Acidophilic actinomycetes of the «Vizeyska» mine dumps: isolation and comprehensive characterization

Aim. The purpose of this study was to investigate the cultural, morphological, physiological, and biochemical properties, as well as the enzymatic activity of the acidotolerant actinomycete isolates Viz 22-4 and Viz 22-5, obtained from the «Vizeiska» mine dumps, and to perform their phylogenetic analysis. Methods. The isolates were cultured on modified R2A medium. Growth at various pH levels was analyzed using Bennett’s medium, while morphological characteristics were evaluated on ISP1-ISP6 media. Hydrolytic activity was determined by standard methods, and the phylogenetic position was established based on 16S rRNA gene sequencing. Results. It was established that both strains are acidotolerant (growing at pH ≥ 4.0) but differ significantly in their phenotype. Strain Viz 22-5 produces abundant aerial mycelium and exhibits caseinolytic activity at pH 4.0. Strain Viz 22-4 grows more slowly, predominantly forming substrate mycelium, and shows no hydrolytic activity towards casein, pectin, starch, or methylcellulose. According to phylogenetic analysis, the isolates belong to the genera Nocardia (Viz 22-4) and Amycolatopsis (Viz 22-5). Conclusions. The isolated actinomycetes exhibit substantial functional heterogeneity and, based on phylogenetic results, were identified as members of the genera Nocardia and Amycolatopsis. The discovery of these microorganisms in the extreme conditions of mine dumps expands current understanding regarding the taxonomic biodiversity of so-called «rare» actinomycetes within mine dump microbiomes, highlighting their capacity for survival and metabolic activity in anthropogenically altered ecosystems.