DENITRIFICATION 4I 



NO 7 and which also possess hydrogenase can use molecular 

 hydrogen as a H-donor in these reductions [28]. Woods [36] 

 thus demonstrated that washed suspensions of CI. zvelchii 

 reduced NOJ, N07 and NH2OH to NH3 , the H2 uptake 

 being in accordance with the following equations: 



NH^OH+H. = NH3+H.O 

 HNO,+3H2 = NH3+2H.,0 

 HNO3+4H, = NH3+3H2O 



The Hg uptake in the third equation is that expected on 

 theoretical grounds if NH2OH and NOT are in fact inter- 

 mediates in the reduction of NO 7- During the early stages 

 of the reduction of NO^", a transient accumulation of NO^ 

 was observed. 



The recent investigations of Verhoeven [30] have done 

 much to confirm and extend the observations and hypotheses 

 of earlier workers in this field [13]. He found that the reduc- 

 tion of NO "3 by the aerobic spore-forming bacilli resulted in 

 the production of NO 7, Ng and sometimes NH3 ; NO 7 

 could be replaced as the H-acceptor by NOT or by NgO. 

 Strains producing large amounts of ammonia did not form 

 appreciable amounts of gaseous end-products, and the con- 

 verse was also true. A detailed study with one strain demon- 

 strated that the reduction process took place in two stages. 

 During the first stage NO 7 was converted to NOT and then 

 to NgO; whilst in the second, the gas evolved was mainly 

 N2 , indicating that NgO is the precursor of Ng . On two 

 occasions, Verhoeven detected NHgOH in denitrifying cul- 

 tures, and thus provided some evidence in support of 

 the contention of Blom that this compound is an inter- 

 mediate in the reduction of NO J. Working with Ps. stutzeri^ 

 Allen and van Niel have come to the conclusion that, at 

 least in this organism, although NgO was reduced, it was 

 not a natural intermediate. They believe that nitramide 

 (NO2.NH2) is a possible intermediate since Ng was formed 

 from a preparation of this compound but not from hypo- 

 nitrous acid [i]. In the presence of a H-donor, cell-free ex- 

 tracts of Ps. stutzeri and B. subtilis reduce nitrate to Ng {Ps. 



