Question

Endospore is resistant to radiation and antibiotic. What is the mechanism behind it？Does endospore contain LPS？

Answer 1

Endospores can survive environmental assaults that would normally kill the bacterium. These stresses include high temperature, high UV irradiation, desiccation, chemical damage and enzymatic destruction. The extraordinary resistance properties of endospores make them of particular importance because they are not readily killed by many antimicrobial treatments.

The exact reason for the high resistance of endospores towards extreme temperature, radiation and chemicals is still unknown. Several explanations are now prevailing in the scientific community to explain this. Some of the possible explanations are given below:

- The DNA of endospores is protected by small, acid-soluble proteins that bind to DNA and alter its conformation, thereby protecting it from photochemical damage.

- A unique spore photo-product is generated by UV light in endospores that functions in enzymatic repair of damaged DNA during endospore germination

Ø Endospores contain high amount of dipicolinic acid in its core (protoplast).

Ø In some endospores, about 15% of the total dry weight of the spore is contributed dipicolinic acid.

Ø The dipicolinic acid in bacterial endospore not occurs in free-state rather, it forms a complex with calcium ions (Ca2+).

Ø High concentration of calcium ions can impart resistance to wet heat and oxidizing agents.

Ø The calcium-dipicolinic acid can stabilize the genetic materials of the endospores.

Ø Large amounts of Small Acid Soluble DNA binding Proteins (SASPs) are reported to occur in the core of endospores.

Ø These proteins can bind to the DNA of endospores and can prevent the DNA from heat, radiations and chemicals.

Ø The binding of SASPs to the DNA changes the molecular structure of DNA from its normal B-form to A-form.

Ø The A-DNA is more compact than B-DNA and thus A-DNA can have higher resistance against pyrimidine dimer formation by UV radiations.

Chemical and antibiotic resistance

Many harmful chemicals kill bacteria via DNA-damaging mechanisms. However, spores have evolved a number of mechanisms that confer chemical resistance. The spore coat is important in the resistance to many oxidizing chemicals such as chlorine dioxide, hypochlorite, ozone and peroxynitrite .It functions by reacting with these chemical agents and detoxifying them before they pass through the spore coat . In addition, the inner membrane’s extremely low permeability prevents both hydrophobic and hydrophilic molecules from entering into the core .SASPs also protect the DNA by binding to it and shielding it from harmful chemical agents that enter the core .

LPS is present in endospores.

LPS is the major component of the outer membrane of Gram-negative bacteria, contributing greatly to the structural integrity of the bacteria, and protecting the membrane from certain kinds of chemical attack.