ИСТИНА

Background: Clostridia and methanogenic archaea can grow under anoxic conditions, but some species, however, are able not only survive but also tolerate oxidative stress. When anaerobes come in contact with O2, reactive oxygen species (ROS) are generated by autooxidation of reduced iron-sulfur proteins and/or flavoproteins. The toxic ROS will damage macromolecules if not immediately removed by the enzymes superoxide dismutase (SOD) and catalase. Objectives: We characterized the iron SODs and monofunctional heme catalases from Methanosarcina barkeri and Methanobrevibacter arboriphilus. The encoding genes were cloned and sequenced. It was shown that sod and kat genes were transcriptionally up-regulated upon different oxidative stresses in Сlostridium acetobutylicum and M. barkeri. Methods: The enzymes were purified with the use of phenyl-Sepharose, Resource Q and ceramic hydroxyapatite columns. The molecular masses were determined by MALDI-TOF (MS). The enzymatic activities were determined spectrophotometrically. qRT-PCR and dot-blot analysis were used to study the genes expression variations. Conclusions: Some Methanosarcina species contain monofunctional catalase. M. arboriphilus, which cannot synthesize heme, exhibited a high catalase activity when the growth medium was supplemented with hemin. The catalase activity in C. acetobutylicum was also depended on exogenous hemin. The presence of SOD in M. barkeri is noteworthy since a sod gene has not been found in Archaeoglobus fulgidus, an archaeon closely related to the Methanosarcinaceae. Archaeal Fe-SODs possessed relative insensitivity to azide and H2O2 in comparison with bacterial Fe-SODs. The transcriptional levels of Fe-SOD and catalase were induced in the cells of clostridia and methanogens in response to ROS exposure.