| The ability to survive exposure to natural UV radiation and prevent or repair DNA damage is a pre-requisite for all organisms which may be exposed to direct sunlight. The ability of UV radiation to cause DNA damage can be exploited by humans to sterilize water using powerful light systems which radiate in the UV spectrum. These UV systems are usually used to sterilize the effluent water at waste water treatment plants. We have discovered a freshwater sponge, Racekiela ryderi, which can grow in close proximity to the sterilizing lights at a waste treatment plant. The radiation from this system is sufficient to neutralize bacteria flowing past in the effluent in a continuous fashion. The sponges grow from late spring to early fall, they establish right before the lights are turned on and then grow under UV exposure. The sponge's survival is possibly due to a combination of DNA repair along with the sponge matrix acting as a sunscreen to absorb or block the UV radiation. We hypothesize that the sponge's matrix is acting as a sunscreen to protect the sponge.;We have determined, using a spectrophotometer, that the matrix absorbs a significant amount of UV radiation and confirmed, using molecular assays, that the matrix can act as a barrier to protect the interior of the sponge. The protection of the matrix is most effective towards the interior of the sponge, blocking more than 90 percent of radiation penetrating deeper than 1cm into tissue. The sponges closer to the UV source also show a lower growth rate and overall size than those further away, an indication that they are likely affected by the UV radiation. However, we were not able to show damage to the exposed sponge's DNA using molecular assays. While we were not able to test for upregulated DNA repair, it was likely occurring to repair DNA damage. Upregulation of DNA repair would be energy intensive and could account for some of the differences in growth rates. |
