Copper uptake in Aspergillus niger during batch growth and in nongrowing mycelial suspensions

Copper accumulation by the filamentous fungus Aspergillus niger from a glucose mineral salts medium containing copper in the concentration range 16 to 157 μ M was maximal in the lag phase of growth. In the subsequent linear growth phase, the mycelial copper contents were dramatically reduced on a per gram dry weight basis. The fungal mycelium exhibited pelleted morphology and exponential growth was not apparent. The medium pH was reduced during growth in flask cultures, but this was not responsible for the reduction in copper uptake as indicated by the similar effect in cultures grown in a stirred-tank fermenter with electronic maintenance of pH at 5.5. Voltammetric analysis of medium which had supported growth of the fungus showed that copper added at a final concentration of 40 μ M was complexed. Energy-dependent copper uptake from 2-( N-morpholino)ethanesulfonic acid buffer at pH 5.5 containing 40 μ M copper could not be demonstrated in nongrowing mycelium. Incubation at 4°C reduced copper uptake while the presence of 10 m M glucose or preincubation of the mycelium in 1 m M sodium azide had no effect on copper uptake.