PLANT GROWTH PROMOTING AND BIOCONTROL ACTIVITIES OF Streptomyces sp. STRAIN BT21

Endophytic actinobacteria play vital roles in plant health and biocontrol, yet their potential in Algerian medicinal plants remains understudied. This research reports the isolation and characterization of Streptomyces sp. strain BT21 from the root of Artemisia herba-alba Asso collected in Batna Province, Algeria. Using morphological, biochemical, physiological, and molecular approaches, strain BT21 was identified and evaluated for its potential as a bioactive agent. Sequence analysis of the 16S rRNA gene (1,454 bp) revealed 99.24% similarity between strain BT21 and Streptomyces specialis GW41-1564T, supporting its morphological identification. Strain BT21 also demonstrated halotolerance and growth over a wide range of temperatures and pH, indicating strong environmental adaptability. This strain also demonstrated plant growth-promoting (PGP) traits, including positive ammonia production and atmospheric nitrogen fixation, although it lacked phosphate solubilization activity. Additionally, the strain exhibited broad-spectrum antibacterial and antifungal activities, with inhibition zones reaching up to 28 mm against Micrococcus luteus ATCC 9314 on SMG and SMA media. Furthermore, the antifungal activity of strain BT21 was observed against all the tested fungi on various media, including SMG, SML, SMA, SSMG, and SSML, with inhibition zones ranging from 13 to 25 mm. Notably, the antimicrobial activities were significantly influenced by culture media composition. The strain produced key extracellular enzymes, including amylases, cellulases, esterases, proteases and chitinases, which are important for nutrient cycling and pathogen suppression. The combined biocontrol and PGP properties of strain BT21 suggest promising applications in sustainable agriculture and biotechnology. Future work will focus on genomic analysis and in vivo evaluation to unlock the full potential of this endophytic Streptomyces strain.