A. L. Brioukhanov

Catalase and Superoxide Dismutase: Distribution, Properties, and Physiological Role in Cells of Strict Anaerobes

This review considers the distribution of the main enzymes of antioxidative defense, superoxide dismutase (SOD) and catalase, in various groups of strictly anaerobic microorganisms: bacteria of the genus Clostridium, Bacteroides, sulfatereducing and acetogenic bacteria, methanogenic archaea, etc. Molecular and biochemical properties of purified Fe-containing SODs, cambialistic SODs, and heme catalases are presented. The physiological role and origin of the enzymes of antioxidative defense in strict anaerobes are discussed. Physiological responses (induction of SOD and catalase) to factors provoking oxidative stress in the cells of strict anaerobes able to maintain viability under aerobic conditions are also considered.

Aerotolerance of Strictly Anaerobic Microorganisms and Factors of Defense against Oxidative Stress: A Review

Effects of aerobic conditions on strictly anaerobic microorganisms belonging to diverse taxa (clostridia, acetogenic bacteria, lactic acid bacteria, bacteroids, sulfate-reducing bacteria, and methanogenic archaea) and differing considerably in their oxygen resistance have been reviewed, with emphasis on the role of aerotolerance in the ecology of anaerobes. Consideration is given to components of nutritive media for anaerobe culturing, which decrease the toxic effects of oxygen and there by contribute significantly to maintenance and storage of industrial cultures of strictly anaerobic microorganisms. Physiological and biochemical factors are described, accounting for the relative resistance of many strict anaerobes to oxygen and products of incomplete reduction thereof. Specific attention is given to regulation of enzymes of antioxidative defense, operating in the cells of strict anaerobes under the conditions of oxidative stress caused by oxygen, superoxide anion, or hydrogen peroxide.

Characterization of a heme-dependent catalase from Methanobrevibacter arboriphilus.

ABSTRACT Recently it was reported that methanogens of the genusMethanobrevibacter exhibit catalase activity. This was surprising, since Methanobrevibacter species belong to the order Methanobacteriales, which are known not to contain cytochromes and to lack the ability to synthesize heme. We report here that Methanobrevibacter arboriphilus strains AZ and DH1 contained catalase activity only when the growth medium was supplemented with hemin. The heme catalase was purified and characterized, and the encoding gene was cloned. The amino acid sequence of the catalase from the methanogens is most similar to that of Methanosarcina barkeri.

Catalase and Superoxide Dismutase in the Cells of Strictly Anaerobic Microorganisms

Strictly anaerobic microorganisms relating to various physiological groups were screened for catalase and superoxide dismutase (SOD) activity. All of the investigated anaerobes possessed SOD activity, necessary 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 representatives 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.

An oxygen reduction chain in the hyperthermophilic anaerobe Thermotoga maritima highlights horizontal gene transfer between Thermococcales and Thermotogales.

The hyperthermophile Thermotoga maritima, although strictly anaerobic, is able to grow in the presence of low amounts of O(2). Here, we show that this bacterium consumes O(2) via a three-partner chain involving an NADH oxidoreductase (NRO), a rubredoxin (Rd) and a flavo-diiron protein (FprA) (locus tags: TM_0754, TM_0659 and TM_0755, respectively). In vitro experiments showed that the NADH-dependent O(2) consumption rate was 881.9 (± 106.7) mol O(2) consumed min(-1) per mol of FprA at 37°C and that water was the main end-product of the reaction. We propose that this O(2) reduction chain plays a central role in the O(2) tolerance of T. maritima. Phylogenetic analyses suggest that the genes coding for these three components were acquired by an ancestor of Thermotogales from an ancestor of Thermococcales via a single gene transfer. This event likely also involved two ROS scavenging enzymes (neelaredoxin and rubrerythrin) that are encoded by genes clustered with those coding for FprA, NRO and Rd in the ancestor of Thermococcales. Such genomic organization would have provided the ancestor of Thermotogales with a complete set of enzymes dedicated to O(2)-toxicity defence. Beside Thermotogales and Thermococcales, horizontal gene transfers have played a major role in disseminating these enzymes within the hyperthermophilic anaerobic prokaryotic communities, allowing them to cope with fluctuating oxidative conditions that exist in situ.

Response of Desulfovibrio vulgaris Hildenborough to hydrogen peroxide: enzymatic and transcriptional analyses

We studied the effect of hydrogen peroxide (H(2)O(2)) stress on the anaerobic sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough. In a lactate/sulfate medium, growth was affected from 0.1 mM H(2)O(2) and totally inhibited at 0.7 mM. Surprisingly, transcript analyses revealed that the PerR regulon exhibited opposite regulation in the presence of 0.1 and 0.3 mM H(2)O(2). The variations in peroxidase- and superoxide dismutase-specific activities in the cell-free extracts of H(2)O(2)-stressed cultures were related to changes in the corresponding transcript abundance. Our data suggest that sod, sor, ngr and tpx genes, in addition to the PerR regulon, belong to the H(2)O(2) stimulon.

Nonheme iron proteins as an alternative system of antioxidant defense in the cells of strictly anaerobic microorganisms: A review

Enzymatic systems accounting for the relative oxygen resistance of multiple strict anaerobes are reviewed, with emphasis on molecular-biological properties and action mechanisms of nonheme iron proteins (neelaredoxins, desulfoferrodoxins, and rubrerythrins). These unique proteins, which are widespread in anaerobes, comprise a system of antioxidant defense against toxic effects of oxygen and products of its incomplete reduction (an alternative to the classic antioxidant system involving superoxide dismutase and catalase). The role of the superoxide reductase-mediated elimination of endogenous superoxide radicals is discussed. This extremely efficient means of rapid superoxide radical detoxification underlies the preferred mechanism for maintaining the optimum balance between oxidized and reduced forms of some proteins in the cells of strict anaerobes.

Purification and characterization of Fe-containing superoxide dismutase from Methanobrevibacter arboriphilus strain AZ

Superoxide dismutase (SOD) was purified from cells of the strict anaerobic methanogenic archaeon Methanobrevibacter arboriphilus strain AZ. The four-step purification procedure resulted in enzyme with specific activity of 3970 units/mg and yield of 22%. It was shown that the SOD is a Fe-containing homotetramer composed of subunits of 21.2 kD each. Sodium azide (13.5 mM), unlike KCN, inhibits the activity of the SOD. Hydrogen peroxide (0.5 mM) inactivates the enzyme, which is consistent with the properties of the known Fe-containing SODs from methanogenic Archaea.