Pyoverdine production and antagonistic activity of native wastewater Pseudomonas sp. strains against Colletotrichum sp. and Fusarium sp

Abstract Pyoverdine, a primary siderophore secreted by Pseudomonas species, plays a crucial role in iron acquisition and phytopathogen biocontrol. This study evaluated pyoverdine production, iron-chelating capacity, and antifungal efficacy of native Pseudomonas sp. wastewater isolates P07 and P38 against Colletotrichum sp. and Fusarium sp. Media optimization showed that succinic acid is essential for pyoverdine synthesis, with medium M1 yielding high baseline levels (105.09 ± 1.63 µmol/L for P07). Formulating minimal media with reduced phosphate and moderate succinic acid (PM2) enhanced both pyoverdine production (up to 152.85 ± 4.43 µmol/L in P07 and 100.18 ± 7.04 µmol/L in P38) and iron-chelating capacity (up to 92.13 ± 0.85% PSU). In dual-challenge assays, strain P38 exhibited superior, iron-independent antagonism, suppressing Colletotrichum sp. (91.6%) and Fusarium sp. (91.39%). Microdilution bioassays revealed that P38 concentrated extracts inhibited Colletotrichum sp. (85.53%), demonstrating strong chemical antibiosis. Mass spectrometric analysis of the P38 extract revealed additional antifungal metabolites, including pyochelin, phenazines, and pyocyanin, confirming a multifaceted antagonistic profile. Native wastewater Pseudomonas sp. strains produce several bioactive compounds, including pyoverdines, which can markedly suppress the mycelial growth of key phytopathogenic fungi. These findings confirm that strain P38's antagonism extends beyond pyoverdine-mediated iron starvation to a rich, co-regulated secretome, establishing strain P38 as a promising candidate for bio-fungicidal tools in sustainable agriculture.