Specific inhibition of candicidin biosynthesis by the lipogenic inhibitor cerulenin

Cerulenin, an inhibitor of fatty acid synthesis, inhibits specifically the biosynthesis of the polyene macrolide candicidin by resting cells of Streptomyces griseus. 50% inhibition was achieved with a cerulenin concentration of 1.5 μg/ml. Cells in which candicidin synthesis was inhibited for 10 h remained capable of candicidin synthesis after removal of the inhibitor. Cerulenin inhibits specifically the incorporation of ¹⁴C] propionate into candicidin but does not affect total protein or RNA synthesis. The uptake of ¹⁴C] propionate was not inhibited under conditions which totally prevented the incorporation of propionate into candicidin. Incorporation of p-amino¹⁴C] benzoic acid NH₂¹⁴C]BzO⁻ into the aromatic moiety of candicidin was also inhibited by cerulenin. The inhibitory action of cerulenin was not reversed by exogenous fatty acids. Since cerulenin is known to block the condensation of malonyl-CoA subunits in the formation of fatty acids, it is concluded that the polyene macrolide candicidin is synthesized via the polyketide pathway by condensation steps similar to those occurring in fatty acid biosynthesis.