Isolation and selection of salt-tolerant, IAA-producing microorganisms from saline soils in Diem Dien, Hung Yen province, Vietnam

Abstract

Soil salinity is a major environmental stress limiting agricultural productivity and plant growth. This study aimed to isolate and characterize salt-tolerant, plant growth-promoting bacteria (PGPB) from saline soils, with a focus on their ability to synthesize indole-3-acetic acid (IAA). Three bacterial strains were isolated and identified through colony morphology and 16S rRNA gene sequencing as Bacillus inaquosorum, Bacillus cabrialesii, and Ensifer sesbaniae. All strains demonstrated tolerance to elevated NaCl concentrations (2%, 4% and 8%) however, the growth and IAA production varied (4.59ug/ml to 43.53 ug/ml) depending on salt levels. B. inaquosorum and B. cabrialesii exhibited the highest IAA production, particularly under moderate salinity (2–4% NaCl), while E. sesbaniae produced lower IAA but maintained growth under salt stress. IAA synthesis decreased substantially at 8% NaCl, indicating that high salinity imposes metabolic constraints on hormone biosynthesis. Overall, the results highlight that B. inaquosorum and B. cabrialesii are strong candidates for use as microbial inoculants to enhance plant growth in saline soils. The findings provide a basis for the development of sustainable biofertilizers for crop cultivation in salt-affected agricultural environments. Keywords: Indole-3-acetic acid, plant growth-promoting bacteria, salt tolerant bacteria, soil rehabilitation