Auxin-Rich Extract from Pseudomonas rhodesiae Enhances Cadmium Tolerance and Uptake in Cattail

Cadmium (Cd) pollution has become an increasing environmental and public health concern. Phytoremediation offers a sustainable strategy for metal removal, and its efficiency can be enhanced by microbial-derived biostimulants. This study investigated an auxin-rich culture supernatant extract from Pseudomonas rhodesiae GRC140 as a biostimulant to improve Cd tolerance and uptake in cattail (Typha latifolia). The supernatant extract, obtained after 84 h of bacterial growth in Luria Bertani medium supplemented with 0.1% L-tryptophan, was characterized by Fourier Transform Infrared (FTIR) spectroscopy, thin layer chromatography (TLC), and gas chromatography-mass spectrometry (GC-MS), confirming the presence of indole-3-acetic acid, indole-3-ethanol, indole, and indole-3-lactic acid. At a low concentration (1.15 mg/L), the extract increased shoot length by 30%, whereas higher concentrations (≥ 2.3 mg/L) inhibited root growth. Under Cd stress, the supernatant extract enhanced shoot biomass and chlorophyll content, reduced electrolyte leakage, and modulated antioxidant defense system in roots. Furthermore, the extract increased Cd accumulation in roots, reduced Cd translocation to shoots, and improved total Cd removal in hydroponic systems. FTIR analysis of root tissues suggested possible cell wall modifications associated with Cd sequestration. These findings indicate that bacterial supernatant extracts may serve as sustainable biostimulants for phytoremediation purposes.