3,6-dibromocarbazole have a significant effect on diversity, community and function of soil microorganisms

In recent years, polyhalogenated carbazoles (PHCZs) have been increasingly detected in soil, potentially posing risks to soil health. 3,6-dibromocarbazole (3,6-BCZ), a representative PHCZ, is frequently found in the soil environment. However, the effects of 3,6-BCZ contamination on microbial communities remain largely unexplored. In this study, we investigated the impact of varying concentrations of 3,6-BCZ on the soil microbiome using 16S rDNA gene amplicon sequencing and quantitative PCR techniques at 3, 10, 80 days (pre-, mid-, final-). α-Diversity analysis revealed that bacterial Shannon indices increased with 3,6-BCZ exposure (0.1 mg kg^-1 1.45 %, 1 mg kg^-1 4.73 %, 10 mg kg^-1 4.45 %, 100 mg kg^-1 5.97 %) at 80 d, compared to solvent soil group (SC). The concentration of 1, 10 and 100 mg kg⁻¹ 3,6-BCZ significantly increased bacterial diversity and altered community structure, enriching genera such as Bacillus, Adhaeribacter, and Nitrospira genera. Network analysis further demonstrated that bacterial interactions within the soil microbiome became more complex and competitive under 3,6-BCZ exposure. Additionally, functional prediction via FAPROTAX indicated significant alterations in microbial community functional groups, particularly those related to carbon and nitrogen cycling. Specifically, 3,6-BCZ promoted bacterial metabolic functions such as aerobic nitrite oxidation, nitrification, nitrogen fixation, hydrocarbon degradation, and methylotrophy, while inhibiting ureolysis and chitinolysis after 80 days of exposure. Notable changes were also observed in genes associated with nitrogen fixation (nifH), nitrification (AOA-amoA and AOB-amoA), and carbon cycling (cbbLR and cbbLG). Overall, our findings suggest that PHCZs can impact soil health and microbial functionality, highlighting the need for further research to inform risk-based policy development.