Process for the improvement of antibiotic production by in vivo genetic recombination

A process for the production of fermentation broths containing aminoglycoside antibiotics from Streptomycetes modified in antibiotic-producing ability by in vivo genetic recombination which comprises preparing a cultivation medium consisting essentially of sucrose and calcium and magnesium salts;

• cultivating genetically marked aminoglycoside antibiotic-producing Streptomycetes in said cultivation medium;
• separately cultivating prototrophic or unmarked aminoglycoside antibiotic-producing Streptomycetes;
• preparing protoplasts of said cultivated genetically marked Streptomycetes and of said cultivated prototrophic or unmarked Streptomycetes;
• chemically or physically inactivating said prototrophic or unmarked Streptomycetes protoplasts to make them nonviable;
• fusing said protoplasts of genetically marked Streptomycetes with said inactivated protoplasts of prototrophic or unmarked Streptomycetes;
• regenerating the fused protoplasts;
• assaying the resulting strains for antibiotic-producing capacity;
• selecting the strains with enhanced antibiotic-producing ability;
• and
• carrying out aerated, submerged fermentations with the novel strains so obtained in a medium containing organic carbon and nitrogen sources, inorganic salts, trace elements, and oils or fats or mixtures thereof.