Unraveling the potential of Acinetobacter calcoaceticus for arsenic resistance and plant growth promotion in contaminated lentil field

The legume crop, lentil is often found to be contaminated with arsenic (As) across the globe, and becomes a serious problem when consumed as dietary component. Bioremediation techniques are considered to be sustainable, and low cost measures to combat this problem. The current study has been aimed at identifying the As-resistant endophytic bacteria from the root nodule of lentil plants grown in As-contaminated soil, assess their capacity to tolerate As, and establish their contribution in plant growth promotion. Four As-resistant endophytic bacteria were isolated from the lentil nodules in the contaminated (17.1 and 1.54 mg kg−1 of total and available As) field (Uttar Panchponta, Nadia, West Bengal, India located at 23° 05′ N and 88° 54′ E). The results showed that among all isolates, ARGNCAR-1 exhibits the highest As resistant capacity (200.0 mM for arsenate and 21.0 mM for arsenite). Interestingly, the ARGNCAR-1(Acinetobacter calcoaceticus, KX882106) is also able to solubilize phosphate (8.59-8.6 µg mL−1 under arsenate stress and 8.0-8.1 µg mL−1 under arsenite stress) and produce significant amount of indole acetic acid (10.2-10.4 µg mL−1 under the arsenate stress and 9.4-9.5 µg mL−1 under arsenite stress). The presence of aoxB gene was detected in these four As (III) oxidizing isolates. A pot experiment was conducted with the contaminated soil and the isolated strains were inoculated. The strain ARGNCAR-1 was found to be the most efficient in reducing about 20% As from soil and 22% As from the lentil seeds and ensured significant plant yield enhancement (5.17 g plant−1) than uninoculated soil (4.54 g plant−1) mainly through their corresponding increase in pod plant−1 (110) and biomass (6.51 g plant−1). Considering the efficacy of curbing As load as well as improving plant growth, the ARGNCAR-1(Acinetobacter calcoaceticus KX882106) emerged as one of the most promising candidates in As contaminated belts.