Salt-tolerant plant growth-promoting (PGP) actinobacteria play an important role in enhancing
plant tolerance to salinity stress and improving crop productivity. Here, 9 morphologically distinct
actinobacterial isolates (A-I) were isolated from the rhizosphere soil of Oryza sativa cultivated in the
Nalgonda district, Telangana, screened for PGP characteristics (nitrogen fixation, indole-3-acetic acid
production (IAA), and phosphate solubilisation) and salt tolerance. Among them, isolate H exhibited
superior PGP activity and salt tolerance, growing in media containing up to 10% NaCl. Hence, it was
selected for further work. Isolate H produced cellulase, lipase, amylase and showed a positive catalase
reaction. It utilised glucose, fructose, galactose, and sucrose, but not maltose. Antibiotic susceptibility
analysis indicated that isolate H was partially resistant to penicillin but sensitive to tetracycline,
ciprofloxacin, and vancomycin. Molecular identification based on 16S rDNA sequencing (1,356 bp)
revealed that isolate H shared 99.78% sequence similarity and 99% query coverage with Streptomyces
levis NBRC 15423(T), suggesting that the isolate belongs to the genus Streptomyces. Seed germination
efficiency (%) revealed that the 24 hrs culture (T1
) of isolate H had a significantly greater effect on rice
seed germination than the 48 hrs culture (T2
). The germination rate of rice seeds in T1
was 86.67%,
followed by T2
(72.00%), the control (62.33%), and distilled water (55.67%), indicating that the 24 hrs
grown culture of isolate H may be used to enhance rice seed germination under salt stress. This study
provides preliminary evidence of the potential of a Streptomyces levis strain as a PGP bacterium under
saline conditions.
Keywords: Actinobacteria, Plant Growth-Promoting Characteristics, Salt-Tolerant Strain, Antibiotic Susceptibility
Analysis, 16S rDNA Sequencing.
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