Oxygen recognition in aerotactic behaviour of Azospirillum brasilense Cd

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Abstract
Oxygen recognition in aerotactic behaviour of Azospirillum brasilense was studied. Spectral studies of membrane preparations of A. brasilense Cd revealed three terminal oxidases: cytochromes aa3, o, and d. The possible involvement of each of these cytochromes in oxygen receptor was evaluated. Since neither reducing the level of cytochrome aa3 in the bacteria nor inhibition of cytochrome aa3 by low concentrations of cyanide affected aerotaxis, it is concluded that cytochrome aa3 is not the oxygen receptor. Cytochromes o and d are inhibited by high concentrations of cyanide which also inhibit aerotaxis. Of these two, cytochrome o seems more likely to be the oxygen receptor, since antimycin A, which inhibits the reduction of this cytochrome (but not that of cytochrome d), completely inhibited aerotaxis. By using tethered cells, it was demonstrated that A. brasilense is microaerophilic, as it is attracted to oxygen concentrations lower than those present in the air (20%).

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