Fluorescent Pseudomonads as Plant Growth Promoting Rhizobacteria and Their Siderophoregenesis

Two fluorescent Pseudomonads, Pseudomonas fluorescens NCIM 5164 and Pseudomonas aeruginosa NCIM 2036 produced siderophores under iron limiting conditions. These Pseudomonas spps. were screened for siderophore production by three different tests commonly used to detect siderophores. Quantitative estimation of siderophores was done by the Chrome Azurol S assay (CAS), the universal test independent of siderophore type. P. fluorescens and P. aeruginosa produced 88% and 83% siderophore units respectively. The type of siderophore was detected by chemical as well as spectrophotometric assay. Pseudomonas fluorescens was found to produce hydroxamate type of siderophore and Pseudomonas aeruginosa produced both the hydroxamate (Pyoverdin) and phenol-catecholate (Pyochelin) siderophores. Evaluation study of siderophore showed that maximum siderophore production was obtained on succinate medium at pH 7.0. Both the Pseudomonas spps. were further tested as seed inoculants and found to be very effective in seed germination and plant growth promotion of Triticum aestivum and Apios americana plants under pot culture conditions. KeyWords - CAS, Catecholate, Hydroxamate, Pyoverdin, Pyochelin, Siderophores.