Ultraviolet Radiation Sensitivity in Cave Bacteria: Evidence of Adaptation to the Subsurface?
Snider Jessica R. | Goin Caitlin | Miller Robert V. | Boston Penelope J. | Northup Diana E.
We hypothesize that a reduced capacity to withstand or repair cellular damage from ultraviolet radiation may be present in caveadaptedmicroorganisms that never experience such conditions. However, a small number of previous studies have shown that somesubsurface bacteria do not show greater sensitivity to ultraviolet radiation (UVR) than surface bacteria. To estimate UVR sensitivity incave bacteria, bacterial isolates were collected from Carlsbad Cavern, New Mexico, U.S.A., and percent survival following exposure tovarious UVC and UVA radiation doses was determined. Cave bacteria from Left Hand Tunnel in Carlsbad Cavern and surface bacteriafrom soil and rocks above Carlsbad Cavern were grown on low and high nutrient media then exposed to 0, 10,000 and 20,000 μWs/cm2 of UVR in a laboratory biological safety cabinet. Incubations were conducted at 15°C or 37ºC, in accordance with the isolates’natural temperature environments. In addition, DNA repair capacity was estimated by exposing the organisms to various doses of UVCradiation and measuring survivability. Gram status and pigmentation also were determined. Results showed that most of the cave isolateswere more sensitive to UVR than the surface isolates, but survivability data suggest that cave microbes retain some of their capacity torepair UV-induced DNA damage. Selection appears to have favored bacteria that can survive in this low nutrient environment, whilenot maintaining (or paying the cost of maintaining) unneeded traits such as UVR resistance. Cave bacteria appear to have maintainedDNA repair capacity, most likely because of the need to repair damage to their DNA from other environmental stressors found in caves.
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