A cadmium-tolerant strain of Neocosmospora vasinfecta shows reduced cadmium influx

Neocosmospora vasinfecta was grown in a defined liquid medium and its growth responses to CdSO 4 were measured. The specific growth rate of mycelium not previously exposed to cadmium was reduced to 50% by 51 μM cadmium. The growth response to concentrations of cadmium above 50 μM was complex, showing declining and then recovery phases. Inoculum taken from a culture grown to the recovery phase in presence of 100 μM cadmium was cadmium tolerant; a cadmium level of 420 μM was required to reduce its specific growth rate by 50%. Tolerance was not lost by growth in the absence of cadmium. The tolerant mycelium showed markedly reduced net uptake of cadmium as compared with the normal (cadmium sensitive) mycelium. This reduction was due to a decrease in the unidirectional influx of cadmium, with little or no change in efflux. Cadmium toxicity in the normal mycelium was strongly antagonized by calcium but only weakly by manganese or zinc. Calcium also inhibited the uptake of cadmium.