Exploring siderophore and hydroxamate production by fungi in the gut of Thai earthworms and their agricultural applications

Sixty-nine fungal isolates were cultured on PDA and YMA media, with 42 testingpositive for siderophore production via the CAS blue agar assay. The highest producers—VL4, RC5, RY1, Mpe9, and RL3—exceeded 80% siderophore units (SU), with RC5 achieving 92.73 ± 0.56% SU. The ferric perchlorate test showed RL3 had the highest hydroxamate siderophore concentration at 1,060.92 ± 3.00 µg/ml. Siderophore production decreased when FeSO₄ was added to the culture medium, and varying media impacted the levels of siderophore and hydroxamate production. Samples from earthworm guts, vermicompost, and organic agricultural soil demonstrated low siderophore production (<60%) and hydroxamate concentrations (<10 µg/ml). Notably, siderophores significantly improved iron uptake in plants, evidenced by increased iron content and shoot height in rice. Morphological and ITS1 region analyses identified RL3 as Aspergillus sp. (closely related to Aspergillus niger) and RC5 as Mucor sp. (related to Talaromyces angelicus). The study concluded that fungi from economic and agricultural earthworm sources are found to be potent producers of siderophores and hydroxamate siderophores, offering potential applications for enhancing plant iron uptake and soil health.