Biology Reference
In-Depth Information
4.2 PROBING THE STRUCTURAL DYNAMICS OF SINGLE
GERMINATING SPORES
Upon exposure to favourable conditions, metabolically dormant
Bacillus
and
Clostridium
spores break dormancy through the process of germination 49-51
and eventually reenter the vegetative mode of replication. A comprehensive
understanding of the mechanisms controlling spore germination is of
fundamental importance both for practical applications related to the
prevention of a wide range of diseases by spore-forming bacteria as well as
for fundamental studies of cell development.
Germination involves an ordered sequence of chemical, biosynthetic
and genetic events. 49-51 Spore coat structure regulates the permeation of
germinant molecules. 51 However, while signiicant progress has been made
in understanding the biochemical and genetic bases for the germination
process, 49 the role of the spore coat in the germination remains unclear. 49-51
We have utilized 7,8 in vitro
AFM methods for molecular-scale examination
of spore coat and germ cell wall dynamics during spore germination and
outgrowth.
4.2.1 Germinaon-Induced Spore Coat Disassembly
To obtain a comprehensive understanding of the role of the spore coat in
germination, AFM imaging on a nanometre scale is required. At this scale,
the outer layer of the
B. atrophaeus
spore coat is composed of a crystalline
rodlet
array ( Fig. 4.8a,b ; Fig. 4.3a,b ) containing a small number of point and
planar (stacking fault) defects. 6 Upon exposure to the germination solution,
disassembly of the rodlet structures was observed. 7 During the initial stages of
germination, the disassembly was initiated through the formation of 2-3 nm
wide micro etch pits in the rodlet layer ( Fig. 4.8b ) . Subsequently, the etch pits
formed issures ( Fig. 4.8b-d ) that were, in all cases, oriented perpendicular
to the rodlet direction. Simultaneously, etching commenced on the stacking
faults ( Fig. 4.8e-f ) , revealing an underlying hexagonal inner spore coat layer
( Fig. 4.8g ) . During later stages of germination, further disintegration of the
rodlet layer ( Fig. 4.8e-f ) proceeded by coalescence of existing issures, by
their autonomous elongation and widening and by continued formation of
new issures.
Currently, it is unclear what causes this breakdown of the rodlet layer.
We have proposed 7 that rodlet structure degradation is caused by speciic
hydrolytic enzyme(s), located within the spore integument and activated
during the early stages of germination. The highly directional rodlet
disassembly process suggests that coat-degrading enzymes could be
 
Search WWH ::




Custom Search