Bioremediation Of Polycyclic Aromatic Hydrocarbons Research Articles

Fine-tuning an aromatic ring-hydroxylating oxygenase to degrade high molecular weight polycyclic aromatic hydrocarbon

Rieske nonheme iron aromatic ring-hydroxylating oxygenases (RHOs) play pivotal roles in determining the substrate preferences of polycyclic aromatic hydrocarbon (PAH) degraders. However, their potential to degrade high molecular weight PAHs (HMW-PAHs) has been relatively unexplored. NarA2B2 is an RHO derived from a thermophilic Hydrogenibacillus sp. strain N12. In this study, we have identified four “hotspot” residues (V236, Y300, W316, and L375) that may hinder the catalytic capacity of NarA2B2 when it comes to HMW-PAHs. By employing structure-guided rational enzyme engineering, we successfully modified NarA2B2, resulting in NarA2B2 variants capable of catalyzing the degradation of six different types of HMW-PAHs, including pyrene, fluoranthene, chrysene, benzo[a]anthracene, benzo[b]fluoranthene, and benzo[a]pyrene. Three representative variants, NarA2B2W316I, NarA2B2Y300F-W316I, and NarA2B2V236A-W316I-L375F, not only maintain their abilities to degrade low molecular weight PAHs (LMW-PAHs), but also exhibited 2-4 times higher degradation efficiency for HMW-PAHs in comparison to another isozyme, NarAaAb. Computational analysis of the NarA2B2 variants predict that these modifications altering the size and hydrophobicity of the active site pocket making it more suitable for HMW-PAHs. These findings provide a comprehensive understanding of the relationship between three-dimensional structure and functionality, thereby opening up possibilities for designing improved RHOs that can be more effectively used in the bioremediation of PAHs.

PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70–95% for fluorene, 44–89% for phenanthrene, 86–97% for anthracene, and 6.5–78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198′s ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.

Preliminary study on the enhanced bioremediation of PAH-contaminated soil in Beijing and assessment of remediation effects based on toxicity tests.

In this study, we focused on soil contaminated by polycyclic aromatic hydrocarbons (PAHs) at typical coking-polluted sites in Beijing, conducted research on enhanced PAH bioremediation and methods to evaluate remediation effects based on toxicity testing, and examined changes in pollutant concentrations during ozone preoxidation coupled with biodegradation in test soil samples. The toxicity of mixed PAHs in soil was directly evaluated using the Ames test, and the correlation between mixed PAH mutagenicity and benzo(a)pyrene (BaP) toxicity was investigated in an effort to establish a carcinogenic risk assessment model based on biological toxicity tests to evaluate remediation effects on PAH-contaminated soil. This study provides a theoretical and methodological foundation for evaluating the effect of bioremediation on PAH-contaminated soil at industrially contaminated sites. The results revealed that the removal rate of PAHs after 5min of O3 preoxidation and 4weeks of soil reaction with saponin surfactants and medium was 83.22%. The soil PAH extract obtained after remediation had a positive effect on the TA98 strain at a dose of 2000μg·dish-1, and the carcinogenic risk based on the Ames toxicity test was 8.98 times greater than that calculated by conventional carcinogenic PAH toxicity parameters. The total carcinogenic risk of the remediated soil samples was approximately one order of magnitude less than that of the original soil samples.

Impact of humic substances on the bioremediation of polycyclic aromatic hydrocarbons in contaminated soils and sediments: A review

Impact of humic substances on the bioremediation of polycyclic aromatic hydrocarbons in contaminated soils and sediments: A review

Enhancing Anaerobic Biodegradation of Phenanthrene in Polluted Soil by Bioaugmentation and Biostimulation: Focus on the Distribution of Phenanthrene and Microbial Community Analysis

The remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soils has received much attention in recent years, and most of the contaminated sites are in anaerobic environments, such as deep soils and flooded soils. We simulated the natural flooded soil environment, selected phenanthrene (PHE) as a model PAH contaminant, and designed batch experiments run for 63 days to comprehensively investigate the effects of the combined addition of anaerobic sludge and granular biochar on microbial community and function and the anaerobic biodegradation of PHE. Firstly, the residue, distribution, and removal of PHE in the flooded soil environment were quantified for each group. Secondly, the effects of bioaugmentation of soil indigenous microorganisms by the addition of anaerobic activated sludge and biostimulation of biochar on the removal of PHE from the soil were analyzed against each other. Lastly, the changes in the structure of the microbial community under the effect of bioaugmentation and biostimulation were illustrated by sequencing analyses. The results of this study showed that the removal efficiency of PHE reached 72.0% after the addition of anaerobic activated sludge. The incorporation of anaerobic activated sludge and biochar resulted in a 25.3% increase in PHE removal compared to a single soil, suggesting that the combination of bioaugmentation and biostimulation can have a synergistic effect on the anaerobic biodegradation of PHE in contaminated soils. The results of sequencing analysis further indicated that the introduction of an exogenous microbial community changed the dominant genera associated with PHE degradation and introduced methanogenic archaea, which enriched the metabolic pathways of the carbon cycle in the system. On this basis, the addition of biochar resulted in higher anaerobic microbial community diversity, functional dominant species were enriched, and the direct interspecies electron transfer (DIET) process between electroactive bacteria (Bacteroides, f_Geobacteraceae) and Methanosaeta was facilitated, which accelerated the degradation of PHE by anaerobic microbial communities. The results of this study provide regulatory tools and basic data support for enhanced bioremediation of PAHs in flooded soils.

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.

Bioremediation of polycyclic aromatic hydrocarbons contaminated soils: recent progress, perspectives and challenges.

The life of all creatures is supported directly or indirectly by soil, which is a significant environmental matrix. The soil has been polluted partly due to increased human activities and population growth, releasing several foreign substances and persistent contaminants. When toxic substances like polycyclic aromatic hydrocarbons (PAHs) are disposed of, the characteristics of the soil are changed, microbial biodiversity is impacted, and items are destroyed. Because of the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and cleanup of PAH-polluted areas represent a severe technological and environmental challenge for long-term growth and development. Although there are several ways to clean up PAH-contaminated soils, much attention is paid to intriguing bacteria, fungus, and their enzymes. Various factors influence PAH breakdown, including pH, temperature, airflow, moisture level, nutrient availability, and degrading microbial populations. This review discusses how PAHs affect soil characteristics and shows that secondary metabolite and carbon dioxide decomposition are produced due to microbial breakdown processes. Furthermore, the advantages of bioremediation strategies were assessed for correct evaluation and considered dependable on each legislative and scientific research level, as analyzed in this review.

Microalgae mediated bioremediation of polycyclic aromatic hydrocarbons: Strategies, advancement and regulations

Polycyclic aromatic hydrocarbons (PAHs) are pervasive in the atmosphere and are one of the emerging pollutants that cause harmful effects in living systems. There are some natural and anthropogenic sources that can produce PAHs in an uncontrolled way. Several health hazards associated with PAHs like abnormality in the reproductive system, endocrine system as well as immune system have been explained. The mutagenic or carcinogenic effects of hydrocarbons in living systems including algae, vertebrates and invertebrates have been discussed. For controlling PAHs, biodegradation has been suggested as an effective and eco-friendly process. Microalgae-based biosorption and biodegradation resulted in the removal of toxic contaminants. Microalgae both in unialgal form and in consortium (with bacteria or fungi) performed good results in bioaccumulation and biodegradation. In the present review, we highlighted the general information about the PAHs, conventional versus advanced technology for removal. In addition microalgae based removal and toxicity is discussed. Furthermore this work provides an idea on modern scientific applications like genetic and metabolic engineering, nanomaterials-based technologies, artificial neural network (ANN), machine learning (ML) etc. As rapid and effective methods for bioremediation of PAHs. With several pros and cons, biological treatments using microalgae are found to be better for PAH removal than any other conventional technologies.

The role of microplastics in the process of laccase-assisted phytoremediation of phenanthrene-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic organic pollutants widely distributed in terrestrial environments and laccase was considered as an effective enzyme in PAHs bioremediation. However, laccase-assisted phytoremediation of PAHs-contaminated soil has not been reported. Moreover, the overuse of plastic films in agriculture greatly increased the risk of co-existence of PAHs and microplastics in soil. Microplastics can adsorb hydrophobic organics, thus altering the bioavailability of PAHs and ultimately affecting the removal of PAHs from soil. Therefore, this study aimed to evaluate the efficiency of laccase-assisted maize (Zea mays L.) in the remediation of phenanthrene (PHE)-contaminated soil and investigate the effect of microplastics on this remediation process. The results showed that the combined application of laccase and maize achieved a removal efficiency of 83.47 % for soil PHE, and laccase significantly reduced the accumulation of PHE in maize. However, microplastics significantly inhibited the removal of soil PHE (10.88 %) and reduced the translocation factor of PHE in maize (87.72 %), in comparison with PHE + L treatment. Moreover, microplastics reduced the laccase activity and the relative abundance of some PAHs-degrading bacteria in soil. This study provided an idea for evaluating the feasibility of the laccase-assisted plants in the remediation of PAHs-contaminated soil, paving the way for reducing the risk of secondary pollution in the process of phytoremediation.

Enhanced biodegradation of phenanthrene and anthracene using a microalgal-bacterial consortium.

Polycyclic aromatic hydrocarbons (PAHs) are chemicals that are released into the environment during activities of the petroleum industry. The bioaccumulation, carcinogenic and mutagenic potential of PAHs necessitates the bioremediation of these contaminants. However, bioremediation of PAHs has a number of limitations including the inability of a single microbe to degrade all of the PAH fraction's environmental constituents. Therefore, a different paradigm, employing microalgal-bacterial consortium (MBC), may be used to effectively remove PAHs contaminants. In this type of interaction, the microalgae and bacteria species in the consortium work together in a way that enhances the overall performance of the MBC. Bacterial species in the consortium provide essential nutrients or growth factors by degrading toxic substances and provide these to microalgae, while the microalgae species provide organic carbon for the bacterial species to grow. For the first time, the ability of Gonium pectorale (G. pectorale) microalgae to break down phenanthrene (PHE) and anthracene (ANT) was investigated. Phenanthrene was shown to be more effectively degraded by G. pectorale (98%) as compared to Bacillus licheniformis (B. licheniformis) 19%. Similarly, G. pectorale has effectively degrade anthracene (98%) as compared with B. licheniformis (45%). The consortia of G. pectorale and B. licheniformis has shown a slight increase in the degradation of PHE (96%) and ANT (99%). Our findings show that B. licheniformis did not inhibit the growth of G. pectorale and in the consortia has effectively eliminated the PAHs from the media. Therefore G. pectorale has a tremendous potential to remove PAHs from the polluted environment. Future research will be conducted to assess Gonium's capacity to eliminate PAHs that exhibit high molar masses than that of PHE and ANT.

Characterization of three rapidly growing novel Mycobacterium species with significant polycyclic aromatic hydrocarbon bioremediation potential.

Mycobacterium species exhibit high bioremediation potential for the degradation of polycyclic aromatic hydrocarbons (PAHs) that are significant environmental pollutants. In this study, three Gram-positive, rapidly growing strains (YC-RL4T, MB418T, and HX176T) were isolated from petroleum-contaminated soils and were classified as Mycobacterium within the family Mycobacteriaceae. Genomic average nucleotide identity (ANI; < 95%) and digital DNA-DNA hybridization (dDDH; < 70%) values relative to other Mycobacterium spp. indicated that the strains represented novel species. The morphological, physiological, and chemotaxonomic characteristics of the isolates also supported their affiliation with Mycobacterium and their delineation as novel species. The strains were identified as Mycobacterium adipatum sp. nov. (type strain YC-RL4T = CPCC 205684T = CGMCC 1.62027T), Mycobacterium deserti sp. nov. (type strain MB418T = CPCC 205710T = KCTC 49782T), and Mycobacterium hippophais sp. nov. (type strain HX176T = CPCC 205372T = KCTC 49413T). Genes encoding enzymes involved in PAH degradation and metal resistance were present in the genomes of all three strains. Specifically, genes encoding alpha subunits of aromatic ring-hydroxylating dioxygenases were encoded by the genomes. The genes were also identified as core genes in a pangenomic analysis of the three strains along with 70 phylogenetically related mycobacterial strains that were previously classified as Mycolicibacterium. Notably, strain YC-RL4T could not only utilize phthalates as their sole carbon source for growth, but also convert di-(2-ethylhexyl) phthalate into phthalic acid. These results indicated that strains YC-RL4T, MB418T, and HX176T were important resources with significant bioremediation potential in soils contaminated by PAHs and heavy metals.

Integrating metal-organic framework ZIF-8 with green modifier empowered bacteria with improved bioremediation

Suspended microorganisms often experience diminished efficacy in the bioremediation of polycyclic aromatic hydrocarbons (PAHs). In this study, the potential of zeolite imidazolate framework-8 (ZIF-8) and the eco-friendly modifier citric acid (CA) was harnessed to generate a biomimetic mineralized protective shell on the surface of Bacillus subtilis ZL09–26, resulting in an enhanced capability for PAH degradation. This investigation encompassed the integrated responses of B. subtilis ZL09–26 to ZIF-8 and ZIF-8-CA at both cellular and proteomic levels. The amalgamation of ZIF-8 and CA not only stimulated the growth and bolstered the cell viability of B. subtilis ZL09–26, but also counteracted the toxic effects of phenanthrene (PHE) stress. Remarkably, the bioremediation prowess of B. subtilis ZL09–26@ZIF-8-CA surpassed that of ZL09–26@ZIF-8 and ZL09–26, achieving a PHE removal rate of 94.14 % within 6 days. After undergoing five cycles, ZL09–26@ZIF-8-CA demonstrated an enduring PHE removal rate exceeding 83.31 %. A complex interplay of various metabolic pathways orchestrated cellular responses, enhancing PHE transport and degradation. These pathways encompassed direct PHE biodegradation, central carbon metabolism, oxidative phosphorylation, purine metabolism, and aminoacyl-tRNA biosynthesis. This study not only extends the potential applications of biomineralized organisms but also offers alternative strategies for effective contaminant management.

Optimization and purification of bioproducts from Bacillus velezensis PhCL fermentation and their potential on industrial application and bioremediation

Bioproduction is considered a promising alternative way of obtaining useful and green chemicals. However, the downstream process of biomolecules has been one of the major difficulties in upscaling the application of bioproducts due to the high purification cost. Acid precipitation is the most common method for purifying biosurfactants from the fermentation broth with high purity. However, the use of strong acids and organic solvents in solvent extraction has limited its application. Hence, in this study, a new strain of Bacillus velezensis PhCL was isolated from phenolic waste, and its production of amylase had been optimized via response surface methodology. After that, amylase and biosurfactant were purified by sequential ammonium sulfate precipitation and the result suggested that even though the purified crude biosurfactant had a lower purification fold compared to the acid precipitation, the yield was higher and both enzymes and biosurfactant also could be recovered for lowering the purification cost. Moreover, the purified amylase and crude biosurfactant were characterized and the results suggested that the purified crude biosurfactant would have a higher emulsion activity and petroleum hydrocarbon removal rate compared to traditional surfactants. This study provided another approach for purifying bioactive compounds including enzymes and biosurfactants from the same fermentation broth and further explored the potential of the crude purified biosurfactant in the bioremediation of polycyclic aromatic hydrocarbons and petroleum hydrocarbons.

Magnetic loofah sponge biochar facilitates microbial interspecies cooperation in surface and subsurface sediments for enhanced PAH biodegradation

Magnetic biochar had been used for the bioremediation of polycyclic aromatic hydrocarbon (PAH)-contaminated sediments. However, the long-term remediation pattern of vertical stratification driven by the application of magnetic biochar and the assembly of microbes had received little attention. In this study, magnetic loofah sponge biochar (MagLsBC), magnetic iron oxide (MagOx) and magnetic coconut shell activated carbon (MagCoAC) were applied for the 900-day remediation of contaminated sediments. Significant (p < 0.05) PAH biodegradation was observed in both the surface and subsurface sediments with MagLsBC addition. However, enhanced PAH biodegradation was observed only in the surface sediments with MagOx and MagCoAC treatments. Magnetotactic bacteria (Magnetococcus) was dominant genera in surface sediments and indigenous PAH degradation bacteria were more abundant in subsurface sediments of MagLsBC relative to other bacterial communities. The network interaction between microbes in surface and subsurface sediments with MagLsBC treatments was a less complex and tighter than those with MagCoAC, MagOx or Control treatments. Long-distance electron transfer rates could be enhanced through cooperation between magnetotactic bacteria and indigenous degradation bacteria, thus accelerating PAH degradation in sediment with MagLsBC treatment, especially in the underlying sediment.

Biotrophic interactions between plant and endophytic bacteria in removal of PAHs and Cd from contaminated soils enhanced by graphene oxide

Graphene oxide (GO)-mediated phytoremediation is a novel strategy for abating polycyclic aromatic hydrocarbons (PAHs) from contaminated soils, but the underlying mechanism has not been fully investigated. In this study, Fire Phoenix plants were grown in soils contaminated by 105.00 mg kg−1 or 154.55 mg kg−1 PAHs, containing 15 mg kg−1 Cd and 0.0, 0.3, 0.4, or 0.5 g kg−1 GO, respectively. After 150 days of plant growth, PAH removal rates from low-PAHs/Cd and high-PAHs/Cd soils amended with 0.4 g kg−1 GO were 78.95% and 73.21%, respectively. GO particularly promoted the biodegradation of high-ring PAHs as the removal rate increased by 55.69% on day 120 of plant growth. Dioxygenase genes including nidA and pdoA2 directly degraded PAHs in GO-induced remediation. GO mediated both upstream and downstream degradation pathways of PAHs, during which the tricarboxylic acid cycle initially dominated the downstream pathway followed by carbohydrate and amino acid metabolisms. Soil Cd was also significantly reduced by GO-enhanced root absorption. This study for the first time elucidated the mechanisms underpinning the interaction of Fire Phoenix plants with microorganisms in remediation of soil PAHs and Cd and illustrated the viability of GO-mediated bioremediation of PAHs and Cd from co-contaminated soils.

Insights into relationships between polycyclic aromatic hydrocarbon concentration, bacterial communities and organic matter composition in coal gangue site

Coal mining usually brought polycyclic aromatic hydrocarbons (PAHs) contamination. Relationships between the concentration of PAHs, bacterial communities and soil environmental factors were important for bioremediation of PAHs in soil. Total 4 kinds of soil samples with different concentrations of PAHs were selected from 7 typical coal gangue（CG） sites in Huainan, Anhui Province. The relationships between microorganisms, dissolved organic matter (DOM) composition and PAHs concentration were systematically analyzed in this work. Total 11 kinds of PAHs were enriched in the soil surface layer. That was attributed to the strong binding of soil organic matter (SOM) to PAHs. PAHs contamination reduced the diversity of soil microbial. The abundance of PAHs-degrading genera such as Arthrobacter decreased with the increasing concentration of PAHs. Mycobacterium increased with the increasing concentration of PAHs in all samples. The microbial activities decreased with increasing concentration of PAHs. The increasing contents of LWM-PAHs and DOM were beneficial to improve the activities of soil microbial. The increasing DOM aromaticity was beneficial to improve the bioavailability of PAHs according to the correlation analysis between PAHs content and DOM structural parameters. The obtained results provide a basis for better understanding the contamination characteristics and microbial communities of coal gangue PAH-contaminated sites.

Recent trends in polycyclic aromatic hydrocarbons pollution distribution and counteracting bio-remediation strategies

Polycyclic aromatic hydrocarbons (PAHs) are distributed worldwide due to long-term anthropogenic pollution sources. PAHs are recalcitrant and highly persistent in the environment due to their inherent properties, such as heterocyclic aromatic ring structures, thermostability, and hydrophobicity. They are highly toxic, carcinogenic, immunotoxic, teratogenic, and mutagenic to various life systems. This review focuses on the unique data of PAH sources, exposure routes, detection techniques, and harmful effects on the environment and human health. This review provides a comprehensive and systematic compilation of eco-friendly biological treatment solutions for PAH remediation, such as microbial remediation approaches utilizing microbial cultures. In situ and Ex situ bioremediation of PAH methods, including composting land farming, biopiles, bioreactors bioaugmentation, and phytoremediation processes, are discussed in detail, as is a summary of the factors affecting and limiting PAH bioremediation. This review provides an overview of emerging technologies that use multi-process combinatorial treatment approaches and answers to generating value-added by-products during PAH remediation.

Bioremediation of polycyclic aromatic hydrocarbons in crude oil by bacterial consortium in soil amended with Eisenia fetida and rhamnolipid.

The present study investigated the concerted effort of Eisenia fetida and rhamnolipid JBR-425 in combination with a five-member bacterial consortium exhibiting elevated degradation levels of low and high molecular weight polycyclic aromatic hydrocarbons (PAH) from soil contaminated with Digboi crude oil. Application of bacterial consortium (G2) degraded 30-89% of selected PAH from the artificial soil after a 45-day post-exposure, in which chrysene showed the highest level of degradation with 89% and benzo(a)pyrene is the lowest with 30%, respectively. Moreover, an acute exposure study observed that earthworm biomass decreased, and mortality rates increased with increasing crude oil concentrations (0.25 to 2%). Earthworms with a 100% survival rate at 1% crude oil exposure suggest the tolerance potential and its mutual involvement in the bioremediation of crude oil with selected bacterial consortia. Bacterial consortium assisted with E. fetida (G3) showed 98% chrysene degradation with a slight change in benzo(a)pyrene degradation (35%) in crude oil spiked soil. Besides, the most dominant PAH in crude oil found in the current work, fluoranthene, undergoes 93% and 70% degradation in G3 and G5 groups, respectively. However, rhamnolipid JBR-425 coupled with the bacterial consortium (G5) has resulted in 97% degradation of chrysene and 33% for benzo(a)pyrene. Overall, bacterial consortium assisted with earthworm group has shown better degradation of selected PAH than bacterial consortium with biosurfactant. Catalase (CAT), glutathione reductase (GST) activity and MDA content was found to be reduced in earthworms after sub-lethal exposure, suggesting oxidative stress prevalence via reactive oxygen species (ROS). Hence, the findings of the present work suggest that the application of a bacterial consortium, along with earthworm E. fetida, has huge potential for field restoration of contaminated soil with PAH and ecosystem sustainability.

The shifting research landscape for PAH bioremediation in water environment: a bibliometric analysis on three decades of development.

Polycyclic aromatic hydrocarbons (PAHs) with their carcinogenic, teratogenic, and mutagenic effects can cause great damage to the ecosystem and public health when present in water. With bioremediation, PAH contamination in water environment can be greatly reduced in an eco-friendly manner. It has thus become the research focus for many environmental scientists. In this study, a bibliometric analysis on three-decade (1990-2022) development of PAH bioremediation in water environment was conducted from temporal and spatial dimensions using CiteSpace. A total of 2480 publications, obtained from Web of Science core collection database, were used to explore the basic characteristics, hotspots, and prospects of the research area. The results showed that (1) bioremediation/biodegradation of PAHs in water environment has been getting researchers' attention since 1990, and is gaining even more traction as time goes on. (2) In terms of countries, China and the USA were the major contributors in this research area, while at the institutional level, the Chinese Academy of Sciences has produced the most research results. However, international cooperation across regions was lacking in the field. (3) Environment Science and Technology, Chemosphere, Applied and Environment Microbiology, Journal of Hazardous Materials, and Environment Pollution were the 5 most cited journals in this field. (4) There were three major stages the field has gone through, each with distinct research hotspots, including initial stage (1990-1994), mechanism investigation (1995-2000), and application exploration (2001-2010; 2011-2022). Finally, research perspectives were proposed, covering three directions, namely, bioavailability, immobilization, and viable but nonculturable (VBNC) bacteria.

Metabolic capacity to alter polycyclic aromatic hydrocarbons and its microbe-mediated remediation

The elimination of contaminants caused by anthropogenic activities and rapid industrialization can be accomplished using the widely used technology of bioremediation. Recent years have seen significant advancement in our understanding of the bioremediation of coupled polycyclic aromatic hydrocarbon contamination caused by microbial communities including bacteria, algae, fungi, yeast, etc. One of the newest techniques is microbial-based bioremediation because of its greater productivity, high efficiency, and non-toxic approach. Microbes are appealing candidates for bioremediation because they have amazing metabolic capacity to alter most types of organic material and can endure harsh environmental conditions. Microbes have been characterized as extremophiles that can survive in a variety of environmental circumstances, making them the treasure troves for environmental cleanup and the recovery of contaminated soil. In this study, the mechanisms underlying the bioremediation process as well as the current situation of microbial bioremediation of polycyclic aromatic hydrocarbon are briefly described.