Characterization of rhizospheric soil streptomycetes from Moroccan habitats and their antimicrobial activities

During an investigation on actinomycetes from rhizospheric soils from Moroccan habitats, 131 streptomycetes were recovered, morphologically characterized and assessed for their antimicrobial activity. Eleven isolates were characterized by the absence of an aerial mycelium. According to the colour of aerial mycelium, the rest were grouped into seven main classes, namely, grey, yellow, cream, white, green, red and polymorphic colours (pink, orange or violet). The grey colour class dominated (40%) and the red one was found only in rhizospheric soil of the Moroccan endemic plant Argania spinosa. About one third of the isolates (34%) produced soluble pigments of various colours and 14% produced melanoid pigments. Most of the isolates (83%) were active against one or more of the organisms tested (one gram-negative bacterium, three gram-positive bacteria, three yeasts and two filamentous fungi). Most antibiotic-producing isolates possess red and white colour. Strong antibiosis was exhibited against Streptomyces scabies, Staphylococcus aureus and Bacillus subtilis (75, 68 and 60% respectively), while only 14 and 8% of isolates displayed an activity against Escherichia coli and Verticillium dahliae respectively.