DENITRIFICATION 43 



conditions produced large amounts of Ng and NgO. How- 

 ever, no such effect was obtained with Pseudomonas organ- 

 isms; they all produced Ng and no NHg . If cultures of 

 the Bacillus and Pseudomonas organisms were sufficiently 

 aerated there was no reduction of NO 7- 



The ability to reduce nitrate has proved to be of value in 

 the classification and identification of micro-organisms, e.g. 

 in the yeasts, the genus Hansenula is differentiated from 

 Pichia on the basis that only the former can grow on NO 7 

 as a source of N. The gaseous products or nitrite formed by 

 the activities of nitrate-reducing organisms are responsible 

 for troublesome and unwelcomed consequences in certain 

 industries. Thus N07 and N07 are commonly used for 

 curing and preserving meat products and spoliation is often 

 due to denitrifying bacteria. Some workers believe that 

 denitrifying micro-organisms convert an appreciable amount 

 of fertilizers such as (NH4)2S04 and KNO3 into gaseous 

 products and thus significantly decrease the amount of 

 nitrogen available for plant growth [cf. 32]. After feeding on 

 oat hay, which frequently contains large amounts of NOs"* 

 sheep may show signs of methaemoglobinaemia (oat hay 

 poisoning) and this condition is due to the absorption of 

 NO 2" formed by micro-organisms in the rumen [17]. If 

 acidic conditions arise during the commercial production of 

 alcohol by the fermentation of sugar molasses, large amounts 

 of nitrogen peroxide are sometimes evolved. This is due to 

 the acidic decomposition of nitrites which were formed from 

 nitrates by micro-organisms during the processing of the 

 molasses [32]. 



REFERENCES 



1. Allen, M. B. and van Niel, C. B. (1952), J. Bact., 64, 397 • 



2. Aubel, E. (1938), C.R. Soc. Biol., Paris, 128, 45 



3. Audus, L. J. (1946), Nature, 158, 419 



4. Baas-Becking, L. G. M. and Parks, G. S. (1927), Physiol. Rev. 



7,85 



5. Beijerinck, M. W. and Minkman, D. C. J. (1910), Centr. 



Bakt. Parasiteiik, (2. Abt.), 25, 30 



6. Bomeke, H. (1939), Arch. MikrobioL, 10, 385 



