Burkholderia sp. ZF6-mediated mitigation of Cd and Zn stress in contaminated soil: effects on Chinese cabbage growth and rhizosphere microbial communities

This study investigated the effects of Burkholderia sp. ZF6, a plant growth-promoting bacterium with heavy metal resistance genes (cadA and zntA), on the growth of Chinese cabbage (Brassica rapa subsp. pekinensis) and cadmium (Cd)/zinc (Zn) removal in contaminated soils. ZF6 inoculation significantly increased root biomass (over twofold) and enhanced soil Cd and Zn removal efficiencies by approximately 2-4 times (19.9% for Cd and 11.5% for Zn). The abundance of cadA and zntA genes increased by 1.2-2.7 times, suggesting an enrichment of heavy metal-resistant microbial populations. Microbial community analysis showed that ZF6 inoculation reshaped the rhizosphere microbiome, increasing the relative abundance of genera such as Klebsiella, Agrobacterium, Burkholderia, Sphingomonas, and Pseudomonas. Notably, the abundance of Burkholderia, corresponding to ZF6, exhibited an increasing trend over time. Network analysis further indicated that microbial interactions became more complex in ZF6-treated soils (1.7-4.5-fold higher connectivity). Correlation analysis revealed that zntA abundance was associated with selected functional genes (e.g., K04565 and K01534) and inversely related to soil Cd concentration, suggesting a potential link between microbial functional potential and metal dynamics. Overall, ZF6 inoculation facilitated the restructuring of soil microbial communities to favor heavy metal-resistant bacteria. These findings highlight the potential of ZF6 as a scalable microbial-assisted phytoremediation strategy, although further validation under field conditions is required.