DNA repair capacity of Great Salt Plain cyanobacterium Aphanothece sp. SP24.

摘要

Scope and Method of Study. Cyanobacteria at the Great Salt Plains (GSP) are constantly exposed to the severe conditions of high salinity, extreme temperatures, and direct UV radiation that cause damage to the organisms' DNA and must be repaired for survival. Various studies have shown that the photoreactivation gene, phrA, is the main factor responsible for repairing DNA damage in cyanobacteria. In the study reported here, our focus has been to investigate whether phrA is a major DNA repair factor in the cyanobacterium Aphanothece from the GSP and if so, is the phrA of Aphanothece more efficient than the phrA of cyanobacteria from regular non-extreme habitats. This study provides insight into the DNA repair capacity of these photosynthetic organisms that have evolved to survive the harsh conditions of the GSP.;Findings and Conclusions. DNA survival curves have been used to estimate repair capacity by exposing the organisms to various doses of UV radiation and determining the percent survival under dark and light incubation conditions. Our results showed that Aphanothece survived higher doses of UV only when incubated in light after UV exposure, indicating the importance of light-induced DNA repair in this organism. When compared to cyanobacteria from regular non-extreme environment, Synechocystis sp. PCC6803, it was seen that Aphanothece survived up to 120 J/m2 in photoreactivating conditions while Synechocystis could survive upto 100 J/m2. To further check if the difference in the two bacteria were significant, the Suv values were calculated at 10% survival. Our working hypothesis that the phrA gene of GSP-isolated Aphanothece is more efficient in DNA repair than similar genes present in cyanobacteria from non-extreme environments (i.e., Synechocystis) in that it is able to transcribe and translate more rapidly was tested by performing comparative survival curve analysis, which showed that Aphanothece survives higher doses of UV irradiation than Synechocystis. Based on these findings PhrA protein was quantified using Western Blot analysis after exposing the bacteria to increasing doses of UV irradiation which showed that they PhrA produced by Aphanothece even though inducible by UV irradiation was not significantly more than that of Synechocystis..