| Abstract |
Bifidobacterium asteroides, originally isolated from honeybee intestine, was found to grow under 20% O(2) conditions in liquid shaking culture using MRS broth. Catalase activity was detected only in cells that were exposed to O(2) and grown in medium containing a haem source, and these cells showed higher viability on exposure to H(2)O(2). Passage through multiple column chromatography steps enabled purification of the active protein, which was identified as a homologue of haem catalase on the basis of its N-terminal sequence. The enzyme is a homodimer composed of a subunit with a molecular mass of 55 kDa, and the absorption spectrum shows the typical profile of bacterial haem catalase. A gene encoding haem catalase, which has an amino acid sequence coinciding with the N-terminal amino acid sequence of the purified protein, was found in the draft genome sequence data of B. asteroides. Expression of the katA gene was induced in response to O(2) exposure. The haem catalase from B. asteroides shows about 70-80% identity with those from lactobacilli and other lactic acid bacteria, and no homologues were found in other bifidobacterial genomes.
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