Screening halotolerant bacteria for their potential as plant growth-promoting and coal-solubilizing agents

The bioconversion of salinized land into healthy agricultural systems by utilizing low-rank coal (LRC) is a strategic approach for sustainable agricultural development. The aims of this study were: (1) to isolate bacterial strains associated with the rhizosphere of native plants in coal-containing soils, (2) to characterize their plant growth-promoting (PGP) and coal-solubilizing capabilities under laboratory conditions and (3) to evaluate their influence on the germination and growth of chia seeds under saline stress. Fourteen bacterial cultures were isolated from the rhizosphere of Artemisia annua L. using culture media containing salt and coal. Based on their PGP activities (nitrogen fixation, phosphate solubilization, siderophore and indole-3-acetic acid production), five strains were selected, belonging to the genera Bacillus, Phyllobacterium, Arthrobacter, and Pseudomonas. Solubilization assays were conducted to confirm the ability of these strains to utilize coal efficiently. Finally, the selected strains were inoculated with chia seeds (Salvia hispanica L.) to evaluate their ameliorating effect under saline stress conditions in coal-containing media. Inoculation with A. subterraneus Y1 resulted in the highest germination and growth metrics of chia seeds. A positive but comparatively weaker response was observed with P. frederiksbergensis AMA1 and B. paramycoides Lb-1 as inoculants. Coal inoculated with halotolerant bacteria can serve as the foundation for humified organic matter in salt-affected environments. The selected halotolerant bacteria enhance coal biotransformation while exhibiting PGP traits.