SCI-TECH & AGRI

Radiation resistant bacteria

APPROPOS TO the article on the discovery of gene responsible for radiation resistance (radio resistance) of bacteria published in these pages on 20 February it appears relevant to mention a couple of points.

Radio resistance is one of the characteristics that enable some bacteria to survive in hostile environments like extreme conditions of heat, cold, pressure, radiation, salinity, dryness, oxygen tension and also to withstand toxic chemicals. These bacteria are called extremophiles.

In absence of this ability, the bacteria would have perished in most of the cases. For example, without the ability to tolerate extremely low temperature, bacteria cannot survive in the glaciers or polar regions and lack of pressure resistance would lead to the destruction of bacteria in the ocean bottom.

However significance of bacterial radio resistance cannot be defined by the same logic. The high dose of ionising radiation that is tolerated by Deinococcus radiodurans is far above the highest dose of radiation occurring anywhere on the globe.

Then what is it meant for? Scientists are not very sure about it. It is known that ionising radiation shears cellular DNA. Similar effect is exerted by some other conditions like extreme dryness. Hence it is postulated that radio resistance is an offshoot of the ability of bacteria to tolerate some other harsh environmental conditions.

The tenability of this postulation is evidenced by the fact that some radio resistant bacteria are also desiccation-tolerant. Some time back it was demonstrated that radio resistance in a bacterium was linked to its ability to tolerate low temperature.

Accumulating evidences from other sources indicate that the extremophiles share some common characteristic features, which enable them to cope with more than one adverse condition at a time.

M.K.Chattopadhyay

CCMB, Hyderabad