Cell-wall-bound metal ions are not taken up in Neurospora crassa

To establish the relevance of the cell wall in metal ion transport, cobalt uptake was examined in Neurospora crassa. Cobalt taken up was largely surface bound (>90%), resulting in a release of calcium and magnesium. Surface-bound cobalt could not enter intracellular locations upon further incubation of mycelia in a metal-free medium. Saturation of the surface with one metal augured subsequent dose-dependent entry of a different metal into intracellular locations. In comparison with the cobalt-resistant mutant, the cobalt-sensitive strain of N. crassa bound less cobalt on the surface but with significant intracellular accumulation. Our results demonstrate the importance of the cell wall in metal transport, toxicity, and resistance in fungi.