EFFECTS ON THE GROWTH OF MICROORGANISMS 269 



killing the bacteria, but no concentration of iodoacetate which inhibits 

 phage proliferation and does not depress bacterial growth could be found. 

 Price (1947) reported that 1 mM iodoacetate reduced staphylococcal ATP 

 and phage multiplication and, taken with the results of other inhibitors, 

 suggested that the mechanism is simply a depletion of energy for phage 

 synthesis. Now that the nature of phage proliferation is fairly well under- 

 stood, there is need of further investigation of the actions of iodoacetate 

 and related inhibitors in order to localize the site of action and to char- 

 acterize more accurately the role of the host cell metabolism in the forma- 

 tion of phage. 



Yeasts and Fungi 



Rapkine (1937) reported that yeast growth is essentially completely inhi- 

 bited by iodoacetate at concentrations around 0.3 mM and at pH 4.5, which 

 is not surprising since fermentation is abolished. The concentration for 50% 

 inhibition of growth was put at 0.011 mM by Loveless et al. (1954), yeast 

 being 10 times as sensitive as E. coli. The growth inhibition is partially 

 overcome by acetate and glutamate, but not by pyruvate (Schmid, 1958). 

 Actually, the effect of the pH is so marked that it is useless to compare the 

 results of different workers. Aldous (1948) demonstrated clearly that 1 mM 

 iodoacetate inhibits completely at pH 3.9 or below, 50% around pH 4.6, 

 and not at all above a pH of 5. How much of the inhibition is due to non- 

 specific damage by penetrating acid is not known. Hansen (1956 a) showed 

 the same relationship for bromoacetate, the concentration for 100% growth 

 inhibition of Tornla utilis being 4.32 mM at pH 5.2, and 0.079 mM at 

 pH 3.2. 



Halogenated fatty acids have been used commercially for their fungistatic 

 activity and again it is found that the effectiveness depends on the pH 

 (Hoffman et al., 1940). Shirk and Gertler (1958) investigated the relative 

 susceptibilities of several fungi to bromoacetate, and found 50% growth 

 inhibition to be given by concentrations between 0.1 and 0.5 mM, with no 

 marked differences between the organisms {Aspergillus, Penicillium, Pullu- 

 laria, Myrothecium, and Trichoderma) . Aspergillus niger growth is arrested 

 by iodoacetate and this is reversed by D-3-P-glycerate but not by cycle 

 intermediates (Behal, 1959). This fungus can convert 3-P-glycerate to hy- 

 droxypyruvate, which can also counteract iodoacetate inhibition, indicating 

 that in this organism there are pathways diverging from the EM pathway 

 which are important for growth (Behal, 1960). Wheat leaf rust {Puccinia 

 recondita) development is inhibited by concentrations of iodoacetate above 

 0.5 mM, but there is also progressive damage to the leaf, so that a selective 

 action on the mold is not possible. If it is possible at all to make compari- 

 sons, it seems that fungi are somewhat less sensitive than most bacteria to 

 iodoacetate, but this could be related to a better penetration of the inhi- 

 bitor into the bacteria. 



