Effect of cadmium and copper on the production of citric acid by Aspergillus niger.

Copper and cadmium inhibited the growth as well as citric acid production (depending on the heavy metal concentrations) by citric-acid-producing Aspergillus niger. Activity of citrate synthase was connected with citrate synthesis in the absence as well as in the presence of heavy metals. The activity of aconitase, and both NAD- and NADP-isocitrate dehydrogenases was strongly inhibited by copper. The contents of DNA and proteins in the cells decreased but the contents of lipids and polysaccharides increased considerably in the presence of both heavy metals.