Plant Growth Promoting Bacterial Consortium Induces Shifts in Indigenous Soil Bacterial Communities and Controls Listeria monocytogenes in Rhizospheres of Cajanus cajan and Festuca arundinacea.

The rhizosphere is a dynamic and complex interface between plant roots and microorganisms. Owing to exudates, a web of interactions establishes among the microbial members of this micro-environment. The present study explored the impact of a bacterial consortium (Azotobacter chroococcum, Bacillus megaterium and Pseudomonas fluorescens, ABP), on the fate of a human pathogen, Listeria monocytogenes EGD-e, in soil and in the rhizospheres of Cajanus cajan and Festuca arundinacea, in addition to its plant growth promoting effect. The study further assessed the impact these bioinoculants exert on the autochthonous soil bacterial communities. Experiments in sterilised soil inoculated with bioinoculants and L. monocytogenes revealed the inhibition of L. monocytogenes by approximately 80-fold compared to that without the consortium. Subsequently, experiments were conducted in non-sterile soil microcosms planted with C. cajan and F. arundinacea, and in bulk soil. The consortium led to a significant increase in plant growth in both plants and prevented growth of L. monocytogenes. However, the presence of resident soil bacterial communities overshadowed this inhibitory effect, and a sharp decline in L. monocytogenes populations (5-6 log reduction) was recorded under non-sterile soil conditions. A shift in the soil resident bacterial communities was observed upon amendment with the bioinoculants. A significant increase of potential Plant Growth Promoting Rhizobacteria (PGPR) and biocontrol agents was observed, while the abundance of potential phytopathogens dropped. The present study opens up new avenues for the application of such a consortium given their dual benefits of plant growth promotion and restricting phytopathogens as well as human pathogen.