Assessment of zinc solubilizing potentiality of Acinetobacter sp. isolated from rice rhizosphere

Abstract

In the present investigation, there were 143 Zinc solubilizing bacterial isolates obtained from rice rhizosphere soil samples using Tris-mineral salt growth medium supplemented with insoluble source of zinc such as Zinc Oxide (ZnO) and Zinc Carbonate (ZnCO3) individually. Among the ZSB isolates, there was maximum zinc solubilizing halo zone observed with the isolate AGM3 followed by AGM9 both on ZnO and ZnCO3 amended solid tris-mineral salt growth medium with the diameter of 13.21 mm, 10.71 mm and 11.74 mm, 7.90 mm respectively. Similarly, in broth assay, the AGM3 showed high value of zinc solubilization than AGM9 in both ZnO and ZnCO3 supplemented medium with a value of 36.54 μg Zn ml−1, 35.40 μg Zn ml−1 and 33.14 μg Zn ml−1, 32.69 μg Zn ml−1 respectively. The SEM images of AGM3 exhibited better solubility of ZnO than ZnCO3. Both AGM3 and AGM9 bacterial isolates were confirmed as Acinetobacter sp. through biochemical and 16S rRNA gene analysis. IAA productivity of isolate AGM3 showed highest at a level of 45.61 μg mL−1 than AGM9 at 37.27 μg mL−1. In pot experiment, among the all treatments, the combined use of AGM3 and AGM9 with ZnO and ZnCO3 resulted maximum in plant growth. The assay of fractionation of soil zinc after harvest showed an increase in exchangeable zinc, manganese oxide found bound zinc, crystalline and amorphours bound zinc and a decrease organically complexed and carbonate bound zinc compared to untreated control.