Keele Research Repository

Heavy metal toxicity was monitored in filamentous fungi by observing the effects of incorporating metal salts in a solid glucose mineral salts (GMS) medium on fungal colony extension. Copper, cadmium and zinc toxicity to Peicillium spinulosum, Trichoderma viride and Aspergillus niger was investigated by monitoring the effects of added metal on biomass production when supplemented in a liquid GMS medium.
Metal accumulation was determined in actively growing mycelium in GMS medium initially buffered at pH 5.5 with 50.0 mM MES containing added metal at non-toxic concentrations. Accumulation of metals appeared to be maximal during the lag phase of growth. This was followed by an apparent reduction in mycelial metal during the linear growth phase. Exponential growth was not observed. The medium pH at inoculation was critical for effective metal uptake.
Metal uptake by non-growing fungal suspensions was investigated by harvesting mycelium in mid-linear growth phase and resuspending in 50.0 mM MES buffer (pH 5.5) containing added metal. Uptake was initially rapid indicating wall binding. No energy dependence was demonstrated in subsequent metal uptake. Similar uptake patterns were observed for mycelium in the presence and absence of 10.0 mM glucose, in the presence of 1.0 mM sodium azide, under anaerobic incubation and also in isolated cell walls. Only incubation at 4 C reduced metal accumulation. Two possible metal binding sites were implicated in Penicillium spinulosum and these were shown to be non-specific for copper. Electron spin resonance measurements on copper loaded biomass indicated copper coordination to either 4 nitrogen or 2 nitrogen and 2 oxygen atoms. The evidence suggested that metal accumulation in filamentous fungi under the experimental conditions employed was a physical process, possibly by adsorption initially onto the cell wall, followed by internalisation by diffusion.