World’s Toughest Bacterium

lake-vida, extreme enviironment

Source: national geographic 2003

What are “extreme environmental conditions”? Most people would consider the harsh environment on Antarctica rather extreme or perhaps the first thing that comes to mind are the chilly nights and hot days in the Sahara. But as a microbiologist you know better. Microbes are everywhere and will find a way to survive even the most extreme conditions.

Some bacteria thrive in battery acid, some grow in lakes so salty that you could use the water for brining. Others grow in water so hot, that it would be boiling if it weren’t for the extreme high pressure at the ocean floor. Yet another is able to use pure electricity as a food source when nothing else is around. These extremophiles love to be outcasts and tend to be difficult to culture in standard laboratory (optimal) conditions.

But there is 1 organism that is ranked the toughest

But there is 1 organism that is ranked the toughest; Deinococcus radiodurans. D. radiodurans can withstand radiation levels over a 1000 times higher than the amount that would eradicate a human being. Discovered during experiments with gamma radiation to sterilize food in 1956 by Arthur W. Anderson. Since its discovery Deinococcus radiodurans has been studied to understand this remarkable capability.

Deinococcus radiodurans is a rather large, spherical bacterium, with a diameter of 1.5 to 3.5 nanometer. Four cells normally stick together, forming a tetrad. The bacteria can easily be cultured and are not known to cause disease. D. radiodurans lives among us as it is often found in habitats rich in organic materials, such as soil, feces, meat, or sewage, but has also been isolated from dried foods, room dust, medical instruments and textiles.

Research has primarily been focussed on D. radiodurans ability to repair major DNA damage, mechanisms that perhaps contain a blueprint for life itself.

Why?

But there is another question that comes to mind when studying this remarkable organism; Why? Why did  D. radiodurans evolve to be so radiation resistant, keeping in mind that radiation of this magnitude has only existed on earth less than 100 years, a fraction in time. In the previously mentioned cases of salt-, temperature- and acid-tolerant bacteria it makes sense. Those environments have existed for million years on earth.

Although not fully understood, it has been discovered that  D. radiodurans is not only resistant to high levels of radiation, but also to desiccation (dehydration) and UV light. In fact the response of  D. radiodurans when exposed to high radiation levels is the same as when the organism is completely depleted of water. Researchers believe that in fact  D. radiodurans evolved to be desiccation tolerant and for this used a mechanism that also rendered it radiation tolerant as a side effect.