摘要：Polar coastal seawaters are saturated by high oxygen concentrations, which impose very effective adaptive strategies to strive against a continuous environmental oxidative stress. We studied these strategies in Euplotes nobilii (Ciliophora: Spirotrichea), a ciliate species dwelling in Antarctic and Arctic coastal seawaters, in comparison with Euplotes raikovi, a sister species living in temperate seawaters. Cell samples of the two species were exposed to hydrogen peroxide (H2O2)-induced oxidative stress and analyzed for their survival rates and levels of expression of the genes encoding the enzyme methionine-sulfoxide reductase (Msr) A, which restores oxidized methionines (in their S form) of damaged proteins to the status of functional methionines. While 6 h of exposure to a 750-µM concentration of H2O2 did not affect E. nobilii viability, these conditions were lethal to E. raikovi. In correlation with this inter-specific difference in the cell survival to oxidative stress, the MsrA-coding genes of the two species showed different mechanisms of expression: constitutive in E. nobilii, elicited by induction in E. raikovi.
