Bacillus sp. L11 Promotes Tomato (Solanum lycopersicum L.) Seedling Growth by Reshaping Rhizosphere Bacterial Communities and Enhancing Root Growth Parameters

Plant growth-promoting rhizobacteria (PGPR) represent a sustainable and eco-friendly strategy to enhance crop productivity and support integrated agricultural systems. Among these, members of the genus Bacillus are highly valued for their resilience and multifaceted beneficial traits. The growth-promoting effects of Bacillus sp. L11 on S. lycopersicum seedlings were investigated in soil and artificial peat-based substrates. Rhizosphere microbial diversity was subsequently analyzed to investigate the interaction between L11 and the indigenous microbiota. We evaluated plant growth parameters, root growth parameters, and rhizosphere bacterial community dynamics using 16S rRNA high-throughput sequencing. Overall, L11 inoculation was associated with significantly improved growth indices of S. lycopersicum seedlings in both cultivation systems. Notably, the phosphate-buffered saline (PBS)-resuspended L11 markedly increased shoot fresh weight and plant height, and enhanced root-associated parameters such as total root length and root surface area. While L11 did not significantly alter alpha diversity, principal coordinates analysis (PCoA) revealed that its presence was associated with substantial restructuring of the rhizosphere bacterial community. Inoculation specifically enriched beneficial genera, including Chitinophaga, Devosia, and Pseudomonas. Correlation analyses showed that these microbial shifts were positively associated with the enhancement of seedling biomass and development. In conclusion, these findings suggest that Bacillus sp. L11 may promote S. lycopersicum growth through direct stimulation and by reshaping the rhizosphere microbiome, positioning it as a promising microbial inoculant for sustainable vegetable production.