Summary: The ability of a variety of 2-substituted benzimidazoles to inhibit germ-tube elongation in conidia was determined. Contact with a solid surface, such as agar or glass-wool strands, was an essential requirement for germination. The degree of inhibition which benzimidazole derivatives exerted on germ-tube elongation varied markedly with the substituted group; 2-(4'-thiazolyl) benzimidazole (TBZ) was most active. Germ-tube elongation proceeded linearly on agar media and was unaffected by benzimidazole derivatives existing as cations. Inhibition occurred only when the pH of the medium neared, or exceeded, the pK of the benzimidazole derivative being tested. Inhibition of respiration with exogenous glucose after 3 to 4 h of exposure of germinating spores to TBZ appeared to be only an indirect effect of TBZ action; TBZ, in concentrations 100 times that necessary to inhibit growth, failed to affect oxygen uptake or respiratory control of isolated mitochondria with a variety of substrates. TBZ inhibition of germ-tube elongation was partially eliminated by high concentrations of vitamin B. TBZ treatment produced distorted mycelial growth with increased vacuo-lation and elevated RNA/DNA ratios. These data suggested a condition of unbalanced growth similar to that caused by vitamin B deficiency in bacterial and mammalian cells. TBZ may act as a precursor (replacing 5,6-dimethyl benzimidazole) in the formation of an inactive vitamin B coenzyme analogue.


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