EXPERIMENTS ON BACTERIAL DENITRIFICATION

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Abstract
Expts. carried out with the denitrifying bacterium Pseudomonas stutzeri showed that neither amino acids and amides of the medium nor nitro genous constituents of the bacteria contribute to the N evolved during reduction of nitrate or nitrite. Appln. of the technic of simultaneous enzymatic adaptation suggested that nitrous oxide either is an intermediate product in denitrification, or is reversibly derived from an intermediate product. Studies on the effect of cyanide on the reduction of nitrate, nitrite, and nitrous oxide revealed that nitrite can still be converted into gaseous products under conditions where reduction of nitrate and nitrous oxide is completely prevented by cyanide. The gas which is produced from nitrite under these conditions is N2, not N2O, hence nitrous oxide cannot be an intermediate product in denitrification. P. stutzeri is unable to produce N2 from hyponitrite; this substance has no effect on N2 evolution from nitrite. Nitramid, on the other hand, is readily converted to N2; the cyanide sensitivity of this process is the same as that of nitrite reduction. Hence nitramid, rather than hyponitrite, must be considered as the precursor of nitrous oxide and N in denitrification. It is concluded that N formation from nitramid involves a simple reduction, rather than an hydration followed by the elimination of peroxide, since a denitrifying fluorescent pseudomonad, which can utilize benzoic acid aerobically, cannot do so anaerobically in the presence of nitramid. The essential stages in the denitrification process have been presented in the form of a simple scheme, as follows:[image].