Biodegradation Of Polycyclic Aromatic Hydrocarbons Research Articles

Genetic redundancy in the naphthalene-degradation pathway of Cycloclasticus pugetii strain PS-1 enables response to varying substrate concentrations.

Polycyclic aromatic hydrocarbon (PAH) contamination in marine environments range from low-diffusive inputs to high loads. The influence of PAH concentration on the expression of functional genes [e.g. those encoding ring-hydroxylating dioxygenases (RHDs)] has been overlooked in PAH biodegradation studies. However, understanding marker-gene expression under different PAH loads can help to monitor and predict bioremediation efficiency. Here, we followed the expression (via RNA sequencing) of Cycloclasticus pugetii strain PS-1 in cell suspension experiments under different naphthalene (100 and 30mg L-1) concentrations. We identified genes encoding previously uncharacterized RHD subunits, termed rhdPS1α and rhdPS1β, that were highly transcribed in response to naphthalene-degradation activity. Additionally, we identified six RHD subunit-encoding genes that responded to naphthalene exposure. By contrast, four RHD subunit genes were PAH-independently expressed and three other RHD subunit genes responded to naphthalene starvation. Cycloclasticus spp. could, therefore, use genetic redundancy in key PAH-degradation genes to react to varying PAH loads. This genetic redundancy may restrict the monitoring of environmental hydrocarbon-degradation activity using single-gene expression. For Cycloclasticus pugetii strain PS-1, however, the newly identified rhdPS1α and rhdPS1β genes might be potential target genes to monitor its environmental naphthalene-degradation activity.

Utilization of lasso peptides for biodegradation of polycyclic aromatic hydrocarbons.

Many microbial genes involved in degrading recalcitrant environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs) have been identified and characterized. However, all molecular mechanisms required for PAH utilization have not yet been elucidated. In this work, we demonstrate the proposed involvement of lasso peptides in the utilization of the PAH phenanthrene in Sphingomonas BPH. Transpositional mutagenesis of Sphingomonas BPH with the miniTn5 transposon yielded 3 phenanthrene utilization deficient mutants, #257, #1778, and #1782. In mutant #1782, Tn5 had inserted into the large subunit of the naph/bph dioxygenase gene. In mutant #1778, Tn5 had inserted into the B2 protease gene of a lasso peptide cluster. This finding is the first report on the role of lasso peptides in PAH utilization. Our studies also demonstrate that interruption of the lasso peptide cluster resulted in a significant increase in the amount of biosurfactant produced in the presence of glucose when compared to the wild-type strain. Collectively, these results suggest that the mechanisms Sphingomonas BPH utilizes to degrade phenanthrene are far more complex than previously understood and that the #1778 mutant may be a good candidate for bioremediation when glucose is applied as an amendment due to its higher biosurfactant production.

Fungal Biodegradation of Polycyclic Aromatic Hydrocarbons (PAHs)

For many years, PAHs have been the subject of intense controversy throughout the world, due to their high toxicity and their presence in almost all environmental media. Their hazardous nature has given rise to a number of legal requirements throughout the world aimed at effectively reducing their content in foodstuffs and certain everyday consumer products. However, technologies for remediating PAH-contaminated soils use chemical and mechanical approaches that are extremely costly and not very environmentally friendly. That's why research is currently focusing on biological approaches that can provide effective, low-cost treatment for PAH-contaminated soils, and avoid environmental repercussions as far as possible. The aim of this paper is to shed light on a biological approach to the treatment of PAHs that is still in its infancy, but which is already showing great promise: biodegradation by fungi, which differ from other organisms in that they secrete enzymes that give them the ability to feed in environments inaccessible to other kingdoms, and to absorb toxic PAH chemicals from the soil and transform them into less harmful compounds.

Dissolved organic matter influences the indigenous bacterial community and polycyclic aromatic hydrocarbons biodegradation in soils

In polycyclic aromatic hydrocarbon (PAH) contaminated soils, bioremediation is superior to other strategies owing to its low cost and environmental friendliness. However, dissolved organic matter (DOM) and indigenous bacterial communities can affect the efficiency of PAH-degrading bacteria (PDB). This study found that exogenous PDB (C1) including the genera Acinetobacter, Stenotrophomonas, and Comamonas, decreased the bacterial diversity of Alfisol, Ultisol, Inceptisol, and Mollisol, and DOM enhanced the diffusion of PDB and the bioavailability of PAH. In addition, bacteria preferred to ingest low molecular weight DOM fractions, and the abundances of lipid-like and protein-like substances decreased by 0.12–3.03 % and 1.73–4.60 %. The DOM fractions had a more marked influence on the indigenous bacteria than the exogenous PDB, and PDB dominated the PAH biodegradation process in the soils. More COO functional groups promoted the utilization of higher molecular weight-related homologue fractions by bacteria, and lower molecular weight fractions carrying more CH2 functional groups declined during biodegradation. This study investigated the variations in bacterial communities during biodegradation and revealed the effects of DOM fractions on biodegradation in PAH-contaminated soils at the molecular level. These results will promote the development of bioremediation strategies for organics-contaminated soil and provide guidance for prediction models of soil biodegradation kinetics.

Marine Microbiota Responses to Shipping Scrubber Effluent Assessed at Community Structure and Function Endpoints.

The use of novel high-throughput sequencing (HTS) technologies to examine the responses of natural multidomain microbial communities to scrubber effluent discharges to the marine environment is still limited. Thus, we applied metabarcoding sequencing targeting the planktonic unicellular eukaryotic and prokaryotic fraction (phytoplankton, bacterioplankton, and protozooplankton) in mesocosm experiments with natural microbial communities from a polluted and an unpolluted site. Furthermore, metagenomic analysis revealed changes in the taxonomic and functional dominance of multidomain marine microbial communities after scrubber effluent additions. The results indicated a clear shift in the microbial communities after such additions, which favored bacterial taxa with known oil and polycyclic aromatic hydrocarbons (PAHs) biodegradation capacities. These bacteria exhibited high connectedness with planktonic unicellular eukaryotes employing variable trophic strategies, suggesting that environmentally relevant bacteria can influence eukaryotic community structure. Furthermore, Clusters of Orthologous Genes associated with pathways of PAHs and monocyclic hydrocarbon degradation increased in numbers at treatments with high scrubber effluent additions acutely. These genes are known to express enzymes acting at various substrates including PAHs. These indications, in combination with the abrupt decrease in the most abundant PAHs in the scrubber effluent below the limit of detection-much faster than their known half-lives-could point toward a bacterioplankton-initiated rapid ultimate biodegradation of the most abundant toxic contaminants of the scrubber effluent. The implementation of HTS could be a valuable tool to develop multilevel biodiversity indicators of the scrubber effluent impacts on the marine environment, which could lead to improved impact assessment. Environ Toxicol Chem 2024;43:1012-1029. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

The discrepant metabolic pathways of PAHs by facultative anaerobic bacteria under aerobic and nitrate-reducing conditions

Studies regarding the facultative anaerobic biodegradation of polycyclic aromatic hydrocarbons (PAHs) were still in the initial stage. In this study, a facultative anaerobe which was identified as Bacillus Firmus and named as PheN7 was firstly isolated from the mixed petroleum-polluted soil samples using phenanthrene and nitrate as the solo carbon resource and electron acceptor under anaerobic condition. The degradation rates of PheN7 towards phenanthrene were detected as 33.17 μM/d, 13.81 μM/d and 7.11 μM/d at the initial phenanthrene concentration of 250.17 μM with oxygen, nitrate and sulfate as the electron acceptor, respectively. The metabolic pathways toward phenanthrene by PheN7 were deduced combining the metagenome analysis of PheN7 and intermediate metabolites of phenanthrene under aerobic and nitrate-reducing conditions. Dioxygenation and carboxylation were inferred as the initial activation reactions of phenanthrene degradation in these two pathways. This study highlighted the significance of facultative anaerobic bacteria in natural PAHs biodegradation, revealing the discrepant metabolic fates of PAHs by one solo bacteria under aerobic and anaerobic environments.

Reduction strategies of polycyclic aromatic hydrocarbons in farmland soils: Microbial degradation, plant transport inhibition, and their mechanistic analysis

This study focuses on the abatement of polycyclic aromatic hydrocarbons (PAHs), a global pollutant, in farmland soils. Seven controlled PAHs in China were used as the target ligands, and four key target receptors degradable PAHs and two key target receptors transport PAHs were used as the target receptors. Firstly, the degradation abilities of the four key target receptors on PAHs were quantified, and the dominant target receptors that could efficiently degrade PAHs were screened out. Then, the co-degradation abilities of PAHs under the coexistence of the dominant target receptors (microbial diversity) were assessed, and 30 external condition-adding schemes to promote the microbial (co-)degradation of PAHs were designed. In addition, the microbial dominant target receptor mutants and the plant key target receptor mutants were obtained, the degradation and transportation of PAHs were improved by 8.06%∼22.27% and 39.86%∼45.43%. Finally, the mechanism analysis of PAHs biodegradation and transportation found that the Van der Waals interactions dominated the enhancement of PAHs’ degradation in soil, and the solvation capacity dominated the decrease of PAHs’ transportation in plant. This study aims to provide theoretical support for the prevention and control of PAHs residue pollution in farmland soil, as well as the protection of human dietary health.

Oil spill bioremediation strategies in Brazilian tropical seawater—The role of polycyclic aromatic hydrocarbons degradation

AbstractFor this research, a 28‐day bioremediation experiment was conducted, simulating an oil spill on the Brazilian coast using mesocosm units and two different bioremediation strategies, adding rate‐limiting nutrients in the form of NPK fertilizer during the first four days (Bior1) and weekly (Bior2). The gas chromatography–mass spectrometry analysis results showed that oil natural degradation (Control) removed 33.8 wt.% of the alkanes on Day 7, while bioremediation processes plus evaporation in Bior1 and Bior2 contributed to minimizing alkanes in 83.4 and 80.8 wt.%, respectively. Bior1 strategy also accelerated the biodegradation of recalcitrant polycyclic aromatic hydrocarbons (PAH) such as phenanthrene, methyl phenanthrenes, and methyl dibenzothiophenes up to the second week when compared to Bior2. Low‐cost NPK fertilizer addition demonstrated efficiency in the bioremediation strategy, especially in the first days of the simulated oil spill (Bior1), leading to savings in time and financial investment in recovering an oil contaminated area. Results also showed the efficiency of the oil‐degrading bacteria Pseudomonas mesophilica, identified for the first time in Brazilian seawater. In addition, results confirmed the influence of tropical temperatures over oil natural natural degradation and bioremediation as an oil spill cleanup solution for recovering contaminated areas in tropical countries, especially in sensitive marine environments.

Effects of electron acceptors and donors on anaerobic biodegradation of PAHs in marine sediments

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants accumulated in the environment. PAHs' bioremediation in sediments can be promoted by adding electron acceptor (EA) and electron donor (ED). Bicarbonate and sulfate were chosen as two EAs, and acetate and lactate were selected as two EDs. Six groups of amendments were added into the sediments to access their role in the anaerobic biodegradation of five PAHs, containing phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene. The concentrations of PAHs, EAs and EDs, electron transport system activity, and microbial diversity were analyzed during 126-day biodegradation in serum bottles. The HA group (bicarbonate and acetate) achieved the maximum PAH degradation efficiency of 89.67 %, followed by the SL group (sulfate and lactate) with 87.10 %. As the main PAHs degrading bacteria, the abundance of Marinobacter in H group was 8.62 %, and the addition of acetate significantly increased the abundance of Marinobacter in the HA group by 75.65 %.

Insight into the interactions between surfactants and microorganisms for the biodegradation of polycyclic aromatic hydrocarbons: Enhancing efficiency, cellular response, and elucidating mechanisms

The response mechanisms of polycyclic aromatic hydrocarbons (PAHs)-degrading strains to Tween 80 concentrations are key elements of microbial remediation efficacy. The degradation characteristics, cell morphology, and microbial metabolic activities of three strains (Arthrobacter (SZ-3), Pseudomonas putida (B6-2), and Klebsiella (CW-D3T)) at different Tween 80 concentrations (0∼2000 mg/L) were investigated. The results showed that the three PAHs degrading strains grow well with the maximum cell activity of 8.75–8.81 log CFU/ml and the electron transfer system activity (ETSA) of 0.341–0.655 μg O2 g−1min−1 at a Tween 80 concentrations range of 1000–2000 mg/L. The best degradation of PAHs by SZ-3 was achieved at a Tween 80 concentration of 500 mg/L. The degradation rates of phenanthrene (PHE), fluoranthene (FLU), and pyrene (PYR) were 91.42%, 54.62%, and 50.76%, respectively. For strains B6-2 and CW-D3T, the highest degradation rates for PHE were achieved at a Tween 80 concentration of 500 mg/L, and the highest degradation rates for FLU and PYR were reached in the absence of Tween 80. The changes of catechol 1,2-dioxygenase were consistent with the PAHs degradation efficiency. The cell surface hydrophobicity (CSH) of SZ-3 and CW-D3T increased with the increase of Tween 80, while that of B6-2 decreased. In addition, the detection of PAHs metabolites showed that SZ-3 had two metabolic pathways, salicylic acid, and phthalic acid. B6-2 metabolized PAHs mainly through the phthalic acid pathway, and CW-D3T mainly through the salicylic acid pathway. Tween 80 did not affect the metabolic pathway of PAHs by each strain.

Potential biodegradation of polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbons by indigenous fungi recovered from crude oil-contaminated soil in Iran

A total of 265 fungal individuals were isolated from soils exposed to heavy oil spills in the Yadavaran oil field in Iran to discover indigenous fungal species with a high potential to biodegrade petroleum hydrocarbon pollutants. Morphological and molecular identification of obtained fungal species led to their assignment into 16 genera and 25 species. Alternaria spp. (78%), Fusarium spp. (5%), and Cladosporium spp. (4%) were the most common genera, along with Penicillium spp., Neocamarosporium spp., Epicoccum sp., Kotlabaea sp., Aspergillus sp., Mortierella sp., and Pleurotus sp. A preliminary screening using the DCPIP indicator revealed that approximately 35% of isolates from Alternaria, Epicoccum, Neocamarosporium, Cladosporium, Fusarium, Stachybotrys, Penicillium, and Stemphylium demonstrated promising tolerance to crude oil. The best-performing isolates (12 fungal individuals) were further investigated for their capacity to mineralize a mixture of four polycyclic aromatic hydrocarbons (PAH) for 47 days, quantified by GC–MS. Eventually, two top-performing isolates, namely 5c-12 (Alternaria tenuissima) and 3b-1 (Epicoccum nigrum), were applied to petroleum-contaminated soil. The GC–MS analysis showed that 60 days after inoculation, these isolates successfully degraded more than 70% of the long-chain hydrocarbons in the soil, including C8-C16 n-alkanes, C36 n-alkane, and Pristane. This study introduces two fungal species (5c-12 and 3b-1) with high potential for biodegrading petroleum compounds and PAHs, offering promising prospects for the decontamination of oil-contaminated soil.

Enhanced Solubilization and Biodegradation of HMW-PAHs in Water with a Pseudomonas mosselii-Released Biosurfactant.

The treatment and reuse of wastewater are crucial for the effective utilization and protection of global water resources. Polycyclic aromatic hydrocarbons (PAHs), as one of the most common organic pollutants in industrial wastewater, are difficult to remove due to their relatively low solubility and bioavailability in the water environment. However, biosurfactants with both hydrophilic and hydrophobic groups are effective in overcoming these difficulties. Therefore, a biosurfactant-producing strain Pseudomonas mosselii MP-6 was isolated in this study to enhance the bioavailability and biodegradation of PAHs, especially high-molecular-weight PAHs (HMW-PAHs). FTIR and LC-MS analysis showed that the MP-6 surfactant belongs to rhamnolipids, a type of biopolymer, which can reduce the water surface tension from 73.20 mN/m to 30.61 mN/m at a critical micelle concentration (CMC = 93.17 mg/L). The enhanced solubilization and biodegradation of PAHs, particularly HMW-PAHs (when MP-6 was introduced), were also demonstrated in experiments. Furthermore, comprehensive environmental stress tolerance tests were conducted to confirm the robustness of the MP-6 biosurfactant, which signifies the potential adaptability and applicability of this biosurfactant in diverse environmental remediation scenarios. The results of this study, therefore, have significant implications for future applications in the treatment of wastewater containing HMW-PAHs, such as coking wastewater.

Insights into electro-bioremediation of PAH-contaminated soil under polarity reversal conditions: Effect of effective current intensity and soil properties on microbial function

Electrical stimulation during electro-bioremediation has the potential to enhance the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil. In this study, we investigated the effective current intensity, referred to as the “window condition,” which promotes the activity of functional microflora. Electro-bioremediation was performed on PAH-contaminated soil using various polarity reversal frequencies (PRF) to study the remediation mechanism. The “window condition” in this study was 20–40 mA. The enhancement of PAH degradation, particularly that of high-PAHs, increased with higher PRF, which accompanied the increasing ratio of the “window condition” to the overall electrification time (RWC). Electro-bioremediation with a 10-minute (EBPR-10 m) and 30-minute (EBPR-30 m) polarity reversal (PR) periods achieved the highest ratios of PAH degradation at 43.9±2.3 % and 37.9±1.8 %, respectively, with RWC of 0.4919 and 0.4056, respectively, after 60 days. The increase in PRF improved the soil physicochemical properties, which were conducive to maintaining effective electrokinetic and biodegradation processes. Redundancy analysis (RDA) and Pearson correlation analyses demonstrated that soil electrical conductivity (EC), dissolved organic carbon (DOC), temperature, and the proportion of macroparticle components (0.195–2.500 um) in soil colloids (Ps/Po) were key factors in explaining the persistence of microbial abundance and community structure. Structural equation models (SEMs) further illustrated the mechanism behind the enhanced PAH biodegradation, including (i) the direct stimulation of microbial activity because of increased RWC and (ii) the indirect optimization of microbial function by improving soil physicochemical properties under optimal PRF.

Overcoming methanogenesis barrier to acid inhibition and enhancing PAHs removal by granular biochar during anaerobic digestion

Alleviating acid inhibition is the most important for optimizing anaerobic digestion (AD), but the recalcitrant organic pollutants in digestates have long been ignored. In this study, we aimed to simultaneously enhance both organics bio-methanation and recalcitrant polycyclic aromatic hydrocarbons (PAHs) removal in AD system by using granule biochar and short-term ethanol stimulation. The results showed that adding biochar effectively alleviated volatile fatty acids (VFAs) accumulation and achieved 313.6 mL CH4/d•g COD average yield. Meanwhile, the efficiency of phenanthrene (PHE) biodegradation, as the model PAHs pollutant, was significantly promoted by 37.1%. Additionally, more and compact extracellular polymeric substances improved electron transfer and mass transfer among microbes, and higher enzymes (ATPase, NADH and α-Amylase) activities met the physiological demanding of efficient microbial metabolism in biochar-added reactor. Microbiological analysis revealed that biochar-mediated direct interspecies electron transfer (DIET) selectively enriched exoelectrogens (Bacteroides, Proteiniphilum, f_Christensenellaceae, etc.) and acetoclastic Methanosaeta, which contributed to increasing biomethane production. The promoted PAHs biodegradation was mainly dependent on the cooperation between fermenting f_Paludibacteraceae and hydrogenotrophic Methanolinea, and potentially related to biochar-mediated DIET. Metabolic analysis indicated that the metabolic pathways of acetogenesis and methanogenesis were significantly strengthened by biochar, thus alleviating acid inhibition. Also, biochar stimulated functional genes expression in PAHs anaerobic biodegradation. These findings were further verified by a series of short-term metabolism tests.

Metatranscriptomic responses and microbial degradation of background polycyclic aromatic hydrocarbons in the coastal Mediterranean and Antarctica

Although microbial degradation is a key sink of polycyclic aromatic hydrocarbons (PAH) in surface seawaters, there is a dearth of field-based evidences of regional divergences in biodegradation and the effects of PAHs on site-specific microbial communities. We compared the magnitude of PAH degradation and its impacts in short-term incubations of coastal Mediterranean and the Maritime Antarctica microbiomes with environmentally relevant concentrations of PAHs. Mediterranean bacteria readily degraded the less hydrophobic PAHs, with rates averaging 4.72 ± 0.5 ng L h−1. Metatranscriptomic responses showed significant enrichments of genes associated to horizontal gene transfer, stress response, and PAH degradation, mainly harbored by Alphaproteobacteria. Community composition changed and increased relative abundances of Bacteroidota and Flavobacteriales. In Antarctic waters, there was no degradation of PAH, and minimal metatranscriptome responses were observed. These results provide evidence for factors such as geographic region, community composition, and pre-exposure history to predict PAH biodegradation in seawater.

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.

The addition of Glomalin-related soil protein and functional microbial consortium increased bound PAH residue degradation in soil

Bound Polycyclic Aromatic Hydrocarbons (PAHs) residues are the “end point” of soil pollution remediation. However, bound PAH residues can be released and become bioavailable exerting ecological and human health impacts. Remediation of soils contaminated with bound PAHs is a critical pollution control issue that support safe and healthy agricultural production We conducted microcosmic experiments to study the degradation of bound PAH residues in the soil by exogenous functional microbial consortium with and without the addition of glomalin-related soil protein (GRSP). Our results showed limited degradation of bound PAHs by the functional microbial consortium, however, a high concentration of 1000 mg/kg could accelerate the process. The removal rates of low molecular weight PAHs, medium molecular weight PAHs, high molecular weight PAHs, and total PAHs increased by 6.6%–14.2%, 8.2%–14.6%, 5.2%–7.5% and 6.7%–12.0%, respectively. The application of high- concentration GRSP increased the content of PAHs degrading bacteria such as Sphingomonas and Arthrobacter in soil and the abundance of some vital functional genes during PAH biodegradation (phe, nahAc, and nidA) thus promoting the degradation of bound PAHs residues. This study fills the cognitive gap of GRSP in regulating the degradation of bound PAH residues in soil, and provides an important basis for the subsequent development of bound PAH residue removal technology. These findings contribute to our understanding of the role of GRSP in regulating the degradation of soil-bound PAHs.

Biochar alters the persistence of PAHs in soils by affecting soil physicochemical properties and microbial diversity: A meta-analysis

Polycyclic aromatic hydrocarbons (PAHs) pollution in soil is a pervasive environmental issue worldwide. Although biochar has the potential to immobilize PAHs in soils, there remains a study gap in the use of systematic analyses to assess the effectiveness of biochar for PAH removal and the factors that affect biochar. Hence, a meta-analysis utilizing 56 published studies was aimed to assess the impact of biochar on the PAH content, soil physicochemical properties, and microbial diversity in PAH-contaminated soils and to elucidate what factors impact the capability of biochar to alter PAH persistence. With biochar application, soil Ctot PAH concentrations were significantly reduced (15.4%), while the levels of Cfree PAHs and Cbioacc PAHs were reduced by 55.6% and 46.5%, respectively. Additionally, biochar improved the physicochemical properties of PAH-contaminated soil and increased the diversity of microorganisms. Particularly, the relative abundance of PAH degraders increased significantly (43.7%), which indicated that PAH biodegradation was significantly enhanced. Soil physicochemical properties and biochar production conditions are indispensable for the study of the PAH persistence. The overall findings revealed that the pyrolysis of woody biochar at 300–500 °C was beneficial for reducing the PAH persistence in acidic, coarse, or fine and high soil organic matter content (>20 g/kg) soils.

Biochar inoculated with Pseudomonas putida alleviates its inhibitory effect on biodegradation pathways in phenanthrene-contaminated soil

Controversial results are reported whereby biodegradation of polycyclic aromatic hydrocarbons (PAHs) can be promoted or inhibited by biochar amendment of soil. Metabolomics was applied to analyze the metabolic profiles of amendment with biochar (BB) and biochar inoculated with functional bacteria (Pseudomonas putida) (BP) involved in phenanthrene (PHE) degradation. Additionally, metagenomic analysis was utilized to assess the impact of different treatments on PHE degradation by soil microorganisms. Results indicated that BB treatment decreased the PHE biodegradation of the soil indigenous bacterial consortium, but BP treatment alleviated this inhibitory effect. Metabolomics revealed the differential metabolite 9-phenanthrol was absent in the BB treatment, but was found in the control group (CK), and in the treatment inoculated with the Pseudomonas putida (Ps) and the BP treatment. Metagenomic analysis showed that biochar decreased the abundance of the cytochrome P450 monooxygenase (CYP116), which was detected in the Pseudomonas putida, thus alleviating the inhibitory effect of biochar on PHE degradation. Moreover, a noticeable delayed increase of functional gene abundance and enzymes abundance in the BB treatment was observed in the PHE degradation pathway. Our findings elucidate the mechanism of inhibition with biochar amendment and the alleviating effect of biochar inoculated with degrading bacteria.