Studies on Physiology of Some Plant Pathogenic Bacteria 
31 
Experiment V—The Influence of Varying Concentrations of Dextrose, 
Saccharose, Lactose and Glycerine Upon the Fermentative Activity 
Since acids are elaborated through the fermentation of carbohydrates by 
bacteria, one would expect on purely theoretical grounds, that the greater the 
concentration of carbohydrates the more potential acid. Under cultural condi¬ 
tions, however, definite optimum carbohydrate concentrations have been found 
to obtain in the case of the several species of bacteria which have been investi¬ 
gated, in order to permit of the production of their characteristic final pH 
' concentrations. Browne (7) found that 1 per cent of lactose for B. coli is 
optimum, that less titrable acid is produced in broth containing less than 1 per 
cent of lactose and that over 1 per cent of this sugar resulted in no increase. 
Sekiguchi (17) noted that 0.5-2.0 per cent of glucose is necessary for the maxi¬ 
mum production of acid by streptococci. Avery and Cullen (2) found that 0.4 
per cent of glucose is sufficient to permit the greatest production of acid with 
pneumococcus. Fred, Peterson and Davenport (13) in studies with xylose 
fermenting organisms found that 2 per cent of this sugar gave the maximum 
acidity. Streptococcus hemolyticus, according to Foster (12) requires between 
0.2 and 0.3 per cent glucose dependent upon initial reaction in order to attain 
its maximum pH value. 
The influence of the factor initial reaction upon final reaction, resultant 
upon fermentation, is furthermore demonstrated in studies by Wolf and Har¬ 
ris (21) with Bacillus Welchii and B. sporogenes, and by Wyeth (25) with B. 
coli. Various phases of another factor, buffer materials and buffer salts, and 
their influence upon the concentration of carbohydrate necessary if the organ¬ 
ism in question is to produce its characteristic final pH concentration, have 
been investigated by Clark (8), Kligler (16), Bronfenbrenner and Schlesinger 
(6) and Foster (12). These studies have established the fact that buffer ma¬ 
terials and buffer salts modify the rate of fermentation, the level of acidity, 
and concentration of sugar necessary in obtaining this final reaction. In the 
present studies which have been summarized in the Tables 6-9, media of the 
same initial reaction and buffer content with a variation only in carbohydrate 
concentration have been employed so that these factors may be disregarded in 
the data as presented. 
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