The influence of anaerobic dechlorination on the aerobic degradation of PCBs in e-waste-contaminated soils in an anaerobic-aerobic two-stage treatment

Enhanced dechlorination and degradation of Aroclor 1260 by resuscitation-promoting factor under alternating anaerobic-aerobic conditions: Superior performance and associated microbial populations

The combined processes of dechlorination and degradation are essential for the effective bioremediation of environments contaminated with complex polychlorinated biphenyl (PCB) mixtures. Although resuscitation-promoting factor (Rpf) has been reported to enhance anaerobic dechlorination and aerobic degradation of PCBs by microorganisms, its impact on microbial populations during alternating anaerobic-aerobic treatments remains unexplored. This study investigated the dechlorination and degradation of Aroclor 1260 under anaerobic (AN), aerobic (AE), and alternating anaerobic-aerobic (AA) conditions, both with and without Rpf supplementation. The results demonstrated that Rpf significantly promoted Aroclor 1260 dechlorination under AN conditions, enhanced degradation under AE conditions, and markedly improved both processes under AA conditions, achieving nearly twice the degradation efficiency compared to AE alone. Furthermore, Rpf supplementation significantly increased the abundance of dechlorination-associated microbial taxa, including members of Firmicutes, Chloroflexi, Bacteroidota, and Desulfobacterota under AN conditions, as well as degradation-associated genera such as Pseudomonas and Sphingomonas under AE and AA conditions. Rpf also strengthened microbial interactions by enhancing positive correlations among functional populations and increasing network complexity. These findings establish Rpf as a powerful enhancer of PCB dechlorination and degradation, which provide valuable insights into its superior efficiency in PCB removal under AA conditions.

Spatiotemporal profiling and succession of microbial communities in landfills based on a cross-kingdom abundance quantification method

Landfill provides a unique niche for both prokaryotic and eukaryotic microorganisms, in which organic matter and physiochemical conditions continuously change with the landfill age and drive the succession of landfill microbiomes. Nonetheless, information on the spatiotemporal changes of landfill microbiomes, particularly the prokaryotic and eukaryotic communities and their interactions, remain scarce. In this study, a new cross-kingdom abundance quantification method was devised to obtain cell abundance of both prokaryotes and eukaryotes based on high-throughput sequencing, and employed to elucidate microbiomes of leachate samples collected from nationwide landfills in China. Results showed the clustering of landfills into two groups primarily based on microbial community compositions, being in line with the change in their landfill ages (i.e., Group-I, <10 years; Group-II, ≧10 years), and 1320.9 and 88.0 times of abundance difference between prokaryotes and eukaryotes in the Group-I and -II communities, respectively. Reducing equivalent was determined as a primary factor governing the landfill microbial abundance, assembly and interactions. In contrast to Group-I characterized by the extensive organic matter fermentation and multi-pathway methanogenesis driven by fermenters and methanogenic archaea, aerobic heterotrophs played a primary role in element cycling and archaea-mediated methanogenic activities were diminished in Group-II communities, in which heterotrophic bacteria and fungi might synergistically degrade recalcitrant organic matter. Interestingly, protozoa and metazoa as bacteria/fungi predators decreased the stability of Group-II communities in a top-down manner. Based on these observations, a scenario was proposed for the energy-driven succession of landfill microbiomes and mediated biogeochemical processes. Our study provided the first large-scale and comprehensive insight into the landfill microbiomes for their future sustainable management.

Effect of polystyrene micro/nanoplastics on PCBs removal in constructed wetlands planted with Myriophyllum aquaticum

The co-occurrence of microplastics (MPs) and nanoplastics (NPs) with polychlorinated biphenyls (PCBs) is an emerging environmental concern. Wetland plants, with their unique anaerobic-aerobic environments, offer a promising approach for PCBs removal. However, the impact of MPs and NPs on PCBs dynamics in constructed wetlands is not well understood. This study examined the influence of polystyrene MPs and NPs of two different sizes on PCBs fate in constructed wetlands featuring Myriophyllum aquaticum. Results showed that although there was no significant difference in overall PCBs removal rates, the presence of MPs increased residues of highly chlorinated PCBs from 331 μg/kg to 379 μg/kg, while the presence of NPs increased residues of lightly chlorinated PCBs from 125 μg/kg to 153 μg/kg. Additionally, MPs and NPs increased plant uptake of PCBs from 0.08% to 0.10-0.14%, despite potential inhibition of plant growth. While MPs/NPs elevated microorganism counts, they did not affect microbial diversity or community structure. Importantly, MPs significantly inhibited the main PCB-dechlorinating bacteria (Dehalococcoidia) and had a greater impact on PCB-degrading enzymes (dioxygenase, K03381) compared to NPs. This study highlights the complex interactions between MPs/NPs and PCBs in wetland environments and their implications for bioremediation strategies.

Mechanism of microplastics promoting sulfamethoxazole biodegradation in activated sludge as revealed by DNA-stable isotope probing

Microplastics (MPs) often coexist with sulfonamide antibiotics (SAs) in the activated sludge of wastewater treatment plants (WWTPs). Microbial degradation is a crucial pathway for SAs removal in the activated sludge, though its response to MPs still yet to be disclosed. Here, we combined DNA-stable isotope probing (DNA-SIP), PICRUSt and MENA techniques to explore the impact of MPs on the microbial biodegradation of sulfamethoxazole (SMX) in the activated sludge. DNA-SIP revealed 20 genera were responsible for the SMX degradation in the activated sludge, with 13 of these genera being firstly linked with sulfonamide biodegradation. The potential SMX-degrading bacteria showed complex synergistic interaction with the other microbes. Eight degradation pathways were constructed based on the nine identified SMX-related degradation genes. MPs addition enhanced the SMX biodegradation by altering the structure of degrading microbes, increasing their relative abundance and promoting the synergistic interactions between potential SMX-degrading bacteria and other microbes in activated sludge. Besides, genes related to abundant energy production and biofilm formation were involved in SMX degradation in the activated sludge with MPs. Our study reveals the MPs influence on SMX biodegradation in activated sludge, and disclose the potential underlying mechanisms, which will benefit the regulation on antibiotic removal in WWTPs.

Enhanced microbial dechlorination of PCBs by anaerobic digested sludge and enrichment of low-abundance PCB dechlorinators

The slow rate of anaerobic microbial dechlorination in natural environments limits the application of polychlorinated biphenyl (PCB) bioremediation. Anaerobic digested sludge (ADS), abundant in nutrients and microorganisms, could be an effective additive to improve microbial dechlorination. This research investigates the influence of ADS on Aroclor 1260 dechlorination performance, microbial community composition, and the abundance of functional genes. Moreover, further enrichment of organohalide-respiring bacteria (OHRB) was examined using tetrachloroethene (PCE) as the electron acceptor, followed by the serial dilution-to-extinction method in conjunction with resuscitation promoting factor (Rpf) supplementation. The results demonstrated that the addition of 5 g/L ADS achieved more extensive and efficient dechlorination of PCBs. ADS enhanced the removal of meta- and para-chlorine without significantly changing the dechlorination pathways. The abundances of dechlorinators, including Dehalobium and Dehalobacter within the Chloroflexi and Firmicutes phyla, as well as non-dechlorinators from the Desulfobacterota, Euryarchaeota, and Bacteroidetes phyla, were significantly increased with ADS amendment. Similarly, an increased abundance of bacteria, OHRB, reductive dehalogenase (RDase) genes, and archaeal 16S rRNA genes was observed. Additionally, obligate OHRB, such as Dehalobacter and Dehalobium, were further enriched. These findings indicate that ADS effectively enhances microbial reductive dechlorination and highlight the potential for enriching and isolating OHRB with Rpf.

The roles of organic amendments and plant treatments in soil polychlorinated biphenyl dissipation under oxic and sequential anoxic-oxic conditions

Understanding polychlorinated biphenyl (PCB) degradation in sequential anaerobic-aerobic remediation is crucial for effective remediation strategies. In this study, microcosm and greenhouse experiments were conducted to dissect the effects of organic amendments (carbon-based) and plant treatments (ryegrass) on soil PCB dissipation under oxic and sequential anoxic-oxic conditions. We analyzed the soil bacterial community in greenhouse experiments using high-throughput sequencing to explore plant-pollutant-microbe interactions. Microcosm results showed that organic amendments alone did not facilitate aerobic PCB removal, but significantly accelerated PCB dechlorination under anoxic conditions altering the profiles of PCB congeners. In standard greenhouses, plant treatments substantially increased PCB dissipation to 50.8 ± 3.9%, while organic amendments aided phytoremediation by promoting plant growth, increasing PCB removal to 65.9 ± 3.2%. In sequential anaerobic-aerobic greenhouses, plant growth was inhibited by flooding treatment while flooding stress was markedly alleviated by organic amendments. Plant treatments alone during sequential treatments did not lead to PCB dissipation; however, dissipation was significantly promoted following organic amendments, achieving a removal of 41.2 ± 5.7%. This PCB removal was primarily due to anaerobic dechlorination during flooding (27.8 ± 0.5% removal), rather than from plant growth stimulation in subsequent planting phase. Co-occurrence network and functional prediction analyses revealed that organic amendments recruited specific bacterial clusters with distinct functions under different conditions, especially stimulating plant-microbe interactions and xenobiotics biodegradation pathways in planted systems. The findings provide valuable guidance for the design of practical remediation strategies under various remedy scenarios, such as in arable or paddy fields.

Burning question: Rethinking organohalide degradation strategy for bioremediation applications

Organohalides are widespread pollutants that pose significant environmental hazards due to their high degree of halogenation and elevated redox potentials, making them resistant to natural attenuation. Traditional bioremediation approaches, primarily relying on bioaugmentation and biostimulation, often fall short of achieving complete detoxification. Furthermore, the emergence of complex halogenated pollutants, such as per- and polyfluoroalkyl substances (PFASs), further complicates remediation efforts. Therefore, there is a pressing need to reconsider novel approaches for more efficient remediation of these recalcitrant pollutants. This review proposes novel redox-potential-mediated hybrid bioprocesses, tailored to the physicochemical properties of pollutants and their environmental contexts, to achieve complete detoxification of organohalides. The possible scenarios for the proposed bioremediation approaches are further discussed. In anaerobic environments, such as sediment and groundwater, microbial reductive dehalogenation coupled with fermentation and methanogenesis can convert organohalides into carbon dioxide and methane. In environments with anaerobic-aerobic alternation, such as paddy soil and wetlands, a synergistic process involving reduction and oxidation can facilitate the complete mineralization of highly halogenated organic compounds. Future research should focus on in-depth exploration of microbial consortia, the application of ecological principles-guided strategies, and the development of bioinspired-designed techniques. This paper contributes to the academic discourse by proposing innovative remediation strategies tailored to the complexities of organohalide pollution.

Environmental transformation and hazards of decachlorobiphenyl on suspended particles under sunlight irradiation

Decachlorobiphenyl (PCB-209) can be widely detected in suspended particles and sediments due to its large hydrophobicity, and some of its transformation products may potentially threaten organisms through the food chain. Here we investigate the photochemical transformation of PCB-209 on suspended particles from the Yellow River. It was found that the suspended particles had an obvious shielding effect to largely inhibit the photodegradation of PCB-209. Meanwhile, the presence of inorganic ions (e.g. Mg2+ and NO3-) and organic matters (e.g. humic acid, HA) in the Yellow River water inhibited the reaction. The main transformation products of PCB-209 were lower-chlorinated and hydroxylated polychlorinated biphenyls (OH-PCBs), and small amounts of pentachlorophenol (PCP) and polychlorinated dibenzofurans (PCDFs) were also observed. The mechanisms of PCP formation by double •OH attacking carbon bridge and PCDFs formation by elimination reaction of ionic state OH-PCBs were proposed using theoretical calculations, which provided some new insights into the inter-transformations between persistent organic pollutants. In combination with VEGA and EPI Suite software, some intermediates such as PCDFs were more toxic to organisms than PCB-209. This study deepens the understanding of the transformation behavior of PCB-209 on suspended particles under sunlight.

The uptake and degradation of polychlorinated biphenyls in constructed wetlands planted with Myriophyllum aquaticum

The unregulated dismantling and improper disposal of electronic waste lead to severe soil contamination by polychlorinated biphenyls (PCBs). Constructed wetlands (CWs) play an important role in PCBs removal as a result of the co-existence of anaerobic and aerobic conditions. However, the effects and mechanisms of different PCBs concentrations in soils on plant uptake and PCBs degradation within CWs are unclear. We evaluated the uptake and degradation of PCBs at different concentrations by Myriophyllum aquaticum (Vell.) Verdc. Planting significantly increased PCBs removal by 8.70% (p < 0.05) in soils with 1500 and 2500 μg/kg PCBs, whereas no significant effect was observed at 500 and 1000 μg/kg. PCBs levels did not significantly affect plant growth and PCBs accumulation. The contribution of plant uptake to PCBs removal was only 0.10-0.12%, indicating that microbial degradation was the dominant pathway for PCBs removal after planting with M. aquaticum. In the treatments with PCBs ≥ 1500 μg/kg, M. aquaticum increased the microbial population, altered the microbial community structure and enriched PCB-degrading bacteria. Functional prediction revealed that microbes in M. aquaticum rhizosphere secreted more peroxidase and glycosyltransferase than non-plant control, which were likely involved in PCBs metabolism.

A novel mechanism of enhanced PCBs degradation associated with nitrogen in the rhizosphere of the wetland plant Myriophyllum aquaticum

Co-contamination of polychlorinated biphenyls (PCBs) and nitrogen (N) is widespread. Here, N removal and PCBs degradation were investigated in constructed wetlands populated with Myriophyllum aquaticum, and the role of N in PCBs degradation was explored as well. Nearly 97% of N was removed in the planted system, whereas less than 40% was removed in the plant-free system. Compared to the treatment with plants and no N amendment, N addition enhanced plant growth by 31.9% and PCBs removal by 9.90%. PCBs attenuation was mainly attributed to microbial degradation rather than plant uptake. Using DNA stable-isotope probing, 26 operational taxonomic units were identified across all treatments, of which 25 were linked to PCBs degradation for the first time. Some PCB-degraders were associated with nitrification/denitrification and were significantly enriched in the treatment that included both plants and N application, indicating that PCBs degradation was promoted by recruiting ammonia-oxidising and denitrifying microbes with PCBs metabolic ability. This was confirmed by the higher A13/A12 ratios for the bphC, amoA, and nirK genes and their significant positive correlations. Overall, the findings clarify the novel mechanism by which N promotes PCBs degradation in constructed wetlands and offers a theoretical basis for efficiently removing inorganic elements and persistent organic pollutants.

In Situ Discrimination and Cultivation of Active Degraders in Soils by Genome-Directed Cultivation Assisted by SIP-Raman-Activated Cell Sorting

The identification and in situ cultivation of functional yet uncultivable microorganisms are important to confirm inferences regarding their ecological functions. Here, we developed a new method that couples Raman-activated cell sorting (RACS), stable-isotope probing (SIP), and genome-directed cultivation (GDC)─namely, RACS-SIP-GDC─to identify, sort, and cultivate the active toluene degraders from a complex microbial community in petroleum-contaminated soil. Using SIP, we successfully identified the active toluene degrader Pigmentiphaga, the single cells of which were subsequently sorted and isolated by RACS. We further successfully assembled the genome of Pigmentiphaga based on the metagenomic sequencing of 13C-DNA and genomic sequencing of sorted cells, which was confirmed by gyrB gene comparison and average nucleotide identity determination. Additionally, the genotypes and phenotypes of this degrader were directly linked at the single-cell level, and its complete toluene metabolic pathways in petroleum-contaminated soil were reconstructed. Based on its unique metabolic properties uncovered by genome sequencing, we modified the traditional cultivation medium with antibiotics, amino acids, carbon sources, and growth factors (e.g., vitamins and metals), achieving the successful cultivation of RACS-sorted active degrader Pigmentiphaga sp. Our results implied that RACS-SIP-GDC is a state-of-the-art approach for the precise identification, targeted isolation, and cultivation of functional microbes from complex communities in natural habitats. RACS-SIP-GDC can be used to explore specific and targeted organic-pollution-degrading microorganisms at the single-cell level and provide new insights into their biodegradation mechanisms.

Unlocking the potential of resuscitation-promoting factor for enhancing anaerobic microbial dechlorination of polychlorinated biphenyls

Microbial dechlorination of polychlorinated biphenyls (PCBs) is limited by the slow growth rate and low activity of dechlorinators. Resuscitation promoting factor (Rpf) of Micrococcus luteus, has been demonstrated to accelerate the enrichment of highly active PCB-dechlorinating cultures. However, it remains unclear whether the addition of Rpf can further improve the dechlorination performance of anaerobic dechlorination cultures. In this study, the effect of Rpf on the performance of TG4, an enriched PCB-dechlorinating culture obtained by Rpf amendment, for reductive dechlorination of four typical PCB congeners (PCBs 101, 118, 138, 180) was evaluated. The results indicated that Rpf significantly enhanced the dechlorination of the four PCB congeners, with residual mole percentages of PCBs 101, 118, 138 and 180 in Rpf-amended cultures being 16.2-29.31 %, 13.3-20.1 %, 11.9-14.4 % and 9.4-17.3 % lower than those in the corresponding cultures without Rpf amendment after 18 days of incubation. Different models were identified as appropriate for elucidating the dechlorination kinetics of distinct PCB congeners, and it was observed that the dechlorination rate constant is significantly influenced by the PCB concentration. The supplementing Rpf did not obviously change dechlorination metabolites, and the removal of chlorines occurred mainly at para- and meta- positions. Analysis of microbial community and functional gene abundance suggested that Rpf-amended cultures exhibited a significant enrichment of Dehalococcoides, Dehalogenimonas and Desulfitobacterium, as well as non-dechlorinators belonging to Desulfobacterota and Bacteroidetes. These findings highlight the potential of Rpf as an effective additive for enhancing PCB dechlorination, providing new insights into the survival of functional microorganisms involved in anaerobic reductive dechlorination.

Bioremediation of PBDEs and heavy metals co-contaminated soil in e-waste dismantling sites by Pseudomonas plecoglossicida assisted with biochar

Biochar-assisted microbial remediation has been proposed as a promising strategy to eliminate environmental pollutants. However, studies on this strategy used in the remediation of persistent organic pollutants and heavy metals co-contaminated soil are lacking, and the effect of the combined incorporation of biochar and inoculant on the assembly, functions, and microbial interactions of soil microbiomes are unclear. Here, we studied 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) degradation and heavy metal immobilization by and biochar-based bacterial inoculant (BC/PP) in an e-waste contaminated soil, and corresponding microbial regulation mechanisms. Results showed that BC/PP addition was more effective in reducing Cu and Pb availability and degrading BDE-47 than inoculant alone. Notably, BC/PP facilitated bound-residue formation of BDE-47, reducing the ecological risk of residual BDE-47. Meanwhile, microbial carbon metabolism and enzyme activities (related to C-, N-, and P- cycles) were enhanced in soil amended with BC/PP. Importantly, biochar played a crucial role in inoculant colonization, community assembly processes, and microbiome multifunction. In the presence of biochar, positive interactions in co-occurrence networks of the bacterial community were more frequent, and higher network stability and more keystone taxa were observed (including potential degraders). These findings provide a promising strategy for decontaminating complex-polluted environments and recovering soil ecological functions.

New mechanisms of biochar-assisted vermicomposting by recognizing different active di-(2-ethylhexyl) phthalate (DEHP) degraders across pedosphere, charosphere and intestinal sphere

Biochar-assisted vermicomposting can significantly accelerate soil DEHP degradation, but little information is known about the underlying mechanisms as different microspheres exist in soil ecosystem. In this study, we identified the active DEHP degraders in biochar-assisted vermicomposting by DNA stable isotope probing (DNA-SIP) and surprisingly found their different compositions in pedosphere, charosphere and intestinal sphere. Thirteen bacterial lineages (Laceyella, Microvirga, Sphingomonas, Ensifer, Skermanella, Lysobacter, Archangium, Intrasporangiaceae, Pseudarthrobacter, Blastococcus, Streptomyces, Nocardioides and Gemmatimonadetes) were responsible for in situ DEHP degradation in pedosphere, whereas their abundance significantly changed in biochar or earthworm treatments. Instead, some other active DEHP degraders were identified in charosphere (Serratia marcescens and Micromonospora) and intestinal sphere (Clostridiaceae, Oceanobacillus, Acidobacteria, Serratia marcescens and Acinetobacter) with high abundance. In biochar-assisted vermicomposting, the majority of active DEHP degraders were found in charosphere, followed by intestinal sphere and pedosphere. Our findings for the first time unraveled the spatial distribution of active DEHP degraders in different microspheres in soil matrices, explained by DEHP dynamic adsorption on biochar and desorption in earthworm gut. Our work highlighted that charosphere and intestinal sphere exhibited more contribution to the accelerated DEHP biodegradation than pedosphere, providing novel insight into the mechanisms of biochar and earthworm in improving contaminant degradation.