Biotechnological Production of Siderophores

Metabolically versatile psychrotolerant Antarctic bacterium Pseudomonas sp. ANT_H12B is an efficient producer of siderophores and accompanying metabolites (SAM) useful for agricultural purposes

BACKGROUND

Bacterial siderophores are chelating compounds with the potential of application in agriculture, due to their plant growth-promoting (PGP) properties, however, high production and purification costs are limiting factors for their wider application. Cost-efficiency of the production could be increased by omitting purification processes, especially since siderophores accompanying metabolites (SAM) often also possess PGP traits. In this study, the metabolism versatility of Pseudomonas sp. ANT_H12B was used for the optimization of siderophores production and the potential of these metabolites and SAM was characterized in the context of PGP properties.

RESULTS

The metabolic diversity of ANT_H12B was examined through genomic analysis and phenotype microarrays. The strain was found to be able to use numerous C, N, P, and S sources, which allowed for the design of novel media suitable for efficient production of siderophores in the form of pyoverdine (223.50-512.60 μM). Moreover, depending on the culture medium, the pH of the siderophores and SAM solutions varied from acidic (pH < 5) to alkaline (pH > 8). In a germination test, siderophores and SAM were shown to have a positive effect on plants, with a significant increase in germination percentage observed in beetroot, pea, and tobacco. The PGP potential of SAM was further elucidated through GC/MS analysis, which revealed other compounds with PGP potential, such as indolic acetic acids, organic acids, fatty acids, sugars and alcohols. These compounds not only improved seed germination but could also potentially be beneficial for plant fitness and soil quality.

CONCLUSIONS

Pseudomonas sp. ANT_H12B was presented as an efficient producer of siderophores and SAM which exhibit PGP potential. It was also shown that omitting downstream processes could not only limit the costs of siderophores production but also improve their agricultural potential.

Modulation of Siderophore Production by Pseudomonas fluorescens Through the Manipulation of the Culture Medium Composition

Pseudomonas fluorescens has the ability to produce the siderophore pyoverdine, a biotechnologically significant iron chelator, which has a wide range of potential applications, such as in agriculture (iron fertilizers) and medicine (development of antibiotics). The present work aimed to evaluate the influence of culture medium composition on the production of siderophores by P. fluorescens DSM 50090, an industrial relevant strain. It was found that the bacterium grown in minimal medium succinate (MMS) had a higher siderophore production than in King B medium. The replacement of succinate by glycerol or dextrose, in minimal medium, originated lower siderophore production. The increase of succinate concentration, the addition of amino acids or the reduction of phosphate in the culture medium did not improve siderophore production by P. fluorescens. The results obtained strongly suggest that (i) MMS is more appropriate than King B for large-scale production of siderophores; (ii) the modification of the culture medium composition, particularly the type of carbon source, influences the level of siderophore secreted; (iii) the production of siderophore by P. fluorescens seems to be a tightly regulated process; once a maximum siderophore concentration has been reached in the culture medium, the bacterium seems to be unable to produce more compound.