Question

Endospores. What are endospores?

When do bacteria make spores?

Briefly describe their structure and formation.

How do endospores differ from vegetative cells?

What is their relevance to humans?

Give examples of bacterial species that form endospores.

Answer 1

Definition: Endospore is a dormant, tough asexual spore produced by some gram positive bacteria and is found within the bacterial cells. This is consists of bacterial DNA, ribosomes and dipicolinic acid. It can survive without nutrient.

Bacteria form spore when they live in environmental stress like lack of nutrient, high temperature, extreme freezing etc. It is the phase in which the bacteria reduce itself by dividing its cell wall and one side of it engulfs the other side. The dormancy is possible due to the presence of a chemical in the spore known as dipicolinic acid.

Structure and formation of spore:

The arrangement of spore layer is as follows from below (inner part) to above (outer part)

1) DNA

2) chromatin like protein

3) Core wall

4) spore cortex

5) Spore coat

6) Exosporium

The spore is composed of spore coat and sometimes over the spore coat a type of thin covering is present is known as exosporium. Spore coat prevents the entry of toxic material and helps in germination due to presence of some enzymes. It is composed of keratin and some protein which makes the structure of endospore hard. Under the spore coat there is cortex consists of peptidoglycan. The core wall lies under the cortex that surrounds the protoplast. The protoplast consists of chromatin like protein in which DNA the genetic material is enclosed or present. This protects the DNA from UV radiation and heat.

Formation of endospore

The endosporium occurs during unfavorable condition of environment. In its first stage the DNA gets replicated and a membrane wall is formed between DNA and rest of the cell. The plasma membrane of cell surrounds the membrane wall and made double membrane around the DNA. and is known as forespore. In forespore dipicolinic acid is present which helps to stabilize the protein and DNA within the endospore. Next a peptidoglycan cortex is formed above the forespore and then new endospore is dehydrated and gets matured before being separated from mother cell.

Difference between endospore and vegetative cells

1) The vegetative cell is lack of small acid soluble protein and dipicolinic acid

Endospore has small acid soluble protein and dipicolinic acid

2) Vegetative cell is low resistant to heat

Endospore is high resistant to heat