Biofertilizer/biopesticide potentiality of zinc solubilizing Pseudomonas aeruginosa FA-9 and Enterobacter sp. FA-11 isolated from the wheat rhizosphere grown in arid zone

Bacterial strains were obtained from wheat rhizosphere and screened for zinc solubilization on agar plates. Two strains FA-9 and FA-11 were found efficient for Zn solubilizing activity and were identified as Pseudomonas aeruginosa and Enterobacter sp. by 16S rRNA and gyrase (gyrB) genes analysis, respectively. The strain FA-9 produced a clear zone diameter of 63 mm, 60 mm and 51 mm on agar plate amended with different zinc ores. The strain FA-11 produced a zone diameter of 17 mm with zinc carbonate and 20 mm with zinc oxide while no zone was observed with zinc phosphate. Both strains showed no visible activity with ZnS ore. Similarly, FA-9 and FA-11 increased maximum soluble zinc content (102 µg ml−1 and 45 µg ml−1) from zinc carbonate ore as compared to zinc oxide ore (102 µg ml−1 and 45 µg ml−1) in liquid broth. It was noted that both strains exhibited less potential (7 µg ml−1 and 0.57 µg ml−1) to solubilize ZnS ore in liquid broth. A comparison between agar plate assay and liquid broth quantification shows that agar plate assay does not present the solubilizing potential of ZSB precisely. The strains FA-9 and FA-11 produced auxin with l-tryptophan (3.25 µg ml−1 and 2.86 µg ml−1) and without l-tryptophan (1.23 µg ml−1 and 1.02 µg ml−1). Both strains expressed exo-polysaccharides (EPS) and siderophores activity along with phosphate (P) solubilization, ACC deaminase and antifungal activities. The ACC deaminase and N-fixation activity was confirmed by the amplification of acdS and nifH genes respectively.