0026-2617/02/7103- $27.00 © 2002 åÄIä “Nauka /Interperiodica” 0281 Microbiology, Vol. 71, No. 3, 2002, pp. 281–285. Translated from Mikrobiologiya, Vol. 71, No. 3, 2002, pp. 330–335. Original Russian Text Copyright © 2002 by Brioukhanov, Thauer, Netrusov. It is well known that the products of oxygen reduc- tion—hydrogen peroxide, superoxide radical, and hydroxyl radical—are highly toxic for cells and bring about damage to cell macromolecules [1]. Therefore, to relieve the toxic effect of oxygen, aerobic and faculta- tively anaerobic microorganisms possess catalase (EC 1.11.1.6), which uses hydrogen peroxide as an electron donor and catalyzes its two-electron reduction to water and oxygen, and superoxide dismutase (SOD, EC 1.15.1.1), which catalyzes the reaction of dispropor- tionation of the superoxide radical. At the early stage of investigation of the enzymes of antioxidant defense, a hypothesis was put forward that the inability of strict anaerobes to grow in the presence of oxygen is due to the lack of catalase, resulting in hydrogen peroxide accumulation in the cells during metabolic processes. However, later, catalase was found in various anaerobic microorganisms, in particu- lar among many representatives of Bacteroides [2]. Fri- dovich failed to find SOD activity in some anaerobic bacteria and hypothesized that this enzyme is specific to aerobic and aerotolerant microorganisms and that cells that do not reduce oxygen do not normally encounter superoxide radicals and do not need SOD; therefore, they are very sensitive to the adverse effect of oxygen [1]. However, other researchers found that not only aerobic and facultatively anaerobic bacteria but also strict anaerobes, Desulfovibrio and Clostridium in particular, possess SOD activity [3, 4]. The occurrence of SOD in strict anaerobes (which is much more fre- quent than it was formerly supposed) raises a question about the physiological role of SOD and its origin in these microorganisms. The fact that strict anaerobes can grow only in oxygen-free environments makes the functions of SOD under such conditions disputable. Probably, only under unfavorable aerobic conditions (which may be encountered by strict anaerobes rather frequently, especially by pathogenic species of Clostridium and Bacteroides), does the synthesis of SOD induced by molecular oxygen provide the defense of an anaerobic organism against the lethal effect of . It has been suggested that only microorganisms possessing SOD can survive the presence of oxygen; the presence of catalase is not so important [3, 4]. The studies of the resistance of microorganisms to oxygen revealed a clear-cut connection with SOD activity: the species with high SOD activity exhibit higher aerotol- erance than species with low SOD activity or species lacking SOD [5]. We studied the catalase and SOD activities in cells of some strict anaerobes with the aim of finding micro- organisms with the highest activities of enzymes of antioxidant defense. MATERIALS AND METHODS This work used the following bacteria: the clostridia Clostridium acetobutylicum 6, C. acetobutylicum 7, C. acetobutylicum 8, C. butyricum 19, C. butyricum 21, C. butyricum 22, and C. butyricum 23 (from the collec- tion of Microbiology Department, Moscow State Uni- O 2 – . EXPERIMENTAL ARTICLES Catalase and Superoxide Dismutase in the Cells of Strictly Anaerobic Microorganisms A. L. Brioukhanov*, R.K. Thauer**, and A.I. Netrusov* *Microbiology Department, Biological Faculty, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia **Max-Planck-Institut for Terrestrial Microbiology, Marburg, Germany Received December 6, 2001; in final form, February 15, 2002 Abstract—Strictly anaerobic microorganisms relating to various physiological groups were screened for cata- lase and superoxide dismutase (SOD) activity. All of the investigated anaerobes possessed SOD activity, nec- essary for protection against toxic products of oxygen reduction. High specific activities of SOD were found in Acetobacterium woodii and Acetobacterium wieringae. Most of the investigated clostridia and acetogens were catalase-negative. A significant activity of catalase was found in Thermohydrogenium kirishiense, in represen- tatives of the genus Desulfotomaculum, and in several methanogens. Methanobrevibacter arboriphilus had an exceptionally high catalase activity after growth in medium supplemented with hemin. Hemin also produced a strong positive effect on the catalase activity in many other anaerobic microorganisms. In methanogens, the activities of the enzymes of antioxidant defense varied in wide ranges depending on the stage of growth and the energy source. Key words: catalase, superoxide dismutase, anaerobes.