In the previous reports^1,2), the author described his studies on the improvement of the strain for the capacity of pyridomycin production. The lactose-utilizing mutants of Streptomyces pyridomyceticus had the high capacity, and the mutant having the highest capacity for pyridomycin production utilized tryptophan as the carbon source. In this paper, media suitable for pyridomycin production and a method of detecting precursors of pyridomycin are presented. This method is considered to be applicable to precursor studies of antibiotics in general.

Among natural products soybean meal was one of the nitrogen sources suitable for pyridomycin production, and among carbohydrates glucose was a suitable carbon source. The addition of phosphate promoted the production. Thus, a complex medium suitable for the practical production of pyridomycin was established. In synthetic media containing glucose and inorganic salts, pyridomycin was produced, when aspartic acid, glutamic acid, asparagine or ammonium phosphate was used as the nitrogen source in the presence of pyridoxine. In the medium containing aspartic acid or glutamic acid with pyridoxine and inorganic salts, pyridomycin was produced, when glucose, gluconic acid, or arabinose was used as the carbon source. The cotton pin method of detecting precursors indicated that there were four kinds of substances promoting pyridomycin production in 40 hours’ shaken-cultured liquid of the pyridomycin-producing strain. Three of them were confirmed to be serine, tryptophan and kynurenine by paper chromatography. The other one was not identified yet, but it has a similar ultraviolet absorption spectrum to that of pyridomycin.

The present studies suggested that, when glucose was metabolized through gluconate and pentose, pyridomycin would be produced, and tryptophan metabolism would have relations to pyridomycin production. Maeda³⁾ confirmed the existence of pyridine nucleus in pyridomycin, and this part is considered to be built through tryptophan.

In the previous report¹⁾, the author presented a complex medium suitable for pyridomycin production and described that 40-hours shaken-cultured broth of the pyridomycin-producing strain contained four kinds of substances promoting pyridomycin production. Three of them were ascertained to be serine, tryptophan, and kynurenine. It was suggested that pyridomycin would be produced through tryptophan and kynurenine. The author also described that pyridomycin was produced in synthetic media from glucose, gluconic acid, and arabinose. These results suggested that, when glucose was metabolized through gluconic acid-pentose, pyridomycin was produced. These points were further studied and presented in this paper.

Homomycin¹⁾, an antibiotic specifically active against bovine and human tubercle bacilli, has been found in the course of screening antituberculous antibiotics using bovine tubercle bacillus BCG as a test organism²⁾. The antibiotic has been obtained from culture filtrates of hitherto undescribed streptomycete, Streptomyces noboritoensis, which was isolated from a soil sample collected at Inada-noborito, Kawasaki City, Kanagawa Prefecture. It is almost nontoxic for mice and showed some therapeutic effect on experimental tuberculosis of mice.

Homomycin has been prepared as its purified powder as well as its crystalline 2, 4-dinitrophenylhydrazone. The analytical data and molecular weights of those indicated the molecular formula to be C₂₃H₂₉NO₁₂. The comparative studies with the similar antibiotic, hygromycin³⁾ indicated both were identical and the formula of hygromycin reported as C₂₅H₃₃NO₁₂ should be corrected*. The taxonomic studies showed St. noboritoensis belonging to the chromogenic type, differs distinctly from St. hygroscopicus, the hygromycin-producing strain. St. noboritoensis simultaneously produces an antibiotic, blastomycin**, specifically active against plant pathogenic fungus, Piricularia oryzae, and a basic antibiotic active against gram-positive bacteria in certain condition of cultivation.

The present paper deals with taxonomic studies of St. noboritoensis, isolation and properties of homomycin as well as the identity with hygromycin.