(a)
(b)
200 µm
EHT = 3.00 kV
(c)
Date: 2 Dec 2010
WD = 11.0 mm
Time: 11:26:05
2 µm
EHT = 3.00 kV
Signal A = SE2
Date: 2 Dec 2010
WD = 8.3 mm
Mag = 5.00 KX
Time: 11:33:24
Figure 2.7
 
 
 
 
 
 
 
34
Bacterial Cellulose
Figure 2.7
(a). Cross. section. of. a. cellulose. tube. after. 4. days. in. culture. (magnification. ×77). (b). Cross.
s . ection.of.a.cellulose.tube.after.7.days.of.cultivation.(magnification.×130)..(c) Higher.magnification.of.the.red.ring.in.(B).(magnification.×5000).illustrating.the.change.in.density.in.the.
cellulose.network.
Density. changes. can. be. monitored. as. early. as. 2. days. after. culture,. when.
a.relatively.stable.tube.structure.has.been.formed..The.gradient.in.the.fiber.
network.can.be.monitored.by.means.of.second.harmonic.generation.(SHG).
. microscopy,. which. enables. visualization. of. spun. fibers. as. the. ordered.
arrangement. of. glucose. units. in. the. cellulose. polymer. chains. induces.
frequency-doubling.of.laser.light.illuminating.the.sample.(Brackmann.et.al..
2010;.Brown.et.al..2003)..Since.this.technique.allows.for.measurements.on.wet.
unmodified. . samples. taken. directly. from. cultivation,. it. could. be. confirmed.
that.the.arrangement.of.cellulose.into.layers.is.a.result.of.the.synthesis.process. and. not. an. artifact. of. the. subsequent. material. purification. procedure..
The SHG.image.in.Figure 2.8A,.measured.on.a.2-day-old.tube,.shows.a.dense.
cellulose. region. of. strong. SHG. signal. (light. gray. color). located. toward. the.
luminal. side. of. the. tube. (left),. whereas. less. compact. regions. of. cellulose.
(darker.gray).can.be.found.on.the.outer.side..Simultaneously.with.the.SHG.
measurements. on. the. unpurified. cellulose,. the. bacterial. distribution. in. the.
material.was.visualized.using.coherent.anti-Stokes.Raman.scattering.(CARS).
microscopy.(Cheng 2007).(Figure 2.8B)..The.profile.in.Figure 2.8B,.corresponding.to.the.cellulose.profile.of.Figure 2.8A,.shows.dense.regions.of.bacteria.in.
the.inner.regions.of.the.tube,.in.particular.the.region.of.high.cellulose.fiber.