Effects of the polyhalogenated carbazoles 3-bromocarbazole and 1,3,6,8-tetrabromocarbazole on soil microbial communities

Soil ecosystems are being more contaminated with polyhalogenated carbazoles (PHCZs), which raising much attention about their impact on soil microorganisms. 3-Bromocarbazole (3-BCZ) and 1,3,6,8-tetrabromocarbazole (1,3,6,8-TBCZ) are two typical PHCZs with high detection rates in the soil environment. However, ecological risk research on these two PHCZs in soil is still lacking. In the present study, after 80 days of exposure, the ecological influence of 3-BCZ and 1,3,6,8-TBCZ was investigated based on 16S rDNA sequencing, ITS sequencing, gene (16S rDNA, ITS, amoA, nifH, narG and cbbL) abundance and soil enzyme activity. The results showed that the bacterial 16S rDNA gene abundance significantly decreased under 3-BCZ and 1,3,6,8-TBCZ exposure after 80 days of incubation. The fungal ITS gene abundance significantly decreased under 1,3,6,8-TBCZ (10 mg/kg) exposure. PHCZs contributed to the alteration of bacteria and fungi community abundance. Bacteria Sphingomonas, RB41 and fungus Mortierella, Cercophora were identified as the most dominant genera. The two PHCZs consistently decreased the relative abundance of Sphingomonas, Lysobacter, Dokdonella, Mortierella and Cercophora etc at 80th day. These keystone taxa are related to the degradation of organic compounds, carbon metabolism, and nitrogen metabolism and may thus have influence on soil ecological functions. Bacterial and fungal functions were estimated using functional annotation of prokaryotic taxa (FAPROTAX) and fungi functional guild (FUNGuild), respectively. The nitrogen and carbon metabolism pathway were affected by 3-BCZ and 1,3,6,8-TBCZ. The soil nitrogen-related functions of aerobic ammonia oxidation were decreased but the soil carbon-related functions of methanol oxidation, fermentation, and hydrocarbon degradation were increased at 80th day. The effects of 3-BCZ and 1,3,6,8-TBCZ on the abundances of the amoA, nifH, narG, and cbbL genes showed a negative trend. These results elucidate the ecological effects of PHCZs and extend our knowledge on the structure and function of soil microorganisms in PHCZ-contaminated ecosystems.

Effects of the emerging contaminant 1,3,6,8-tetrabromocarbazole on the NF-κB and correlated mechanism in human hepatocellular carcinoma cells

1,3,6,8-Tetrabromocarbazole (1368-BCZ) is identified as an emerging contaminant that exerts angiogenic effects. Multiple studies indicated there was a positive correlation between angiogenesis and nuclear factor kappa B (NF-κB) activation. While the role of NF-κB in inflammation and apoptosis has been well known, the potential biological effects of 1368-BCZ on NF-κB signaling and related mechanism remain unclear. We, therefore, explored the possible effects of 1368-BCZ on the NF-κB pathway at the gene and protein levels and confirmed that NF-κB activation by 1368-BCZ exposure caused an augmented phosphorylated protein level, induction of NF-κB response element (κBRE)-driven luciferase activity and upregulation of transcriptional level of downstream responsive genes. Although 1368-BCZ did not produce detectable changes in hepatic fibrosis in vivo, it obviously altered the apoptosis in human hepatocellular carcinoma (HepG2) cells. Furthermore, the induction of apoptosis was confirmed by the increased cleaved caspase-3 level. These data revealed the activating effects of 1368-BCZ on NF-κB and its involvement in the underlying mechanisms, providing additional information for toxicology studies of emerging contaminants and introducing a mechanism-based toxicological evaluation of emerging pollutants.

Isolation and identification of 1,3,6,8-tetrabromocarbazole - degrading bacteria

Halogenated carbazoles are a new class of persistent organic pollutants with dioxin-like toxicity, and this study focused on the microbial degradation of 1,3,6,8-tetrabromocarbazole. In this study, a novel 1,3,6,8-tetrabromocarbazole (1,3,6,8-TBCZ) degrading strain TB-1 was isolated from contaminated soil and identified as Achromobacter sp. based on its 16S rRNA gene sequence analysis, morphological, physiological, and biochemical characteristics. The soil sample was collected from a pharmaceutical factory in Suzhou, China. The strain was able to effectively degrade 1 mg L^-1 1,3,6,8-TBCZ in 7 d at pH 7.0 and 30 °C with 80% degradation rate. During the process, the intermediate metabolites were identified as Tribromocarbazole, dibromocarbazole and bromocarbazole via gas chromatography mass spectrometry (GC-MS). The results indicated that strain TB-1 may contribute to the bioremediation of polyhalogenated carbazoles (PHCs) in contaminated environment.

Sorption of 3,6-dibromocarbazole and 1,3,6,8-tetrabromocarbazole by microplastics

Microplastics and organic pollutants are typical contaminants in the marine environment. However, little is known about their interactions. In this study, the sorption of 3,6-Dibromocarbazole(3,6-BCZ) and 1,3,6,8-Tetrabromocarbazole (1,3,6,8-BCZ) by Polypropylene microplastic in simulated seawater was studied. Factors, including particle size, salinity and concentration, were investigated, and the experimental results were simulated using a mathematical model. Results showed that the pseudo-second-order kinetic model was more suitable to describe the sorption of polyhalogenated carbazole by microplastics, with equilibrium sorption times of 6 h and 8 h for 3,6-BCZ and 1,3,6,8-BCZ, respectively. Sorption capacity increased with decreasing particle size and the adsorption capacity increased initially and then decreased with increasing salinity, with a maximum sorption occurring at salinity of 14%. Moreover, the sorption amount increased with the increasing concentration of polyhalogenated carbazole. The sorption isotherms were confirmed as the extended Langmuir model and the extended Freundlich model, both of which were S-type.