Rhamnolipid from Pseudomonas sp. as a green surfactant for enhanced phytoremediation

Microbial biosurfactants are valued for their surface activity and emulsifying properties; among them, rhamnolipids-primarily produced by Pseudomonas species-are the most prominent. Pseudomonas sp., a plant growth-promoting rhizobacterium, is also known to enhance heavy metal (HM) uptake in Helianthus annuus L. In this study, we produced biosurfactants from Pseudomonas aeruginosa strain ZF2MGHSO (Rha1) and Pseudomonas sp. strain AHE16 (Rha2). Gas chromatography-mass spectrometry (GC-MS) analysis confirmed that the purified biosurfactant was composed of rhamnolipids. We evaluated the effects of Rha1 and Rha2 on Cd and Zn uptake and HaZIP1 gene expression in sunflower plants grown in contaminated soil. Both rhamnolipids significantly increased Zn and Cd accumulation in roots and shoots, with the highest root Zn (724 ± 3 mg g⁻¹ DW) and Cd (173 ± 2 mg g⁻¹ DW) levels recorded in Rha1-treated plants. In shoots, Zn concentrations reached 460 ± 4 mg g⁻¹ DW with Rha1 and 426 ± 3 mg g⁻¹ DW with Rha2, compared to 405 ± 3 mg g⁻¹ DW in control. The relative expression of HaZIP1 was significantly upregulated in both roots and shoots under rhamnolipid treatments. In Rha1-treated plants, expression levels increased ~ 6.9-fold in roots and ~ 4.8-fold in shoots compared to control. Rha2 treatment led to ~ 6.0-fold and ~ 4.1-fold increases in roots and shoots, respectively. Our findings suggest that HaZIP1 plays a pivotal role in the uptake and accumulation of zinc and cadmium in sunflower plants grown in contaminated soil. Overall, our study highlights the potential of biosurfactant-enhanced phytoremediation using sunflower plants as an efficient, environmentally sustainable strategy for remediating heavy metal-contaminated soils.