Cellulose
CS
Glucose
ATP
UDPG1c
GK
UGP
ADP
PGM
G6PDH
Glc1P
Glc6P
PGA
(NAD, NADP)
Pentose
FK
PGI
phosphate
cycle
Krebs
Fructose
Fru6P
Gluconeocycle
ATP
ADP
genesis
PTS
FBP
1PFK
Fru1P
FrubiP
Figure 2.2
22
Bacterial Cellulose
Bacterial Cellulose Production: A Part of the
Carbon Metabolism in G. xylinus
The. production. of. BNC. in. G. xylinus. is. a. part. of. its. carbon. metabolism.
(Figure 2.2).. Depending. on. the. main. carbon. source. used. in. the. growth.
media,.different.initial.pathways.toward.the.central.metabolites,.x.and.y,.are.
used.. The. initial. pathways. for. fructose. and. glucose. are. separate,. but. both.
lead.to.the.central.carbon.metabolite.glucose-6-phosphate.(Figure 2.2).
G. xylinus can.use.carbon.sources.such.as.manitol,.glycerol,.sucrose,.and.
galactose,.in.addition.to.glucose.and.fructose.(Mikkelsen.et.al..2009)..When.
G. xylinus is.cultivated.in.glucose-.or.sucrose-based.media,.2-.and.5-ketogluconate. .acids.are.produced.by.the.conversion.of.glucose.into.gluconate.by.the.
enzyme.glucose.oxidase..The.production.of.ketogluconate.acids.lowers.the.
yield.of.BNC.produced.and.contributes.to.a.decrease.in.pH..De Wulf.et.al..
(1996).demonstrated.that.G. xylinus.mutants,.restricted.in.ketogluconic.acids.
synthesis,.are.able.to.produce.more.BNC.compared.to.wild-type.G. xylinus..
Figure 2.2
Illustration. of. the. carbon. metabolism. in. G. xylinus.. Figure. adapted. from. Ross. et. al.. (1991)..
CS:. . cellulose. synthase;. FBP:. fructose-1,6-biphosphate. phosphatase;. FK:. glucokinase;. G6PDH:.
isomerase;.PGM:.phosphoglucomutase;.PTS:.system.of.phosphotransferases;.UGP:.pyrophosphorylase.UDPGlc;.Fru-bi-P:.fructose-1,6-bi-phosphatase;.Fru-6-P:.fructose-6-phosphate;.Glc-6(1)-P:.
glucose-6(1)phosphate;.PGA:.phosphogluconic.acid;.UDPGlc:.uridine.diphosphoglucose.
CS
Glucose
ATP
UDPG1c
GK
UGP
ADP
PGM
G6PDH
Glc1P
Glc6P
PGA
(NAD, NADP)
Pentose
FK
PGI
phosphate
cycle
Krebs
Fructose
Fru6P
Gluconeocycle
ATP
ADP
genesis
PTS
FBP
1PFK
Fru1P
FrubiP
Figure 2.2
22
Bacterial Cellulose
Bacterial Cellulose Production: A Part of the
Carbon Metabolism in G. xylinus
The. production. of. BNC. in. G. xylinus. is. a. part. of. its. carbon. metabolism.
(Figure 2.2).. Depending. on. the. main. carbon. source. used. in. the. growth.
media,.different.initial.pathways.toward.the.central.metabolites,.x.and.y,.are.
used.. The. initial. pathways. for. fructose. and. glucose. are. separate,. but. both.
lead.to.the.central.carbon.metabolite.glucose-6-phosphate.(Figure 2.2).
G. xylinus can.use.carbon.sources.such.as.manitol,.glycerol,.sucrose,.and.
galactose,.in.addition.to.glucose.and.fructose.(Mikkelsen.et.al..2009)..When.
G. xylinus is.cultivated.in.glucose-.or.sucrose-based.media,.2-.and.5-ketogluconate. .acids.are.produced.by.the.conversion.of.glucose.into.gluconate.by.the.
enzyme.glucose.oxidase..The.production.of.ketogluconate.acids.lowers.the.
yield.of.BNC.produced.and.contributes.to.a.decrease.in.pH..De Wulf.et.al..
(1996).demonstrated.that.G. xylinus.mutants,.restricted.in.ketogluconic.acids.
synthesis,.are.able.to.produce.more.BNC.compared.to.wild-type.G. xylinus..
Figure 2.2
Illustration. of. the. carbon. metabolism. in. G. xylinus.. Figure. adapted. from. Ross. et. al.. (1991)..
CS:. . cellulose. synthase;. FBP:. fructose-1,6-biphosphate. phosphatase;. FK:. glucokinase;. G6PDH:.
isomerase;.PGM:.phosphoglucomutase;.PTS:.system.of.phosphotransferases;.UGP:.pyrophosphorylase.UDPGlc;.Fru-bi-P:.fructose-1,6-bi-phosphatase;.Fru-6-P:.fructose-6-phosphate;.Glc-6(1)-P:.
glucose-6(1)phosphate;.PGA:.phosphogluconic.acid;.UDPGlc:.uridine.diphosphoglucose.