There is a type of bacteria named Deinococcus radiodurans (Latin for “terrific berry that withstands radiation”) that is very resistant to damage by ionizing radiation. It is known as an extremophilic bacterium meaning that it is very tough. In addition to being able to withstand radiation it can also survive dehydration, extremely low temperatures, some acids and even vacuum. This classifies it as a polyextrmophile or a bacterium that can survive a number of different things that kill most other bacteria.. Radiodurans is a specific species within the genus Deinococcus which also contains other radiation resistant species of bacteria.
”Grays” are units of measurement for the absorption of energy associated with radiation. One Gray is equivalent to the absorption of one joule of energy by one kilogram of matter. One joule is the amount of work necessary to generate one watt of electrical energy for one second. The Gray is often used to measure energy absorption by human tissue. Five to ten Grays can kill a human being. Two thousand Grays can sterilize a culture of Escherichia coli also known as E. coli which is found in human intestines and can sometimes cause food poisoning. Ten thousand Grays can kill any bacteria other than Deinococcus radiodurans.
Scientists have been studying Deinococcus radiodurans since its discovery in 1956 trying to find out how it survives huge doses of radiation. At first it was thought that they had special repair enzymes that were much more resistant to the damage that radiation causes to DNA in all living creatures. They were thought to have special repair processes that could rapidly repair radiation damage to segments of both single strand and double stranded DNA. Ongoing research has come to question this DNA repair hypothesis.
It now appears that the unique ability of radiodurans to resist radiation damage may lie in its ability minimize protein damage by radiation. While DNA damage caused by radiation seems to be very similar in all living organisms, protein damage is much more variable. The key feature of radiation resistance seems to be high concentrations of an orthophosphate complex of manganese. Cells susceptible to radiation damage suffer oxidation of their proteins which causes cell death. Radiodurans utilizes the high levels of the manganese compound to protect cellular protein against oxidation.
Researchers have been able to prepare extracts of the manganese peptide complexes from radiodurans as a vaccine. Tests have shown that cells treated with the radiodurans compound have been able to withstand doses of radiation which would kill their untreated counterparts. This vaccine approach has been used to protect mice from radiation exposure by boosting immune system functioning and defend cellular proteins. This treatment can also protect the mice against infectious bacteria and viruses. The vaccine can be easily and rapidly prepared in large batches.
Given the current concern with radiation exposure from nuclear accidents and bombs as well as the threat of bioterrorism, the development of a human vaccine from radiodurans in seen a very promising possibility.
