THE INFLUENCE OF OXYGEN AVAILABILITY ON THE DEGREE OF NITRATE REDUCTION BY SEUDOMONAS DENITRIFICANS

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Abstract
An attempt has been made to correlate nitrate reduction by Pseudomonas denitrificans with oxygen concentration in solution.Evidence has been obtained which indicates that nitrate reduction occurs only when the oxygen concentration is below the critical level at which the oxygen utilizing enzymes are saturated. Whilst precise data on the quantitative relationship between nitrate reduction and oxygen reduction at oxygen concentrations between 0 and 0.3 p.p.m. are lacking, it has been clearly established that nitrate reduction occurring in so-called "aerated" solutions is due mainly to the activity of cells deprived of an oxygen supply and that there is a direct relationship between nitrate reduction and the oxygen solution rate. No reduction was detectable at an oxygen concentration above 0.2 p.p.m.It has also been shown that with gas dispersed at the bottom of a fluid the breaking of the foam accumulating on the surface contributes markedly to the oxygen concentration in the solution.Procedures employed in the study are described in detail and implications of results on nitrate reduction in soils have been discussed.