MELANOGENIC ACTINOMYCETES (STREPTOMYCES SPP) FROM BRAZILIAN SOILS

Melanogenic actinomycetes were isolated from cerrado soils. Starch agar with a neutral pH was the best medium for selecting pigment-producing colonies. A pigmentation screening test selected 52% of these as possible melanin producers. Tests on liquid (organic and inorganic) and solid (peptone and tyrosine) media, and enzymatic tests, confirmed about 90% as melanin producers, 68% as dihydroxyphenylalanine (DOPA)-melanin and 32% as possible other kinds of melanin producers. Melanin production occurred mostly with an organic N, or an inorganic N with an additional organic N source. An exception was observed with three strains, which were able to produce melanins with an entirely inorganic N source in the medium. Instability of melanin production was a common feature in many strains. Further characterization of melanins produced by actinomycetes compared with soil humic acids may clarify the possible role of melanogenic actinomycetes in soil organic matter formation.