28
Bacterial Cellulose
BNC.production.rate.has.been.found.(Naritomi.et.al..1998)..This.phenomenon.
is.probably.due.to.the.activity.of.fructokinase.being.enhanced.by.ATP.and.
the. fact. that. ATP. inhibits. the. enzyme. glucose-6-phosphate. dehydro. genase.
(Figure 2.5)..This.enzyme.is.a.key.enzyme.that.shuffles.glucose-6-phosphate.
into.the.pentose.phosphate.pathway.(Kornmann.et.al..2003).
ethanol
The. oxidation. of. ethanol. has. the. potential. to. produce. extra. energy. for. the.
. bacteria.in.a.similar.way.as.lactate.(Figure 2.5)..However,.the.effect.of.adding.
ethanol. to. the. growth. medium. is. not. as. great. as. for. the. addition. of. lactate,.
which. probably. depends. on. the. fact. that. the. oxidation. of. ethanol. produces.
higher.levels.of.acetate..A.high.concentration.of.acetate.has.a.negative.effect.
on.the.bacteria,.which.is.also.true.for.acetic.acid.bacteria..The.ethanol.must.be.
completely.oxidized.before.the.oxidation.of.acetate.can.start.and.an.increase.
in.biomass.can.be.observed..The.conclusion.is.that.ethanol.can.increase.BNC.
production.via.higher.energy.production,.but.not.as.efficiently.as.lactate.due.to.
the.delay.of.biomass.production.(Kornmann.et.al..2003;.Matsuoka.et.al..1996).
Carbon Substrate
The.concentration.of.the.carbon.source.has.also.been.shown.to.affect.the.rate.
of. cellulose. synthesis,. and. when. the. substrate. concentration. increases,. the.
utilization.of.the.substrate.decreases..Therefore.an.optimal.level.of.substrate.
is.needed.to.obtain.high,.consistent.cellulose.production.throughout.the.cultivation.(Embuscado.et.al..1994)..Regardless.of.the.carbon.source.used,.there.
are. two. different. main. phases. according. to.Kornmann.et.al.. (2003).. In. the.
first. phase,. biomass. is. produced. and. acetate. oxidation. occurs.. The. second.
phase.begins.when.all.the.acetate.is.oxidized.and.only.sugar.is.assimilated.
(Kornmann.et.al..2003).
Corn Steep Liquor
Corn. steep. liquor. (CSL). can. be. used. as. a. component. of. complex. microbial.growth.media..CSL.contains.different.amino.acids.where.methionine.
is.the.essential.one.(Matsuoka.et.al..1996)..Methionine.stimulates.growth.
of.the.bacteria.during.the.early.stages.of.cultivation.and.also.reduces.the.
lag. time.. An. addition. of. different. amino. acids,. including. methionine,. to.
the. culture. medium. has. been. shown. to. induce. an. increase. in. cellulose.
production..The.same.increase.in.cellulose.production.has.been.observed.
when.only.methionine.is.added.to.the.medium,.clearly.demonstrating.that.
methionine.is.an.important.component.of.CSL..Methionine.increases.biomass.production.during.the.early.stages.of.cultivation,.which.in.turn.has.
a. positive. effect. on. BNC. production. (Matsuoka. et. al.. 1996).. Amino. acids.
together.with.ammonium.in.CSL.account.for.more.than.95%.of.the.total.