Characterization of mercury ameliorating rhizobacteria for enhancing growth and yield of Triticum Aestivum L. in the field: An in-vitro and in- silico study

Mercury (Hg) resistant and indole 3-acetice acid (IAA)-producing rhizobacteria were isolated from mercury-contaminated areas. Among the 60 Hg-resistant bacterial isolates, three were selected based on high Hg-resistance (MIC-30 µg/ml) and IAA production (15–40 µg/ml). Selected isolates were subjected to biochemical and molecular characterization, and High-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC–MS) analyses were performed to confirm IAA production by these rhizobacteria. Pot and field experiments were conducted under controlled conditions on Triticum aestivum L. with a bacterial consortium consisting of AZ-3, Z-A15, and Z-A22. The selected isolates were identified as Bacillus cereus AZ-3, Enterobacter cloacae Z-A15, and Pseudomonas putida Z-A22, respectively. B. cereus AZ-3 showed 90 % resistance against HgCl₂ at 40 µg/ml due to the presence merT gene. E. cloacae Z-A15 and P. putida Z-A22 showed high production of IAA at 20 and 36 µg/ml respectively. High-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC–MS) confirmed IAA production by the selected bacteria. In greenhouse experiments, the inoculation of T. aestivum L. with bacterial consortium A7 (AZ-3, Z-A15, and Z-A22) with Hg resulted in 35 %, 60 %, 22 %, 98 % and 100 % increase while without Hg showed 32 %, 60 %, 30 %, 56 %, and 120 % increase in shoot length, tillers, spike length, number of spikelets, and seed weight/200 g respectively. In field experiments, the A7 showed 17 %, 66 %, 17 %, 27 %, 40 % and 70 % increases in shoot length, tillers, spike length, number of spikelets, dry weight and yield/acre in T. aestivum L. respectively (p < 0.05). The structural determination of MerT protein of B. cereus AZ-3 was carried out using bioinformatics tools, i.e., DISOPRED, SwissModel, ERRAT, Verify3D and PROCHECK. These tools predicted the structural-based functional homology of MerT transmembrane protein in bacterial Hg-detoxification system. The use of the bacterial consortium A7 as a biofertilizer to reduce mercury pollution while promoting plant growth in contaminated soils offers a novel approach to maintaining sustainable agricultural land in polluted environments.