Effects of aerobic conditions on strictly anaerobic microorganisms belonging to diverse taxa (clostridia, acetogenic bacteria, lactic acid bacteria, bacteroids, sulfate-reducing bacteria, and...

Methanosarcina barkeriis a strictly anaerobic methanogenic archaeon, which can survive oxidative stress. The oxidative stress agent paraquat (PQ) suppressed growth ofM. barkeriat concentrations of 50–200 μM. Hydrogen peroxide (H₂O₂) inhibited growth at concentrations of 0.4–1.6 mM. Catalase activity in cell-free extracts ofM. barkeriincreased about threefold during H₂O₂stress (1.3 mM H₂O₂, 2–4 h exposure) and nearly twofold during superoxide stress (160 μM PQ, 2 h exposure). PQ (160 μM, 2–4 h exposure) and H₂O₂(1.3 mM, 2 h exposure) also influenced superoxide dismutase activity in cell-free extracts ofM. barkeri. Dot-blot analysis was performed on total RNA isolated from H₂O₂- and PQ-exposed cultures, using labelled internal DNA fragments of thesodandkatgenes. It was shown that H₂O₂but not PQ strongly induced up-regulation of thekatgene. PQ and to a lesser degree H₂O₂induced the expression of superoxide dismutase. The results indicate the regulation of the adaptive response ofM. barkerito different oxidative stresses.

Recently it was reported that methanogens of the genus Methanobrevibacter 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 .