Pyrene Degradation Research Articles

Novel insights into the synergetic degradation of pyrene by microbial communities from mangroves in China

Pyrene is a high molecular weight polycyclic aromatic hydrocarbon (HMW-PAHs). It is a ubiquitous, persistent, and carcinogenic environmental contaminant that has raised concern worldwide. This research explored synergistic bacterial communities for efficient pyrene degradation in seven typical Southern China mangroves. The bacterial communities of seven typical mangroves were enriched by pyrene, and enriched bacterial communities showed an excellent pyrene degradation capacity of > 95% (except for HK mangrove and ZJ mangrove). Devosia, Hyphomicrobium, Flavobacterium, Marinobacter, Algoriphahus, and Youhaiella all have significant positive correlations with pyrene (R>0, p < 0.05) by 16SrRNA gene sequencing and metagenomics analysis, indicated that these genera play a vital role in pyrene metabolism. Meanwhile, the functional genes were involved in pyrene degradation that was enriched in the bacterial communities, including the genes of nagAa, ndoR, pcaG, etc. Furthermore, the analyses of functional genes and binning genomes demonstrated that some bacterial communities as a unique teamwork to cooperatively participate in pyrene degradation. Interestingly, the genes related to biogeochemical cycles were enriched, such as narG , soxA, and cyxJ, suggested that bacterial communities were also helpful in maintaining the stability of the ecological environment. In addition, some novel species with pyrene-degradation potential were identified in the pyrene-degrading bacterial communities, which can enrich the resource pool of pyrene-degrading strains. Overall, this study will help develop further research strategies for pollutant removal.

Enhancing bioremediation potential of microalgae Chlorella vulgaris and Scenedesmus acutus by NaCl for pyrene degradation.

Microalgae are increasingly recognized as promising organisms for bioremediation of organic pollutants. This study investigates the potential of enhancing the bioremediation efficiency of pyrene (PYR), a polycyclic aromatic hydrocarbon (PAH), through NaCl induced physiological and biochemical alterations in two microalgae species, Chlorella vulgaris and Scenedesmus acutus. Our findings reveal significant improvement in PYR removal when these microalgae were cultivated in the presence of 0.1% NaCl where PYR removal increased from 54 to 74% for C. vulgaris and from 26 to 75% for S. acutus. However, it was observed that NaCl induced stress had varying effects on the two species. While C. vulgaris exhibited increased PYR removal, it experienced reduced growth and biomass production, as well as lower photosynthetic efficiency when exposed to PYR and PYR + NaCl. In contrast, S. acutus displayed better growth and biomass accumulation under PYR + NaCl conditions, making it a more efficient candidate for enhancing PYR bioremediation in the presence of NaCl. In addition to assessing growth and biochemical content, we also investigated stress biomarkers, such as lipid peroxidation, polyphenol and proline contents. These findings suggest that S. acutus holds promise as an alternative microalgae species for PYR removal in the presence of NaCl, offering potential advantages in terms of bioremediation efficiency and ecological sustainability. This study highlights the importance of understanding the physiological and biochemical responses of microalgae to environmental stressors, which can be harnessed to optimize bioremediation strategies for the removal of organic pollutants like PYR.

Neural network establishes co-occurrence links between transformation products of the contaminant and the soil microbiome

It remains challenging to establish reliable links between transformation products (TPs) of contaminants and corresponding microbes. This challenge arises due to the sophisticated experimental regime required for TP discovery and the compositional nature of 16S rRNA gene amplicon sequencing and mass spectrometry datasets, which can potentially confound statistical inference. In this study, we present a new strategy by combining the use of 2H-labeled Stable Isotope-Assisted Metabolomics (2H-SIAM) with a neural network-based algorithm (i.e., MMvec) to explore links between TPs of pyrene and the soil microbiome. The links established by this novel strategy were further validated using different approaches. Briefly, a metagenomic study provided indirect evidence for the established links, while the identification of pyrene degraders from soils, and a DNA-based stable isotope probing (DNA-SIP) study offered direct evidence. The comparison among different approaches, including Pearson's and Spearman's correlations, further confirmed the superior performance of our strategy. In conclusion, we summarize the unique features of the combined use of 2H-SIAM and MMvec. This study not only addresses the challenges in linking TPs to microbes but also introduces an innovative and effective approach for such investigations.Environmental Implication: Taxonomically diverse bacteria performing successive metabolic steps of the contaminant were firstly depicted in the environmental matrix.

Enhanced photocatalytic degradation of polycyclic aromatic hydrocarbons (PAHs) Using NiO nanoparticles

The oncogenic and genetic properties of anthracene, a member of the polycyclic aromatic hydrocarbons (PAHs) family, pose a significant health threat to humans. This study aims to investigate the photocatalytic decomposition of anthracene under various conditions, such as different concentrations of PAHs, varying amounts of NiO (nickel oxide) nanoparticles, and different pH levels under ultraviolet light and sunlight. The synthesized NiO nanoparticles showed surface plasma resonance at 230 and 360 nm, while XRD and SEM analysis confirmed the nanoparticles were cubic crystalline in structure with sizes ranging between 37 and 126 nm. NiO nanoparticles exhibited 79% degradation of pyrene at 2 μg/mL of anthracene within 60 min of treatment. NiO at 10 μg/mL concentration showed significant adsorption of 57%, while the adsorption method worked efficiently (72%) at 5 pH. Photocatalytic degradation was confirmed by isotherm and kinetic studies through monolayer adsorption and pseudo-first-order kinetics. Further, the absorption process was confirmed by performing GC-MS analysis of the NiO nanoparticles. On the other hand, NiO nanoparticles showed antimicrobial activity against Gram negative and Gram-positive bacteria. Therefore, the present work is one of its kind proving the dual application of NiO nanoparticles, which makes them suitable candidates for bioremediation by treating PAHs and killing pathogenic bacteria.

Evaluation of Zn–Cd–Sn–S nanostructures for in vitro pyrene degradation and antimicrobial activity

The present work describes the fabrication of the quaternary Zn–Cd–Sn–S nanostructure and its use in photocatalytic remediation of the biological contaminant pyrene from water resources. Nanostructures fabricated were characterized by XRD, UV-DRS, FTIR, DLS, EDX, and SEM. In addition, an agar well diffusion test was conducted to determine the antimicrobial activity. Zn–Cd–Sn–S (ZCSS) nanostructures were evaluated for their photocatalytic degrading potential by using pyrene as a model pollutant and evaluating the effects of parameters like initial pyrene concentration, nanocatalyst dosage, solution pH, and light sources during batch adsorption. Nanostructures had a size of 16.74 nm according to the XRD analysis. With a 300 min time interval, ZCSS nanostructures achieved the highest removal rate of 86.3%. Pyrene degradation metabolites were identified using GC-MS analysis of the degraded samples. A Freundlich isothermal (R2 0.9) and pseudo-first-order (R2 0.952) reaction kinetic path best fit the adsorption results for pyrene by the fabricated ZCSS nanostructure, based on the adsorption and kinetic studies. Zn–Cd–Sn–S exhibited the highest antibacterial activity against Staphylococcusaureus (22.4 mM). Due to the combined synergistic actions of the constituent metals, this quaternary nanostructure exhibited exceptional photocatalytic activity. To our est knowledge, the ZCSS nanostructure was made and used to remove pyrene by photocatalysis and fight microbes. Ultimately, the ZCSS nanostructure was found to be an effective photocatalyst for eradicating pathogenic microbes from water.

Isolation and characterization of distinctive pyrene-degrading bacteria from an uncontaminated soil.

Considerable efforts that isolate and characterize degrading bacteria for polycyclic aromatic hydrocarbons (PAHs) have focused on contaminated environments so far. Here we isolated three distinctive pyrene (PYR)-degrading bacteria from a paddy soil that was not contaminated with PAHs. These included a novel Bacillus sp. PyB-9 and efficient degraders, Shigella sp. PyB-6 and Agromyces sp. PyB-10. All three strains could utilize naphthalene, phenanthrene, anthracene, fluoranthene and PYR as sole carbon sources, and degraded PYR in a range of temperatures (27-37°C) and pH (5-8). Strains PyB-6 and PyB-10 almost completely degraded 50mgL-1 PYR within 15days, and 75.5% and 98.9% of 100mgL-1 PYR in 27days, respectively. The kinetics of PYR biodegradation was well represented by the Gompertz model. Ten and twelve PYR metabolites were identified in PYR degradation process by strains PyB-6 and PyB-10, respectively. Chemical analyses demonstrated that the degradation mechanisms of PYR were the same for strains PyB-6 and PyB-10 with initial dioxygenation mainly on C-4,5 positions of PYR. The degradation of 4,5-phenanthrenedicarboxylic acid was branched to 4-phenanthrenecarboxylic acid pathway and 5-hydroxy-4-phenanthrenecarboxylic acid pathway, both of which played important roles in PYR degradation by strains PyB-6 and PyB-10. To our knowledge, Shigella sp. and Agromyces sp. were found for the first time to possess the capability for PAHs degradation. These findings contributed to upgrading the bank of microbial resource and knowledge on PAH biodegradation.

Incorporation of N-doped biochar into submicron zero-valent iron for efficient peroxydisulfate activation in soil remediation: Performance and mechanism

The development of strategic methods to enhance the catalytic reactivity and electron efficiency of biochar-modified zero-valent iron (BC-ZVI) via mechanochemistry is highly important and desirable for the use of peroxydisulfate-based advanced oxidation processes (PDS-AOPs) in soil remediation. Herein, novel amphiphilic ball-milled N-doped biochar-ZVI composites (NBC-ZVIbm) were fabricated to activate PDS for efficient pyrene degradation in soil. The N-doped site- and alloying heterojunction-induced surface charge redistribution, directional electron transfer, and amphiphilicity of NBC-ZVIbm were verified, all of which improved the interactions among NBC-ZVIbm, PDS and pyrene. Specifically, NBC incorporation optimized PDS oxidation and pyrene adsorption on NBC-ZVIbm, forming a reaction center that efficiently accelerated the reaction. As a result, 95.5 % of 98.3 mg/kg pyrene in soil was degraded by NBC-ZVIbm/PDS within 7 d, which was 2.3 and 1.5 times greater than that of ball-milled ZVI and BC-ZVIbm, respectively; additionally, the electron efficiency of this process increased to 85.2 %. Characterization of the reaction process suggested that NBC incorporation induced directional electron transfer from ZVI to NBC for PDS activation and SO4•- generation. Subsequently, the amphiphilicity of NBC-ZVIbm promoted soil phase-pyrene desorption and migration, thereby increasing pyrene degradation. This NBC-incorporation method provides a strategy for constructing highly efficient ZVI-based catalysts for the use of PDS-AOPs in soil remediation.

Functionally coherent transcriptional responses of Jatropha curcas and Pseudomonas fragi for rhizosphere mediated degradation of pyrene

Pyrene is an extremely hazardous, carcinogenic polycyclic aromatic hydrocarbon (PAH). The plant–microbe interaction between Pseudomonas fragi DBC and Jatropha curcas was employed for biodegradation of pyrene and their transcriptional responses were compared. The genome of P. fragi DBC had genes for PAH degrading enzymes i.e. dioxygenases and dehydrogenases, along with root colonization (trpD, trpG, trpE and trpF), chemotaxis (flhF and flgD), stress adaptation (gshA, nuoHBEKNMG), and detoxification (algU and yfc). The transcriptional expression of catA and yfc that respectively code for catabolic enzyme (catechol-1, 2-dioxygnase) and glutathione-s-transferase for detoxification functions were quantitatively measured by qPCR. The catA was expressed in presence of artificial root exudate with or without pyrene, and glucose confirming the non-selective approach of bacteria, as desired. Pyrene induced 100-fold increase of yfc expression than catA, while there was no expression of yfc in absence of pyrene. The transcriptome of plant roots, in presence of pyrene, with or without P. fragi DBC inoculation was analysed. The P. fragi DBC could upregulate the genes for plant growth, induced the systemic acquired resistance and also ameliorated the stress response in Jatropha roots.

Superefficient non-radical degradation of benzo[a]pyrene in soil by Fe-biochar composites activating persulfate

Efficient decomposition of organic pollutants in complex soil environments through non-radical pathways is vital but challenging. Herein, biochar supported nZVI (nZVI@BC800) fabricated by carbothermal reduction method was prepared for persulfate activation, exhibiting ultrafast degradation efficiency of benzo[a]pyrene of 71.80 % within 5 min with excellent adaptability to wide pH range of 3.0–9.0 and high anti-interference capacity to coexisting substances in soil. In nZVI@BC800/persulfate system, non-radical pathways including singlet oxygen (1O2) and electron transfer made dominant contributions to benzo[a]pyrene degradation. 1O2 could be produced not only by the reaction between C = O on BC800 and persulfate, but also via the transformation of O2∙- and ∙OH. On the other hand, biochar as an electron shuttle could accelerate electron transfer from benzo[a]pyrene to persulfate adsorbed on the catalyst. Additionally, possible degradation pathways of benzo[a]pyrene in nZVI@BC800/persulfate system were inferred through GC–MS and DFT calculations. Furthermore, the system could modulate the soil microbial community to further improve plant stress resistance. Therefore, this study provided a promising strategy via developing carbon-supported iron catalyst for carrying out persulfate-based non-radical pathways to remediate organic-polluted soil.

Adaptation strategies and functional transitions of microbial community in pyrene-contaminated soils promoted by lead with Pseudomonas veronii and its extracellular polymeric substances

Pyrene was designated as a remediation target in this study, and low contamination of lead (Pb) was set to induce heavy metal stress. Pseudomonas veronii and its extracellular polymeric substances (EPSs) were chosen for biofortification, with the aim of elucidating the structural, metabolic, and functional responses of soil microbial communities. Community analysis of soil microorganisms using high-throughput sequencing showed that the co-addition of P. veronii and EPSs resulted in an increase in relative abundance of phyla associated with pyrene degradation, and formed a symbiotic system dominated by Firmicutes and Proteobacteria, which involved in pyrene metabolism. Co-occurrence network analysis revealed that the module containing P. veronii was the only one exhibiting a positive correlation between bacterial abundance and pyrene removal, indicating the potential of bioaugmentation in enriching functional taxa. Biofortification also enhanced the abundance of functional gene linked to EPS production (biofilm formation-Pseudomonas aeruginosa) and pyrene degradation. Furthermore, 17 potential functional bacteria were screened out using random forest algorithm. Lead contamination further promoted the growth of Proteobacteria, intensified cooperative associations among bacteria, and increased the abundance of bacteria with positive correlation with pyrene degradation. The results offer novel perspectives on alterations in microbial communities resulting from the synergistic impact of heavy metal stress and biofortification.

Efficient benzo(a)pyrene degradation by coal gangue-based catalytic material for peroxymonosulfate activation

A low cost and green peroxymonosulfate (PMS) activation catalyst (CG-Ca-N) was successfully prepared with coal gangue (CG), calcium chloride, and melamine as activator. Under the optimal conditions, the CG-Ca-N can remove 100 % for benzo(a)pyrene (Bap) in an aqueous solution after 20 min and 72.06 % in soil slurry medium within 60 min, which also display excellent reuse ability toward Bap after three times. The removal of Bap is significantly decreased when the initial pH value was greater than 9 and obviously inhibited in the presence of HCO3− or SO42−. The characterization results indicated that the addition of calcium chloride could stabilize and increase the content of pyridinic N during thermal annealing, resulting in the production of •OH, SO4•− and 1O2. Based on electron paramagnetic resonance (EPR) and active radical scavenging experiments, 1O2 could be identified to be the dominant role in Bap degradation. Overall, this work opened a new perspective for the low cost and green PMS catalysts and offered great promise in the practical remediation of organic pollution of groundwater and soil.

Biodegradation of pyrene by bacterial consortia: Impact of natural surfactants and iron oxide nanoparticles

Polycyclic aromatic hydrocarbons (PAHs) are potentially hazardous compounds that could cause a severe impact on many ecosystems. They are very challenging to remove using conventional methods due to their hydrophobic nature. However, this issue can be resolved by utilizing surface-active molecules to increase their bioavailability. In this study, pyrene was chosen as the PAH compound to explore its degradability by the effect of individual bacterial strains (Pseudomonas stutzeri NA3 and Acinetobacter baumannii MN3) and mixed consortia (MC) along with natural surfactant derived from Sapindus mukorossi and iron oxide nanoparticles (NPs). Additionally, fatty acids esters, dipeptides, and sugar derivative groups were identified as potent bioactive components of natural surfactants. Various techniques, such as XRD, VSM, TEM, and FE-SEM with EDX, were utilized to characterize the pristine and Fenton-treated iron oxide NPs. The analytical results confirmed that the Fe3O4 crystal phase and spherical-shaped NPs exhibited excellent magnetic properties. The impact of natural surfactants and iron oxide NPs has significantly contributed to the biodegradation process, resulting in a prominent decrease in chemical oxygen demand (COD) levels. Gas chromatography-mass spectrometry (GC-MS) analysis showed that biodegradation systems produced primary hydrocarbon intermediates, which underwent oxidative degradation through Fenton treatment. Interestingly, synthesized iron oxide NPs effectively produced hydroxyl radical (•OH) during the Fenton reaction, which was confirmed by electron paramagnetic resonance (EPR) spectra, and the pristine iron oxide NPs underwent a material transformation observed. The study demonstrated an integrated approach for biodegradation and the Fenton reaction process to enhance the pyrene degradation efficiency (90%) compared to other systems. Using natural surfactants and iron oxide NPs in aquatic environments serves as a crucial platform at the interface of microorganisms and contaminated oil products. This interaction offers a promising solution for PAHs bioremediation.

Insight into the High-Efficiency Benzo(a)pyrene Degradation Ability of Pseudomonas benzopyrenica BaP3 and Its Application in the Complete Bioremediation of Benzo(a)pyrene.

Polycyclic aromatic hydrocarbons (PAHs) are common carcinogens. Benzo(a)pyrene is one of the most difficult high-molecular-weight (HMW) PAHs to remove. Biodegradation has become an ideal method to eliminate PAH pollutants from the environment. The existing research is mostly limited to low-molecular-weight PAHs; there is little understanding of HMW PAHs, particularly benzo(a)pyrene. Research into the biodegradation of HMW PAHs contributes to the development of microbial metabolic mechanisms and also provides new systems for environmental treatments. Pseudomonas benzopyrenica BaP3 is a highly efficient benzo(a)pyrene-degrading strain that is isolated from soil samples, but its mechanism of degradation remains unknown. In this study, we aimed to clarify the high degradation efficiency mechanism of BaP3. The genes encoding Rhd1 and Rhd2 in strain BaP3 were characterized, and the results revealed that rhd1 was the critical factor for high degradation efficiency. Molecular docking and enzyme activity determinations confirmed this conclusion. A recombinant strain that could completely mineralize benzo(a)pyrene was also proposed for the first time. We explained the mechanism of the high-efficiency benzo(a)pyrene degradation ability of BaP3 to improve understanding of the degradation mechanism of highly toxic PAHs and to provide new solutions to practical applications via synthetic biology.

Sepiolite promotes photodegradation of pyrene under visible light

Mechanochemistry and photocatalysis are emergent technologies for the remediation of polycyclic aromatic hydrocarbons (PAHs) in soils. In this work, mechanochemistry and photocatalysis are combined for pyrene degradation. The photodegradation of pyrene, when in contact with sepiolite under pressure application, is studied. The mechanical treatment leads to a pyrene crystal phase transformation. In this new phase, pyrene undergoes a fast photodegradation in the 320–420 nm range. We show that sepiolite is superior as a photocatalyst in pyrene degradation to TiO2, the most exploited photocatalyst. A broad physicochemical characterization is carried out to propose a mechanism in which the photoexcitation of mechanically altered pyrene leads to an electron transfer to sepiolite matrix, which triggers the PAH degradation. Finally, we want to highlight that the pyrene/sepiolite combination is a simplified system to shed light on how PAH photodegradation may occur in soils.

Impact of organic matter on transformation during thermal remediation of pyrene-contaminated substrates

Thermal remediation (TR) is a broadly applicable technology that is effective at removing volatile and semi-volatile contaminants from soil. However, TR can be costly and inefficient in practice, with underlying removal and transformation mechanisms poorly understood. To better understand the role organic matter plays in removal, a series of experiments was performed with a humic substance, humic modified silica, and a natural soil in the presence of pyrene from 100 to 500 °C and compared to prior experiments using pure minerals. Detection of by-products confirmed that pyrene was removed by transformation in addition to volatilization. Oxidation via hydroxyl radical formation and reductive hydrogenation were both indicated as possible reaction mechanisms promoted by organic matter. Because the presence of bulk water did not impact the extent of pyrene degradation or transformation, it is hypothesized that hydroxyl radicals were produced from soil organic matter functional groups, such as carboxyl and phenol groups, and possibly bound water at elevated temperatures in dry experiments. Additionally, the average oxidation state of carbon in detected by-products increased with temperature in experiments with humic modified silica and soil but not humic substance alone, though the extent of degradation did not significantly change. This shift in oxidation state may indicate that attachment of organic matter to another surface may increase interaction between reactive species. The results of this study show that contaminant transformation in soils during TR significantly contributes to removal, even at temperatures lower than those used in traditional treatment. This information will help to guide the design and operation of TR systems, potentially reducing energy requirements and highlighting the necessity of testing for transformation by-products.

Nitrogen transfer and cross-feeding between Azotobacter chroococcum and Paracoccus aminovorans promotes pyrene degradation

Nitrogen is a limiting nutrient for degraders function in hydrocarbon-contaminated environments. Biological nitrogen fixation by diazotrophs is a natural solution for supplying bioavailable nitrogen. Here, we determined whether the diazotroph Azotobacter chroococcum HN can provide nitrogen to the polycyclic aromatic hydrocarbon-degrading bacterium Paracoccus aminovorans HPD-2 and further explored the synergistic interactions that facilitate pyrene degradation in nitrogen-deprived environments. We found that A. chroococcum HN and P. aminovorans HPD-2 grew and degraded pyrene more quickly in co-culture than in monoculture. Surface-enhanced Raman spectroscopy combined with 15N stable isotope probing (SERS − 15N SIP) demonstrated that A. chroococcum HN provided nitrogen to P. aminovorans HPD-2. Metabolite analysis and feeding experiments confirmed that cross-feeding occurred between A. chroococcum HN and P. aminovorans HPD-2 during pyrene degradation. Transcriptomic and metabolomic analyses further revealed that co-culture significantly upregulated key pathways such as nitrogen fixation, aromatic compound degradation, protein export, and the TCA cycle in A. chroococcum HN and quorum sensing, aromatic compound degradation and ABC transporters in P. aminovorans HPD-2. Phenotypic and fluorescence in situ hybridization (FISH) assays demonstrated that A. chroococcum HN produced large amounts of biofilm and was located at the bottom of the biofilm in co-culture, whereas P. aminovorans HPD-2 attached to the surface layer and formed a bridge-like structure with A. chroococcum HN. This study demonstrates that distinct syntrophic interactions occur between A. chroococcum HN and P. aminovorans HPD-2 and provides support for their combined use in organic pollutant degradation in nitrogen-deprived environments.

Understanding the effective breakdown of PAH s in water through the use of g–C3N4–Ag–Cu–Ni nanocomposites

The research work aimed to explore the suitability of using a novel g- C3N4–Ag–Cu–Ni nanocomposite for the simultaneous degradation of pyrene in wastewater. The outcome revealed that the g- C3N4 phase was successfully fabricated on the g–C3N4–based compound, and the existence of the g- C3N4-based compound beneficially stabilized the Ag–Cu–Ni particles. The g- C3N4–Ag–Cu–Ni nanocomposite demonstrated excellent performance in pyrene degradation under various conditions. The degradation of pyrene increased with a rise in the dosage of g- C3N4–Ag–Cu–Ni. These findings indicate that the g- C3N4–Ag–Cu–Ni nanocomposite could be a promising material for water purification, especially for the simultaneous photocatalytic and antimicrobial treatment of contaminated water bodies. The study provides a helpful guide for future research in this field.

Phylloremediation of pyrene and anthracene by endophytic fungi inhabiting tea leaves (Camellia sinensis (L.) Kuntze) in Sri Lanka

ABSTRACT Polyaromatic hydrocarbons (PAHs) released from vehicular emissions and oil refineries deposit on the phyllosphere, compromising the quality of leaf-based food products by posing many health issues. Nevertheless, the tea phyllosphere harbours a variety of endophytes that are highly effective at degrading polyaromatic hydrocarbons, anthracene, and pyrene. The present study attempts to analyse the pyrene and anthracene degrading capability of phyllosphere endophytic fungi that inhabit Camellia sinensis (L.) Kuntze leaves. The frequency of occurrence of endophytic fungi in different leaf tissue layers was examined using light and scanning electron microscopy (SEM). The best pyrene and anthracene degrading strains were selected based on the High-Performance Liquid Chromatography (HPLC) results, and further kinetic assays. Light microscopy and SEM observations highlighted a heterogeneous endophytic fungal distribution among leaf tissue layers; the upper epidermis had the highest fungal distribution compared to other leaf layers. HPLC results revealed that Phyllosticta capitalensis, Colletotrichum gloeosporioides, Colletotrichum siamense, Pseudopestalotiopsis chinensis, and Daldinia eschscholtzii, have higher pyrene and anthracene degradation respectively and their PAH degradation kinetics follow the first-order kinetic model. The best anthracene and pyrene degrader, P. capitalensis showed the lowest half-life. The present investigation highlights the potential of P. capitalensis, the best pyrene and anthracene degrader that can remediate PAHs deposited on the phyllosphere of tea leaves.

Pyro-Catalytic Degradation of Pyrene by Bentonite-Supported Transition Metals: Mechanistic Insights and Trade-Offs with Low Pyrolysis Temperature.

Transition metal catalysts can significantly enhance the pyrolytic remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Significantly higher pyrene removal efficiency was observed after the pyrolytic treatment of Fe-enriched bentonite (1.8% wt ion-exchanged content) relative to natural bentonite or soil (i.e., 93% vs 48% and 4%) at the unprecedentedly low temperature of 150 °C with only 15 min treatment time. DFT calculations showed that bentonite surfaces with Fe3+ or Cu2+ adsorb pyrene stronger than surfaces with Zn2+ or Na+. Enhanced pyrene adsorption results from increased charge transfer from its aromatic π-bonds to the cation site, which destabilizes pyrene allowing for faster degradation at lower temperatures. UV-Vis and GC-MS analyses revealed pyrene decomposition products in extracts of samples treated at 150 °C, including small aromatic compounds. As the pyrolysis temperature increased above 200 °C, product distribution shifted from extractable compounds to char coating the residue particles. No extractable byproducts were detected after treatment at 400 °C, indicating that char was the final product of pyrene decomposition. Tests with human lung cells showed that extracts of samples pyrolyzed at 150 °C were toxic; thus, high removal efficiency by pyrolytic treatment does not guarantee detoxification. No cytotoxicity was observed for extracts from Fe-bentonite samples treated at 300 °C, inferring that char is an appropriate treatment end point. Overall, we demonstrate that transition metals in clay can catalyze pyrolytic reactions at relatively low temperatures to decrease the energy and contact times required to meet cleanup standards. However, mitigating residual toxicity may require higher pyrolysis temperatures.

Metagenomics reveals mechanism of pyrene degradation by an enriched bacterial consortium from a coking site contaminated with PAHs

A bacterial consortium, termed WPB, was obtained from polycyclic aromatic hydrocarbons (PAHs) contaminated soil from a coking site. The consortium effectively degraded 100 mg L−1 pyrene by 94.8 % within 12 days. WPB was also able to degrade phenanthrene (98.3 %) and benzo[a]pyrene (24.6 %) in 12 days, while the individual isolates showed no PAHs degrading ability. Paracoccus sp. dominated the bacterial consortium (65.0–86.2 %) throughout the degradation process. Metagenomic sequencing reveals the proportion of sequences with xenobiotics biodegradation and metabolism increased throughout the degradation process indicating the great potential of WPB to degrade pollutants. The annotation of genes by metagenomic analysis help reconstruct the degradation pathways (“phthalate pathway” and “naphthalene degradation”) and reveal how different bacteria contribute to the degradation process. Mycobacterium gilvum was found to carry nidAB genes that catalyze the first step of high-molecular-weight (HMW) PAHs in the degradation process despite Mycobacterium gilvum accounting for only 0.005–0.06 %. In addition, genomes of Paracoccus denitrificans and some other genera affiliated with Devosia, Pusillimonas caeni and Eoetvoesia caeni were successfully recovered and were found to carry genes responsible for the degradation of the intermediates of pyrene. These results enable further understanding of the metabolic patterns of pyrene-degrading consortia and provide direction for further cultivation and discovery of key players in complex microbial consortia.