Abstract
Twenty fluorescent Pseudomonas isolates were tested for their ability to produce siderophores on chrome azurol S (CAS) agar plates and their antagonistic activity against six plant pathogenic fungal isolates was assessed. Scaling-up production of siderophores from the promising isolates, P. aeruginosa F2 and P. fluorescens JY3 was performed using batch and exponential fed-batch fermentation. Finally, culture broth of the investigated bacterial isolates was used for the preparation of two economical bioformulations for controlling Fusarium oxysporum and Rhizoctonia solani. The results showed that both isolates yielded high siderophore production and they were more effective in inhibiting the mycelial growth of the tested fungi compared to the other bacterial isolates. Exponential fed-batch fermentation gave higher siderophore concentrations (estimated in 10 µL), which reached 67.05% at 46 h and 45.59% at 48 h for isolates F2 and JY3, respectively, than batch fermentation. Formulated P. aeruginosa F2 and P. fluorescens JY3 decreased the damping-off percentage caused by F. oxysporum with the same percentage (80%), while, the reduction in damping-off percentage caused by R. solani reached 87.49% and 62.5% for F2 and JY3, respectively. Furthermore, both formulations increased the fresh and dry weight of shoots and roots of wheat plants. In conclusion, bio-friendly formulations of siderophore-producing fluorescent Pseudomonas isolates can be used as biocontrol agents for controlling some plant fungal diseases.
Highlights
Siderophores are a group of low-molecular-weight molecules (400–1500 Da) with a high affinity to ferric ions
Fluorescent Pseudomonas isolates were recognized by the formation of green fluorescence pigments in and around the colonies when exposed to ultraviolet light
All isolates that formed a yellow to orange zone around the pure colony indicated a positive siderophore production
Summary
Siderophores are a group of low-molecular-weight molecules (400–1500 Da) with a high affinity to ferric ions. These molecules are secreted by different microorganisms in response to low-iron conditions;. Fe-siderophore complex is transported into cell periplasm, wherever it facilitates iron uptake [1,2]. Siderophores are iron chelators that have many. The role of siderophore production in the biocontrol of Erwinia carotovora was demonstrated by Kloepper et al, 1980, who were the first to use pseudobactin-producing. Pseudomonas fluorescens, a type of siderophore, as a biocontrol agent. Several species of fluorescent pseudomonads are able to secrete siderophores such as P. aeruginosa, P. fluorescens and P. syringae [4,5]
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