Morphological and molecular characterization of plant growth promoting salt-tolerant bacteria associated with halophytes in the Southeast seaside of Vietnam

Abstract

Halophytes are found in high-salt environments naturally, and their roots may be associated with promising microbial candidates for promoting crop growth and salt tolerance. In this study, halotolerant bacteria were isolated from soil and root samples of Rhizophora apiculate (R. apiculate), Avicennia ofcinalis (A. ofcinalis), Thespesia populnea (T. populnea), Acanthus ilicifolius (A. ilicifolius) and Trichophorum cespitosum (T. cespitosum), five native halophytes of southeast seaside of Vietnam. Isolates were tested for maximum salt tolerant and screened for the ability of phosphate solubilization and indole acetic acid (IAA) production. Colony morphology, pigmentation, and Gram staining of each IAA production halotolerant isolate were determined. The bacterial isolates showed the highest salt tolerance and IAA production were identifed by sequencing the 16S rRNA gene. A total of 54 isolates which were able to grow in the presence of up to NaCl 3M were isolated. Twenty-three halotolerant bacterial isolates had the capacity of IAA production, 60.9% from which were Gram positive with a cocci shape, colony in opaque/transparent yellow or opaque/off white, 1 - 2 mm or 2 - 3 mm in diameter with the convex surface. Three isolates VTDD1, VTTD2, and KGOR1 were able to solubilize insoluble phosphorus. The highest IAA production was observed in VTDR1 (93.77 µg/mL) followed by VTMR1 (75.23 µg/mL) and VTDR2 (60.00 µg/mL), while the smallest IAA production was observed in CGOD1 (0.50 µg/mL). The isolates VTDR1 and VTDR2 were identifed as Salinicola tamaricis (99.58% and 99.67% identity respectively), while VTMR1 was found to be Salinicola peritrichatus (98.37% identity).