Bioinoculation with Pseudomonas aeruginosa P4 enhances the peanut root nodulation and nutrient status while enriching the plant-beneficial bacteria in rhizosphere

Fluorescent Pseudomonas species are well-known as effective plant growth promoting rhizobacteria (PGPR), yet are relatively less explored for their multitrophic benefits. This study demonstrates the impact of P. aeruginosa P4 (P4) on peanut growth, nutrient status of plant and soil as well as the rhizobacterial community. Enhanced root length (53%), root weight (74%) and shoot weight (48%) in P4-treated plants, with increased potash and phosphorus levels of rhizospheric soil, correlated with indole-3-acetic acid and organic acid producing abilities of P4. Remarkably, increased nodule (87%) and pod (47%) numbers in P4-treated plants could be attributed to ∼16.3 % higher accumulation of iron, which in turn could be due to siderophore producing ability of P4. Amplified Ribosomal DNA Restriction Analysis (ARDRA)-based analysis at the approximate onset of nodulation and subsequent 16S rDNA-based metagenomic analysis estimated a significant distinction in the rhizomicrobial community diversity and abundance across control and P4-treated rhizospheres, plausibly due to P4-induced alterations in root exudate composition. Enrichment of plant-beneficial genera like Planctomyces, Mesorhizobium, Ensifer, Azospirillum, Bacillus, Nitrospira and Candidatus Nitrososphaera in P4-treated rhizosphere, could be driven by both altered root exudation and enhanced mineral nutrient availability in soil. In contrast, reduced abundance of Pseudomonas genus in P4-treated peanut rhizosphere could be attributed to direct or indirect competition between the inoculant and the resident Pseudomonas species. Collectively, a non-nitrogen-fixer P4 benefited nitrogen fixation in peanut, apparently indirectly by improving the iron nutrition and mobilization of plant-beneficial rhizobacterial species; an aspect that could be useful in determining PGPR efficacy and strategizing PGPR-mediated rhizosphere engineering.