetylglucosamine.(GlcNAc).residues.into.BC..Ogawa.
et. al.. (1992). characterized. the. enzymatic. susceptibility. of. BNC. containing.
N-acetylglucosamine.residues.for.cellulase,.lysozyme,.and.chitinase.hydrolysis..The.results.showed.that.modified.BNC.possesses.high.susceptibility.
for. lysozyme. (proportional. to. the. GlcNAc. content). and. cellulase,. but. only.
slight. susceptibility. for. chitinase.. The. random. distribution. of. GlcNAc. residues. on. modified. BNC. is. responsible. for. the. higher. lysozyme. reactivity. ..
This. approach. was. also. studied. by. Shirai. et. al.. (1994),. who. described. a.
G. xylinus strain.adapted.to.a.medium.containing.GlcNAc.that.was.used.to.
prepare.a.novel.cellulosic.polysaccharide.containing.residual.GlcNAc..The.
amino.sugar.content.in.the.pellicles. was.measured.after. cultivation. of.the.
bacteria.in.the.presence.of.various.ammonium.salts..Ammonium.chloride.
seems.to.be.the.best.additive.to.enhance.GlcNAc.incorporation,.under.rotatory.and.aerobic.conditions..The.maximum.amount.of.N-acetylglucosamine.
(GlcNAc).incorporation.was.found.to.be.4%.(on.a.molar.basis).and.the.resulting. . polysaccharide. was. lysozyme. susceptible.. The. acceleration. of. GlcNAc.
incorporation.in.the.presence.of.ammonium.salts.seems.to.be.due.to.a.shift.
in.the.aminotransferase.equilibrium.in.the.presence.of.a.high.concentration.
of.ammonium.ion.
The.production.of.similar.polysaccharides.was.obtained.by.incubation.of.
G. xylinus in. a. modified. Hestrin–Schramm. medium. containing. lysozymesusceptible. phosphoryl. chitin. (P-chitin). and. D-glucose. (Shirai. et. al.. 1997)..
Analysis.of.the.culture.medium.by.high-performance.liquid.chromatography.
(HPLC).showed.that.the.P-chitin.is.depolymerized.to.monomeric.and.oligomeric. residues. during. the. incubation,. and. these. were. utilized. as. a. carbon. .
source. by. the. bacteria.. Furthermore,. monomeric. GlcNAc. 6-phosphate. was.
also. found. to. enhance. the. incorporation. of. GlcNAc. residues. into. the. polysaccharide..Also,.Ciechanska.(2004).obtained.a.modified.BNC.by.adding.two.
different.chitosan.forms.(chitosan.acetate.and.chitosan.lactate).to.the.culture.
medium.during.bacterial.growth..The.authors.showed.that.glucosamine.and.
N-acetylglucosamine. units. were. incorporated. into. the. cellulose. chain. following. degradation. of. chitosan. modifiers. present. in. the. nutrient. medium.
within.the.biosynthesis.process..The.modified.BNC.obtained.presented.good.
ties..Enzymatic.degradation.assays.demonstrated.that.modified.BNC.is.susceptible. to. lysozyme. degradation.. Furthermore,. modified. BNC. possesses.
bacteriostatic. activity. against. Gram-negative. and. Gram-positive. . bacteria.
and. bactericidal. activity. against. Gram-positive. bacteria.. Lee. et. al.. (2001).