Evaluation of chromium stress tolerance in endophytic bacteria isolated from chickpea root nodules and their plant growth-promoting traits

Endophytic bacteria reside within plant tissues and are frequently associated with plant growth promotion (PGP). The study aimed to isolate and screen endophytic bacteria associated with chickpea plants in heavy metal (HM)- contaminated agricultural fields. Chromium (Cr) was used as an HM to evaluate its potential to sustain PGP under Cr (VI) stress conditions. A total of 15 bacterial strains were isolated and screened for Cr (VI) tolerance, out of which two bacterial strains were selected for the production of PGP traits. Basic local alignment search tool alignment of 16S rRNA gene sequences confirmed the bacterial strains as Serratia spp. strain SMAJ_44 and Enterobacter spp. strain SMAJ_47. The IC50 value of Cr (VI) for strains SMAJ_44 and SMAJ was 500 and 270 μM. PGP traits were evaluated for both strains; strain SMAJ_47 showed high indole acetic acid production. Our findings indicate that both strains exhibited key PGP traits under lower Cr concentrations. In addition, the strains demonstrated tolerance to other HMs such as arsenic (As), cadmium (Cd), cobalt (Co), copper (Cu), as well as resilience to salt and drought stress. These findings highlight the potential of bacterial strains as bioinoculants for enhancing plant growth and supporting sustainable agriculture and bioremediation efforts.