The co-fermentation water-dispersible granules of two PGPR strains enhances growth, yields and quality of pepper by increasing soil nutrients and changing soil bacterial community

To safeguard the sustainable development of Guizhou's pepper industry from soil degradation, there is a critical demand for innovative microbial fertilizers as alternatives to minimize chemical fertilizer application. This study developed a novel water-dispersible granule (WDG) formulation based on co-fermented plant growth-promoting rhizobacteria (PGPR), and evaluated its potential to enhance pepper yield and nutritional quality, and improve soil health. The co-fermentation medium and formulation for Burkholderia pyrrocinia P10 and Bacillus flexus HGD12 were optimized using single-factor experiments and response surface methodology, resulting in a P10-HGD12 WDG with excellent performance (viable count: 6.78×10⁸ CFU/g, wetting time: 21.19 s, suspension rate: 81.33%). In pot trials, relative to 100% chemical fertilizer treatment, the P10-HGD12 WDG treatment resulted in a markedly higher pepper yield (60.04%) and elevated levels of key nutraceuticals—ascorbic acid (51.79%), total phenolics (130.08%), and total flavonoids (77.63%). It enhanced the abundances of Actinobacteriota and Myxococcota, along with soil organic matter and available nitrogen content, at both the seedling and fruit-setting stages. During the full-fruit stage, the P10-HGD12 WDG treatment enriched beneficial bacteria positively associated with pepper growth and nutritional indices—such as Actinobacteriota, Gemmatimonadota, unidentified_Gemmatimonadaceae, Luteimonas , and Lysobacter , while concurrently improving soil nutrient availability and utilization. The P10-HGD12 WDG + 80% chemical fertilizer treatment demonstrated secondary efficacy, with its specifically enriched bacterial phyla showing significant correlations with soil nutrient indicators, fruit growth, and nutritional parameters. The study effectively address the dual challenge of improving soil health and enhancing crop yield and quality, providing a viable strategy for sustainable agricultural systems.