The influence of mercury on the antioxidant enzyme activity of rumen bacteria Streptococcus bovis and Selenomonas ruminantium

Studies were undertaken to investigate the activity response of the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSHPx), glutathione reductase (GR) and mercury reductase (MR) of rumen bacteria Streptococcus bovis and Selenomonas ruminantium following exposure to HgCl2. SOD activity of S. bovis which was considered as Mn-SOD increased when incubated with 5 μg Hg2+ ml−1 in anaerobic or aerobic conditions. A significant increase in the aerobic activities of GSHPx, GR and MR was observed in the presence of Hg2+. The anaerobic activities of these enzymes were unchanged and increased production of thiobarbituric acid reactive substances was observed. S. ruminantium was tolerant to 10 times higher concentrations of Hg2+ than S. bovis. As a reduction of GSHPx, GR and MR activities after exposure to Hg2+ was observed, we assume that the production of sulfides prevented the toxic effect of mercury on this bacterium.