GROWTH AND HYDROGENASE ACTIVITY OF A NEW BACTERIUM, HYDROGENOMONAS FACILIS

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Abstract
H. facilis, a new species of bacterium capable of utilizing H2, is an obligate aerobe that develops heterotrophically on many substrates. It grows autotrophically in traces of O2 up to 30% 02 but not 40%. In manometric expts. autotrophically-grown cells reduce nitrate to nitrite and oxidize H2 to H2O. For these reactions with 02 and nitrate as H-acceptors, average QH2 (mg) values of about 720 and 70, respectively, were obtained. The hydrogenase of H. facilis was most active near pH 6.5, 5% O2, and [image]/30 phosphate buffer. In addition to nitrate and 62, methylene blue was an effective H-acceptor. Acetate, pyruvate, fumarate, malate, oxalacetate, alpha-ketoglutarate, formate, acetaldehyde, acetone, nitrite, 1% CO2 in N2, and elementary S were not reduced. Of these substances, the Krebs cycle intermediates were respired by autotrophically-grown cells of H. facilis rapidly, without adaptation, and at approx. the same rate. Citrate, acetone, nitrite, thiosulfate and elementary S were not oxidized. Hydrogenase was present in H. facilis grown on organic media. This enzyme was reversibly inactivated by pO2 above 5% and was not inhibited by N2 or NH3. The physiological stability and hardiness of H. facilis recommend it for studies of H2 utilization.

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