Effect of azo dyes on growth and metabolism of Neurospora crassa. I. Relative resistance of Neurospora strains to azo dye inhibition.

Bobb, Dolores (Palo Alto Medical Research Foundation, Palo Alto, Calif.), Dorothy Liebes, and David A. Salzberg. Effect of azo dyes on growth and metabolism of Neurospora crassa. I. Relative resistance of Neurospora strains to azo dye inhibition. J. Bacteriol. 84:242-249. 1962.-Under conditions where growth factors were not limiting, 3'-methyl-4-monoaminoazobenzene, a rat hepatocarcinogen, inhibited growth of six Neurospora strains studied. The strains could be divided into three groups with regard to sensitivity. A wild-type and a leucine-requiring mutant were the most resistant, and the riboflavine-deficient strain, 51602, showed greatest susceptibility. Results suggested a possible correlation between the inhibition of strain 51602 and the ability of the mutant to synthesize riboflavine from its precursors. Inhibition was not dependent on the utilization of externally supplied riboflavine. The azo dye inhibition of all strains resulted primarily in a prolonged lag phase, although growth rates were affected to some degree. Spore germination did not appear to be retarded. A dose-response curve was developed to measure quantitatively the growth inhibition by azo dyes; it was based on the time required for inhibited and control cultures to reach identical growth weights.