Occurrence of actinomycetes in forest soil

Abstract: Actinomycetes from the genus Streptomyces are Gram-positive bacteria commonly and in large numbers isolated from the soil, which is their natural habitat. Due to their metabolic activity and high adaptative capabilities they are an important link in the circulation of matter and energy. They play an impor-tant role in the formation of bioactive metabolites, mainly antibiotic compounds. In contrast to numerous elaborations concerning actinomycetes of cultivated soils, little is known about their occurrence in forest soils. The main factor limiting actinomycete development in forest soils is believed to be the low pH, as the development of most actinomycetes is facilitated by a neutral or alkaline soil reaction. However, these microorganisms have also been isolated from strongly acidic soils, which was confirmed in our studies. The pH value of analysed soils was in the range 4.0–4.3 (4.0 for bulk soil of alder; 4.1 for bulk soil of Scots pine; 4.3 for bulk soil of birch). Root soil of the analyzed trees contained more microorganisms than soil outside the range of the roots. This also concerned actinomycetes, eubacteria as well as saprophytic fungi. In our investigations the greatest num-ber of eubacteria were connected with the alder (bulk soil, rhizosphere and rhizoplane), and the smallest number with the pine, whereas actinomycetes were the most numerous in the birch rhizosphere. The analyzed actinomycete strains were identified to 18 taxa, with a dominant species Streptomyces exfoliatus