article · Journal of Genetic Engineering and Biotechnology
Soil pollution caused by heavy metals such as hexavalent chromium limits plant growth and reduces the success of phytoremediation. This study investigated how plant growth-promoting rhizobacteria can enhance chromium tolerance and plant growth in Medicago sativa, commonly known as alfalfa. Twenty-seven bacterial isolates were tested and confirmed to possess growth-promoting traits alongside chromium resistance. Four leading isolates maintained these beneficial traits under chromium stress and improved plant root and shoot dry weights. One particular isolate, identified as a strain of Pseudomonas species, proved the most effective. Inoculation with this strain nearly doubled shoot and root dry weights under chromium exposure compared to untreated controls, boosted chlorophyll content, and lowered biochemical markers of stress. The bacterium also increased chromium concentration in plant roots alongside biomass, indicating strong potential for phytostabilisation in contaminated soils.
Hexavalent chromium is a toxic soil contaminant that hinders plant growth, making environmental clean-up difficult. Identifying beneficial soil bacteria that protect plants and boost their biomass under metal stress offers a biological method to stabilise toxic metals in roots, helping rehabilitate contaminated soils without reliant use of harsh chemicals.
This research could enable bio-inoculants for environmental remediation firms and agricultural land managers dealing with chromium-polluted soils. By pairing specific Pseudomonas strains with Medicago sativa, practitioners could improve phytostabilisation projects. The work represents applied laboratory-stage research, meaning field validation, formulation stability, and scaling tests would be needed before commercial deployment.
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BACKGROUND: Soil pollution by heavy metals increases the bioavailability of metals like hexavalent chromium (Cr (VI)), subsequently limiting plant growth and reducing the efficiency of phytoremediation. Plant growth-promoting rhizobacteria (PGPR) have substantial potential to enhance plant growth as well as plant tolerance to metal stress. The aim of this research was to investigate Cr (VI) phytoremediation enhancement by PGPR. RESULTS: The results showed that the 27 rhizobacterial isolates studied were confirmed as Cr (VI)-resistant PGPR, by using classical biochemical tests (phosphate solubilization, nitrogen fixation, indole acetic acid, exopolysaccharides, hydrogen cyanide, siderophores, ammonia, cellulase, pectinase, and chitinase production) and showed variable levels of Cr (VI) resistance (300-600 mg/L). The best four selected Cr (VI)-resistant PGPR (NT15, NT19, NT20, and NT27) retained most of the PGP traits in the presence of 100-200 mg/L concentrations of Cr (VI). The inoculation of Medicago sativa with any of these four isolates improved the shoot and root dry weight. The NT27 isolate identified using 16S rDNA gene sequence analyses as a strain of Pseudomonas sp. was most effective in terms of plant growth promotion and stress level decrease. It increased shoot and root dry weights of M. sativa by 97.6 and 95.4%, respectively, in the presence of Cr (VI) when compared to non-inoculated control plants. It also greatly increased chlorophyll content and decreased the levels of stress markers, malondialdehyde, hydrogen peroxide, and proline. The results of the effect of Pseudomonas sp. on Cr content and bioaccumulation factor (BAF) of the shoots and roots of M. sativa plants showed the increase of plant biomass concomitantly with the increase of Cr root concentration in inoculated plants. This would lead to a higher potential of Cr (VI) phytostabilization. CONCLUSIONS: This study demonstrates that the association M. sativa-Pseudomonas sp. may be an efficient biological system for the bioremediation of Cr (VI)-contaminated soils.
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DOI: 10.1186/s43141-021-00254-8
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