Polycyclic aromatic hydrocarbons (PAHs) are persistent environmental pollutants threatening soil ecosystems and human health. While soil microbial communities possess intrinsic PAH degradation potential, the dynamics of bacterial populations and degradation-associated genes during natural attenuation remain poorly understood. This study investigated the self-purification capacity of PAH-contaminated soil through a 32-day microcosm experiment using three model PAHs: naphthalene (NAP), phenanthrene (PHE), and pyrene (PYR). Results demonstrated high PAH dissipation rates (94.36 %, 72.60 %, and 47.70 % for NAP, PHE, and PYR, respectively). High-throughput sequencing revealed that PAH exposure (10–100 mg kg −1 ) shifted bacterial community structure, enriching Actinobacterial taxa (Mycobacterium, Rhodococcus, Nocardioides) linked to PAH degradation and strengthening bacterial interactions. Quantitative PCR further indicated substrate-specific gene responses: Actinobacteria harboring nahAC preferentially degraded NAP, while nidA and phe genes were upregulated under PHE/PYR stress. These findings highlight Actinobacteria as keystone degraders and propose leveraging microbial community assembly strategies to optimize bioremediation of PAH-contaminated soils.
Biorefractory humic substances (HS) that are ubiquitously present in nitrogen-rich wastewater streams, such as landfill leachate and livestock waste after anaerobic digestion, can potentially impact nitritation–anammox processes. In this study, multiple sequencing methods (e.g., 16S rRNA sequencing, clone library analysis, and metagenome sequencing) were employed to reveal the response of nitrosifying microbiota to HS at various concentrations (0–50 mg/L). Long-term reactor operation revealed that the nitrite yield was overall stable during all of the experimental days; however, fluctuations were observed as a result of sudden HS loads. The characterization by 16S rRNA sequencing indicated a decreased abundance of the phylum Proteobacteria (from 90.8% in HS0 to 52.1% in HS50) and an increased abundance of the phylum Bacteroidetes (from 4.7% in HS0 to 35.3% in HS50) upon exposure to HS. Both 16S rRNA sequencing and metagenome sequencing revealed that the family Nitrosomonadaceae, which was dominated by the genus Nitrosomonas, dramatically decreased, i.e., from ca. 70% in HS0 to ca. 40% in HS50. Both amoA-based clone libraries and metagenome sequencing suggested a substantial shift of AOB species, e.g., the emergence and enrichment of Nitrosomonas mobiliz upon exposure to HS. Interestingly, the amoABC gene was initially inhibited by 5 mg/L HS and then recovered at a higher level of HS (50 mg/L). In comparison, levels of hao gene were reduced with increasing HS (0, 5, and 50 mg/L). In addition, the abundance of genes assigned to membrane transport decreased after the addition of HS, and this reduction was likely associated with the electron shuttle roles of HS. Overall, the findings of this study provide insights into the response of core species and key genes to HS in nitritation systems.
Ziyi Dong,Mengchang He,Chunye Lin,Wei Ouyang,Xitao Liu
Antimony (Sb) is a toxic pollutant, with Sb(V) being one of its main forms in the environment, but the process and mechanism of plant uptake of Sb(V) remain unclear. To investigate the process of Sb(V) uptake by plants, Arabidopsis thaliana plants were exposed to water culture media supplemented with different Sb(V) concentrations. The distribution, content, and forms of Sb(V) in Arabidopsis roots, and the accumulation and fixation of Sb(V) in Arabidopsis plants were studied. In addition, inhibitor experiments and analyses of gene expression changes were conducted to elucidate the underlying mechanism of its toxicity. Sb(V) entering the roots was mainly adsorbed on the cell wall, and the Sb(V) content in both apoplastic solution and symplastic solution increased with increasing external Sb(V) concentration. Sb(V) concentration in apoplast and symplast were approximately linearly correlated (R 2 =0.980), indicating low affinity of cells for Sb(V) absorption. Moreover, uncouplers significantly inhibited the entry of Sb(V) into the symplast, suggesting that the transmembrane transport of Sb(V) is energy-consuming. Sb(V) entering the cell could be partially reduced to Sb(III), and significant changes in glutathione metabolism gene expression were detected, indicating the important role of glutathione metabolism in the detoxification of Sb(V). From the perspective of the whole plant, although Sb(V) is absorbed by the roots, it is mainly fixed in the leaves and stems. This study revealed the pattern of Sb(V) uptake by plants and elucidated the mechanism of Sb(V) uptake by plants from the perspectives of kinetics, physiology, and genetics.
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