The abundance and taxonomic diversity of actinomycetes in soils and plant litter in the Pu Hoat Nature Reserve of Central Vietnam were estimated. The number of mycelial actinobacteria in the studied substrates varied from 2.0 x 10(4) to 9.2 x 10(6) CFU/g. The largest number was recorded in the litter of the broadleaf forest in the Zut Suoi River valley. The length of the actinomycetal mycelium determined using direct luminescence microscopy varied from 178 to 800 m/g. The length of mycelium in the alluvial soils under broadleaf forest (Fluvisols) and in the mountain red-yellow ferralic soils under coniferous forest (Ferralsols) did not differ. The dominant species in the actinomycetal complex of the studied substrates were streptomycetes of sections Cinereus and Albus of the Achromogenes, Chromogenes, and Albus series. High taxonomic diversity was noted in the "suspended" soil from the baskets of epiphytes of the family Dryopteridaceae. Analysis of growth in the media with different pH values demonstrated the dominance of acidophilic forms of actinomycetes in the studied tropical soils. The study of temperature range of growth of the isolated cultures made it possible to classify them as thermotolerant and optionally thermophilic bacteria. The capacity for cellulose decomposition and the high antibiotic activity of pure cultures of actinomycetes from the studied soils attest to their considerable biotechnological potential.
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