HYDROGEN‐ION EQUILIBRIUM OF MYCELIAL MATS OF FUSARIUM LYCOPERSICI IN SALT SOLUTIONS AND ITS RELATION TO GROWTH AND TOXICITY

Abstract

In earlier publications Robbins and Scott (4), and Scott (6) presented experimental evidence which showed that when living mycelial mats of certain filamentous fungi grown in nutrient solutions were thoroughly washed in distilled water and placed in dilute single-salt solutions at different hydrogen-ion concentrations, the reaction was shifted in a short time to a pH value which was specific for each form studied. Thus, for a strain of Gibberella Saubinetii the equilibrium point occurred at pH 6.4; for a strain of Fusarium oxysporum, at pH 4.9; and for a strain of Fusarium Lycopersici, at pH 5.4-5.5. In other words, when the washed mats were placed in salt solutions acid to the equilibrium point of the strain used, the reaction was quickly changed to less acid until the equilibrium point was reached, whereas in salt solutions alkaline to the equilibrium point the reaction was quickly changed to more acid until the equilibrium point was reached. In solutions at the equilibrium point little or no change in reaction occurred. Robbins (2) has also demonstrated in the case of Fusarium Lycopersici that acid dyes are held by the mycelial mats on the acid side of pH 5.5, while basic dyes are held on the alkaline side of this point. Scott (5) showed that a reaction of culture media at or near pH 5.5 gave a minimum of growth of this same organism, and later (6) reported that spore germination was at a minimum at this critical point. Toxic anions inhibited spore germination most on the acid side of pH 5.5, whereas toxic cations inhibited germination to the greatest extent on the alkaline side of this point. Shuck (7), working in our laboratories, has determined that the equilibrium point for another strain of Gibberella Saubinetii in dilute solutions of sodium chlorid was at pH 5.7; for a strain of Fusarium vasinfectum at pH 5.4; and for a strain of Fusarium moniliformne, at pH 5.9. These same points were also found by Shuck to be critical in the uptake of acid or basic dyes by the fungous mats at different hydrogen-ion concentrations. In all of the earlier work done in these laboratories the mycelial mats were removed from the culture solutions and thoroughly washed in a number of changes of distilled water before proceeding with the equilibrium