Rhizosphere of rice plants harbor bacteria with multiple plant growth promoting features

Abstract

114 diazotrophic bacteria from the rice rhizosphere of five districts of Eastern Uttar Pradesh (India) were isolated and screened for plant growth promoting (PGP) activities employing standard microbiological and biochemical techniques. All these isolates showed nitrogenase activity in the range of 0.23 to 1.72 μmol C₂H₄ mg^-1 protein h^-1. Further analysis showed that 84 (73.68%) isolates were Indole-3-acetic acid (IAA) producer; the value of IAA production ranged from 10.1 to 353.0 μg IAA mg^-1 protein. IAA production occurred solely in the medium supplemented with tryptophan. P solubilization activity was observed in 28 (24.56%) isolates, the activity being in the range of 38.50 to 321.0 P released μg mg^-1 protein. 45 (39.46%) isolates were capable of producing siderophore, the range of production being 4.50 to 223.26 μg mg^-1 protein. Analysis of molecular diversity was made by amplified ribosomal DNA restriction analysis (ARDRA) and denaturating gradient gel electrophoresis (DGGE), which exhibited distinct differences among all the isolates. Of the 114 isolates, twenty one (21) isolates showed multiple plant growth promoting traits and were potent in terms of PGP activities. These isolates were identified on the basis of 16S rDNA sequencing and belonged to the genera Pantoea, Bacillus, Microbacterium, Pseudomonas, Sphingomonas, Ancylobacter, Enterobacter, Advenella, γ-proteobacterium strain VA3S1, Rhizobium and Agrobacterium. Findings of this study suggest that certain isolates may be exploited for developing a potential source of biofertilizer.

Key words: Plant growth promoting rhizobacteria, N₂ fixation, amplified ribosomal DNA restriction analysis, indole-3-acetic acid, siderophore, denaturing gradient gel electrophoresis, temperature gradient gel electrophoresis