The blacker the better… especially in Chernobyl

ResearchBlogging.org by Piter Kehoma Boll

We all know that plants use chlorophyll and other pigments to harvest energy from light and store it in synthesized molecules, a phenomenon called photosynthesis. It’s chlorophyll that makes plants (all well as some bacteria and algae) green. This ability to create their own food via photosynthesis is what separates cyanobacteria, algae and plants from other organisms, such as animals, fungi and protozoan, as the latter are usually seen as unable to harvest energy directly from the medium.

This view is changing, however, especially for fungi.

As most organisms, fungi also have pigments, and one of the most important ones is melanin (yes, the same pigment that makes our skin, hair and eyes dark). For some time it is known that fungi living in areas with a higher incidence of solar radiation are richer in melanin than those in less illuminated areas. It happens, for example, in the black mould, Aspergillus niger, a species that attacks many vegetables, but also exists all over the world in the soil.

Aspergillus niger, the black mold, is a melaized fungus found worldwide and that seems to love ionizing radiation. Photo by wikimedia user Y_tambe.*

Aspergillus niger, the black mold, is a melaized fungus found worldwide and that seems to love ionizing radiation. Photo by wikimedia user Y_tambe.*

The simple fact that fungi exposed to higher radiation levels are darker could simply mean that they are protecting themselves using melanin from the nocive light striking them. After all, that’s what happens in animals, including humans, right?

But that’s not the case. Melanized fungi actually seem to thrive in environments with high levels of ionizing radiation (ultraviolet, x and gamma rays), which is usually seen as very dangerous to life. The walls of the damaged nuclear reactor of Chernobyl are covered in melanized fungi and they also are found living very happy on board of the Internation Space Station. Experiments showed that these melanized species of fungi seem to benefit from radiation, increasing their growth and germination.

How could this happen? Well, the only reasonable answer seems to be that melanin is acting like a photosynthetic pigment, allowing fungi to use ionizing radiation as a source of energy! And several experiments confirmed that!

Aspergillus niger growing on an onion. Image extracted from gardener.wikia.com.*

Aspergillus niger growing on an onion. Image extracted from gardener.wikia.com.*

So, the next time you see a big black mold growing somewhere, remember that it’s color is as important to it as the green is for the plants. They are really able to use melanin as plants use chlorophyll and yet they can do it using radiation that would be lethal to other lifeforms.

In the end, fungi are more similar to plants than we thought when we used to considered them to be plants too.

Too bad that we cannot use the melanin in our own skin for the same purpose…

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Reference:

Dadachova, E., & Casadevall, A. (2008). Ionizing radiation: how fungi cope, adapt, and exploit with the help of melanin Current Opinion in Microbiology, 11 (6), 525-531 DOI: 10.1016/j.mib.2008.09.013

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This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

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Filed under Ecology, Fungi

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