Fundamental Food Microbiology, Third Edition - Fuad Fathir

MICROBIAL SPORULATION AND GERMINATION 97
unfavorable conditions occur. Adenosine bistriphosphate (Abt) could be one of the
triggering compounds, as it is synthesized by sporeformers under carbon or phosphorous
depletion.
Sporulation events can be divided into about seven stages 1,2,4 (Figure 8.3):
\
1. Termination of DNA replication, alignment of chromosome in axial filament, and
formation of mesosome
2. Invagination of cell membrane near one end and completion of septum
3. Engulfment of prespore or forespore
4. Formation of germ cell wall and cortex, accumulation of Ca 2+ , and synthesis of
DPN
5. Deposition of spore coats
6. Maturation of spore: dehydration of protoplast, resistance to heat, and refractile
appearance
7. Enzymatic lysis of wall and liberation of spore
The process is reversible before Stage 3. However, once the process has entered
Stage 3, a cell is committed to sporulation. 1,2
B. Dormancy
Spores are formed in such a manner as to remain viable in unfavorable conditions.
This is achieved by increasing their resistance to extreme environments and reducing
metabolic activity to dormancy. Dehydration of the core and reduced molecular
movement have been attributed to dormancy.
In a suitable environment, the dormancy of a spore can be ended through a series
of biochemical reactions involved in spore activation, germination, outgrowth, and
growth. Some spores may need a long time before they go through the sequences
of germination, and are called superdormant spores. They are quite common in
Bacillus and Clostridium. Superdormancy is thought to be the consequence of the
inherent nature of a spore, spore injury, and environmental factors. Some spores
have stringent germination needs and do not germinate with other spores. Injured
spores need to repair their injury before they can germinate and outgrow. Some
component in the media can prevent germination of some spores. In food, superdormant
spores could cause problems. Following processing, they may not be
detected in a food by conventional testing methods. But during storage, they can
germinate and outgrow and subsequently cause spoilage of a food, or, if a pathogen,
a spore can make a food unsafe for consumption. 1,2
C. Activation
Spore activation before germination is accompanied by reorganization of macromolecules
in the spores. Spores can be activated in different ways, such as sublethal
heat treatment, radiation, high pressure treatment with oxidizing or reducing agents,
exposure to extreme pH, treatment with high pressure, and sonication. These treatments
probably accelerate the germination process by increasing the permeability
of spore structures to germinating agents for macromolecular reorganization. This