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

Abstract Mercury resistant (HgR) and indole-3-acetic acid (IAA) producing rhizobacteria were isolated from mercury-contaminated areas near Itehad Chemicals (PVT) Limited, Kala Shah Kaku, District Sheikhupura and tanneries of district Kasur, Punjab, Pakistan. Out of 60 mercury-resistant bacterial isolates, three were selected based on high mercury resistance (20–40 µg/ml) and IAA production (15–40 µg/ml). Selected isolates were subjected to biochemical and molecular characterization. HPLC and GC-MS analyses were performed for the confirmation of IAA production by selected rhizobacterial in methanol extract. 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. Selected bacterial isolates were identified as Bacillus cereus AZ-3, Enterobacter cloacae Z-A15, and Pseudomonas putida Z-A22. 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 the production of IAA by selected bacteria. Greenhouse experiment showed plant growth promoting ability of mercury resistant bacterial isolates with T. aestivum in both HgCl2 amended as well as in HgCl2 non-amended soils. Inoculation of bacterial consortium A7 (AZ-3, Z-A15, and Z-A22-Hg) posed a substantial increase such as 90, 3.2, 19.2, 70.4, and 13.2 in shoot length, tillers, spike length, number of spikelets/spike and seed weight/200 g respectively, as compared to (AZ-3, Z-A22, and Z-A15 + Hg). Field experiments showed 17, 40, 67, 13, 27, and 70% increases in shoot length, dry weight, number of tillers, spike length, number of spikelets, and yield per acre respectively in T. aestivum. In silico analysis showed the structural determination of MerT protein encoded by the merT gene of B. cereus AZ-3 (OM039465) using Domain and Motif analysis, physiochemical features, secondary and tertiary structure prediction, and structure validation by Ramachandran plot. These bioinformatics tools predicted the structural-based functional homology of MerT transmembrane protein associated with mer operon harboring bacteria involved in the Hg-detoxification system. It is concluded that the selected bacterial consortium A7 of the present study can be used as an excellent biofertilizer for lessening Hg pollution and promoting plant growth in Hg-contaminated soil to maintain sustainable agricultural land.