Effects of bioaugmentation by isolated Achromobacter xylosoxidans BP1 on PAHs degradation and microbial community in contaminated soil

Optimized bacterial consortium-based strategies for bioremediation of PAHs-contaminated soils: insights into microbial communities, and functional responses

Microbial technologies hold great promise for in situ remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils. However, the selection of enhancement measures and corresponding remediation strategies remains insufficiently understood. In this study, a series of enhancement treatments, including bacterial consortium inoculation (comprising Achromobacter denitrificans BP1, Rhodococcus aetherivorans BW2, and Lysinibacillus sp. BS3), nutrient addition, and bio-ventilation, were implemented to develop effective in situ remediation strategies for PAHs-contaminated soil. Over a 60-day incubation, the enhancement treatments achieved phenanthrene (PHE) degradation efficiencies of 68.0-94.7 % and benzo[a]pyrene (BaP) degradation efficiencies of 12.9-82.4 %. Degradation rates across soil layers followed the pattern: upper layer > lower layer > middle layer. Enhancement treatments significantly boosted soil dehydrogenase (DH) and fluorescein diacetate (FDAH) activities. Among these, the sequential consortium inoculation with nutrient addition treatment (T6) demonstrated the highest degradation efficacy. In the treatment T6, the relative abundance of consortium genera was significantly increased, playing critical roles in PAHs degradation. The connectivity and stability of the soil bacterial network were enhanced, providing greater resilience to pollutants. Quantitative PCR analysis showed that the enhancement strategy increased RHDα-GN gene abundance by 1.98-fold at the initial and maintained a positive correlation with PAHs residues throughout the process (p < 0.05), and the phe gene exhibited a continuous upward trend during remediation, ultimately reaching 1.61-1.96 times its initial abundance. Overall, this study provides a strong candidate of integrated enhancement strategies to advance in situ bioremediation of PAH-contaminated sites.

Research on bioaugmented slurry remediation of PAHs in actual contaminated soil: Screening microbial agents and optimizing key parameters

Bioaugmented slurry technology is a sustainable remediation technology for PAHs-contaminated soil. However, the lack of experimental data on the remediation of complex, actual contaminated soils has hindered the practical application of this technology. This study explored the bioaugmented degradation of PAHs using actual soil slurry with and without the addition of microbial agents in the microscopic world. NS4 has the highest degradation efficiency. The response surface method was used to determine the effects of water-soil ratio, temperature, aeration rate and their interaction on the degradation of PAHs. Temperature significantly affects the degradation of phenanthrene, and the aeration rate significantly affects the degradation of pyrene. The influence of each factor follows the order: aeration rate > temperature > water-soil ratio. The highest degradation rates of phenanthrene and pyrene are observed at a water-soil ratio of 3:1, a temperature of 30 °C, and an aeration rate of 2 L/min. Under the optimal conditions, the addition of either peptone or Tween-80 increased the degradation rate. Peptone and Tween-80 can effectively enhance the growth rate of microorganisms and the release of PAHs in actual contaminated soil. In conclusion, by screening microbial agents suitable for real contaminated soils and maintaining the dynamic stability of the bioaugmented slurry system by optimizing key influencing factors, efficient, green, and low-energy remediation of PAHs-contaminated sites can be achieved.

A novel immobilized bacteria consortium enhanced remediation efficiency of PAHs in soil: Insights into key removal mechanism and main driving factor

The remediation of sites co-contaminated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) poses challenges for efficient and ecofriendly restoration methods. In this study, three strains (Pseudomonas sp. PDC-1, Rhodococcus sp. RDC-1, and Enterobacter sp. EDC-1) were isolated from sites contaminated with PAHs and HMs. The constructed bacteria consortium was then immobilized using biochar, bentonite, and peat. The immobilized bacteria consortium (IBC) demonstrated efficient removal ability of phenanthrene (58.1 %-73.4 %) and benzo[a]pyrene (69.6 %-83.5 %) during 60 days. Additionally, the IBC decreased soil bacterial richness and diversity, but increased the relative abundance of Proteobacteria phylum and Ochrobactrum genus, which were capable of degrading PAHs. Soil microbial co-occurrence network with IBC was classified into three main modules, and 14 genera were identified as keystone taxa linked to PAHs degradation and HMs resistance. The IBC enhanced the dioxygenase metabolic pathways for PAHs degradation, including phthalic acid and salicylic acid pathways, which became the main driving factor affecting PAHs removal efficiency based on the structural equation modeling analysis. This study confirmed the potential application of the constructed IBC in the bioremediation of soil co-contaminated with PAHs-HMs, and provides insights into key removal mechanism and main driving factor of the enhanced elimination of PAHs.

Degradation of anthracene and phenanthrene by strain Streptomyces sp. M-1 and its application in the treatment of PAHs-contaminated water

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants with mutagenicity, carcinogenicity and teratogenicity, widely distributed in the environment. Effective biodegradation of PAHs is highly required, especially in wastewater. An efficient PAHs degrading strain Streptomyces sp. M-1 was isolated from polluted kerosene. The degradation capacity of anthracene and phenanthrene was evaluated under various PAHs concentrations, pH, and temperatures by M-1. To find the degradation pathways, the key intermediates were detected by mass spectrometry and the enzyme-encoding genes were analyzed by many bioinformatics tools. Furthermore, the potential of the strain for bioremediation in PAH-contaminated water was evaluated. The results showed that the maximal degradation rate of anthracene and phenanthrene reached 93.14% (100 mg L-1, 7 days) and 49.25% (50 mg L-1, 7 days), respectively. Their average degradation rate increased within the concentration of 50-800 mg L-1 and reached 2.72 mg d-1 for anthracene and 1.28 mg d-1 for phenanthrene at 800 mg L-1. M-1 exhibited high and stable anthracene degradation rate under tested pH and temperatures, and high phenanthrene degradation under tested pH and higher temperatures. Based on the analysis of both intermediates and enzyme-encoding genes, it is proposed that anthracene undergoes degradation via the phthalic acid pathway, while phenanthrene follows the salicylic acid pathway. Finally, 98.98% degradation of anthracene and 72.77% degradation of phenanthrene in water was realized over 14 days. We thus propose that Streptomyces sp. M-1 is an effective degrader for bioremediation of PAHs pollution.

Genetic and species rearrangements in microbial consortia impact biodegradation potential

Genomic reorganisation between species and horizontal gene transfer have been considered the most important mechanism of biological adaptation under selective pressure. Still, the impact of mobile genes in microbial ecology is far from being completely understood. Here we present the collection and characterisation of microbial consortia enriched from environments contaminated with emerging pollutants, such as non-steroidal anti-inflammatory drugs. We have obtained and further enriched two ibuprofen-degrading microbial consortia from two unrelated wastewater treatment plants. We have also studied their ability to degrade the drug and the dynamics of the re-organisations of the genetic information responsible for its biodegradation among the species within the consortium. Our results show that genomic reorganisation within microorganisms and species rearrangements occur rapidly and efficiently during the selection process, which may be facilitated by plasmids and/or transposable elements located within the sequences. We show the evolution of at least two different plasmid backbones on samples from different locations, showing rearrangements of genomic information, including genes encoding activities for IBU degradation. As a result, we found variations in the expression pattern of the consortia after evolution under selective pressure, as an adaptation process to the new conditions. This work provides evidence for changes in the metagenomes of microbial communities that allow adaptation under a selective constraint -ibuprofen as a sole carbon source- and represents a step forward in knowledge that can inspire future biotechnological developments for drug bioremediation.

Integration of physiology, genomics and microbiomics analyses reveal the biodegradation mechanism of petroleum hydrocarbons by Medicago sativa L. and growth-promoting bacterium Rhodococcus erythropolis KB1

Despite the effectiveness of microbial-phytoremediation for remediating total petroleum hydrocarbons (TPH)-contaminated soil, the underlying mechanisms remain elusive. This study investigated the whole-genome and biological activity of Rhodococcus erythropolis KB1, revealing its plant growth promotion (PGP), TPH degradation, and stress resistance capabilities. Phytoremediation (using alfalfa) and plant-microbial remediation (using alfalfa and KB1) were employed to degrade TPH. The highest TPH degradation rate, reaching 95%, was observed with plant-microbial remediation. This is attributed to KB1's ability to promote alfalfa growth, induce the release of signaling molecules to activate plant antioxidant enzymes, actively recruit TPH-degrading bacteria (e.g., Sphingomonas, Pseudomonas, C1-B045), and increase soil nitrogen and phosphorus levels, thereby accelerating TPH degradation by both plants and microorganisms. This study demonstrates that R. erythropolis KB1 holds great potential for enhancing the remediation of TPH-contaminated soil through its multifaceted mechanisms, particularly in plant-microbial remediation strategies, providing valuable theoretical support for the application of this technology.

Remediation of a diesel contaminated soil by means of anionic and non-ionic surfactants: Effect on soil phosphorus availability and Vicia Faba L. growth

In the present study, the effectiveness of two surfactants (Polysorbate 80 - Tween 80 and Sodium Dodecyl Benzensulphonate - SDBS) was investigated for the remediation of a hydrocarbon-contaminated soil. Moreover, it was elucidated the impact of surfactants on soil phosphorus (P) availability and phytotoxic effect on the growth of Vicia Faba L. An experimental laboratory-scale apparatus (bench and pilot scale) was set up for the simulation of a soil flushing intervention. Different surfactant concentrations and flushing flow rates were investigated. Hydrocarbon extraction efficiency was evaluated after treatment and phytotoxicity tests were performed by means of germination index (GI). The treated soil with the pilot scale apparatus was then used for Vicia Faba (faba beans) cultivation in pots. The growth of Vicia Faba plants was monitored and, at the end of the growth period, the plants were uprooted and subjected to biometric and chemical analyses. Results highlighted that the use of surfactants significantly increased the efficiency of hydrocarbons extraction compared to flushing test with water (19.6 %, 53.9 %, and 65.6 % for water, 0.1 % by weight of Tween 80 and SDBS, respectively, at pilot scale). Referring to Vicia Faba L., the plants grown in the blank control and in the soil treated with Tween 80 reached the same average height thus suggesting that this surfactant does not inhibit plant growth. In contrast, the lowest plant growth occurred in the soils treated with SDBS; this suggests a negative impact on plant growth. Due to the reduced plant growth, total P uptake was the lowest in plants grown in SDBS-treated soils, although such soils experienced a 20 % increase of soil available P. This increase could be ascribed to P supplied by the surfactant or high P availability as a consequence of soil pH decrease.

Reductive soil disinfestation influences microbial aging of low-density polyethylene and polyhydroxyalkanoate microplastics and microbial communities in plastispheres

The extensive use of plastic products has led to the accumulation of microplastics (MPs) in agricultural soils, raising concerns about their fate in various environments. Reductive soil disinfestation (RSD) treatment is increasingly being adopted in various countries to address agricultural soil health issues. However, the treatment can alter the soil microbial environment, potentially affecting the fate of contaminants, including MPs. The effect of RSD on the aging of low-density polyethylene (LDPE) and polyhydroxyalkanoates (PHA) MPs was studied through an incubation experiment. The mechanism involved was further investigated by microbial community analysis. The characterization results shown that RSD treatment inhibited the aging of LDPE but promoted the aging of PHA. The results indicated that RSD reshaped the microbial community and reduced the relative abundance of lipid metabolism in the LDPE plastisphere, thereby hindering LDPE aging. Predicted functional genes in the plastispheres were primarily involved in metabolism (77.15-87.48%) and genetic information processing (8.774-12.62%). The enrichment of bacteria related to poly(3-hydroxybutyrate) depolymerase (phaZ) in the PHA plastisphere explained the higher aging degree of PHA during RSD. Some fungus also involved in the MPs aging, while some fungus pathogens can proliferate in the MPs plastispheres. The 3DEEM analysis indicated that PHA MPs aging increased tyrosine-like substances in soil extracts. These findings provide new insights into the ecological implications of RSD and enhance our understanding of microbial communities within plastispheres.

Competitive adsorption of polycyclic aromatic hydrocarbons on phosphorus tailing-modified sludge biochar provides mechanistic insights

Biochar has been widely used to solve the wastewater pollution of polycyclic aromatic hydrocarbons (PAHs). However, the competition of PAHs with different benzene ring numbers (e.g., phenanthrene [Phe], pyrene [Pyr], and benzo[a]pyrene [BaP]) for adsorption sites on biochar has received little attention. In this study, biochar was produced by co-pyrolysis of sludge and phosphorus tailing at different temperatures (300, 500, or 800 °C) to adsorb PAHs. The results show that phosphorus tailing increased the adsorption of PAH by increasing the biochar's BET surface area (SBET), micropore volume, hydrophobicity (at low temperatures) and aromaticity (at high temperatures). The maximum adsorption capacities were 29.90 µmol/g for Phe, 25.58 µmol/g for Pyr and 20.45 µmol/g for BaP, respectively. Importantly, the types and functions of groups involved in the adsorption of various PAHs were discussed. Adsorption of Phe and Pyr on the biochar mainly involved C=O and C-O-C functional groups, and there was a certain degree of competition between these PAHs for those sites. In contrast, BaP mainly adsorbed at C-OH and C=C moieties, without competing with Phe or Pyr at C-OH sites. The competitive edge of BaP was also stronger than that of Phe and Pyr on C=C functional groups. The adsorption mechanisms involving pore filling, hydrophobic interactions, and π-π interactions governed the adsorption of the evaluated PAHs. Overall, the adsorption of PAHs on biochar followed a heterogeneous chemical adsorption process.

Synergism of endophytic microbiota and plants promotes the removal of polycyclic aromatic hydrocarbons from the Alfalfa rhizosphere

Endophytic bacteria can promote plant growth and accelerate pollutant degradation. However, it is unclear whether endophytic consortia (Consortium_E) can stabilize colonisation and degradation. We inoculated Consortium_E into the rhizosphere to enhance endophytic bacteria survival and promote pollutant degradation. Rhizosphere-inoculated Consortium_E enhanced polycyclic aromatic hydrocarbon (PAH) degradation rates by 11.5-13.1 % compared with sole bioaugmentation and plant treatments. Stable-isotope-probing (SIP) showed that the rhizosphere-inoculated Consortium_E had the largest number of degraders (8 amplicon sequence variants). Furthermore, only microbes from Consortium_E were identified among the degraders in bioaugmentation treatments, indicating that directly participated in phenanthrene metabolism. Interestingly, Consortium_E reshaped the community structure of degraders without significantly altering the rhizosphere community structure, and strengthened the core position of degraders in the network, facilitating close interactions between degraders and non-degraders in the rhizosphere, which were crucial for ensuring stable functionality. The synergistic effect between plants and Consortium_E significantly enhanced the upregulation of aromatic hydrocarbon degradation and auxiliary degradation pathways in the rhizosphere. These pathways showed a non-significant increasing trend in the uninoculated rhizosphere compared with the control, indicating that Consortium_E primarily promotes rhizosphere effects. Our results explore the Consortium_E bioaugmentation mechanism, providing a theoretical basis for the ecological restoration of contaminated soils.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

Unveiling genomic features linked to traits of plant growth-promoting bacterial communities from sugarcane

Microorganisms are ubiquitous, and those inhabiting plants have been the subject of several studies. Plant-associated bacteria exhibit various biological mechanisms that enable them to colonize host plants and, in some cases, enhance their fitness. In this study, we describe the genomic features predicted to be associated with plant growth-promoting traits in six bacterial communities isolated from sugarcane. The use of highly accurate single-molecule real-time sequencing technology for metagenomic samples from these bacterial communities allowed us to recover 17 genomes. The taxonomic assignments for the binned genomes were performed, revealing taxa distributed across three main phyla: Bacillota, Bacteroidota, and Pseudomonadota, with the latter being the most representative. Subsequently, we functionally annotated the metagenome-assembled genomes (MAGs) to characterize their metabolic pathways related to plant growth-promoting traits. Our study successfully identified the enrichment of important functions related to phosphate and potassium acquisition, modulation of phytohormones, and mechanisms for coping with abiotic stress. These findings could be linked to the robust colonization of these sugarcane endophytes.

Fulvic acid enhancing pyrene biodegradation by immobilized Stenotrophomonas maltophilia: Effect and mechanism

Immobilization technology is a promising way to improve effectiveness and stability of microbial remediation for polycyclic aromatic hydrocarbons (PAHs), in which carrier material is one of key factors restricting removal efficiency. In this study, fulvic acid-wheat straw biochar (FA/WS) composites were applied for immobilization of an efficient PAHs degrading bacterium Stenotrophomonas maltophilia (SPM). FA/WS&SPM showed superior degradation capacity than free bacteria and biochar-immobilized bacteria, with the removal efficiency of pyrene (20 mg L-1) reaching 90.5 % (7 days). Transcriptome analysis revealed that FA in the carrier materials can promote transportation and degradation of pyrene, and cell growth, as well as inhibit cell apoptosis. Enzyme activity and degradation products detection showed that SPM utilized both phthalic acid and salicylic acid metabolic pathways to degrade pyrene. Practicality of FA/WS&SPM for different kinds of PAHs remediation had been verified in contaminated soil, demonstrating a great potential in the field of PAHs polluted sites remediation.

Isolation and characterization of a newly chrysene-degrading Achromobacter aegrifaciens

Polycyclic aromatic hydrocarbons (PAHs) are considered substances of potential human health hazards because of their resistance to biodegradation and carcinogenic index. Chrysene is a PAH with a high molecular weight (HMW) that poses challenges for its elimination from the environment. However, bacterial degradation is an effective, environmentally friendly, and cost-effective solution. In our study, we isolated a potential chrysene-degrading bacteria from crude oil-contaminated seawater (Bizerte, Tunisia). Based on 16SrRNA analysis, the isolate S5 was identified as Achromobacter aegrifaciens. Furthermore, the results revealed that A. aegrifaciens S5 produced a biofilm on polystyrene at 20 °C and 30 °C, as well as at the air-liquid (A-L) interface. Moreover, this isolate was able to swim and produce biosurfactants with an emulsification activity (E24%) over 53%. Chrysene biodegradation by isolate S5 was clearly assessed by an increase in the total viable count. Confirmation was obtained via gas chromatography-mass spectrometry (GC-MS) analyses. A. aegrifaciens S5 could use chrysene as its sole carbon and energy source, exhibiting an 86% degradation of chrysene on day 7. In addition, the bacterial counts reached their highest level, over 25 × 1020 CFU/mL, under the conditions of pH 7.0, a temperature of 30 °C, and a rotary speed of 120 rpm. Based on our findings, A. aegrifaciens S5 can be a potential candidate for bioremediation in HMW-PAH-contaminated environments.

Identification of an efficient phenanthrene-degrading Pseudarthrobacter sp. L1SW and characterization of its metabolites and catabolic pathway

Phenanthrene, a typical chemical of polycyclic aromatic hydrocarbons (PAHs) pollutants, severely threatens health of wild life and human being. Microbial degradation is effective and environment-friendly for PAH removal, while the phenanthrene-degrading mechanism in Gram-positive bacteria is unclear. In this work, one Gram-positive strain of plant growth-promoting rhizobacteria (PGPR), Pseudarthrobacter sp. L1SW, was isolated and identified with high phenanthrene-degrading efficiency and great stress tolerance. It degraded 96.3% of 500 mg/L phenanthrene in 72 h and kept stable degradation performance with heavy metals (65 mg/L of Zn2+, 5.56 mg/L of Ni2+, and 5.20 mg/L of Cr3+) and surfactant (10 CMC of Tween 80). Strain L1SW degraded phenanthrene mainly through phthalic acid pathway, generating intermediate metabolites including cis-3,4-dihydrophenanthrene-3,4-diol, 1-hydroxy-2-naphthoic acid, and phthalic acid. A novel metabolite (m/z 419.0939) was successfully separated and identified as an end-product of phenanthrene, suggesting a unique metabolic pathway. With the whole genome sequence alignment and comparative genomic analysis, 19 putative genes associated with phenanthrene metabolism in strain L1SW were identified to be distributed in three gene clusters and induced by phenanthrene and its metabolites. These findings advance the phenanthrene-degrading study in Gram-positive bacteria and promote the practical use of PGPR strains in the bioremediation of PAH-contaminated environments.

Unlocking bioremediation potential for site restoration: A comprehensive approach for crude oil degradation in agricultural soil and phytotoxicity assessment

Crude oil contamination has inflicted severe damage to soil ecosystems, necessitating effective remediation strategies. This study aimed to compare the efficacy of four different techniques (biostimulation, bioaugmentation, bioaugmentation + biostimulation, and natural attenuation) for remediating agricultural soil contaminated with crude oil using soil microcosms. A consortium of previously characterized bacteria Xanthomonas boreopolis, Microbacterium schleiferi, Pseudomonas aeruginosa, and Bacillus velezensis was constructed for bioaugmentation. The microbial count for the constructed consortium was recorded as 2.04 ± 0.11 × 108 CFU/g on 60 d in augmented and stimulated soil samples revealing their potential to thrive in chemically contaminated-stress conditions. The microbial consortium through bioaugmentation + biostimulation approach resulted in 79 ± 0.92% degradation of the total polyaromatic hydrocarbons (2 and 3 rings ∼ 74%, 4 and 5 rings ∼ 83% loss) whereas, 91 ± 0.56% degradation of total aliphatic hydrocarbons (C8-C16 ∼ 90%, C18-C28 ∼ 92%, C30 to C40 ∼ 88% loss) was observed in 60 d. Further, after 60 d of microcosm treatment, the treated soil samples were used for phytotoxicity assessment using wheat (Triticum aestivum), black chickpea (Cicer arietinum), and mustard (Brassica juncea). The germination rates for wheat (90%), black chickpea (100%), and mustard (100%) were observed in 7 d with improved shoot-root length and biomass in both bioaugmentation and biostimulation approaches. This study projects a comprehensive approach integrating bacterial consortium and nutrient augmentation strategies and underscores the vital role of innovative environmental management practices in fostering sustainable remediation of oil-contaminated soil ecosystems. The formulated bacterial consortium with a nutrient augmentation strategy can be utilized to restore agricultural lands towards reduced phytotoxicity and improved plant growth.

Microbiome based approaches for the degradation of polycyclic aromatic hydrocarbons (PAHs): A current perception

Globally, polycyclic aromatic hydrocarbons (PAHs) pollution is primarily driven by their release into the air through various combustion processes, including burning fossil fuels such as coal, oil, and gas in motor vehicles, power plants, and industries, as well as burning organic matter like wood, tobacco, and food in fireplaces, cigarettes, and grills. Apart from anthropogenic pollution sources, PAHs also occur naturally in crude oil, and their potential release during oil extraction, refining processes, and combustion further contributes to contamination and pollution concerns. PAHs are resistant and persistent in the environment because of their inherent features, viz., heterocyclic aromatic ring configurations, hydrophobicity, and thermostability. A wide range of microorganisms have been found to be effective degraders of these recalcitrant contaminants. The presence of hydrocarbons as a result of numerous anthropogenic activities is one of the primary environmental concerns. PAHs are found in soil, water, and the air, making them ubiquitous in nature. The presence of PAHs in the environment creates a problem, as their presence has a detrimental effect on humans and animals. For a variety of life forms, PAH pollutants are reported to be toxic, carcinogenic, mutation-inducing, teratogenic, and immune toxicogenics. Degradation of PAHs via biological activity is an extensively used approach in which diverse microorganisms (fungal, algal, clitellate, and protozoan) and plant species and their derived composites are utilized as biocatalysts and biosurfactants. Some microbes have the ability to transform and degrade these PAHs, allowing them to be removed from the environment. The goal of this review is to provide a critical overview of the existing understanding of PAH biodegradation. It also examines current advances in diverse methodologies for PAH degradation in order to shed light on fundamental challenges and future potential.

Endophytic Bacillus sp. R1 and Its Roles in Assisting Phytoremediation and Alleviating the Toxicity of Aluminum Combined Phenanthrene Contaminations in Brassica napus

The release of organic and inorganic contaminants into soil from industry, agriculture, and urbanization has become a major issue of international concern, particularly the heavy metals such as aluminum (Al) and the chemical phenanthrene (PHE). Due to their potential toxicity and non-biodegrade in the environment, efficient remediation methods are urgently needed. Recently, research has comprehensively discussed using plants and their endophytes in bioremediation efforts. Endophytic Bacillus sp. R1, isolated from Brassica napus permanently contaminated with Al and PHE, has growth-promoting properties and can efficiently detoxify these contaminants. The pot experiment indicated that compared to the Al combined PHE contaminated soil alone treatment, the R1 treatment led to increased Al accumulation in canola roots across different levels of PHE, Al, and combined PHE and Al contamination. However, Al accumulation in canola shoots and seeds remained unchanged for all treatments. Moreover, PHE in canola roots and shoots was decreased by R1 inoculation and thereby reducing 26.12-60.61% PHE translocated into canola seeds. Additionally, R1 inoculation significantly increased the proportion of extractable Al and, decreased the proportion of acid-soluble inorganic Al and humic-acid Al, but did not affect the concentration of organically complexed Al. In summary, endophyte R1 can degrade PHE, improve canola roots' Al uptake by increasing soil available Al, and scavenge the reactive oxygen species through production of antioxidant enzymes to help alleviate the toxicity of canola co-contaminated with aluminum and phenanthrene.

Effects of nanoscale zinc oxide treatment on growth, rhizosphere microbiota, and metabolism of Aconitum carmichaelii

Trace elements play a crucial role in the growth and bioactive substance content of medicinal plants, but their utilization efficiency in soil is often low. In this study, soil and Aconitum carmichaelii samples were collected and measured from 22 different locations, followed by an analysis of the relationship between trace elements and the yield and alkaloid content of the plants. The results indicated a significant positive correlation between zinc, trace elements in the soil, and the yield and alkaloid content of A. carmichaelii. Subsequent treatment of A. carmichaelii with both bulk zinc oxide (ZnO) and zinc oxide nanoparticles (ZnO NPs) demonstrated that the use of ZnO NPs significantly enhanced plant growth and monoester-type alkaloid content. To elucidate the underlying mechanisms responsible for these effects, metabolomic analysis was performed, resulting in the identification of 38 differentially expressed metabolites in eight metabolic pathways between the two treatments. Additionally, significant differences were observed in the rhizosphere bacterial communities, with Bacteroidota and Actinobacteriota identified as valuable biomarkers for ZnO NP treatment. Covariation analysis further revealed significant correlations between specific microbial communities and metabolite expression levels. These findings provide compelling evidence that nanoscale zinc exhibits much higher utilization efficiency compared to traditional zinc fertilizer.

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.

Thermally enhanced biodegradation of benzo[a]pyrene and benzene co-contaminated soil: Bioavailability and generation of ROS

In this study, a set of comprehensive experiments were conducted to explore the effects of temperature on the biodegradation, bioavailability, and generation of reactive oxygen species (ROS) by thermally enhanced biodegradation (TEB) under benzene and BaP co-contaminated conditions. The biodegradation rates of benzene increased from 57.4% to 88.7% and 84.9%, and the biodegradation efficiency of BaP was enhanced from 15.8% to 34.6% and 28.6%, when the temperature was raised from the ambient temperature of 15 °C to 45 °C and 30 °C, respectively. In addition, the bioavailability analysis results demonstrated that the water- and butanol-extractable BaP increased with elevated temperatures. High enzymatic activities and PAH-RHD_α gene in gram-positive bacteria favored the long-term elevated temperatures (30 and 45 °C) compared to gram-negative bacteria. Moreover, ROS species (O₂^•- and •OH) generation was detected which were scavenged by the increased superoxide dismutase and catalase activities at elevated temperatures. Soil properties (pH, TOC, moisture, total iron, Fe³⁺, and Fe²⁺) were affected by the temperature treatments, revealing that metal-organic-associated reactions occurred during the TEB of benzene-BaP co-contamination. The results concluded that biodegradation of benzene-BaP co-contamination was greatly improved at 45 °C and that microbial activities enhanced the biodegradation under TEB via the increased bioavailability and generation and degradation of ROS.