Cobalt transport in nickel-resistant strains ofNeurospora crassa

Uptake of Co²⁺ by three nickel-resistant strains (Ni^R1, Ni^R2, and Ni^R3) ofNeurospora crassa that differed in resistance to Co²⁺ has been studied. Uptake was linear with Co²⁺ concentration (up to 1 mM), with time (up to 6 h), and with pH between 3 and 6. Uptake rates were in the order Ni^R2>Ni^R1>Ni^R3. In all strains, there was gradual increase in Co²⁺ uptake between 10° and 28°C, with a much sharper increase between 28° and 40°C. Metabolic inhibitors decreased Co²⁺ uptake partially in all strains, except for KF in Ni^R3. About 50–80 g Co²⁺/100 mg dry weight was surface bound. Ni²⁺, Zn²⁺, and Mn²⁺ competed with Co²⁺, the effects being strain specific. Mg²⁺ inhibited Co²⁺ uptake in all strains with preformed mycelia. In Ni^R1 and Ni^R2 only with young mycelia (40 h old) was Mg²⁺ inhibitory to Co²⁺ uptake,during growth in the presence of Co²⁺. The results suggested the presence of two transport systems for Co²⁺ in Ni^R1 and Ni^R2, only one of which was sensitive to Mg²⁺; in contrast, Ni^R3 had a single system, which was sensitive to Mg²⁺.