Isolation and characterization of halotolerant bacteria from Indonesian sand dunes ecosystem and their plant growth-promoting properties

Abstract The Parangkusumo sand dune is a tropical coastal ecosystem in Indonesia with unique characteristics, such as high salinity, high temperatures, and limited nutrient availability. This study isolated and characterized halotolerant plant growth-promoting rhizobacteria (PGPR) from the rhizosphere and soil of the halophyte Calotropis gigantea in this unique environment. Ten bacterial isolates dominated by genus Bacillus were identified. Functional assays revealed significant properties among the isolates, including phosphate solubilization, nitrogen fixation, cellulolytic activity, and anti-phytopathogenic. Three Bacillus species, B. aryabhattai , B. subtilis, and B. subtilis subsp. spizizenii exhibited superior salt tolerance and plant growth-promoting attributes under normal and high-salinity conditions. The three bacterial isolates demonstrated synergistic activity through antagonistic testing, indicating their potential for biofertilizer consortium. Notably, a consortium of these strains significantly enhanced sesame ( Sesamum indicum ) seed germination and biomass under salt stress, outperforming single-strain inoculations. These findings highlight the potential of these halotolerant PGPR as biofertilizers for sustainable agriculture in saline or nutrient-poor environments. The results of this study suggested further possibilities of field applications to optimize these strains for broader agricultural use.