Process for producing A73A, a new Efrotomycin-like antibiotic in fermentation broth

A method of producing A73A having the following structure:

• ##STR3## wherein the pyran has the following configuration at its asymmetric centers:
• S at the hemiketal carbon 2, R at the hydroxyl bearing carbon 4, and S at the pentadienyl side chain bearing carbon 6 which comprises cultivating an A73A-producing strain of Streptomyces viridifaciens in a fermentation broth containing assimilable sources of carbohydrates, nitrogen and inorganic salts under aerobic conditions until a substantial amount of A73A is produced in the fermentation broth and recovering said antibiotic.