Biopriming of Pseudomonas aeruginosa Abates Fluoride Toxicity in Oryza sativa L. by Restricting Fluoride Accumulation, Enhancing Antioxidative System, and Boosting Activities of Rhizospheric Enzymes

Plant growth-promoting bacteria (PGPB) are free-living microorganisms that actively reside in the rhizosphere and affect plant growth and development. These bacteria employ their own metabolic system to fix nitrogen, solubilize phosphate, and secrete hormones to directly impact the metabolism of plants. Generating sustainable agricultural production under various environmental stresses requires a detailed understanding of mechanisms that bacteria use to promote plant growth. In the present study, Pseudomonas aeruginosa (MW843625), a PGP soil bacterium with a minimum inhibitory concentration (MIC) of 150 mM against fluoride (F), was isolated from agricultural fields of Chhattisgarh, India, and was assessed for remedial and PGP potential. This study concentrated on biomass accumulation, nutrient absorption, and oxidative stress tolerance in plants involving antioxidative enzymes. By determining MDA accumulation and ROS (O₂•⁻ and H₂O₂) in Oryza sativa L. under F (50 ppm) stress, oxidative stress tolerance was assessed. The results showed that inoculation with P. aeruginosa enhanced the ability of O. sativa L. seedlings to absorb nutrients and increased the amounts of total chlorophyll (Chl), total soluble protein, and biomass. In contrast to plants cultivated under F-stress alone, those inoculated with P. aeruginosa along with F showed considerably reduced concentrations of F in their roots, shoots, and grains. The alleviation of deleterious effects of F-stress on plants owing to P. aeruginosa inoculation has been associated with improved activity/upregulation of antioxidative genes (SOD, CAT, and APX) in comparison to only F-subjected plants, which resulted in lower O₂•⁻, H₂O₂, and MDA content. Additionally, it has also been reflected from our study that P. aeruginosa has the potential to increase the activities of soil enzymes such as urease, phosphatase, dehydrogenase, nitrate reductase, and cellulase. Accordingly, the findings of the conducted study suggest that P. aeruginosa can be exploited not only as an ideal candidate for bioremediation but also for enhancing soil fertility and the promotion of growth and development of O. sativa L. under F contamination.