Plant growth-promoting bacteria (PGPB) inoculants enhance the bacterial network connectivity more than non-PGPB in heavy metal-contaminated soil

Optimizing the performance of plant growth-promoting bacteria (PGPB) inoculants in phytoremediation requires a deeper understanding of their interactions with the indigenous soil microbiome. However, current knowledge is particularly limited regarding how PGPB versus non-PGPB inoculants interact with indigenous microbes and establish colonization persistence in the rhizosphere. In this study, we employed amplicon sequencing to compare the impacts of PGPB versus non-PGPB inoculants on the indigenous rhizosphere and bulk soil microbiome of Indian mustard in heavy metal-contaminated soil, and their interactions within the indigenous bacterial networks. Our results showed that both PGPB and non-PGPB inoculants significantly altered the composition and diversity of the rhizosphere microbiome. However, only PGPB inoculants enhanced the complexity and stability of bacterial co-occurrence networks. PGPB inoculants not only maintained rhizosphere persistence but also actively integrated into the network, enhancing associations with indigenous bacterial taxa. Notably, they established enhanced co-occurrence associations with native bacterial taxa characterized as potential PGPB, including <i>Lysinimonas</i>, <i>Sinomonas</i>, <i>Nocardioides</i>, <i>Actinoalloteichus</i>, <i>Amycolatopsis</i>, <i>Bradyrhizobium</i>, <i>Novosphingobium</i> etc., and these interactions were predominantly positive. These findings highlight the important role of PGPB versus non-PGPB inoculants in reshaping the rhizosphere microbiome under heavy metal stress, indicating a potential approach for improving phytoremediation efficiency by fostering a more resilient and cooperative soil microbiome.