30 
BULLETIN 782, TJ. S. DEPARTMENT OF AGRICULTURE. 
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 shown 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 in the 
0.2 per cent beef extract 11 cultures reduced the nitrates, while 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. 
Culture 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 
per cent potas- 
sium nitrate. 
Sodium nitrate, 
0.2 per cent: so- 
dium-lactate, 
0.25 per cent; 
sodium-dibasic 
phosphate, 0.1 
per cent. 
Podium nitrite, 
0.2 per cent: so- 
dium lactate, 
0.25 per rent: 
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. 
- 
- 
- 
-005 
- 
—0.10 
10 
+ 
z i 
- 
- 
- 
+ * 
+ 
+ 
+ 
-4- 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
02 
+ 
+ 
+ 
+ 
- .61 
- .93 
- .15 
- .93 
-1.20 
. —1.15 
-1.05 
-1.18 
-1 21 
- .5S 
0i 
- .95 
- .95 

- .84 
- .92 
-1.12 
- .82 
—0.72 
12 
— .84 
31 
+ 
-4- 
— .59 
49 
— -76 
59 
-1.28 
60 
—1.08 
61 
-1..1 
62 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
-131 
66 
—1.16 
72 
- .66 
73 
- .42 
101 
- .99 
102 
1 + 1 1 1 +11 
+ + II + ++ 1 
- .95 
103 

104 
- .87 
105 
-1.26 
106 
- .86 
107 
- .49 
108 
+ - .89 
+ -1-27 
- - .90 
Ill 
- -1.05 
"0"' means no change in titration. 
2 "0" under nitrite test means no growth of culture. 
