Biotechnological potential of Astragalus armatus rhizobacteria for heavy metal phytoremediation

Abstract

Despite elevated heavy metal concentrations in the Zeïda mining area (High Moulouya, Morocco), the rhizosphere of the native metallophyte Astragalus armatus harbored a diverse community of rhizobacteria with strong plant growth-promoting capacities. This study aimed to evaluate the biotechnological potential of these rhizobacteria through genetic, biochemical, and physiological characterization of key functional traits to identify robust strains suitable for bioinoculant development. Five bacterial strains were isolated from the rhizospheric soil of A. armatus and identified by 16S rDNA phylogenetic analysis as members of the genera Bacillus and Acinetobacter. Functional assays revealed multiple plant growth-promoting traits, including indole-3-acetic acid production, ACC deaminase activity, phosphate solubilization, ammonia and siderophore production, and lytic enzyme activities. Most strains exhibited strong resistance to lead and variable tolerance to zinc, copper, and cadmium, reflecting adaptation to metal-contaminated environments. Comparative analysis revealed functional complementarity among strains, with Bacillus subtilis AaR115 showing high nutrient mobilization and antifungal activity, while Acinetobacter soli AaR56 demonstrated greater tolerance to abiotic stress. These findings indicate that native rhizobacteria associated with A. armatus represent promising candidates for phytoremediation and sustainable restoration of metal-degraded soils.