HYDROGEN-ION CHANGES INDUCED BY SPECIES OF 
RHIZOPUS AND BY BOTRYTIS CINEREA 1 
By J. L. WeimER, Pathologist , and L. L. Harter, Pathologist , Office of Cotton, Truck 
and Forage Crop Disease Investigations, Bureau of Plant Industry, United States 
Department of Agriculture. 
Investigations with certain species of Rhizopus grown on nutrient 
solutions have suggested that some of them increase the hydrogen-ion 
concentration, while other closely related species decrease or have no 
action on the acidity. These results, obtained more or less incidentally, 
suggested that no sweeping generalizations could be drawn for all fungi 
from the results obtained from a few. In fact, they suggested that the 
results obtained from the study of one or more species could not be applied 
to all species of a single genus. It has been demonstrated by different 
investigations that Sterigmatocystis niger ( 12 ), 2 Aspergillus niger (j), Peni- 
cillium glaucum , and Botrytis cinerea (9), Citromyces pfejjerianus , C. 
glaber (6 ), and others produce acids (not the same acid in all cases) 
when grown in artificial culture media. Matsumoto (u) in a physio¬ 
logical study of 15 different isolations of Rhizoctonia found that the 
general tendency of these organisms was to increase the actual acidity 
during growth, the increase seemingly being proportional to the increase 
in growth. 
In investigations carried out by the writers it was shown that when 
Rhizopus tritici Saito was grown on sweet-potato decoction, a vigorous 
cell-wall-splitting enzym was produced, which separated the cells of 
sweet-potato disks along the line of the middle lamellae so that coherence 
was entirely lost. It was found, however, that when a modified Czapek’s 
nutrient solution with glucose as a source of carbon was employed as a 
substrate, the enzym was not produced but that a certain amount of 
maceration of the tissue of raw disks resulted, which was found to be 
caused by the acid formed. The hydrogen-ion concentration was about 
P H 1.70 to 1.80. If, on the other hand, pectin obtained from the carrot 
was substituted for glucose in the substratum, the cell-splitting enzym 
was secreted and the highest hydrogen-ion concentration was about 
P H 3.5. This is some increase in acidity over that of the original solution, 
but the total acidity was not sufficient to dissolve the middle lamellae. 
The writers (4) found that the different species of Rhizopus varied 
considerably in the amount of pectinase produced under identical condi¬ 
tions. They also found that some of the species whose enzym acted 
feebly upon raw disks, decayed sweet potatoes, under natural conditions, 
quite as vigorously as those which macerated tissue rapidly. With 
these facts in mind it was suspected that some relationship might exist 
between the ability of the different species to produce acids and their 
capacity for decaying sweet potatoes under natural conditions. It was 
shown that Rhizopus nigricans Ehrnb. did not decay sweet potatoes as 
rapidly as R. tritici; also that the action of the enzym in the solution 
in artificial culture on which it grew was very much slower than that of 
the latter organism. It was thought that this difference between some of 
1 Accepted for publication May 2, 1923. 
* Reference is made by number (italic) to “ Literature cited,” p. 163-164. 
( I 5S) 
Journal of Agricultural Research, 
Washington, D. C. 
afq 
Vol. XXV, N0.3 
July 21, 1923 
Key No. G-320 
