Molecular characterization of potential zinc solubilizing bacterial isolates from onion rhizosphere and validation of solubilization ability of PantoeaeucrinaZSC9 using FE-SEM and EDS

Abstract

Abstract Zinc (Zn) is essential for optimal growth and nutrition of plant and zinc solubilizing bacteria (ZSB) enhance its accessibility for plants by converting insoluble forms into usable ones. The primary objective of current research was to isolate and identify Zn solubilizing strains from onion rhizosphere and evaluate their ability to solubilize different insoluble Zn compounds, including ZnO, ZnCO3 and Zn3(PO4)2. Out of the nineteen bacterial isolates retrieved, fifteen were found to be proficient in solubilizing inorganic Zn minerals based on plate assay techniques. The Zn solubilizing bacterial strains chosen through qualitative assessment were subjected to quantitative testingin the broth culture using AAS and FE-SEM-EDS. Seven most potential bacterial isolates with the ability to solubilize Zn were identified using 16S rRNA gene amplification and sequence analysis. The isolates were found to be affiliated with Pantoeaeucrina, Pantoeadispersa, Pseudomonas aeruginosa, Bacillus velezensis and Pseudomonas fluorescens. To the best of our knowledge, this appears to be the first finding demonstrating Pantoeaeucrina as a potential ZSB. The maximum Zn solubilization index (8.85) and the highest soluble Zn content (624 mg/l) among the three insoluble Zn salts was exhibited by the strain Pantoea eucrina ZSC9 on the 10th day of incubation in ZnO enriched basal medium. Among the three insoluble Zn compounds, all of the bacterial isolates were more effective at solubilizing ZnO compared to ZnCO3 and Zn3(PO4)2. The solubilization of Zn led to a significant drop in pH of the broth and Pantoeaeucrina ZSC9 exhibited the maximum reduction in pH (3.82) in ZnO supplemented medium. A negative correlation was observed between the pH of broth and Zn solubilization by all the isolates. Based on our results, it is suggested that the identification of promising ZSB isolates and their application as biofertilizers has the potential to enhance plant growth and development.