Exploring the potential of indigenous coal mine isolates Pseudomonas aeruginosa (PM55) and Enterobacter cloacae (PM56) for Cr(VI) bioremediation and plant growth promotion.

In the current study, Cr(VI) tolerance strains were first time isolated from soil samples collected from the coal mines area of the district Chakwal for a bioremediation study of Cr(VI). Twenty bacterial strains were isolated and screened against different concentrations of Cr(VI). The two best strains, Pseudomonas aeruginosa (PM55) and Enterobacter cloacae (PM56) were selected that can tolerate Cr(VI) up to 350 ppm. Both strains possess the ability of plant growth promotion by producing exopolysaccharides (EPS), indole acetic acid (IAA), and ACC-deaminase under Cr(VI) stress conditions. The ChrR reductase gene, which is responsible for catalyzing the reduction process of Cr(VI) to Cr(III), was also identified in these isolates. Batch experiment was performed under varying condition of pH (2, 3, 5, 7, and 9), optimal temperature (25 °C, 30 °C, 35 °C, 40 °C and 45 °C) time (20 min, 40 min, 60 min, 80 min and 100 min) and different Cr(VI) concentration (25 mg/L, 50 mg/L, 100 mg/L, 150 mg/L and 200 mg/L) to determined biosorption capacity and isotherms. It was found that adsorption was well defined by Langmuir isotherm models, and Freundlich models and kinetics, Pseudo-second-order and intra-diffusion models. But the adsorption capacity of Pseudomonas aeruginosa (PM55) was greater than that of Enterobacter cloacae (PM56). Different characterization, such as FTIR, SEM, and EDX, was also performed to confirm the biosorption capacity of selected strains. The strain Pseudomonas aeruginosa (PM55) promotes the growth of linum seedlings under different stress conditions of Cr(VI). Thus, the selected strain Pseudomonas aeruginosa (PM55) can be used to remediate the toxic effect of Cr(VI) and promote the growth of plants that help in sustainable agriculture.