Terminal oxidases of Bacillus subtilis strain 168: One quinol oxidase, cytochrome aa(3) or cytochrome bd, is required for aerobic growth

The gram-positive endospore-forming bacterium Bacillus subtilis has, under aerobic conditions, a branched respiratory system comprising one quinol oxi dase branch and one cytochrome oxidase branch. The system terminates in one of four alternative terminal oxidases. Cytochrome caa(3) is a cytochrome c oxidase, whereas cytochrome bd and cytochrome aa(3) are quinol oxidases. A fourth terminal oxidase, YthAB, is a putative quinol oxidase predicted fro m DNA sequence analysis. None of the terminal oxidases are, by themselves, essential for growth. However, one quinol oxidase (cytochrome aa(3) or cyto chrome bd) is required for aerobic growth of B. subtilis strain 168. Data i ndicating that cytochrome aa(3) is the major oxidase used by exponentially growing cells in minimal and rich medium are presented. We show that one of the two heme-copper oxidases, cytochrome caa(3) or cytochrome aa(3), is re quired for efficient sporulation of B. subtilis strain 168 and that deletio n of YthAB in a strain lacking cytochrome aa(3) makes the strain sporulatio n deficient.