Interrelationships Between Exogenous Plant Growth-Promoting Rhizobacteria and Wheat Rhizosphere Microbiome

Abstract

The rhizosphere microbiome is modulated by a diverse array of factors, including exogenous bio-inoculants that can exert either beneficial or detrimental effects on native microorganisms and plant growth. The potential consequences of inoculation on plant root-associated microbial communities warrant further investigation. This study aims to clarify the impact of inoculation with plant growth-promoting rhizobacteria (PGPR) on the wheat rhizospheric microbiome under greenhouse conditions. The PGPR strains utilized in this study, namely Bacillus subtilis, Pseudomonas putida, and Serratia marcescens, were previously isolated and characterized by Abd El-Azeem (2007). A quantitative assessment of microbiome activity was conducted in wheat rhizospheric soil, encompassing various microbial populations, including phosphate-solubilizing bacteria, cellulose-degrading microorganisms, ammonium oxidizers, siderophore-producing bacteria, and nitrogen-fixing Azotobacter, in addition to total bacterial, actinobacterial, and fungal counts. The application of PGPR strains exerted a positive influence on all examined beneficial native rhizospheric microbial populations. The responses of microbial populations varied significantly with plant age and the specific PGPR strain employed. Notably, wheat plants inoculated with Pseudomonas putida exhibited the highest microbial populations compared to other strains. Our findings indicate that the type of inoculant strain, plant age, and soil microbial community composition are critical factors influencing the response of the soil microbial community. We recommend further field evaluation of these PGPR strains prior to their widespread adoption as biofertilizers.