30 



BULLETIJSI^ 782, U. S. DEPARTMENT OF AGEICULTUEE. 



REDUCTION OF NITRATES AND NITRITES. 



In view of the fact that all the organisms of the alkali-forming 

 group of bacteria could utilize nitrogen from nitrates, it is certain 

 there must be a reducing action. It is of interest, therefore, to 

 point out the action of these bacteria in reducing nitrates to nitrites, 

 as is shown by the ordinary tests for reduction generally used in 

 bacteriological work. The reduction of nitrate to nitrite was first 

 tried in the ordinary nitrate broth, which consisted of 0.1 per cent 

 peptone and 0.02 per cent potassium nitrate. Cultures were incu- 

 bated in the broth for seven days at 30° C, then tested for the 

 presence of nitrite. The results of these tests are sho^vn in Table 

 14. It will be seen that according to this test only seven cultures 

 reduced nitrate to nitrite. Reduction of nitrate was then tested 

 by using a medium in which beef extract was the source of nitrogen. 

 In one case 0.2 per cent extract was used with 0.02 per cent nitrate, 

 and in another case 0.1 per cent extract with the same amount of 

 nitrate. The results in the table show that after 24 hours ui the 

 0.2 per cent beef extract 11 cultures reduced the nitrates, whUe in 

 the 0.1 per cent beef extract 18 cultures gave a nitrite test. After 

 seven days' incubation 47 cultures reduced nitrate in 0.2 per cent 

 beef extract and 40 cultures in 0.1 per cent beef extract. 



Table 14. — Reduction of nitrates and nitrites in simple and complex media. 



Cul-ture No. 



0.1 per 



cent 

 pep- 

 tone, 



0.02 per 

 cent 



potas- 

 sium 



nitrate. 



0.2 per cent beef 

 extract, 0.02 



per cent potas- 

 sium nitrate. 



0.1 per cent beef 

 extract, 0.02 



p6r cent potas- 

 sium nitrate. 



Sodium nitrate, 



0.2 per cent; so- 



dium-lactate, 



0.25 per cent; 



sodium-dibasic 



phosphate, 0.1 



per cent. 



Sodium nitrite, 

 0.2 per cent; so- 

 dium lactate, 

 0.25 per cent; 

 sodium-dibasic 

 phosphate, 0.1 

 per cent. 





Nitrite 



test, 7 

 days. 



Nitrite 

 test, 24 

 hours. 



Nitrite 

 test, 7 

 days. 



Nitrite 

 test, 24 

 hours. 



Nitrite 

 test, 7 

 days. 



Nitrite 

 test, 14 

 days. 



Change 

 in titra- 

 tion. 



Ammo- 

 nia test, 

 14 days. 



Chanee 

 in titra- 

 tion. 





- 



- 



- 



- 



- 



- 



-0 05 



- 



-0.10 







10 



Mill 1111+ Mill 1 1 1 II 



II II 1 1111+ 1 1 II 1 II 1 11 



++ 1 ++ + 11 ++ ++ 11 + 1 + 1 ++ 



l+lll +111+ l+lll Mill 



++ 11 + ++ 1 ++ ++ 11 + 1 II II 



++ 1 ++ +++++ +++0+ +++++ 



- .61 



- .93 



- .15 



- .93 

 -1.20 



-1.15 

 -1.05 

 -1.18 

 -1.21 



- .58 



01 



- .95 



- .95 







- .84 



- .92 

 -1.12 



- .82 



- .89 

 -1.27 



- 



—0.72 



12 



— .84 



31 



— .59 



49 



— .76 



59 



—1.28 



60 



-1.08 



61 



— 1.21 



62 



-131 



66 



— 116 



72 



— .66 



73 



- .42 



101 



- .99 



102 



- .95 



103 







104 



- .87 



105 



106 



-1.26 



- .86 



107 



- .49 



lOS 



- .90 



Ill 



-1.05 



1 "0" means no change in titration. 



2 "0" under nitrite test means no growth of culture. 



