Biotin deficiency has been found to result in greatly diminished ability to synthesize fatty acid, causing decrease in the lipid content of the mold. This decrease is accompanied by considerable increase in protein content of the mat.There is 30% reduction in lipid content of the mitochondria of the biotin-deficient molds. This should have resulted in the loss of mitochondrial integrity affecting the general metabolism of A. nidulans. On the other hand, under these conditions the mat weight of the mold increases.