Synergistic interaction in mixed pant growth promoting rhizobacteria consortium enhances biofilm formation and rhizosphere colonization to promote tomato (Solanum lycopersicum) growth

• The D1–28/LAD co-inoculation synergistically enhanced biofilm formation and production of plant growth-promoting factors;. • Inoculation with the D1–28/LAD consortium significantly stimulated tomato growth and remodeled root architecture;. • Co-inoculation strengthened rhizosphere colonization and upregulated expression of auxin biosynthesis and nitrogen transport-related genes in tomato roots. While plant growth-promoting rhizobacteria (PGPR) consortia show enhanced benefits over single strains, the systematic design of functionally complementary synthetic communities and their synergistic mechanisms through biofilm-mediated root colonization remain poorly explored. This study aimed to screen and construct functionally complementary PGPR consortia, systematically evaluate their synergistic effects on biofilm formation in the tomato rhizosphere, and elucidate the underlying mechanisms regulating plant growth through enhanced root colonization and metabolic interactions. Three PGPR strains — Pantoea ananatis D1–28, Bacillus aryabhattai LAD, and Burkholderia cepacia 4–5—were selected for individual and combinatorial inoculation experiments. The results demonstrated that the D1–28/LAD combination exhibited significant synergistic advantages in both biofilm formation and plant growth promotion. This consortium markedly enhanced rhizosphere colonization and the synthesis of growth-promoting factors (such as N, P, siderophores, and IAA), thereby significantly improving tomato growth and up-regulating auxin biosynthesis and nitrogen transporter gene expression in roots. At an inoculum concentration of 10 6 cfu·mL −1 , the fresh and dry weights of tomato shoots increased by 186.40 % and 278.57 %, respectively, while root fresh and dry weights increased by 327.62 % and 543.68 %. Plant height, root length, root surface area, and root volume increased by 117.19 %, 207.29 %, 531.36 %, and 525.69 %, respectively. This study provides theoretical insights into the role of microbial interactions in plant growth promotion and lays a technical foundation for the development of efficient and stable microbial biofertilizers, with promising applications in sustainable agriculture.