Enhancing Copper (Cu) Phytostabilization Efficiency of Commelina communis by Inoculating with Endophytic Bacillus sp. D2: Impacts on Plant Growth, Soil Ecological Characteristics, and Underground Bacterial Community

Phytoremediation assisted by endophytic bacteria is a promising strategy to enhance the remediation efficiency of heavy metals in contaminated soil. In this study, the capacity and role of the endophytic Bacillus sp. D2, previously isolated from Commelina communis growing near a copper (Cu) mine, in assisting the phytoremediation were evaluated. Results showed that inoculation of Bacillus sp. D2 significantly enhanced the biomass production of C. communis by 131.06% under high level of Cu stress. Additionally, the oxidative damages caused by Cu toxicity in C. communis tissues were alleviated as evidenced by significant reductions in malondialdehyde (MDA), superoxide anion (O₂^•−) and proline content following Bacillus sp. D2 inoculation. Meanwhile, the activities of antioxidant enzymes in plant leaves presented upward trends after Bacillus sp. D2 inoculation. Notably, Bacillus sp. D2 inoculation significantly decreased Cu uptake and translocation by C. communis, while enhancing the Cu stabilization in contaminated soils. Furthermore, soil enzyme activities (acid phosphatase, catalase, and urease), as well as the richness of soil bacterial communities in Cu-contaminated soil increased following Bacillus sp. D2 inoculation. Importantly, the inoculation specifically augmented the relative abundance of key bacterial taxa (including Pseudomonas and Sphingomonadaceae) in the rhizosphere soil, which was positively correlated with soil nutrients cycling and plant growth. Our findings suggest that the endophytic strain Bacillus sp. D2 can strengthen the phytostabilization efficiency of Cu by C. communis through its beneficial effects on plant physio-biochemistry, soil quality and bacterial microecology, which provides a basis for the relative application to Cu-contaminated soils.

Graphical Abstract