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Had a random thought. I was wondering if a uranium deposits underwater could result in radiotrophic plants or bacteria to sustain an ecosystem.

One issue with this, is radiation has very short attenuation lengths in water. So it is questionable if the plants or creatures could remain the correct distance from the radiation to subsist.

There's also the question whether such uranium deposits would be in the open ocean to provide their radiation, and whether the theoretical life would have everything it needs near a uranium deposit.

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    $\begingroup$ See Desulforudis audaxviator, bacterium that only thrive on uranium mine deposit and nothing else. $\endgroup$ – user6760 Oct 26 '16 at 4:50
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Yes; but only in groundwater, not in the ocean

There does exist a bacteria in the division Firmicutes that uses uranium and water to generate its own energy chemotrophically. This is slightly deceptive, the bacteria don't actually use the Uranium, they rely on radiation from Uranium decay to produce hydrogen gas from decomposition of water. The bacteria then use the hydrogen gasses and dissolved sulfates to generate energy.

These bacteria are found in rock formations with sufficient Uranium content and groundwater. Unfortunately, Uranium has a concentration of 0.0033 ppm in the ocean, presumably as dissolved Uranium salts. As such, they would be very hard to concentrate through any natural process, and thus the concentration would just be too low to provide enough energy for similar bacteria.

Ocean floors are mostly made from tholeiitic basalt which erupts in mid ocean ridges and is conveyed outwards to continental margins where it is subducted under continental plates. Basalt in general, and mid-ocean ridge basalt in general has an exceptionally low concentration of uranium (see section 2.1 here). So does the mantle in general, with respect to the 'black smokers' that allow chemotrophic sulfur based ecosystems. Thus you are unlikely to find sufficient concentrated uranium ores underwater. So these bacteria would have to stick with groundwater near concentrated uranium ores to get sufficient energy.

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  • $\begingroup$ That would be the uranium concentration in normal sea water at 3.5% salinity. In this case, I was taking about a large uranium deposit on the sea floor or in walls of rock. I'm not sure if it is geologically possible for uranium to be found in such places, and it may dissolve over many years if it was. $\endgroup$ – J. Doe Oct 26 '16 at 13:57
  • $\begingroup$ @J.Doe I edited my answers. Basically Uranium is much more common in continental granites than in ocean basalts, so you are unlikely to get a good uranium concentration on the sea floor. $\endgroup$ – kingledion Oct 26 '16 at 14:48
  • $\begingroup$ Great answer! Ground water does sometimes filter slowly into the ocean, though I'm not sure at what depth (but I'd think it would only be the shallower waters). It's possible you could get enough uranium charged bacteria from that to start up an ecosystem near the continent. If I can't get a large uranium deposit near the deep ocean, I may have to look into radioactive artifacts similar to uranium which sit on the sea floor. $\endgroup$ – J. Doe Oct 26 '16 at 21:00
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    $\begingroup$ @J.Doe The North Atlantic does have a series of ~200 lb uranium deposits in artifacts. $\endgroup$ – kingledion Oct 26 '16 at 22:17
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Radiation is detrimental to DNA, as it will induce mutations. Though some bacteria on Earth have developed radiation-resistant DNA-repairing enzymes.
See: https://en.wikipedia.org/wiki/Deinococcus_radiodurans

But, Radiotrophic fungus exists: https://en.wikipedia.org/wiki/Radiotrophic_fungus With a combination of melanin, photosynthesis, and chemosynthesis, they convert gamma radiation to chemical energy.

Furthermore, High energy radiation gets absorbed by water fairly quickly. If the deposit is large enough to sustain a nuclear reaction, you would have a heated zone that would be more favorable to other lifeforms too, like a geothermal vent.
See: https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

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Perhaps creatures would only need to 'feed' from deposits according to something like an circadian rhythm. Also, you could have certain creatures that sift/dig for deposits and maybe hold them orally or in some specialized organ - which could prove useful as a defense mechanism in some situations.

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