RESOLVING THE HIGH-RESOLUTION ARCHITECTURE, ASSEMBLY AND FUNCTIONAL REPERTOIRE OF BACTERIAL SYSTEMS BY IN VITRO ATOMIC FORCE MICROSCOPY - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 83

(a) (e)

(b) (f)

(c) (g)

(d)

Figure 4.8. Disintegration of the spore coat rodlet layer. (a) The intact rodlet layer
covering the outer coat of dormant B . atrophaeus spores is ~11 nm thick and has a
periodicity of ~8 nm. 6 (b -d) Series of AFM height images tracking the initial changes
of the rodlet layer after (b) 13 min., (c) 113 min., and (d) 295 min. of exposure to
germination solution. Small etched pits (indicated with arrows in (b) evolve into
issures, indicated with an arrow in (c), perpendicular to the rodlet direction.
The issures expand both in length and width. (e, f ) AFM images showing another
germinating spore. The spore long axis, as well as major rodlet orientation is left-
right. Enhanced etching at stacking faults running from left to centre and indicated
with an arrow in (e), as well as increased etching at the perpendicular gaps were
visible following (e) 135 min. and (f ) 240 min. of germination. Fissure width and
length increased from 10-15 nm and 100-200 nm (135 min.) to 15 -30 nm and
125-250 nm (240 min.), respectively. (g) Etching and/or fracture of the rodlet
layer at a stacking fault revealed the underlying hexagonal layer of particles with a
10-13 nm lattice period. Images reproduced with permission from Ref. 7 © (2007)
National Academy of Sciences, U.S.A.

localized at the etch pits and either recognize their structural features or the
etch pits are predisposed to structural deformation during early stages of
spore coat disassembly. The gradual elongation of the issures suggests that
once hydrolysis is initiated at an etch pit, processive hydrolysis propagates
perpendicular to the rodlet direction and to neighbouring rodlets.
The locations of the small etch pits may coincide with point defects in the
rodlet structure. These point defects could be caused by misoriented rodlet
monomers or by the incorporation of impurities into the crystalline structure.
In both cases, point defects could facilitate access of degradative enzymes to
their substrate in an otherwise tightly packed structure.