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 center dot-) 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.

Endophytic bacteria derived from metal hyperaccumulators have demonstrated potential for improving copper (Cu) remediation in host plants; however, their potential application in non-host crops remains unclear. In this study, endophytic bacteria isolated from Commelina communis growing in mining areas and their mitigation effects on Cu toxicity in non-host rice were comprehensively evaluated. Among the isolated endophytes, Bacillus sp. D2 exhibited the highest Cu resistance, producing indole-3-acetic acid (IAA) at a concentration of 0.93 mg/L and exhibiting ACC deaminase activity of 13.88 mu mol/mg & sdot;h under 200 mg/L Cu stress. Pot-experiment results revealed that Bacillus sp. D2 addition significantly increased the biomass and lengths of shoots under Cu stress conditions by 47.6% and 14.2%, respectively. Furthermore, Bacillus sp. D2 inoculation significantly reduced oxidative damage, enhanced antioxidant responses, and modulated plant hormone levels in Cu-exposed rice. Notably, Bacillus sp. D2 inoculation substantially decreased the upward translocation of Cu from underground roots to aboveground tissues. Moreover, Bacillus sp. D2 effectively alleviated Cu toxicity in rice plants by regulating the expression levels of genes involved in antioxidant systems (tAPx, Csd2, and FeSOD1), Cu transporters (AtPDR8 and HMA3), as well as metallothionein (MT2c). These results highlight the value of Bacillus sp. D2 as a bioinoculant for improving crop growth while reducing the risks associated with copper contamination in naturally Cu-contaminated soils.