Oxygen affinities of the hydrogenosome-containing protozoa Tritrichomonas foetus and Dasytricha ruminantium, and two aerobic protozoa, determined by bacterial bioluminescence.

Oxygen-dependent bioluminescence of Photobacterium (Vibrio) fischeri was used to measure oxygen affinities of four protozoa. The aerobic organisms Acanthamoeba castellanii and Tetrahymena pyriformis showed apparent Km values for O2 of 0.42 and 2.43 microM respectively. The aerotolerant anaerobe Tritrichomonas foetus, and the more strictly anaerobic rumen ciliate Dasytricha ruminantium, both of which have hydrogenosomes, respired with apparent Km values of 1.08 and 1.70 microM-O2. We conclude that mitochondrial respiration is not the only process conferring on organisms a high affinity for O2.