302 
Journal of Agricultural Research 
Vol. XXIV, No. 4 
Tabl^ V. Oxidation of sulphur by pure cultures of bacteria at various reactions 
Ph value. 
Soluble 
sulphates 
(sulphur) 
in zoo gm. 
of soil after 
50 days’ 
incubation. 
Type of culture. 
Initial 
reaction 
of soil. 
16 days 
after. 
30 days 
after. 
so days 
after. 
f 
5-2 
5-3 
S -4 
Mgm. 
10. 2 
5-6 
5-6 
5-6 
13 - 7 
Control. 
5-8 
5-8 
5 - 7 
II. 0 
6. 0 
6. 0 
5.8 
5.8 
13 - 7 
6. 2 
6. 2 
6. 2 
6. 2 
13 - 7 
8. 4 
8.4 
8.2 
8.2 
1 21.9 
5-2 
5-2 
3^4 
2.8 
315- I 
5*6 
5-4 
3-0 
2.8 
314. 6 
5-8 
5 - 6 
5 - 5 
S* 5 
20. 6(?) 
Thiobacillus thiooxidans . 
6. 0 
5.8 
3-0 
2. 6 
358. 0 
6. 2 
5-4 
2.8 
2.8 
380.0 
6.6 
6.6 
6.6 
3-0 
304-4 
8.4 
8. 4 
8.2 
8.0 
27.4 
5-2 
5-3 
5-2 
5-4 
39 - 7 
5-6 
5-3 
5-2 
5 - 2 
20. 6 
5-8 
5 - 5 
5 ‘ 5 
5 * 4 
21. 9 
Thiobacillus B .< 
6. 0 
6. 0 
5-5 
5 - 5 
15. 2 
6. 2 
6. 0 
5.8 
5-4 
19. 2 
6.6 
6.6 
6.6 
6.4 
24. 7 
8.4 
8. 2 
8.0 
7.8 
5-2 
5-2 
3-4 
2.8 
3 ° 2 -S 
5-6 
3 * I 
2.8 
2. 6 
287. 7 
5.8 
2.8 
2. 8 
2. 6 
3II. I 
T, thiooxidans-\-T. B .< 
6. 0 
2.8 
2. 6 
2. 6 
308.3 
6. 2 
2.8 
2. 8 
2. 6 
367.0 
6.6 
3 - I 
2.8 
2. 8 
274.0 
8.4 
8. 2 
8. 0 
7*4 
Both the reaction and the sulphur content of the control indicate 
that no sulphur or only traces of it were oxidized under sterile conditions. 
However, in the presence of the sulphur-oxidizing bacteria, the oxida¬ 
tion of the sulphur took place very rapidly, with the transformation of 
large quantities of sulphur to sulphuric acid. When the reaction of 
the soil was acid, the oxidation of the sulphur in 50 days was carried 
on entirely by Thiohacillus thiooxidans. Thiohacillus B oxidized only 
very small quantities of sulphur; but, in the presence of both organisms, 
the speed of the reaction was hastened, as indicated by the measurements 
of the Ph values obtained in 16 days. This may be explained by either 
of two assumptions: (i) If we suppose a so-called “lag phase’' in bac¬ 
terial development, Thiohacillus B produces substances which appre¬ 
ciably shorten the “lag phase” of T. thiooxidans; (2) Thiohacillus B 
may oxidize the sulphur not directly to sulphates but to other compounds 
of sulphur, which are then rapidly oxidized to sulphates by T. thiooxidans. 
This is made clear in the study of the pure cultures of Thiohacillus By 
with sodium thiosulphate as a source of energy, when a large part of the 
thiosulphate is transformed to persulphates, a part to elementery sul¬ 
phur, and only a part to sulphates. This preparatory function of the 
Thiohacillus B may explain a number of hitherto unexplained difficulties 
observed in the study of sulphur oxidation by microorganisms in the soil. 
Of these we need mention only a few. 
