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 (EC of 231.1 mg·L), Cu, and Cr (EC of 24.9 and 26.7 mg·L), and displayed plant growth-promoting traits. The EPS extracted from W18 (107.3 mg·L) 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. In the contaminated soils with Pb (500 mg·kg) and Cr (100 mg·kg), W18 inoculation significantly enhanced pakchoi shoot length and biomass by 1.1 to 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.