The main objective of the study is the evaluation of the diversity of actinobacteria associated with Polytrichum strictum — dominant species of widespread Antarctic Тall moss turf subformation and their characteristics as the producers of biologically active compounds. The actinobacterial isolates were isolated by direct inoculation, phenol pretreatment, and heated treatment. The cultural properties of the isolates were evaluated using diagnostic media. The antimicrobial activity of the isolates was determined by the point inoculations method. The phylogenetic analysis was based on sequence analysis of the 16S rRNA gene. The biosynthetic genes screening was performed using polymerase chain reaction. A total of 23 actinobacterial isolates associated with P. strictum were isolated, the four identified genera being Streptomyces (7 isolates), Micromonospora (14 isolates), Kribbella (1 isolate), and Micrococcus (1 isolate). Eight psychrotrophic strains of all identified genera were identified. The optimal pH values for all isolates were in the range 6–10. Four isolates grew on the medium with 7.5% NaCl. A significant number of the isolates showed a wide range of enzymatic activities. Antagonists of a wide range of pathogenic microorganisms were found, including against multidrug-resistant strain of Candida albicans and Methicillin-resistant Staphylococcus aureus. Some strains were active against phytopathogenic bacteria, namely three strains against Erwinia amylovora, one strain against Agrobacterium tumefaciens, and one strain against Pectobacterium carotovorum. More than half of the isolates showed antifungal activity against Fusarium oxysporum and Aspergillus niger. The biosynthetic genes involved in synthesizing a wide range of bioactive compounds were found in more than 80% of isolates. Antarctic actinobacteria isolated in this study demonstrate potential as the producers of a wide range of biologically active compounds. Further studies of these actinobacteria may lead to the identification of previously unknown biologically active compounds.

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Hrunyk N. I., Shalovylo Yu. I., Yusypovych Yu. M., Roman I. I., Nesmelova I. V., Kovaleva V. A. Prokaryotic expression and purification of bioactive defension 2 from Pinus sylvestris L. Studia Biolo gica, 2019: 13(2); 29-40 • DOI: https://doi.org/10. 30970/sbi.1302.603 N. I. Hrunyk, Yu. I. Shalovylo, Yu. M. Yusypovych, I. I. Roman, I. V. Nesmelova, V. A. Kovaleva ISSN 1996 • ISSN 2311-0783 (on-line) • Біологічні Студії / Studia Biologica • 2019 • Том 13/№2 • С. 29-40 using the ion exchange on the SP-Sepharose Fast Flow column and a step gradient of 0.05-1 M NaCl. The purity of obtained recombinant PsDef2 was higher than 95 %, as verified by 16.5 % SDS-PAGE. The recombinant peptide PsDef2 showed activity against phytopathogenic Fusarium sporotrichiela fungus and Phythophtora gonapodyides oomycete at 5 µM concentration. The availability of recombinant PsDef2 gives an option not only to examine its antimicrobial properties but to study its structure by spectroscopic methods (circular dichroism, NMR) in order to esta blish relationships between the structure and function of pine defensins.

Microbial natural products are among the main sources of compounds used in the medical biotechnology field for the purpose of drug development. However, as antibiotic resistance in pathogenic microorganisms is known to be increasing dramatically, there exists a need to develop new antibiotics. Actinomycetia have proven to be a good source of biologically active compounds, although the rediscovery of previously known compounds significantly slows down the introduction of new antibiotics. As a consequence, increasing attention is being paid to the isolation of actinomycete strains from previously unexplored sources, which can significantly increase the likelihood of discovering new biologically active compounds. This study investigated the diversity and bioactive potential of 372 actinomycete strains isolated from the rhizosphere soil of Juniperus excelsa M. Bieb. The examined actinomycete strains belonged to 11 genera, namely, Actinoplanes , Actinorectispora , Amycolatopsis , Kribbella , Micrococcus , Micromonospora , Nocardia , Promicromonospora , Rhodococcus , Saccharopolyspora and Streptomyces . The bioactive potential of each isolated actinomycete strain was determined on the basis of its ability to produce antimicrobial metabolites against Gram-positive and Gram-negative bacteria and yeast. Some 159 strains (42.74%) exhibited antimicrobial activity against at least one of the tested microbial strains. The dereplication analysis of the extract of the Streptomyces sp. Je 1–651 strain, which exhibited strong antimicrobial activity, led to the annotation of spiramycins and stambomycins. Moreover, the phylogenetic analysis based on the 16S rRNA gene sequence of the Je 1–651 strain revealed it to be close to the S. ambofaciens . Supplementary Information The online version contains supplementary material available at 10.1007/s12223-023-01047-x.

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