Extremophiles Living Organisms in Extreme Conditions

This article is about a very strange extremophile bacterium called D. Radiodurans. The story of Radiodurans is old but surprisingly few have heard of it. Although in its original form it was beautifully equipped to evolve into what it evolved into, who would have thought that it would survive and thrive inside nuclear reactors?

Radiodurans was adapted to very hot, dry, conditions, and I would guess in the open exposed to UV, which has a very hammering effect, or something comparable. In order to explain, I must digress for those who never took biology.

Bacteria are prokaryotic cells, very primitive ones unlike the more advanced Eukaryotic cells of all other organisms except blue-green algae. Eukaryotic cells have a membrane-bound nucleus with DNA inside, and other specialized organelles to carry out cellular metabolism. Bacteria do not, having only a semi-circle of naked DNA inside the cell. But it does make the most of this. Bacteria often have plasmids, circular loops of DNA often called “lifesavers” because of their shape, and because they often can save the life of the cell by helping it adapt. These plasmids contain genes that can be thought of as “spare parts” for damaged DNA. Bacterial cells can actually trade plasmids. When genes from an outside source are incorporated into the main DNA this process is called recombination. Bacteria acquire antibiotic resistance in exactly this way, by obtaining genes from the plasmids of other bacteria that code for resistance to antibiotics. This form of adaptation is a necessary requirement for survival in any habitat with a lot of ionizing radiation, and Radiodurans has a lot of plasmids to repair that damage. In addition, it has the highest levels ever measured of antioxidant enzymes all living things must have to quench free radical cascades from the normal metabolic processes in the body, or from high levels of radiation. If yours were shut off, you would die in a few minutes from the propagation of radicals from your own metabolism which is what happens when a salmon spawns-the act of mating hits a biological switch that turns these enzymes off.

Since this bug always had fascinated me, I wanted to do a project with it when I took Microbiology, but I found this was impossible because of how difficult it is to maintain the extreme conditions in a lab. Getting Radiodurans is not that difficult. Those shelf dinners that have been sterilized with ionizing radiation to preserve them-they are sterile of pathogenic bacteria, but Radiodurans is so heat and radiation-resistant that if you can find some irradiated, sterilized meat from a source like this you can get some of the bacteria. But you can’t put it on agar in a petri dish and expect it to grow.

Now I don’t know much about nuclear power plants, but at least in the most primitive ones, water is pumped through a hot, radioactive core, which then emerges as superheated steam, which drives a turbine, which produces electrical power. Radiodurans can live and thrive in that water.

Because it can, I have read an occasional speculative article about bioengineering Radiodurans that can metabolize Mercury, a toxic by-product of these power plants into something less harmful, but I’ve never heard of anyone trying it.

Many extremophiles sought out extreme conditions because they thrived before Earth had an oxygen atmosphere, and oxygen is a poison-it’s just that we have evolved to breathe it. Radiodurans, on the other hand, seems to have sought out a place where it would seem that nothing could ever survive. It is but another example of the power of the “will to life” on Earth and perhaps throughout an infinite creation.