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Abstract
The rates of growth of five strains of Aspergillus niger (m, mubli, nrrl 334, nrrl 323, nrrl 346) were followed in an optimum nutrient solution. The time course of growth of all the strains showed a steep decrease after 3 days, except that of strain NRRL 346 which tended to flatten out. A correlation between sporulation and mycelial dry weight was observed. All the five strains showed a marked decrease in mycelial yield in the absence of manganese from the basal medium. Their quantitative responses to graded concentrations of Mn in the medium were compared with spore and mycelial inocula. Statistical analyses of the result suggest that strain mubli is the most suitable test organism for the bioassay of Mn. The effective range of concentrations of Mn which coincided with the maximum differences in mycelial dry weights was 0·001–0·006 μg./ml.
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