Germicidin A is a pyranone originally derived from S. viridochromogenes that acts as a reversible, autoregulative inhibitor of spore germination and hyphal elongation in the genus Streptomyces at concentrations as low as 200 pM. During germination, spores of Streptomyces excrete germicidin A along with other germicidin homologs, which inhibit germination of its own arthrospores. At higher concentrations, germicidin A can inhibit the porcine Na+/K+-activated ATPase (ID50 = 100 ?M) and prevent the germination of the cress L. sativum.