Abstract: High titers of polyether antibiotics are obtained in a fermentation broth by inoculating a nutrient fermentation broth with a microorganism capable of producing a polyether antibiotic. Growth of the microorganism is established in the broth by incubating the inoculated broth at a physiologically acceptable temperature until pH of the broth begins to rise upon establishment of growth of the microorganism. A free fatty acid then is fed into the broth to achieve and maintain a free fatty acid concentration in the broth of about 0.1% by weight or greater but less than a level at which the free fatty acid is toxic to the microorganism. The free fatty acid is fed into the broth during the remainder of fermentation at about a rate at which the free fatty acid is consumed by the microorganism, to product high titers of the polyether antibiotic.

Abstract: A polyether and antibiotic material is prepared by forming discrete polyether antibiotic-containing agglomerates which are separable from an aqueous medium, by producing a polyether antibiotic through cultivation of a polyether antibiotic-producing microorganism in a generally aqueous nutrient-containing fermentation broth under conditions wherein at the end of fermentation, a lipid is present in the broth in a sufficient amount to form discrete agglomerates with polyether and antibiotic in the fermentation broth, whereupon the applomerates are separated from the broth.