Living in a hot redox soup: antioxidant defences of the hydrothermal worm <i>Alvinella pompejana</i>

The hydrothermal Pompeii worm Alvinella pompejana lives very close to the walls of black smokers and is therefore exposed to high-temperature venting fluid containing high concentrations of sulphides and metals. The highly aerobic metabolism of these annelids, together with these extreme physico-chemical conditions, theoretically accelerates redox processes in and around the worm, potentially increasing oxidative threat by reactive oxygen species (ROS). This prompted us to analyse activity of antioxidant enzymes in A. pompejana tissues and investigate whether they are adjusted to the endogenous production of ROS by oxidative phosphorylations and/or to the environmental conditions. This was investigated by comparing antioxidant and metabolic enzyme activities in gills, head, body wall, pygidium and guts of A. pompejana collected at different vent sites of the East Pacific Rise. The antioxidant defence arsenal of A.&nbsp;pompejana is peculiar, showing very low catalase (CAT) activity and very high superoxide dismutase (SOD) activity in most tissues. It is very likely that CAT is not expressed in A. pompejana, as this haemic enzyme could be inhibited by the high sulphide concentrations prevailing in the worm’s environment. A. pompejana does not compensate for the low hydrogen peroxide scavenging activity of CAT by higher glutathione peroxidase (GPX) activity levels. This latter enzyme correlates well with cytochrome c oxidase and citrate synthase in most tissues, suggesting that oxidative metabolism represents the main source of peroxides managed by GPX. On the&nbsp;contrary, SOD shows no correlation with any metabolic enzyme and is likely adjusted to respiration-independent ROS generation. Source variations in enzyme activities are mainly observed in the animal’s gills and gut, possibly reflecting differences in the vent fluid thermal regime and/or chemistry