SOME ASPECTS OF NITRATE REDUCTION 



GENERAL CONSIDERATIONS ON TRUE DISSIMILATORY 

 NITRATE REDUCTION 



The merit of first having clearly described true dissimilatory nitrate 

 reduction goes to the French investigators Gayon and Dupetit [1886], 

 who reported on the results of their extensive and careful studies on 

 nitrogen losses sometimes occurring in water and soil. They established 

 that these losses were due to a conversion of nitrates to molecular 

 nitrogen - or in some cases to nitrous oxide - and demonstrated that 

 this conversion was due to the activity of bacteria which evidently 

 were able to substitute nitrate-oxygen for free oxygen in the oxidation 

 of organic substrates. They introduced the term 'denitrification' for 

 those nitrate conversions which lead to the mentioned gaseous nitrogen 

 compounds, but they also found that in certain cases the reduction of 

 the nitrate did not go beyond the nitrite stage, whilst in other cases 

 part of the nitrate-nitrogen was found back in its ultimate reduction 

 stage, i.e., ammonia. 



Since then it has been found that the property of true dissimilatory 

 nitrate reduction is not the prerogative of a few very specific bacteria, 

 but is encountered amongst representatives of several genera of aerobic 

 bacteria. Especially in the genus Pseudomonas several well-known spe- 

 cies are active 'denitrifiers'. This holds for instance for Pseudomonas 

 stutzeri ( = Bacterium denitrificans fi of Gayon and Dupetit), Pseudomonas 

 aeruginosa and for certain strains closely related to Pseudomonas fluores- 

 ces which have been collected in the separate species Pseudomonas 

 denitrofluorescens. However, Beijerinck has made part of his classical in- 

 vestigation with an immotile organism not belonging to Pseudomonas 

 and which he has named Micrococcus denitrificans. In addition true dis- 

 similatory nitrate reductions have been reported for representatives 

 of the genera Spirillum and Bacillus. 



It will be clear that an insight into the true dissimilatory nitrate re- 

 duction asks primarily for a thorough study of the fate of the nitrate- 

 nitrogen and of that of the organic substrate acting as the hydrogen 

 donator in the process. As for the former nitrite, nitrous oxide, gaseous 

 nitrogen and ammonia have been found with certainty amongst the 

 reduction products, but these findings are at least partly related to 

 different organisms so that the interpretation of their appearance has 

 remained fragmentary. As for the fate of the organic substrate it is 



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