The inhibition of growth of a wild strain ofNeurospora crassa by Cu²⁺ is counteracted by histidine, histidine methyl ester, histidinol and Mn²⁺. In the presence of Cu²⁺, the total free amino acid content decreased by 30%. The decreased free amino acid pools of arginine, histidine and tyrosine were restored on the addition of Mn²⁺. Histidinol phosphate phosphatase showed a decrease in activity in the presence of Cu²⁺. This inhibition was reversed on the addition of excess Mn²⁺. The data suggest that copper toxicity in the mould is due to suppression of histidine biosynthesis.

Uptake of Co²⁺ by cobalt-resistant strain is dependent on Co²⁺ concentration in the medium and is linear with time. The uptake is unaffected by metabolic inhibitors and decreased at low pH values. The uptake is independent of temperature in the range 0–40‡ C. The transport system is a passive diffusion process, unlike in the parent wild type strain where it is energy-dependent. It is possible that Mg²⁺ transport system is not involved in Co²⁺ transport in this strain, since the Co²⁺ uptake is not suppressed by Mg²⁺ as in the parent strain.

Bacitracin was more growth-inhibitory toNeurospora crassa on a minimal magnesium medium than on a normal magnesium-medium. Both magnesium and manganese were able to counteract the growth inhibition. The antifungal activity of bacitracin was potentiated by zinc. Potassium could not counteract the growth inhibition by this antibiotic. The mycelial magnesium levels were low in bacitracin-inhibited cultures.

Neurospora crassa Em 5297a can utilize sodium Β-glycerophosphate as a sole phosphorous source (in the place of KH2PO4). Under these conditions a repressible alkaline phosphatase is elaborated which has different pH optimum towards Β-glycerophosphate (10.2) and pyrophosphate (9.0) as substrates. This enzyme does not require any metal ion for its activity and could be assayed in the presence of EDTA. However, under conditions of cobalt toxicity, the activity of this enzyme is high and is decreased in copper and nickel toxicities.