Aug. 19,1918 
Reaction on Nitrogen-Assimilating Bacteria 
333 
INFLUENCE OF NITROGEN-ASSIMILATING BACTERIA ON THE REAC¬ 
TION OF THE MEDIUM 
Since the legume bacteria show a difference in behavior toward reaction 
of the culture medium, it was thought that the growth of the different 
strains might cause a noticeable variation in the reaction of the medium. 
Accordingly, the reaction was measured by titrating the cultures with 
N/20 acid or alkali at the time of inoculation and again four weeks later. 
The results of titrations failed to show any decided change in the reaction 
of the culture medium after the growth of the different organisms, 
although there was a slight increase in acidity. Similar results were 
reported in an earlier publication (9). 
The results of hydrogen-ion measurements of the inoculated and unin¬ 
oculated culture solutions showed a small but distinct increase in acidity. 
In this test saccharose solution was used in place of the mannitol. In 
Table IX only the averages of duplicate cultures are given. As a rule, 
the change in the reaction due to the growth of R. leguminosarum in the 
saccharose solution was from P H 0.1 to 0.4, the average about P H 0.2. 
This gain in acidity is very small when compared with that produced by 
Azotobacter—namely, 2.1. Because of the turbidity of the culture 
medium, which is caused by the great number of bacteria, it seems 
strange that there is only a slight change in the hydrogen-ion concen¬ 
tration. Determinations of the amount of sugar consumed by these 
organisms in liquid media offer an explanation for the small increase in 
acid. It has been found that R. leguminosarum may develop in enormous 
numbers without consuming more than 4 to 5 per cent of the total 
amount of sugar in the medium (9). 
SUMMARY 
The behavior of the legume bacteria as well as Azotobacter toward 
small amounts of acid or alkali depends upon many factors: Chief among 
these are the nature of the medium and the dissociation of the acid and 
alkali. 
All the results point to the fact that i?. leguminosarum regardless of 
strain, does not persist for any length of time in a medium, the reac¬ 
tion of which prevents reproduction. 
In these experiments, which were arranged to study the influence 
of reaction on the nitrogen-assimilating bacteria, 21 strains of R. 
leguminosarum and two of Azotobacter were studied. In general, R . 
leguminosarum showed similar cultural characteristics—that is, bacteria 
from different legumes. The most noticeable difference was that 
of rate of growth certain strains developing much more rapidly 
than others. On the ordinary culture media R. leguminosarum 
does not show any very characteristic growth. The identity of the 
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