A pilot survey on antimicrobial activity and diversity of soil-derived actinobacteria from different depths in Gudzhirganskoe saline lake in Eastern Siberia

To explore pharmaceutical actinobacteria from salty environments in Siberia, 8 soil samples were collected from different depths of Gudzhirganskoe saline lake, the Republic of Buryatia, Russia. Totally, 635 actinobacterial strains affiliated with 21 genera in 12 families of 7 orders were obtained by culture-dependent approaches. The predominant genus was Streptomyces (74.5%), followed by Microbacterium (4.9%), Agromyces (3.5%), Nocardiopsis (3.0%), and Kitasatospora (2.5%). Seven strains showed relatively low 16S rRNA similarities (<98.65%) with validly described species. Seventy-seven strains were selected as representatives to evaluate their antimicrobial activities and underlying mechanisms by paper-disk diffusion method and a double fluorescent protein reporter system (pDualrep2), respectively. Streptomyces sp. S6b3-1 was highlighted due to its strong inhibitory activities against Gram-positive bacteria and underlying antibacterial mechanism by inducing the SOS response in the reporter system. LG-1, (R)-6-[1-(benzoyloxy) ethyl]-phenazine-1-carboxylic acid, an analogue of saphenamycin was finally isolated from the culture broth of Streptomyces strain. This study preliminarily explored the actinobacterial diversity of soil samples collected in the highly alkaline and saline lake Gudzhirganskoe by culture-dependent approach and their capacity to produce antibiotics for the first time, which revealed that it deserves to make more efforts to discover new actinobacterial species and potential new antibiotics from the saline lake in Eastern Siberia.