Response of the microaerophilic Bifidobactetium species, B-boum and B-thermophilum, to oxygen

We investigated the effects of 0(2) on Bifidobacterium species using liquid shaking cultures under various 0(2) concentrations. Although most of the Bifidobacterium species we selected showed 0(2) sensitivity, two species, R boum and B. thermophilum, demonstrated microaerophilic profiles. The growth of B. bifidum and B. longum was inhibited under high-O-2 conditions accompanied by the accumulation of H2O2 in the medium, and growth was restored by adding catalase to the medium. B. boum and B. thermophilum grew well even under 20% O-2 conditions without H2O2 accumulation, and growth was stimulated compared to anoxic growth. H2O-forming NADH oxidase activities were detected dominantly in cell extracts of B. boum and R thermophilum under acidic reaction conditions (pH 5.0 to 6.0).