SUMMARY: Of 20 unidentified Streptomyces isolates tested, all inhibited and 18 inhibited in agar. Agar discs from inhibition zones, or paper discs placed beneath inhibition zones, of nine of the Streptomyces isolates caused new inhibition zones when transferred to fresh, seeded agar plates. Transferable inhibition zones were not produced by the other 11 isolates. Inhibitory substances were produced in liquid cultures by eight of the nine isolates which produced them in agar media, whereas no antibiotics were detected in liquid cultures of the other 11 isolates. conidia, which do not require exogenous nutrients for germination, germinated in liquid cultures of non-antibiotic-producing streptomycetes, but failed to germinate in cultures of antibiotic-producing streptomycetes. Inhibition zones produced by non-antibiotic streptomycetes decreased in size with increasing concentration of nutrients, whereas those of antibiotic streptomycetes were unchanged. Glucose and glutamic acid levels in agar rapidly decreased adjacent to streptomycete colonies. Agar, leached of nutrients by sterilized distilled water running slowly through a groove cut in the agar, developed clear inhibition zones. Therefore, inhibition of fungi by streptomycetes in agar, in some cases, appears to be due to nutrient deprivation.


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