Amendment of Microbial Metabolites to Develop Next-Generation Formulations for Enhancing Plant Growth and Resilience

The environmental concerns linked with the overuse of chemical fertilizers necessitate eco-friendly alternatives for sustainable agriculture. Plant growth-promoting (PGP) bioinoculants offer a viable solution; however, their inconsistent performance and short shelf life limit their widespread application. Microbial metabolites, known for boosting plant growth and stress resilience, present a promising alternative. This study evaluated the effectiveness of cell-based and metabolite-based formulations derived from the PGP strain Bacillus haynessi (SD2) on pigeon pea growth under saline conditions. The experiment involved metabolic profiling of SD2 cell-free supernatant (CFS), followed by the development of cell- (SD2 cells) and metabolite-based (exopolysaccharides and CFS) formulations and their application under controlled and natural conditions. Metabolic profiling of CFS revealed the presence of key metabolites linked to plant growth and stress management. Under salt stress, plant growth, total chlorophyll (31.14%), and potassium content declined, while proline (77.52%), malondialdehyde (44.80%), and sodium uptake increased. Both cell- and metabolite-based formulations mitigated the impact of stress by improving plant growth, chlorophyll content, and antioxidant enzyme activities (catalase and ascorbate peroxidase) while reducing the levels of stress markers and sodium-potassium ion ratio. CFS-based formulations were effective under controlled conditions, but exhibited limited performance in natural environment. In contrast, other formulations demonstrated consistent effectiveness. This study highlights the potential of EPS-based formulations as a sustainable and eco-friendly alternative to traditional cell-based formulations, significantly enhancing crop resilience in saline environments.