Enhancement of the phytoremediation performance in heavy metal-contaminated soil using a multifunctional EPS-producing bacterium Kosakonia sp. W18

The use of exopolysaccharide (EPS)-producing bacteria for the phytoremediation of heavy metal-contaminated soil is emerging as a promising approach. This study explores the potential of Kosakonia sp. W18, an EPS-producing bacterium isolated from Suaeda japonica habitat, in the phytoremediation of heavy metal-contaminated soils. Strain W18 exhibited the highest tolerance to Pb (EC₅₀ of 231.1 mg L⁻¹), Cu, and Cr (EC₅₀ of 24.9 and 26.7 mg L⁻¹), and displayed plant growth-promoting traits. The EPS extracted from W18 (107.3 mg L⁻¹) showed 58% emulsification against chloroform, remarkable 2,2-Diphenyl-1-picrylhydrazyl (38%) and hydroxyl radical (83%) scavenging activities. Extracted EPS also exhibited a Pb-removal efficiency exceeding 79%, with an adsorption capacity for Pb of 499.2 ± 7.7 mg·g-EPS⁻¹. In the contaminated soils with Pb (500 mg kg⁻¹) and Cr (100 mg kg⁻¹), W18 inoculation significantly enhanced pakchoi shoot length and biomass by 1.1–1.3 times after 20 days. The presence of pakchoi decreased bioavailable Pb and Cr concentrations in soil by 46%, which elevated to 76% for Pb and 72% for Cr post-inoculation with W18. Furthermore, W18 enhanced Pb uptake in pakchoi roots, increasing the bioconcentration factor by over 1.5 times and large macroaggregates (>2 mm) formation exceeded 75%. Overall, this study highlights Kosakonia sp. W18's multifunctional abilities to promote pakchoi growth and improve its effectiveness in phytoremediation of heavy metals in contaminated soils.