Screening of Siderophore-Producing PGPRs Isolated from Groundnut (Arachis hypogaea L.) Rhizosphere and Their Influence on Iron Release in Soil

Iron is indispensable for the growth and metabolism of all living organisms but its availability in soil is limited due to very low solubility of dominant ferric iron (Fe3+). Plant growth-promoting rhizobacteria (PGPRs) have the ability to synthesize low molecular weight siderophores having high affinity for iron. Considering the siderophore-producing ability of PGPRs, a study was designed to isolate potential siderophore-producing bacteria from the rhizosphere of groundnut grown in the Potohar region. A total of 120 (MGS-1 to MGS-120) different bacterial isolates were obtained and screened for siderophore production. Under the quantitative estimation of siderophores, the maximum (73%) siderophore production was observed in MGS-14 followed by MGS-11 (69%) and MGS-91 (68%). Furthermore, these isolates were used for the incubation study which was conducted to evaluate the effect of SPB isolates on iron release in the soil. The soil was incubated at 28°C for 96 days and field capacity was maintained with distilled water from time to time. The results of the study revealed that the three SPB isolates (MGS-11, MGS-14, and MGS-91) which produced maximum siderophore units (>60% SU) showed an increase in iron release and 82%, 71%, and 69% over control on 32nd day of incubation, respectively. Moreover, the efficient bacterial isolates were characterized through 16S rRNA gene sequence analysis. The identified bacterial isolates were Bacillus subtilis, Bacillus halotolerans, and Bacillus safensis.