DBP degradation and PGPR-mediated enhancement: Mechanisms of Enterobacter sp. X1 revealed by maize (Zea mays L.) transcriptome and rhizosphere microbiome analysis

Dibutyl phthalate (DBP), a common plasticizer in industrial production, is often detected in agricultural fields and exhibits significant endocrine disrupting effects on humans. Recently, plant growth promoting rhizobacteria (PGPR) have received considerable attention for their application in enhancing phytoremediation of soil organic pollutants. However, few studies have revealed the underlying mechanisms of gene expression changes in the PGPR-assisted phytoremediation process through plant transcriptome and rhizome microbiome analyses. Therefore, a DBP-degrading bacterium with multiple PGP traits was isolated, characterized and named strain X1. The effects of strain X1 inoculation on the promotion of maize (Zea mays L.) to remediate DBP-contaminated soil were then evaluated. The results showed that, compared to the DBP group, the soil DBP removal efficiency in the DBP + X1 treatment group increased 29.3 % (P < 0.05), accompanied by a significant reduction in DBP accumulation in maize (14.5 %) (P < 0.05). On one hand, transcriptome analysis further revealed that gene expression of detoxifying enzymes and antioxidants in plant tissues was up-regulated after inoculation with strain X1, which could prevent the excessive DBP accumulation in maize. Additionally, strain X1 could improve maize photosynthesis by inducing the expression of genes encoding proteins involved in the photosynthetic signaling pathway. On the other hand, the introduction of strain X1 greatly adjusted the diversity of the soil microbial community, enriched the abundance of DBP-degrading bacteria and improved soil enzyme activities in DBP-contaminated soil. In particular, this study also found that the expression of some plant genes was closely related to the relative abundance of rhizosphere microorganisms, such as Massilia and Devosia were associated with up-regulation of the expression of genes involved in the synthesis of alkaline phosphatase, which was of great importance in further exploration of microbial-plant interaction mechanisms. Consequently, this study investigated the role of PGPR on plant growth and the remediation of DBP-contaminated soil during phytoremediation through plant transcriptome and rhizosphere microbiome analysis, which provided a new perspective for future mechanism research on the remediation of contaminated farmland.