A thermostable superoxide dismutase from a thermophilic bacterium, called Geobacillus wiegeli (GWE1), isolated from the interior of a sterilization drying oven, was purified by anion-exchange and molecular size-exclusion liquid chromatography. On the basis of SDS-PAGE, the purified enzyme was found to be homogeneous and showed an estimated subunit molecular mass of 23.9 kDa. The holoenzyme is a homotetramer of 97.3 kDa. Superoxide dismutase exhibited maximal activity at pH 8.5 and at temperature around 60 ºC. The enzyme was thermostable maintaining 50% of its activity even after 4.5 hours incubation at 60 ºC and more than 70% of its activity after 30 min at 80 ºC. When the microorganism was irradiated with UVA, an increase in the specific activity of superoxide dismutase was observed which was correlated with decreasing levels of anion superoxide, indicating the direct involvement of this enzyme in the capture of reactive oxygen species. This study reports the effects of UV radiation on a superoxide dismutase from a thermophilic bacterium isolated from an anthropogenic environment.

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Microorganisms present in Antarctica have to deal not only with cold temperatures but also with other environmental conditions, such as high UV radiation, that trigger the generation of reactive oxygen species. Therefore, Antarctic microorganisms must have an important antioxidant defense system to prevent oxidative damage. One of these defenses are antioxidant enzymes, such as catalase, which is involved in the detoxification of hydrogen peroxide produced under oxidative conditions. Here, we reported the isolation and partial characterization of an Antarctic bacterium belonging to the Serratia genus that was resistant to UV-C radiation and well-adapted to cold temperatures. This microorganism, denominated strain I1P, was efficient at decreasing reactive oxygen species levels produced after UV-C irradiation. Genomic and activity assays suggested that the enzymatic antioxidant defense mechanisms of strain I1P, especially its catalase enzyme, may confer UV resistance. This catalase was active in a wide range of temperatures (20–70 °C), showing optimal activity at 50 °C (at pH 7.0), a remarkable finding considering its psychrotolerant origin. In addition, this enzyme was thermostable, retaining around 60% of its activity after 6 h of incubation at 50 °C. The antioxidant defense systems of strain I1P, including its surprisingly thermoactive and thermostable catalase enzyme, make this microorganism a good source of biocompounds with potential biotechnological applications.

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