The Impact of Synthetic Osmoprotectants and Salsola vermiculata on Growth of Streptomyces sp.AH1 Isolated from an Arid-Soil

Soil salinity is a major environmental constraint that adversely affects microbial growth and plant productivity. Actinomycetes are recognized as important producers of phytohormones, particularly indole-3-acetic acid (IAA), while halophytes possess the ability to produce and accumulate osmoprotective compounds. This study aimed, first, to isolate actinomycetes from arid soil and screen the isolates for high IAA production and, second, to evaluate the osmoprotective effects of the halophyte Salsola vermiculata and the synthetic osmoprotectants glycine betaine, proline, and trehalose on the growth of an actinomycete strain isolated under saline conditions. Eleven actinomycete strains were isolated from soil collected in southern Setif, Algeria, using starch-casein agar medium. Based on cultural characteristics, strain AH1 was identified as Streptomyces sp. AH1 and produced a high level of IAA (84.30 ± 0.3 μg mL-¹). Neutral pH and temperatures of 25 and 30°C were found to be favorable for IAA production, yielding 64.00 ± 0.4, 81.18 ± 0.4, and 85.25 ± 0.2 μg mL-¹, respectively. The growth of Streptomyces sp. AH1 under high NaCl concentrations was significantly enhanced by the addition of glycine betaine, proline, and trehalose. Similarly, Salsola vermiculata exhibited a pronounced osmoprotective effect, significantly increasing actinomycete growth under saline stress. Growth rates increased by 10.69 times and 10.01 times at 0.5 and 0.8 M NaCl, respectively. Overall, S. vermiculata significantly improved the growth of Streptomyces sp. AH1 in the presence of NaCl, demonstrating its strong osmoprotective potential. The combined use of beneficial actinomycetes and halophytes as biofertilizers or biostimulants could help mitigate the detrimental effects of soil salinity and represents a promising approach for improving plant growth and agricultural productivity in saline soils.