So who or what is the toughest of them all?
A really good contender for the title of the toughest life form on earth is not a human at all, but a bacterium. It is Deinococcus radiodurans, a bacterium that can survive extreme cold, acid, vacuum, and dehydration. As if this wasn’t enough, it can also survive a huge amount of radiation. According to Wikipedia:
D. radiodurans is capable of withstanding an acute dose of 5,000 Gy (500,000 rad) of ionizing radiation with almost no loss of viability, and an acute dose of 15,000 Gy with 37% viability. A dose of 5,000 Gy is estimated to introduce several hundred double-strand breaks (DSBs) into the organism’s DNA (~0.005 DSB/Gy/Mbp (haploid genome)). For comparison, a chest X-ray or Apollo mission involves about 1 mGy, 5 Gy can kill a human, 200-800 Gy will kill E. coli, and over 4,000 Gy will kill the radiation-resistant tardigrade.
That is pretty freaking amazing. No wonder deinococcus radiodurans is called a “polyextremophile”. All humans could go extinct due to a nuclear holocaust, and this little bacterium would survive. Its ability to survive extreme radiation is due to a very robust DNA self-repair mechanism. This ability makes it useful in bioremediation:
Deinococcus has been genetically engineered for use in bioremediation to consume and digest solvents and heavy metals, even in a highly radioactive site. For example, the bacterial mercuric reductasegene has been cloned from Escherichia coli into Deinococcus to detoxify the ionicmercury residue frequently found in radioactive waste generated from nuclear weapons manufacture. Those researchers developed a strain of Deinococcus that could detoxify both mercury and toluene in mixed radioactive wastes.
It’s great to know that it is possible to decontaminate even some of the most dangerously polluted sites in the world, thanks to this powerful bacteria.