Abstract

Twenty three halotolerant bacteria were isolated from the rhizosphere of some halophytic plants (Avicennia marina, Suaeda monoica, Aeluropus lagopoides, and Capsella rubella) in Jazan, Saudi Arabia. The effect of the rhizobacteria on the germination of Vigna radiata seeds and Zea mays grains was evaluated. The morphological and biochemical characterization in addition to the antibiotic resistance profile of the most effective isolates were studied. Using 16S rRNA gene sequencing analysis, the isolates were identified as Halomonas sp. M3, Bacillus subtilis M4, Bacillus thuringiensis A3, and Pseudomonas sp A5. The maximum growth was recorded at 0.5 M NaCl for B. subtilis, B. thuringiensis, and Pseudomonas sp. while the highest growth of Halomonas sp. was recorded at 1.0 M NaCl. A clear enhancement of the growth parameters of V. radiata and Z. mays seedlings treated with halotolerant rhizobacteria under salinity stress was recorded. Gas chromatography–mass spectrometry revealed the presence of various bioactive compounds in the bacterial exudates where the heterocyclic organic compounds including pyrrolo [1,2-a]pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)- and pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro-3-(phenylmethyl)- were the most abundant metabolites. The ameliorative influence of the halotolerant rhizobacteria on the growth of plant seedlings under salinity stress could be attributed to the presence of a broad spectrum of secondary metabolites.

Key words: Halotolerant – rhizobacteria – salinity – seedlings – GC/MS- metabolites.