Spore Forming Bacteria
Spore-forming bacteria are those bacteria that can form spores under unfavourable conditions. Spores are the dormant form of bacteria that can tolerate all the fluctuations in the environment. Spores have the least metabolic activity. When favourable conditions arrive, these spores germinate into a new bacterium that has all the properties of the parent bacteria. The bacteria that germinate from spore can grow and start a new progeny.
Examples:
Clostridium botulinum, Bacillus anthracis
Why bacteria produce spores?
Bacteria grow moderately in favourable condition. During unfavourable conditions i.e. depletion of nutrient, high in temperature and pH and dehydration, bacteria forms spores.
Spores have the following characters:
- Non-reproductive
- Dormant
- Loss of metabolic activity
- Resistance to environmental stress
- Resistance to temperature and pH change
Composition of spore:
There are 3 major components of spore
- Spore coat
- Cortex
- Core
Spore coat:
It is a thin covering around the spore that acts as a sieve. It excludes large molecules such as lysozyme and toxins from the spore. It is composed of keratin that has the enzymes that allow the germination of spore.
Cortex:
Cortex lies beneath the coat and it mainly composed of peptidoglycan. Peptidoglycan is needed for the synthesis of the cell wall.
Core:
The core contains the bacterial DNA that is enclosed into Small acid-soluble spore protein (SASPs). SASPs help in the protection of the DNA from UV radiation and heat. They also contain ribosomes and enzymes that are metabolically inactive. Calcium dipicolinate is present in high concentration that stabilizes the DNA molecule present in spore.
Dipicolinaic acid helps the spore to resist the heat fluctuations in the environment and calcium helps the spore from oxidizing agents.
Location of spore:
Spores are present in three positions
- Some spores are present in the centre of the cell.
- Terminal spores are those that are present in the terminal of the cell.
- Some spores are present sub-terminally that are present between the two extremes of the cell.
Destruction of spore:
when favourable conditions arrive, spores germinate into bacteria which is called sporulation. A membrane between the DNA and cortex is present that is called as septum. DNA replicates and septum form between genetic material and the rest of the cell. Forespore is formed by pinching the membrane into the cell. It leaves a double membrane around the DNA. Calcium dipicolinate is present in Forespore. Spore coat is formed by the formation of peptidoglycan layer between 2 layers.
Reactivation:
When favourable conditions arrive, spores reactivate into new bacteria. Spore germination includes the following
- Metabolic activity start
- Dormancy break
- Spore coat absorbs
- Endospore swell
- Environmental resistance lost
