The Growth and Respiration of Nitrosocystis Oceanus at Different Partial Pressures of Oxygen

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Abstract
The following effects of different partial pressures of oxygen p(O2) on the growth and on the oxidation of ammonium to nitrite by N. oceanus in liquid and on solid sea-water media were observed. Nearly pure O2 was toxic to the organism when it was exposed to the oxygen on agar medium. In normal air the growth on agar medium was variable; usually a large proportion of the inoculum organisms never started to divide. At low p(O2) values the formation of microcolonies took place. In liquid medium the organism was less affected by high p(O2) values than on agar. The lower limit of oxygen concentration which permitted oxidation of ammonium in liquid medium corresponded to about 0[center dot]05 ml O2/l. In respiration experiments a high p(O2) in the gas phase resulted in twice as much oxygen uptake at the beginning as from air. Respiration at low p(O2) was comparatively high. These results seem to indicate that the inorganic respiration is accelerated by an increased p(O2) whereas growth is inhibited. Possible explanations are discussed.
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