Journal of Ecosystem & Ecography
Open Access

Abstract

Legumes develop symbiotic relationship with rhizobia following complex exchange of signals. Regardless of high specificity of symbiosis, isolation of rhizobacteria from surface sterilized root nodules has been reported. To explore how these rhizobacteria enter root hairs and colonize root nodules, we hypothesized that host specific rhizobia initiate the signaling process to form infection thread (IT), which is invaded by rhizobacteria to breach host specificity. To experimentally prove the hypothesis, fluorescently tagged predominant rhizobacteria Pseudomonas fluorescens and a facultative aerobe Klebsiella pneumoniae were coinoculated with native host nodulating rhizobia Ensifer adhaerens to Vigna radiata seedlings and root hair infection was monitored at 5 days post inoculation (DPI) using confocal microscope. and K. pneumoniae adhered to surface and base of root hairs and failed to enter root hairs independently but successfully colonized root hairs when coinoculated with E. adhaerens. Recovery and confirmation of inoculated tagged strains through confocal laser scanning microscopy and 16S rDNA sequencing validated nodule occupancy by test rhizobacteria at 50 DPI. This is the first study that addresses the fundamental question of how non-rhizobia invade root nodules and experimentally proves that non-rhizobia invade IT of host nodulating native rhizobial strain and colocalize in root nodules. We also isolated eight non-rhizobia with predominance of gram positive Paenibacillus and Bacillus among other gram-negative species of Klebsiella, Ensifer, Agrobacterium, Blastobacter, Dyadobacter and Chitinophaga from field grown V. radiata root nodules.

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