Microbial Sporulation and Germination ◾ 95
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 components 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
it’s a pathogen, a spore can make a food unsafe for consumption. 2,3
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, highpressure 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 process is reversible, that is, a spore does not have to germinate after activation if the
environment is not suitable. 2,3
Germination
Several structural and functional events occur during germination. Once the germination process
starts, the dormant stage is irreversibly terminated. Structural changes involve hydration of core,
excretion of Ca 2
+
and DPN, and loss of resistance and refractile property. Functional changes
include initiation of metabolic activity, activation of specific proteases and cortex-lytic enzymes,
and release of cortex-lytic products. Generally, germination is a metabolically degradative process.
Germination can be initiated (triggered) by low pH, high temperature, high pressure, lysozyme, nutrients (amino acids, carbohydrates), calcium-DPN, and other factors. The process can be
inhibited by d-alanine, ethanol, EDTA, NaCl (high concentrations), NO 2 , and sorbate. 2,3
Outgrowth
Outgrowth constitutes the biosynthetic and repair processes between the periods following germination of a spore and before the growth of a vegetative cell. The events during this phase include
swelling of the spore as a result of hydration and nutrient uptake; repair and synthesis of RNA,
proteins, and materials for the membrane and cell wall; dissolution of coats; cell elongation; and
DNA replication. The factors that can enhance the process include favorable nutrients, pH, and
temperature. With the termination of the outgrowth stage, vegetative cells emerge from spores
and enter the vegetative cell cycle of growth by binary fission. 2,3,6
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 components 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
it’s a pathogen, a spore can make a food unsafe for consumption. 2,3
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, highpressure 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 process is reversible, that is, a spore does not have to germinate after activation if the
environment is not suitable. 2,3
Germination
Several structural and functional events occur during germination. Once the germination process
starts, the dormant stage is irreversibly terminated. Structural changes involve hydration of core,
excretion of Ca 2
+
and DPN, and loss of resistance and refractile property. Functional changes
include initiation of metabolic activity, activation of specific proteases and cortex-lytic enzymes,
and release of cortex-lytic products. Generally, germination is a metabolically degradative process.
Germination can be initiated (triggered) by low pH, high temperature, high pressure, lysozyme, nutrients (amino acids, carbohydrates), calcium-DPN, and other factors. The process can be
inhibited by d-alanine, ethanol, EDTA, NaCl (high concentrations), NO 2 , and sorbate. 2,3
Outgrowth
Outgrowth constitutes the biosynthetic and repair processes between the periods following germination of a spore and before the growth of a vegetative cell. The events during this phase include
swelling of the spore as a result of hydration and nutrient uptake; repair and synthesis of RNA,
proteins, and materials for the membrane and cell wall; dissolution of coats; cell elongation; and
DNA replication. The factors that can enhance the process include favorable nutrients, pH, and
temperature. With the termination of the outgrowth stage, vegetative cells emerge from spores
and enter the vegetative cell cycle of growth by binary fission. 2,3,6