Isolation and characterization of actinobacteria of the genus Streptomyces under salt stress conditions

This study presents a comprehensive characterization of actinobacteria isolated from soils subjected to both anthropogenic pollution and secondary salinization. As a result of microbiological screening, two promising strains were selected - Streptomyces violaceorubidus strain N3 and Streptomyces rochei strain N4 - which demonstrated high salt tolerance, active colony and biomass formation, and pronounced antagonistic activity against several phytopathogenic fungi. Molecular genetic identification based on 16S rRNA gene sequencing, followed by phylogenetic analysis, confirmed the taxonomic affiliation of the isolates. Experimental data showed that both strains produce the phytohormone indole-3-acetic acid (IAA), exopolysaccharides (EPS), and the enzyme ACC deaminase, both under normal conditions and under salt stress (300 mM NaCl). Under saline conditions, an increase was observed in IAA production (by 31-34%), EPS synthesis (by 39-47%), and ACC deaminase activity (up to 42.8 nmol α-ketobutyrate/mg protein/h). The revealed physiological and biochemical traits suggest that S. violaceorubidus N3 and S. rochei N4 have high potential as microbial inoculants for enhancing plant resistance to abiotic (salt stress) and biotic (phytopathogens) environmental factors.