Metal ion influence on the growth inhibition ofNeurospora crassa by bacitracin

The growth-inhibitory activity of bacitracin onNeurospora crassa is dependent on the source of nitrogen and phosphate, as well as the presence of certain divalent metal ions in the medium. Whereas supplementation of manganese, calcium, and magnesium resulted in the mitigation of the growth inhibition by bacitracin, supplemental copper, in contrast, potentiated it more than 30-fold over controls, as evidenced by 50% growth-inhibitory (I₅₀) values. Bacitracin interfered with the transport of metal ions, as observed with an altered contents of Mn²⁺, Cu²⁺, Na⁺, and K⁺ in bacitracin ±Cu²⁺-treated cultures vs. controls. The decreased K⁺ content in bacitracin ±Cu²⁺-treated cultures indicated possible membrane damage as the mechanism of action. Alterations in amino acid pool size and total nitrogen content induced by bacitracin are secondary effects as a consequence of the loss of membrane permeability.