Studies on Physiology of Some Plant Pathogenic Bacteria 
17 
Table 2.—Tolerance of Various Organisms to Acids in- Agar 
Name of 
Organism 
pH 4.4 
pH 4.6 
pH 4.8 
pH 5.0 
pH 
5.4 
pH 
5.6 
pH 
5.8 
Hydrochloric 
Sulphuric 
Oxalic 
Hydrochloric 
Sulphuric 
Oxalic 
Hydrochloric 
Sulphuric 
Oxalic 
Acetic 
Hydrochloric 
Sulphuric 
Oxalic 
Acetic 
Acetic 
Acetic 
Acetic 
Acetic 
Bacterium cam- 
pestre - _ 
-+ 
+ 
+ 
— 
+ 
+ 
+ 
— 
— 
-+ 
+ 
+ 
Bacillus caro- 
tovorus__ 
— 
-+ 
— 
+ 
+ 
+ 
+ 
+ 
+ 
— 
+ 
+ 
+ 
+ 
+ 
-+ 
—+ 
+ 
Bacterium gly- 
cineum . _ - 
— 
— 
— 
— 
+ 
— 
—+ 
+ 
— 
— 
+ 
+ 
+ 
— 
— 
— 
— 
+ 
Bacterium sojae_ 
— 
— 
— 
— 
— 
— 
+ 
+ 
— 
— 
+ 
+ 
+ 
— 
— 
— 
— 
+ 
Bacterium angu- 
latum.. _ _ 
— 
— 
— 
— 
— 
— 
+ 
+ 
— 
— 
+ 
+ 
+ 
— 
— 
— 
— 
+ 
Bacterium tabacum 
~ 
-+ 
+ 
" 
+ 
+ 
+ 
“ 
-+ 
+ 
More recently, Cohen and Clark (3) from cultural studies on B. coli pointed 
out that the factor or factors which obscure the effect of the H-ion are quite 
unknown. They noted that this organism grew well at pH 5.0 when adjust¬ 
ment was made with HC1, but at pH 5.45 with acetic acid the same organism 
declined in numbers. Other organisms exhibited the same difference in con¬ 
duct with reference to these two acids. They explain this as probably due to a 
synergic effect of the free acetate radicle upon the disinfecting power of the 
hydrogen ion, a view in accord with those who hold that the anions and un- 
dissociatecf molecules play an important role in the kinetics of disinfection by 
accelerating the action of the hydrogen ion. They also suggest the probability 
that this difference corresponds to a difference in permeability of the organ¬ 
ism to mineral and organic acid. 
Were one in possession of full knowledge of the unknown factor involved in 
the foregoing observations, he could no doubt explain what is believed to be a 
comparable condition reported by Svanberg (4). He found that Streptococcus 
lactis (Bacterium lactis acidi) in milk is capable of producing an acidity which 
corresponds to the value pH=4. When, however, lactic acid is added to 
milk, growth is checked at pH=4.4-4.7 and acetic acid at pH=4.8-5.1. 
The plant pathogenes used in the present investigation appear to respond 
differently toward the various acids just as did the several organisms em¬ 
ployed in these several studies. This may be taken to indicate that the various 
acids exert a specific effect. Granted that the effect is specific, it is not clear 
how one could employ this fact in explaining the general shift of the limit of 
tolerance of 0.2-0.4 pH as occurs between bouillon and nutrient agar. It is 
felt, however, that this observation should be reported at this time on its own 
merit, subject to verification, and with the admission that no adequate expla¬ 
nation of the cause is known to us. It is believed that the fact of a greater 
pH tolerance on solid media is of significance in studies which attempt to cor¬ 
relate the acidity of juices of certain plants with tolerance in culture of forms 
parasitic on these same plants. 
3 
