Bacteria-mediated phthalic acid esters degradation and related molecular mechanisms

A novel and efficient strategy for the biodegradation of di(2-ethylhexyl) phthalate by Fusarium culmorum

Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer that is used worldwide and raises concerns because of its prevalence in the environment and potential toxicity. Herein, the capability of Fusarium culmorum to degrade a high concentration (3 g/L) of DEHP as the sole carbon and energy source in solid-state fermentation (SSF) was studied. Cultures grown on glucose were used as controls. The biodegradation of DEHP by F. culmorum reached 96.9% within 312 h. This fungus produced a 3-fold higher esterase activity in DEHP-supplemented cultures than in control cultures (1288.9 and 443.2 U/L, respectively). In DEHP-supplemented cultures, nine bands with esterase activity (24.6, 31.2, 34.2, 39.5, 42.8, 62.1, 74.5, 134.5, and 214.5 kDa) were observed by zymography, which were different from those in control cultures and from those previously reported for cultures grown in submerged fermentation. This is the first study to report the DEHP biodegradation pathway by a microorganism grown in SSF. The study findings uncovered a novel biodegradation strategy by which high concentrations of DEHP could be biodegraded using two alternative pathways simultaneously. F. culmorum has an outstanding capability to efficiently degrade DEHP by inducing esterase production, representing an ecologically promising alternative for the development of environmental biotechnologies, which might help mitigate the negative impacts of environmental contamination by this phthalate. KEY POINTS: • F. culmorum has potential to tolerate and remove di(2-ethylhexyl) phthalate (DEHP) • Solid-state fermentation is an efficient system for DEHP degradation by F. culmorum • High concentrations of DEHP induce high levels of esterase production by F. culmorum.

Complete genome sequence of the 4-hydroxybenzoate-degrading bacterium Gymnodinialimonas sp. 57CJ19, a potential novel species from intertidal sediments

A bacterium Gymnodinialimonas sp. 57CJ19, was isolated from the intertidal sediments of Aoshan Bay, and further assays showed that it has the ability to degrade the antibacterial preservative 4-hydroxybenzoate. The complete genome sequence was sequenced, and phylogenomic analyses indicated that strain 57CJ19 represents a potential novel species in the genus Gymnodinialimonas (family Rhodobacteraceae). Its genome contains a 3,861,607-bp circular chromosome with 61.25% G + C content. Gene prediction revealed 3716 protein-encoding genes, 41 tRNA genes, 3 rrn operons, and 3 non-coding RNA genes. Functional annotation revealed a complete metabolic pathway for 4-hydroxybenzoate. The genome sequence of strain 57CJ19 provides new insights into the potential and underlying genomic basis of aromatic compound pollutant degradation by marine bacteria.

Interspecies synergistic interactions mediated by cofactor exchange enhance stress tolerance by inducing biofilm formation

Metabolic exchange plays a crucial role in shaping microbial community interactions and functions, including the exchange of small molecules such as cofactors. Cofactors are fundamental to enzyme catalytic activities; however, the role of cofactors in microbial stress tolerance is unclear. Here, we constructed a synergistic consortium containing two strains that could efficiently mineralize di-(2-ethylhexyl) phthalate under hyperosmotic stress. Integration of transcriptomic analysis, metabolic profiling, and a genome-scale metabolic model (GEM) facilitated the discovery of the potential mechanism of microbial interactions. Multi-omics analysis revealed that the vitamin B12-dependent methionine-folate cycle could be a key pathway for enhancing the hyperosmotic stress tolerance of synergistic consortium. Further GEM simulations revealed interspecies exchange of S-adenosyl-L-methionine and riboflavin, cofactors needed for vitamin B12 biosynthesis, which was confirmed by in vitro experiments. Overall, we proposed a new mechanism of bacterial hyperosmotic stress tolerance: bacteria might promote the production of vitamin B12 to enhance biofilm formation, and the species collaborate with each other by exchanging cofactors to improve consortium hyperosmotic stress tolerance. These findings offer new insights into the role of cofactors in microbial interactions and stress tolerance and are potentially exploitable for environmental remediation.

IMPORTANCE

Metabolic interactions (also known as cross-feeding) are thought to be ubiquitous in microbial communities. Cross-feeding is the basis for many positive interactions (e.g., mutualism) and is a primary driver of microbial community assembly. In this study, a combination of multi-omics analysis and metabolic modeling simulation was used to reveal the metabolic interactions of a synthetic consortium under hyperosmotic stress. Interspecies cofactor exchange was found to promote biofilm formation under hyperosmotic stress. This provides a new perspective for understanding the role of metabolic interactions in microbial communities to enhance environmental adaptation, which is significant for improving the efficiency of production activities and environmental bioremediation.

Season and side-chain length affect the occurrences and behaviors of phthalic acid esters in wastewater treatment plants

Emerging pollutants (EPs) are prevalent in aquatic environments globally. Researchers strive to understand their occurrence and behavior prior to their release into the environment. In this study, we examined five wastewater treatment plants (WWTPs), collected 50 wastewater samples and 10 sludge samples. We explored the sources and destinations of phthalic acid esters (PAEs) within these WWTPs using mass balance equations. Wastewater treatment diminished the frequency and concentration of PAEs, and decreased the fraction of short-chain PAEs. We confirmed the increased concentration of PAEs post-primary treatment and modified the mass balance equation. Calculations suggest that weaker "the mix" in winter than in summer and stronger sedimentation in winter than in summer resulted in high efficiency of PAEs removal by winter wastewater treatment. The mass flux of biodegradation was influenced by the combination of biodegradation efficiency and the strength of the particular type of PAEs collected, with no seasonal differences. Mass fluxes for sludge sedimentation were mainly influenced by season and were higher in winter than in summer. This study enhances our understanding of emerging pollutants in manual treatment facilities and offers insights for optimizing wastewater treatment methods for water professionals.

Molecular insights into the catalytic mechanism of a phthalate ester hydrolase

Phthalate esters (PAEs) are emerging hazardous and toxic chemicals that are extensively used as plasticizers or additives. Diethyl phthalate (DEP) and dimethyl phthalate (DMP), two kinds of PAEs, have been listed as the priority pollutants by many countries. PAE hydrolases are the most effective enzymes in PAE degradation, among which family IV esterases are predominate. However, only a few PAE hydrolases have been characterized, and as far as we know, no crystal structure of any PAE hydrolases of the family IV esterases is available to date. HylD1 is a PAE hydrolase of the family IV esterases, which can degrade DMP and DEP. Here, the recombinant HylD1 was characterized. HylD1 maintained a dimer in solution, and functioned under a relatively wide pH range. The crystal structures of HylD1 and its complex with monoethyl phthalate were solved. Residues involved in substrate binding were identified. The catalytic mechanism of HylD1 mediated by the catalytic triad Ser140-Asp231-His261 was further proposed. The hylD1 gene is widely distributed in different environments, suggesting its important role in PAEs degradation. This study provides a better understanding of PAEs hydrolysis, and lays out favorable bases for the rational design of highly-efficient PAEs degradation enzymes for industrial applications in future.

Biodegradation of PVCs through in-vitro identification of Bacillus albus and computational pathway analysis of ABH enzyme

Microplastics pose significant challenges to ecosystems and organisms. They can be ingested by marine and terrestrial species, leading to potential health risks and ecological disruptions. This study aims to address the urgent need for effective remediation strategies by focusing on the biodegradation of microplastics, specifically polyvinyl chloride (PVC) derivatives, using the bacterial strain Bacillus albus. The study provides a comprehensive background on the accumulation of noxious substances in the environment and the importance of harnessing biodegradation as an eco-friendly method for pollutant elimination. The specific objective is to investigate the enzymatic capabilities of Bacillus albus, particularly the alpha/beta hydrolases (ABH), in degrading microplastics. To achieve this, in-silico studies were conducted, including analysis of the ABH protein sequence and its interaction with potential inhibitors targeting PVC derivatives. Docking scores of - 7.2 kcal/mol were obtained to evaluate the efficacy of the interactions. The study demonstrates the promising bioremediation prospects of Bacillus albus for microplastics, highlighting its potential as a key player in addressing microplastic pollution. The findings underscore the urgent need for further experimental validation and practical implementation of Bacillus albus in environmental remediation strategies.

Molecular insights into the catabolism of dibutyl phthalate in Pseudomonas aeruginosa PS1 based on biochemical and multi-omics approaches

A comprehensive understanding of the molecular mechanisms underlying microbial catabolism of dibutyl phthalate (DBP) is still lacking. Here, we newly isolated a bacterial strain identified as Pseudomonas aeruginosa PS1 with high efficiency of DBP degradation. The degradation ratios of DBP at 100-1000 mg/L by this strain reached 80-99 % within 72 h without a lag phase. A rare DBP-degradation pathway containing two monobutyl phthalate-catabolism steps was proposed based on intermediates identified by HPLC-TOF-MS/MS. In combination with genomic and transcriptomic analyses, we identified 66 key genes involved in DBP biodegradation and revealed the genetic basis for a new complete catabolic pathway from DBP to Succinyl-CoA or Acetyl-CoA in the genus Pseudomonas for the first time. Notably, we found that a series of homologous genes in Pht and Pca clusters were simultaneously activated under DBP exposure and some key intermediate degradation related gene clusters including Pht, Pca, Xyl, Ben, and Cat exhibited a favorable coexisting pattern, which contributed the high-efficient DBP degradation ability and strong adaptability to this strain. Overall, these results broaden the knowledge of the catabolic diversity of DBP in microorganisms and enhance our understanding of the molecular mechanism underlying DBP biodegradation.

The release, degradation, and distribution of PVC microplastic-originated phthalate and non-phthalate plasticizers in sediments

This study investigated the leaching of phthalate and non-phthalate plasticizers from polyvinyl chloride microplastics (MPs) into sediment and their degradation over a 30-d period via abiotic and biotic processes. The results showed that 3579% of plasticizers were released into the sediment from the MPs and > 99.9% degradation was achieved. Although a significantly higher degradation was found in plasticizer-added microcosms under biotic processes (overall, 94%), there was a noticeable abiotic loss (72%), suggesting that abiotic processes also play a role in plasticizer degradation. Interestingly, when compared with the initial sediment-water partitioning for plasticizers, the partition constants for low-molecular-weight compounds decreased in both microcosms, whereas those for high-molecular-weight compounds increased after abiotic degradation. Furthermore, changes in the bacterial community, abundance of plasticizer-degrading bacterial populations, and functional gene profiles were assessed. In all the microcosms, a decrease in bacterial community diversity and a notable shift in bacterial composition were observed. The enriched potential plasticizer-degrading bacteria were Arthrobacter, Bacillus, Desulfovibrio, Desulfuromonas, Devosia, Gordonia, Mycobacterium, and Sphingomonas, among which Bacillus was recognized as the key plasticizer degrader. Overall, these findings shed light on the factors affecting plasticizer degradation, the microbial communities potentially involved in biodegradation, and the fate of plasticizers in the environment.

Biodegradation of DEP, DIBP, and BBP by a psychrotolerant Sphingobium yanoikuyae strain P4: Degradation potentiality and mechanism study

Phthalic acid esters (PAEs) are human made chemicals widely used as plasticizers to enhance the flexibility of plastic products. Due to the lack of chemical bonding between phthalates and plastics, these materials can easily enter the environment. Deleterious effects caused by this chemo-pollutant have drawn the attention of the scientific community to remediate them from different ecosystem. In this context, many bacterial strains have been reported across different habitats and Sphingobium yanoikuyae strain P4 is among the few psychrotolerant bacterial species reported to biodegrade simple and complex phthalates. In the present study, biodegradation of three structurally different PAEs viz., diethyl phthalate (DEP), di-isobutyl phthalate (DIBP), and butyl benzyl phthalate (BBP) have been investigated by the strain P4. Quantitative analyses through High-performance liquid chromatography (HPLC) revealed that the bacterium completely degraded 1 g/L of DEP, DIBP, and BBP supplemented individually in minimal media pH 7.0 within 72, 54, and 120 h of incubation, respectively, at 28 °C and under shake culture condition (180 rpm). In addition, the strain could grow in minimal media supplemented individually with up to 3 g/L of DEP and 10.0 g/L of DIBP and BBP at 28 °C and pH 7.0. The strain also could grow in metabolites resulting from biodegradation of DEP, DIBP, and BBP, viz. n-butanol, isobutanol, butyric acid, ethanol, benzyl alcohol, benzoic acid, phthalic acid, and protocatechuic acid. Furthermore, phthalic acid and protocatechuic acid were also detected as degradation pathway metabolites of DEP and DIBP by HPLC, which gave an initial idea about the biodegradation pathway(s) of these phthalates.

Activated DBP degradation and relevant signal transduction path via quorum sensing autoinducers in Streptomyces sp. SH5

Microbe-mediated DBP (dibutyl phthalate) mineralization is acknowledged to be affected by diverse extracellular factors. However, little is known about the regulatory effects from quorum sensing (QS) signals. In this study, extracellularly applied QS signals A-like (hydroxymethyl dihydrofuran) was discovered to significantly enhance DBP degradation efficiency in Streptomyces sp. SH5. Monobutyl phthalate, protocatechuic acid and beta-ketoadipate were discovered as degradation intermediates by HPLC-TOF-MS/MS. Multi-omics analysis revealed the up-regulation of multiple hydrolases, transferases and decarboxylases that potentially contributed to A-like accelerated DBP degradation. Transcription of Orf2708, an orthologue of global transcriptional activator, was significantly induced by A-like. Orf2708 was demonstrated to interact specifically with the promoter of hydrolase orf2879 gene by EMSA, and the overexpression of orf2879 led to an enhanced DBP degradation in SH5. Taken together with the molecular docking studies showing the stability of ligand-receptor complex of A-like and its potential receptor Orf3712, a hierarchical regulatory cascade underlying the QS signal mediated DBP degradation was proposed as A-like/Orf3712 duplex formation, enhanced orf2708 expression and the downstream specific activation of hydrolase Orf2879. Our study presents the first evidence of GBLs-type promoted DBP degradation among bacteria, and the elucidated signal transduction path indicates a universal application potential of this activation strategy.

Optimizing concentration and interaction mechanism of Demodesmus sp. and Achromobacter pulmonis sp. consortium to evaluate their potential for dibutyl phthalate removal from synthetic wastewater

A green approach of Desmodesmus sp. to Achromobacter pulmonis (1:1) coculture ratios was optimized to improve the removal efficiency of dibutyl phthalate (DBP) from simulated wastewater. High DBP resistance bacterial strains and microalgae was optimized from plastic contaminated water and acclimation process respectively. The influence of various factors on DBP removal performance was comprehensively investigated. Highest DBP removal 93 % was recorded, when the ratios algae-bacteria 1:1, with sodium acetate, pH-6, shaking speed-120 rpm and lighting periods L:D-12:12. Enough nutrient (TN/TP/TOC) availability and higher protein-108 mg/L and sugar-40 mg/L were observed in presences of 50 mg/L DBP. The degradation and sorption were calculated 81,12; 27,39 & 43,12 % in algae-bacteria, only algae and only bacteria system respectively. The degradation kinetics t1/2 3.74,22.15,12.86 days were evaluated, confirming that algae-bacteria effectively degrade the DBP. This outcome leading to promote a green sustainable approach to remove the emerging contamination from wastewater.

Comparing the removal efficiency of diisobutyl phthalate by Bacillariophyta, Cyanophyta and Chlorophyta

The utilization of microalgae for both removing phthalate esters (PAEs) from wastewater and producing bioenergy has become a popular research topic. However, there is a lack of studies comparing the effectiveness of different types of microalgae in removing these harmful compounds. Therefore, the present study aimed to evaluate and compare the efficiency of various processes, such as hydrolysis, photolysis, adsorption, and biodegradation, in removing diisobutyl phthalate (DiBP) using six different species of microalgae. The study indicated that the average removal efficiency of DiBP (initial concentrations of 5, 0.5, and 0.05 mg L-1) by all six microalgae (initial cell density of 1 × 106 cells mL-1) was in the order of Scenedesmus obliquus (95.39 %) > Chlorella vulgaris (94.78 %) > Chroococcus sp. (91.16 %) > Cyclotella sp. (89.32 %) > Nitzschia sp. (88.38 %) > Nostoc sp. (84.33 %). The results of both hydrolysis and photolysis experiments revealed that the removal of DiBP had minimal impact, with respective removal efficiencies of only 0.89 % and 1.82 %. The adsorption efficiency of all six microalgae decreased significantly with increasing initial DiBP concentrations, while the biodegradation efficiency was elevated. Chlorella vulgaris and Chroococcus sp. demonstrated the highest adsorption and biodegradation efficiencies among the microalgae tested. Scenedesmus obliquus was chosen for the analysis of the degradation products of DiBP due to its exceptional ability to remove DiBP. The analysis yielded valuable results, identifying monoisobutyl phthalate (MiBP), phthalic acid (PA), and salicylic acid (SA) as the possible degradation products of DiBP. The possible degradation pathways mainly included dealkylation, the addition of hydroxyl groups, and decarboxylation. This study lays a theoretical foundation for the elimination of PAEs in the aquatic environment.

Biodegradation of Typical Plastics: From Microbial Diversity to Metabolic Mechanisms

Plastic production has increased dramatically, leading to accumulated plastic waste in the ocean. Marine plastics can be broken down into microplastics (<5 mm) by sunlight, machinery, and pressure. The accumulation of microplastics in organisms and the release of plastic additives can adversely affect the health of marine organisms. Biodegradation is one way to address plastic pollution in an environmentally friendly manner. Marine microorganisms can be more adapted to fluctuating environmental conditions such as salinity, temperature, pH, and pressure compared with terrestrial microorganisms, providing new opportunities to address plastic pollution. Pseudomonadota (Proteobacteria), Bacteroidota (Bacteroidetes), Bacillota (Firmicutes), and Cyanobacteria were frequently found on plastic biofilms and may degrade plastics. Currently, diverse plastic-degrading bacteria are being isolated from marine environments such as offshore and deep oceanic waters, especially Pseudomonas spp. Bacillus spp. Alcanivoras spp. and Actinomycetes. Some marine fungi and algae have also been revealed as plastic degraders. In this review, we focused on the advances in plastic biodegradation by marine microorganisms and their enzymes (esterase, cutinase, laccase, etc.) involved in the process of biodegradation of polyethylene terephthalate (PET), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP) and highlighted the need to study plastic biodegradation in the deep sea.

Biodegradation of di-2-ethylhexyl phthalate by Bacillus firmus MP04 strain: parametric optimization using full factorial design

Di-2-ethylhexyl phthalate (DEHP) is used as a plasticizer in making plastics and released from landfills. This study attempted to degrade DEHP using microbial isolates. Isolates of Bacillus spp. were tested for their efficacy in degrading DEHP. Degradation was assessed using liquid chromatography-mass spectrometry (LC-MS). The most efficient DEHP degradation was achieved by Bacillus firmus MP04, which has been identified as Bacillus firmus MP04. This strain was found to use DEHP as the sole source of carbon without carbon source supplementation. Full factorial design was used to optimize the conditions for DEHP degradation which revealed the suitability of pH 7, 5% salt concentration, 20 to 37 °C temperature, and yeast extract as a nitrogen source. LC-MS elucidated the possible degradation mechanism via benzoic acid formation. However, prolonged incubation formed a typical compound denatonium benzoate due to reactions with other compounds. As maximum degradation was achieved in 4 days, prolonged incubation is not suggested. It can be concluded that new strain Bacillus firmus MP04 is the most efficient strain among all the tested strains for DEHP degradation.

Synthetic bacterial consortia enhanced the degradation of mixed priority phthalate ester pollutants

Dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DOP) are hazardous chemicals listed as priority pollutants that disrupt endocrine systems. According to available reports, these six priority phthalate esters (PAEs) are considered the most polluting; however, no studies have been conducted on the efficient remediation of these PAEs. We therefore designed and constructed a synthetic bacterial consortium capable of the simultaneous and efficient degradation of six priority PAEs in minimal inorganic salt medium (MSM) and soil. The consortium comprised Glutamicibacter sp. ZJUTW, which demonstrates priority for degrading short-chain PAEs; Cupriavidus sp. LH1, which degrades phthalic acid (PA) and protocatechuic acid (PCA), intermediates of the PAE biodegradation process; and Gordonia sp. GZ-YC7, which efficiently degrades long-chain priority PAEs, including DEHP and DOP. In MSM containing the six mixed PAEs (250 mg/L each), the ZJUTW + YC + LH1 consortium completely degraded the four short-chain PAEs within 48 h, and DEHP (100%) and DOP (62.5%) within 72 h. In soil containing the six mixed PAEs (DMP, DEP, BBP, and DOP, 400 mg/kg each; DBP and DEHP, 500 mg/kg, each), the ZJUTW + YC + LH1 consortium completely degraded DMP, DEP, BBP, and DBP within 6 days, and 70.84% of DEHP and 66.24% of DOP within 2 weeks. The consortium efficiently degraded the six mixed PAEs in both MSM and soil. We thus believe that this synthetic microbial consortium is a strong candidate for the bioremediation of environments contaminated with mixed PAE pollutants.

Multi-level biological effects of diverse alkyl chains phthalate esters on cotton seedlings (Gossypium hirsutum L.): Insights into individual, physiological-biochemical and molecular perspectives

Phthalate esters (PAEs) are organic contaminants that pose environmental threat and safety risks to soil health and crop production. However, the ecological toxicity of different PAEs to cotton and the underlying mechanisms are not clear. This study investigated the ecotoxic effects and potential mechanisms of different alkyl-chain PAEs, including dioctyl phthalate (DOP), dibutyl phthalate (DBP), and diethyl phthalate (DEP) on cotton seedlings at multiple levels. The results showed that PAEs significantly hindered the growth and development of cotton. The chlorophyll content decreased by 1.87-31.66 %, accompanied by non-stomatal photosynthetic inhibition. The antioxidant system was activated by the three PAEs in cotton seedlings, while the osmotic potential was boosted intracellularly. Additionally, PAEs significantly interfered with functional gene expression and exhibited genotoxicity. Risk assessment results indicated that the ecotoxicity was DOP >DBP >DEP, with a "dose-response" relationship. The affinity between the three PAEs and catalase increased as the alkyl chain length increased, further supporting the toxicity sequence. Surprisingly, the bioconcentration factors of short-chain DEP were 8.07 ± 5.89 times and 1837.49 ± 826.83 times higher than those of long-chain DBP and DOP, respectively. These results support the ecological risk assessment of PAEs in cotton and provide new insights into determining the toxicity levels of different PAEs.

Reutilization of scrap tyre for the enhanced removal of phthalate esters from water: immobilization performance, interaction mechanisms, and application

Waste scrap tyre as microbial immobilization matrix enhanced degradation of phthalate esters (PAEs), di (2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and diethyl phthalate (DEP). The hybrid (physical adsorption and microbial immobilization) degradation process performance of scrap tyres was examined for the PAEs degradation. The scrap tyre was shown with competitive adsorption capacity toward PAEs, influenced by pH, temperature, dosage of adsorbent (scrap tyre), and concentration of PAE. The primary adsorption mechanism for tyres toward PAEs was considered hydrophobic. The immobilization of previously isolated Bacillus sp. MY156 on tyre surface significantly enhanced PAEs degradation as well as bacterial growth. The enzymatic activity results implied immobilization promoted dehydrogenase activity and decreased esterase activity. The cell surface response during PAEs degradation, in terms of morphological observation, FTIR and XRD analyses, and extracellular polymeric substance (EPS) release, was further assessed to better understand the interactions between microorganisms and tyre surface. Waste scrap tyres could be a promising potential candidate to be reused for sustainable environmental management, including contaminants removal.

Insights into molecular mechanism of plasticizer biodegradation in Dietzia kunjamensis IITR165 and Brucella intermedia IITR166 isolated from a solid waste dumpsite

AIMS

Isolation of phthalate esters (PAEs) degrading bacteria from a solid waste dumpsite could degrade many plasticizers efficiently and to investigate their degrading kinetics, pathways, and genes.

METHODS AND RESULTS

Based on their 16S rRNA gene sequence the strains were identified as Dietzia kunjamensis IITR165 and Brucella intermedia IITR166, which showed a first-order degradation kinetic model under lab conditions. The quantification of phthalates and their intermediate metabolites identification were done by using ultra-high-performance liquid chromatography (UHPLC) and gas chromatography-tandem mass-spectrometry (GC-MS/MS), respectively. Both the bacteria utilized >99% dibutyl phthalate at a high concentration of 100-400 mg L-1 within 192 h as monitored by UHPLC. GC-MS/MS revealed the presence of metabolites dimethyl phthalate (DMP), phthalic acid (PA), and benzoic acid (BA) during DBP degradation by IITR165 while monobutyl phthalate (MBP) and PA were identified in IITR166. Phthalate esters degrading gene cluster in IITR165 comprised two novel genes coding for carboxylesterase (dkca1) and mono-alkyl phthalate hydrolase (maph), having only 37.47% and 47.74% homology, respectively, with reported phthalate degradation genes, along with the terephthalate dioxygenase system (tphA1, A2, A3, and B). However, IITR166 harbored different gene clusters comprising di-alkyl phthalate hydrolase (dph_bi), and phthalate dioxygenase (ophA, B, and C) genes.

CONCLUSIONS

Two novel bacterial strains, Dietzia kunjamensis IITR165 and Brucella intermedia IITR166, were isolated and found to efficiently degrade DBP at high concentrations. The degradation followed first-order kinetics, and both strains exhibited a removal efficiency of over 99%. Metabolite analysis revealed that both bacteria utilized de-methylation, de-esterification, and decarboxylation steps during degradation.

Whole-genome analysis of Comamonas sp. USTBZA1 for biodegrading diethyl phthalate

Extensive use of phthalic acid esters (PAEs) as plasticizer causes diffusion into the environment, which posed a great threat to mankind. It was reported that Comamonas sp. was a potentially robust aromatic biodegrader. Although the biodegradation of several PAEs by Comamonas sp. was studies, the comprehensive genomic analysis of Comamonas sp. was few reported. In the present study, one promising bacterial strain for biodegrading diethyl phthalate (DEP) was successfully isolated from activated sludge and characterized as Comamonas sp. USTBZA1 based on the 16S rRNA sequence analysis. The results showed that pH 7.5, 30 °C and inoculum volume ratio of 6% were optimal for biodegradation. Initial DEP of 50 mg/L could be completely biodegrade by strain USTBZA1 within 24 h which conformed to the Gompertz model. Based on the Q-TOF LC/MS analysis, monoethyl phthalate (MEP) and phthalic acid (PA) were identified as the metabolic products of DEP biodegradation by USTBZA1. Furthermore, the whole genome of Comamonas sp. USTBZA1 was analyzed to clarify the molecular mechanism for PAEs biodegradation by USTBZA1. There were 3 and 41 genes encoding esterase/arylesterase and hydrolase, respectively, and two genes regions (pht34512 and pht4253) were responsible for the conversion of PA to protocatechuate (PCA), and two genes regions (ligCBAIKJ) were involved in PCA metabolism in USTBZA1. These results substantiated that Comamonas sp. USTBZA1 has potential application in the DEP bioremediation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03736-3.

Biochemical and Multi-Omics Approaches To Obtain Molecular Insights into the Catabolism of the Plasticizer Benzyl Butyl Phthalate in Rhodococcus sp. Strain PAE-6

Phthalate diesters are extensively used as plasticizers in manufacturing plastic materials; however, because of their estrogenic properties, these chemicals have emerged as a global threat to human health. The present study investigated the course of degradation of a widely used plasticizer, benzyl butyl phthalate (BBP), by the bacterium PAE-6, belonging to the genus Rhodococcus. The metabolism of BBP, possessing structurally dissimilar side chains, was evaluated biochemically using a combination of respirometric, chromatographic, enzymatic, and mass-spectrometric analyses, depicting pathways of degradation. Consequently, the biochemical observations were corroborated by identifying possible catabolic genes from whole-genome analysis, and the involvement of inducible specific esterases and other degradative enzymes was validated by transcriptomic, reverse transcription-quantitative PCR (RT-qPCR) and proteomic analyses. Nonetheless, phthalic acid (PA), an intermediate of BBP, could not be efficiently metabolized by strain PAE-6, although the genome contains a PA-degrading gene cluster. This deficiency of complete degradation of BBP by strain PAE-6 was effectively managed by using a coculture of strains PAE-6 and PAE-2. The latter was identified as a Paenarthrobacter strain which can efficiently utilize PA. Based on sequence analysis of the PA-degrading gene cluster in strain PAE-6, it appeared that the alpha subunit of the multicomponent phthalate 3,4-dioxygenase harbors a number of altered residues in the multiple sequence alignment of homologous subunits, which may play a role(s) in poor turnover of PA. IMPORTANCE Benzyl butyl phthalate (BBP), an estrogenic, high-molecular-weight phthalic acid diester, is an extensively used plasticizer throughout the world. Due to its structural rigidity and hydrophobic nature, BBP gets adsorbed on sediments and largely escapes the biotic and abiotic degradative processes of the ecosystem. In the present study, a potent BBP-degrading bacterial strain belonging to the genus Rhodococcus was isolated that can also assimilate a number of other phthalate diesters of environmental concern. Various biochemical and multi-omics analyses revealed that the strain harbors all the required catabolic machinery for the degradation of the plasticizer and elucidated the inducible regulation of the associated catabolic genes and gene clusters.

Di (2-ethyl) hexyl phthalate induces liver injury in chickens by regulating PTEN/PI3K/AKT signaling pathway via reactive oxygen species

Di (2-ethyl) hexyl phthalate (DEHP) is a common environmental endocrine disruptor that induces oxidative stress, posing a significant threat to human and animal health. Oxidative stress can activate the PTEN/PI3K/AKT pathway, which is closely related to cell apoptosis. However, it is unclear whether DEHP induces apoptosis of chicken liver cells by regulating the PTEN/PI3K/AKT pathway through oxidative stress. In this experiment, male laying hens were continuously exposed to 400 mg/kg, 800 mg/kg, and 1600 mg/kg DEHP for 14 d, 28 d, and 42 d. The results showed that liver injury was aggravated with the dose of DEHP gavage, and the ROS/MDA levels in L, M, and H DEHP exposure groups were significantly increased, while the T-AOC/T-SOD/GSH-PX levels were decreased. Meanwhile, DEHP exposure up-regulated the mRNA and protein expression levels of PTEN/Bax/Caspase-9/Caspase-3 and down-regulated the mRNA and protein expression levels of PI3K/AKT/BCL-2, indicating that DEHP may lead to hepatocyte apoptosis through ROS regulation of PTEN/PI3K/AKT axis. In order to further clarify the relationship between oxidative stress and liver injury, we treated chicken hepatocellular carcinoma cell line (LMH) with 2.5 mM N-acetylcysteine (NAC). NAC attenuated these phenomena. In summary, our study suggests that DEHP can induce apoptosis of chicken liver through ROS activation of the PTEN/PI3K/AKT axis.

Substrate-enzyme interactions and catalytic mechanism in a novel family VI esterase with dibutyl phthalate-hydrolyzing activity

Microbial degradation has been confirmed as effective and environmentally friendly approach to remediate phthalates from the environment, and hydrolase is an effective element for contaminant degradation. In the present study, a novel dibutyl phthalate (DBP)-hydrolyzing carboxylesterase (named PS06828) from Pseudomonas sp. PS1 was heterogeneously expressed in E. coli, which was identified as a new member of the lipolytic family VI. Purified PS06828 could efficiently degrade DBP with a wide range of temperature (25-37 °C) and pH (6.5-9.0). Multi-spectroscopy methods combined with molecular docking were employed to study the interaction of PS06828 with DBP. Fluorescence and UV-visible absorption spectra revealed the simultaneous presence of static and dynamic component in the fluorescence quenching of PS06828 by DBP. Synchronous fluorescence and circular dichroism spectra showed inconspicuous alteration in micro-environmental polarity around amino acid residues but obvious increasing of α-helix and reducing of β-sheet and random coil in protein conformation. Based on the information on exact binding sites of DBP on PS06828 provided by molecular docking, the catalytic mechanism mediated by key residues (Ser113, Asp166, and His197) was proposed and subsequently confirmed by site-directed mutagenesis. The results can strengthen our mechanistic understanding of family VI esterase involved in hydrolysis of phthalic acid esters, and provide a solid foundation for further enzymatic modification.

Enzymatic Characterization of a Novel HSL Family IV Esterase EstD04 from Pseudomonas sp. D01 in Mealworm Gut Microbiota

Pseudomonas sp. D01, capable of growing in tributyrin medium, was isolated from the gut microbiota of yellow mealworm. By using in silico analyses, we discovered a hypothesized esterase encoding gene in the D01 bacterium, and its encoded protein, EstD04, was classified as a bacterial hormone-sensitive lipase (bHSL) of the type IV lipase family. The study revealed that the recombinant EstD04-His(6x) protein exhibited esterase activity and broad substrate specificity, as it was capable of hydrolyzing p-nitrophenyl derivatives with different acyl chain lengths. By using the most favorable substrate p-nitrophenyl butyrate (C₄), we defined the optimal temperature and pH value for EstD04 esterase activity as 40 °C and pH 8, respectively, with a catalytic efficiency (k_cat/K_m) of 6.17 × 10³ mM^-1 s^-1 at 40 °C. EstD04 demonstrated high stability between pH 8 and 10, and thus, it might be capably used as an alkaline esterase in industrial applications. The addition of Mg²⁺ and NH₄⁺, as well as DMSO, could stimulate EstD04 enzyme activity. Based on bioinformatic motif analyses and tertiary structural simulation, we determined EstD04 to be a typical bHSL protein with highly conserved motifs, including a triad catalytic center (Ser¹⁶⁰, Glu²⁵³, and His²⁸³), two cap regions, hinge sites, and an oxyanion hole, which are important for the type IV enzyme activity. Moreover, the sequence analysis suggested that the two unique discrete cap regions of EstD04 may contribute to its alkali mesophilic nature, allowing EstD04 to exhibit extremely distinct physiological properties from its evolutionarily closest esterase.

Biodegradation of di(2-ethylhexyl) phthalate by a new bacterial consortium

Di(2-ethylhexyl) phthalate (DEHP) with continuous high concentration was used as the sole carbon and energy source to isolate a new bacterial consortium (K1) from agricultural soil covered with plastic film for a long time. Unclassified Comamonadaceae, Achromobacter, and Pseudomonas in K1 were identified as major genera of the consortium by high-throughput sequencing, and unclassified Commanadaceae was first reported to be related to DEHP degradation. Response surface method (RSM) showed that the optimum conditions for K1 to degrade DEHP were 31.4 °C, pH 7.3, and a concentration of 420 mg L^-1. K1 maintains normal cell viability and stable DEHP degradation efficiency in the range of 10-3000 mg L^-1 DEHP concentration, which is superior to existing research. The biodegradation of DEHP followed first-order kinetics when the initial concentration of DEHP was between 100 and 3,000 mg L^-1. GC-MS analysis of different treatment groups showed that DEHP was degraded by the consortium group through the de-esterification pathway, and treatment effect was significantly better than that of the single bacteria treatment group. The subsequent substrate utilization experiment further confirmed that K1 could quickly mineralize DEHP. In addition, K1 has high degradation capacity for the most common phthalate acid esters in the environment.

Underlying Degradation of Phthalates via Microbials in Dust from Different Microenvironments

Phthalate monoesters (me-PAEs) have been used as biomarkers for assessing human exposure to phthalate esters (PAEs) for a long time, and studies on the sources and distribution of me-PAEs in the environment are limited. In this study, dust samples from microenvironments were collected to measure the occurrence of PAEs and me-PAEs, as well as the bacterial diversity. The results indicated that me-PAEs coexisted with PAEs in different microenvironmental dust samples, with concentrations of nine PAEs and 16 me-PAEs ranging from 108 to 1450 μg/g (median range) and 6.00 to 21.6 μg/g, respectively. The concentrations of several low molecular weight me-PAEs (e.g., monomethyl phthalate and monoethyl phthalate) in dust were even significantly higher than those of their parents. The bacteria in the dust were mainly predominant with Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes (total abundance >90%). Bacteria from bus and air conditioning dust samples had the highest species richness and species diversity. Seven genes of suspected enzymes with the ability to degrade PAEs were selected, and the concentration of me-PAEs increased with increasing abundance of enzyme function. Our findings will provide useful information on the profiles of me-PAEs and their potential sources in indoor dusts, which will benefit the accurate estimation of human exposure.

Cloning and rational modification of a cold-adapted esterase for phthalate esters and parabens degradation

Phthalate esters (PAEs) and parabens are environmental pollutants that can be toxic to human health. Herein, a cold-adapted esterase from the Mao-tofu metagenome named Est1260 was screened for its PAE-hydrolyzing potential in cold temperatures. The results showed that purified Est1260 could degrade a variety of PAEs and parabens at temperatures as low as 0 °C. After careful analysis of the structural information and molecular docking, site-saturation mutation was conducted at the identified hotspots. Protein expression of variant A1B6 doubled, and its thermal stability significantly improved (24 times) without sacrificing activity at low temperatures. In addition, Est1260 and its variants were activated by NaCl and demonstrated resistance to high concentrations of saline (up to 5 M), making it a potential biocatalyst for bioremediation of PAE and paraben-polluted environments.

Complete genome of Mycolicibacterium phocaicum RL-HY01, a PAEs-degrading marine bacterial strain isolated from Zhanjiang Bay, China

Mycolicibacterium phocaicum RL-HY01, a marine bacterial strain with the capability to degrade phthalic acid esters (PAEs), was isolated from Zhanjiang Bay, China. Here, the complete genome sequence of strain RL-HY01 was presented. The genome of strain RL-HY01 contains one circular chromosome of 6,064,759 bp with a G + C content of 66.93 mol%. The genome contains 5681 predicted protein-encoding genes, 57 tRNA genes, and 6 rRNA genes. Genes and gene clusters potentially involved in the metabolism of PAEs were further identified. The genome Mycolicibacterium phocaicum RL-HY01 will be helpful for advancing our understanding of the fate of PAEs in marine ecosystem.

Evaluation of distinct molecular architectures and coordinated regulation of the catabolic pathways of oestrogenic dioctyl phthalate isomers in Gordonia sp

Bacterial strain GONU, belonging to the genus Gordonia, was isolated from a municipal waste-contaminated soil sample and was capable of utilizing an array of endocrine-disrupting phthalate diesters, including di-n-octyl phthalate (DnOP) and its isomer di(2-ethylhexyl) phthalate (DEHP), as the sole carbon and energy sources. The biochemical pathways of the degradation of DnOP and DEHP were evaluated in strain GONU by using a combination of various chromatographic, spectrometric and enzymatic analyses. Further, the upregulation of three different esterases (estG2, estG3 and estG5), a phthalic acid (PA)-metabolizing pht operon and a protocatechuic acid (PCA)-metabolizing pca operon were revealed based on de novo whole genome sequence information and substrate-induced protein profiling by LC-ESI-MS/MS analysis followed by differential gene expression by real-time PCR. Subsequently, functional characterization of the differentially upregulated esterases on the inducible hydrolytic metabolism of DnOP and DEHP revealed that EstG5 is involved in the hydrolysis of DnOP to PA, whereas EstG2 and EstG3 are involved in the metabolism of DEHP to PA. Finally, gene knockout experiments further validated the role of EstG2 and EstG5, and the present study deciphered the inducible regulation of the specific genes and operons in the assimilation of DOP isomers.

Application of NMR spectroscopy for the detection and quantification of phthalic acid in fish muscles: The case of Atlantic Cod from Norwegian Sea

Plastic litter might contain phthalates that can be transferred to marine environment or can be introduced into the marine food chain. Phthalic acid is the final product of phthalate decomposition in marine organisms. Here we used NMR spectroscopy to determine and quantify phthalic acid and dimethyl phthalate in fish muscles. Spike-and-recovery experiments were carried out to confirm assignment of phthalates resonance signals in NMR spectra and to evaluate the method specificity, accuracy, and linearity. The LOQ and LOD of the rapid ¹H NMR experiment with a standard setting were respectively 23.0 and 8.0 mg of phthalic acid in kg of fish muscles. Phthalic acid was detected in 13 out of 113 Atlantic cod and none in farmed Atlantic salmon from Norwegian sea.

Bioremediation of PAEs-contaminated saline soil: The application of a marine bacterial strain isolated from mangrove sediment

Phthalic acid esters (PAEs) are known as the most widely used plasticizer as well as one of the ubiquitously distributed emerging pollutants. Biodegradation and bioremediation via application of PAEs-degrading microbes is promising. In this study, a novel marine microbe, Gordonia hongkongensis RL-LY01, was isolated from mangrove sediment showing high di-(2-ethylhexyl) phthalate (DEHP) degradation capacity. Strain RL-LY01 could degrade a wide range of PAEs and the degradation kinetics of DEHP followed the first-order decay model. Meanwhile, good environmental adaptability, preference to alkaline conditions and good tolerance to salinity and metal ions was shown. Further, metabolic pathway of DEHP in strain RL-LY01 was proposed, with di-ethyl phthalate, phthalic acid, benzoic acid and catechol as intermediates. Additionally, one known mono-alkyl phthalate hydrolase gene (mehpH) was identified. Finally, the excellent performance during bioremediation of artificial DEHP-contaminated saline soil and sediment indicated strain RL-LY01 employs great application potential for the bioremediation of PAE-contaminated environments.

The fate of phthalate acid esters in wastewater treatment plants and their impact on receiving waters

Phthalates (PAEs) are gaining attention and being researched as an endocrine disruptor as global plastic use surge. There is an urgent need to explore the key factors affecting the removal of PAEs from wastewater and the impact of wastewater effluent on receiving water. Here we investigated the levels and distribution patterns of 16 typical PAEs in surface water and five wastewater treatment plants (WWTPs) along the Dongyang River from Yiwu, China, collecting 42 surface water and 31 wastewater samples. We found that influent PAEs concentration and treatment process were the key factors affecting the degradation efficiency of PAEs in primary and secondary treatment, respectively. In primary treatment, long-chain PAEs were more easily removed (and sometimes less likely to accumulate) than short-chain PAEs, regardless of the influent PAEs concentration (a key factor in primary treatment), while in secondary treatment, short-chain PAEs were easily removed regardless of the treatment process (a factor in secondary treatment). This was not the case for long-chain PAEs, which were only more readily removed in the A/A/O process. In addition, by comparing the significant differences between wastewater and surface water, we found that the total PAEs in the treated effluent were significantly lower than in surface water upstream and in built-up urban areas, indicating that wastewater discharges in the study area did not increase PAEs in the receiving water. Finally, river in the city center and artificial treatment facilities in the study area were identified as requiring priority attention. The results of this study can serve as a model for controlling PAEs in other similar developing cities in China and provide valuable information on the fate of endocrine disruptor from wastewater treatment in China and their impact on surface water.

Molecular insights into the catalytic mechanism of plasticizer degradation by a monoalkyl phthalate hydrolase

Phthalate acid esters (PAEs), a group of xenobiotic compounds used extensively as plasticizers, have attracted increasing concern for adverse effects to human health and the environment. Microbial degradation relying on PAE hydrolases is a promising treatment. However, only a limited number of PAE hydrolases were characterized to date. Here we report the structures of MehpH, a monoalkyl phthalate (MBP) hydrolase that catalyzes the reaction of MBP to phthalic acid and the corresponding alcohol, in apo and ligand-bound form. The structures reveal a positively-charged catalytic center, complementary to the negatively-charged carboxyl group on MBP, and a penetrating tunnel that serves as exit of alcohol. The study provides a first glimpse into the enzyme-substrate binding model for PAE hydrolases, leading strong support to the development of better enzymes in the future.

Improving the activity and expression level of a phthalate-degrading enzyme by a combination of mutagenesis strategies and strong promoter replacement

Phthalic acid esters (PAEs) are widely used plasticizers found in consumer products, which enter the environment and pose severe threats to human health. Here, a new PAE-degrading enzyme EstJ6 was modified by combining mutagenesis strategies and a strong promoter replacement to improve its catalytic activity and expression level. Four mutants with enhanced activity were obtained by random mutation, among which EstJ6M1.1 exhibited the highest catalytic activity with an increase in catalytic activity by 2.9-fold toward dibutyl phthalate (DBP) than that of the wild-type (WT) enzyme. With these mutants as a template, a variant EstJ6M2 with 3.1-fold higher catalytic activity and 4.61 times higher catalytic efficiency (Kcat/Km) was identified by staggered extension PCR. Targeting four mutation sites of EstJ6M2, a variant EstJ6M3.1 was gained by site-directed saturation mutagenesis and displayed 4.3-fold higher activity and 5.97 times higher Kcat/Km than WT. The expression level of three mutants EstJ6M1.1, EstJ6M2, and EstJ6M3.1, as well as the WT, increased nearly threefold after a strong promoter replacement. These results provide a proof-theoretical basis and practicable pipeline for applying PAE-degrading enzymes.

Adaptation of bacterial community in maize rhizosphere for enhancing dissipation of phthalic acid esters in agricultural soil

Rhizospheric degradation is a green and in situ strategy to accelerate dissipation of organic pollutants in soils. However, the mechanism on microbial degradation of phthalic acid esters (PAEs) in rhizosphere is still unclear. Here, the bacterial community and function genes in bulk and rhizospheric soils of maize (Zea mays L.) exposed to gradient concentrations of di-(2-ethylhexyl) phthalate (DEHP) were analyzed with 16 S rRNA, metagenomic sequencing and quantitative PCR (qPCR). Maize rhizosphere significantly increased the dissipation of DEHP by 4.02-11.5% in comparison with bulk soils. Bacterial community in rhizosphere exhibited more intensive response and shaped its beneficial structure and functions to DEHP stress than that in bulk soils. Both rhizospheric and pollution effects enriched more PAE-degrading bacteria (e.g., Bacillus and Rhizobium) and function genes in rhizosphere than in bulk soil, which played important roles in degradation of PAEs in rhizosphere. The PAE-degrading bacteria (including genera Sphingomonas, Sphingopyxis and Lysobacter) identified as keystone species participated in DEHP biodegradation. Identification of PAE intermediates and metagenomic reconstruction of PAE degradation pathways demonstrated that PAE-degrading bacteria degraded PAEs through cooperation with PAE-degrading and non-PAE-degrading bacteria. This study provides a comprehensive knowledge for the microbial mechanism on the superior dissipation of PAEs in rhizosphere.

Water stable MOFs as emerging class of porous materials for potential environmental applications

Metal-organic frameworks (MOFs) are extensively recognized for their wide applications in a variety of fields such as water purification, adsorption, sensing, catalysis and drug delivery. The fundamental characteristics of the majority of MOFs, such as their structure and shape, are known to be sensitively impacted by water or moisture. As a result, a thorough evaluation of the stability of MOFs in respect to factors linked to these property changes is required. It is quite rare for MOFs in their early stages to have strong water-stability, which is necessary for the commercialization and development of wider applications of this interesting material. Also, numerous applications in presence of water have progressed considerably as a "proof of concept" stage in the past and a growing number of water-stable MOFs (WSMOFs) have been discovered in recent years. This review discusses the variables and processes that affect the aqueous stability of several MOFs, including imidazolate and carboxylate frameworks. Accordingly, this article will assist researchers in accurately evaluating how water affects the stability of MOFs so that effective techniques can be identified for the advancement of water-stable metal-organic frameworks (WSMOFs) and for their effective applications toward a variety of fields.

Use of nanoparticle-coated bacteria for the bioremediation of organic pollution: A mini review

Nanoparticle (NP)-coated (immobilized) bacteria are an effective method for treating environmental pollution due to their multifarious benefits. This review collates a vast amount of existing literature on organic pollution treatment using NP-coated bacteria. We discuss the features of bacteria, NPs, and decoration techniques of NP-bacteria assemblies, with special attention given to the surface modification of NPs and connection mechanisms between NPs and cells. Furthermore, the performance of NP-coated bacteria was examined. We summarize the factors that affect bioremediation efficiency using coated bacteria, including pH, temperature, and agitation, and the possible mechanisms involving them are proposed. From future perspectives, suitable surface modification of NPs and wide application in real practice will make the NP-coated bacterial technology a viable treatment strategy.

The occurrence, fate, toxicity, and biodegradation of phthalate esters: An overview

Phthalate esters (PAEs) are a class of emerging xenobiotic compounds that are extensively used as plasticizers. In recent times, there has been an increasing concern over the risk of this pervasive pollution exposure causing endocrine disruption and carcinogenicity in humans and animals. The widespread use of PAEs in home and industrial applications has resulted in their discharge in aquatic bodies via leaching, volatilization, and precipitation. In this overview, the current state of PAE pollution, its potential origins, its fate, as well as its effects on the aquatic environment are discussed. A state-of-the-art review of several studies in the literature that focus on the biological degradation of PAEs is included in this study. The paper aims to provide a comprehensive view of current research on PAEs in the environment, highlighting its fate and alleviated risks on the aquatic biotas, their challenges, future prospects, and the need for good management and policies for its remediation. PRACTITIONER POINTS: Occurrence of phthalate esters was summarized in various environmental matrices along with its serious ecotoxicological implications on biota. Wastewater is the prime source of PAEs contamination. Lack of species-specific effects on biota due to dose, exposure route, and susceptibility. The predominant route to mineralization in PAEs is biodegradation. A critical analysis of worldwide PAE production and consumption identifies the necessity for global PAE production, consumption, and release policies.

Dimethyl phthalate inhibits the growth of Escherichia coli K-12 by regulating sugar transport and energy metabolism

Dimethyl phthalate (DMP) is one of the most widely used plasticizers, and it is easily released into the environment, posing a threat to microbes. In this study, the impact of DMP on the uptake and metabolism of sugars in E. coli K-12 was assessed using proteomics, computational simulation analysis, transcriptome analysis, and sugar utilization experiments. DMP contamination inhibited the growth of E. coli K-12 and downregulated the expression of proteins in ATP-binding cassette (ABC) transporters and the phosphotransferase (PTS) system of E. coli K-12, which are primarily involved in the transmembrane transport of sugars. DMP formed a stable complex with sugar transporters and changed the rigidity and stability of the proteins. Furthermore, DMP treatment decreased the utilization of L-arabinose, glucose, D-xylose, and maltose. Moreover, carbon metabolism and oxidative phosphorylation were also downregulated by DMP. Our study shows that DMP reduces the uptake of sugars and ATP production and subsequently inhibits the growth of E. coli K-12.

Major biotransformation of phthalic acid esters in Eisenia fetida: Mechanistic insights and association with catalytic enzymes and intestinal symbionts

Phthalic acid esters (PAEs) are an important group of organic pollutants that are widely used as plasticizers in the environment. The PAEs in soil organisms are likely to be biotransformed into a variety of metabolites, and the combined toxicity of PAEs and their metabolites might be more serious than PAEs alone. However, there are only a few studies on PAE biotransformation by terrestrial animals, e.g. earthworms. Herein, the key biotransformation pathways of PAEs and their association with catalytic enzymes and intestinal symbionts in earthworms were studied using in vivo and in vitro incubation approaches. The widely distributed PAE in soil, dibutyl phthalate (DBP), was proven to be biotransformed rapidly together with apparent bioaccumulation in earthworms. The biotransformation of PAE congeners with medium or long side chains appeared to be faster compared with those with short side chains. DBP was biotransformed into butyl methyl phthalate (BMP), monobutyl phthalate (MBP), and phthalic acid (PA) through esterolysis and transesterification. Besides, the generation of small quantities of low-molecular weight metabolites via β-oxidation, decarboxylation or ring-cleavage, was also observed, especially when the appropriate proportion of NADPH coenzyme was applied to transfer electrons for oxidases. Interestingly, the esterolysis of PAEs was mainly regulated by the cytoplasmic carboxylesterase (CarE) in earthworms, with a Michaelis constant (K_m) of 0.416 mM in the catalysis of DBP. The stronger esterolysis in non-intestinal tissues indicated that the CarE was primarily secreted by non-intestinal tissues of earthworms. Additionally, the intestinal symbiotic bacteria of earthworms could respond to PAE stress, leading to the changes in their diversity and composition. The enrichment of some genera e.g. Bacillus and Paracoccus, and the enhancement of metabolism function, e.g. amino acids, energy, lipids biosynthesis and oxidase secretion, indicated their important role in the degradation of PAEs.

Health risks of phthalates: A review of immunotoxicity

Phthalates (PAEs) are known environmental endocrine disruptors that have been widely detected in several environments, and many studies have reported the immunotoxic effects of these compounds. Here, we reviewed relevant published studies, summarized the occurrence and major metabolic pathways of six typical PAEs (DMP, DEP, DBP, BBP, DEHP, and DOP) in water, soil, and the atmosphere, degradation and metabolic pathways under aerobic and anaerobic conditions, and explored the molecular mechanisms of the toxic effects of eleven PAEs (DEHP, DPP, DPrP, DHP, DEP, DBP, MBP, MBzP, BBP, DiNP, and DMP) on the immune system of different organisms at the gene, protein, and cellular levels. A comprehensive understanding of the mechanisms by which PAEs affect immune system function through regulation of immune gene expression and enzymes, increased ROS, immune signaling pathways, specific and non-specific immunosuppression, and interference with the complement system. By summarizing the effects of these compounds on typical model organisms, this review provides insights into the mechanisms by which PAEs affect the immune system, thus supplementing human immune experiments. Finally, we discuss the future direction of PAEs immunotoxicity research, thus providing a framework for the analysis of other environmental pollutants, as well as a basis for PAEs management and safe use.

Analysis of the performance of the efficient di-(2-ethylhexyl) phthalate-degrading bacterium Rhodococcus pyridinovorans DNHP-S2 and associated catabolic pathways

The widespread use of plastic has led to the global occurrence of phthalate esters (PAEs) pollution. PAEs can be effectively removed from polluted environments by microbe-mediated degradation. Di-(2-ethylhexyl) phthalate (DEHP) has the highest residual concentration in agricultural soil-contaminated areas compared to other PAEs in most of China. The Rhodococcus pyridinovorans DNHP-S2 microbial isolate identified was found to efficiently degrade DEHP. Within a 72 h period, the bacteria were able to degrade 52.47% and 99.75% of 500 mg L^-1 DEHP at 10 °C and 35 °C, respectively. Dimethyl phthalate (DMP) was first identified as an intermediate metabolite of DEHP, which is different from the previously reported DEHP catabolic pathway. Genomic sequencing of DNHP-S2 identified benzoate 1,2-dioxygenase and catechol 2,3/1,2-dioxygenase as potential mediators of DEHP degradation, consistent with the existence of two downstream metabolic pathways governing DEHP degradation. Three targets DEHP metabolism-related enzymes were found to be DEHP-inducible at the mRNA level, and DNHP-S2 was able to mediate the complete degradation of DEHP at lower temperatures, as confirmed via RT-qPCR. DNHP-S2 was also found to readily break down other PAEs including DMP, di-n-butyl phthalate (DBP), di-n-octyl phthalate (DnOP), and n-butyl benzyl phthalate (BBP). Together, these results thus highlight DNHP-S2 as a bacterial strain with great promise as a tool for the remediation of PAE pollution. In addition to providing new germplasm and genetic resources for use in the context of PAE degradation, these results also offer new insight into the potential mechanisms whereby PAEs undergo catabolic degradation, making them well-suited for use in PAE-contaminated environments.

Composting and green technologies for remediation of phthalate (PAE)-contaminated soil: Current status and future perspectives

Phthalate esters (PAEs) are hazardous organic compounds that are widely added to plastics to enhance their flexibility, temperature, and acidic tolerance. The increase in global consumption and the corresponding environmental pollution of PAEs has caused broad public concerns. As most PAEs accumulate in soil due to their high hydrophobicity, composting is a robust remediation technology for PAE-contaminated soil (efficiency 25%-100%), where microbial activity plays an important role. This review summarized the roles of the microbial community, biodegradation pathways, and specific enzymes involved in the PAE degradation. Also, other green technologies, including biochar adsorption, bioaugmentation, and phytoremediation, for PAE degradation were also presented, compared, and discussed. Composting combined with these technologies significantly enhanced removal efficiency; yet, the properties and roles of each bacterial strain in the degradation, upscaling, and economic feasibility should be clarified in future research.

Phthalates - A family of plasticizers, their health risks, phytotoxic effects, and microbial bioaugmentation approaches

Phthalates are a family of reprotoxicant compounds, predominantly used as a plasticizer to improve the flexibility and longevity of consumable plastic goods. After their use these plastic products find their way to the waste disposal sites where they leach out the hazardous phthalates present within them, into the surrounding environment, contaminating soil, groundwater resources, and the nearby water bodies. Subsequently, phthalates move into the living system through the food chain and exhibit the well-known phenomenon of biological magnification. Phthalates as a primary pollutant have been classified as 1B reprotoxicants and teratogens by different government authorities and they have thus imposed restrictions on their use. Nevertheless, the release of these compounds in the environment is unabated. Bioremediation has been suggested as one of the ways of mitigating this menace, but studies regarding the field applications of phthalate utilizing microbes for this purpose are limited. Through this review, we endeavor to make a deeper understanding of the cause and concern of the problem and to find out a possible solution to it. The review critically emphasizes the various aspects of phthalates toxicity, including their chemical nature, human health risks, phytoaccumulation and entry into the food chain, microbial role in phthalate degradation processes, and future challenges.

Biodegradation of Dibutyl Phthalate by the New Strain Acinetobacter baumannii DP-2

Optimizing the culture conditions of DBP degradation by bacteria and investigating its biodegradation pathways have a great importance to develop effective PAEs pollution control strategies. In this study, we investigated the cultivation condition optimization, degradation kinetics, and degradation pathways of a newly isolated dibutyl phthalate (DBP) degradation strain, which was isolated from activated sludge and identified as Acinetobacter baumannii DP-2 via morphological observation, biochemical identification, and 16S rDNA sequence analysis. The degradation conditions were optimized based on the results of single-factor experiments and response surface optimization experiments. The DBP degradation rate of Acinetobacter baumannii DP-2 reached up to 85.86% when the inoculation amount was 17.14%, the DBP concentration was 9.81 mg·L^-1 and the NaCl concentration was 5 g·L^-1. The GC-MS analysis results indicated that the intermediate metabolites of Acinetobacter baumannii DP-2 mainly consisted of DMP, MBP, PA, and benzoic acid derivatives, which confirmed the degradation pathway from DBP to PA under aerobic pathway and then to BA under anaerobic pathway. In summary, Acinetobacter baumannii DP-2 shows great potential for the degradation of DBP in contaminated soils.

Phthalate hydrolase: distribution, diversity and molecular evolution

The alpha/beta-fold superfamily of hydrolases is rapidly becoming one of the largest groups of structurally related enzymes with diverse catalytic functions. In this superfamily of enzymes, esterase deserves special attention because of their wide distribution in biological systems and importance towards environmental and industrial applications. Among various esterases, phthalate hydrolases are the key alpha/beta enzymes involved in the metabolism of structurally diverse estrogenic phthalic acid esters, ubiquitously distributed synthetic chemicals, used as plasticizer in plastic manufacturing processes. Although they vary both at the sequence and functional levels, these hydrolases use a similar acid-base-nucleophile catalytic mechanism to catalyse reactions on structurally different substrates. The current review attempts to present insights on phthalate hydrolases, describing their sources, structural diversities, phylogenetic affiliations and catalytically different types or classes of enzymes, categorized as diesterase, monoesterase and diesterase-monoesterase, capable of hydrolysing phthalate diester, phthalate monoester and both respectively. Furthermore, available information on in silico analyses and site-directed mutagenesis studies revealing structure-function integrity and altered enzyme kinetics have been highlighted along with the possible scenario of their evolution at the molecular level.

Maize root-associated niches determine the response variation in bacterial community assembly and function to phthalate pollution

Plant root-associated microbiome can be influenced by environmental stress like pollution. However, how organic pollution influences microbial communities in different root-associated niches and plant-microbe interaction remains unclear. We analyzed maize root-associated bacterial communities under stress of di-(2-ethylhexyl) phthalate (DEHP). The results demonstrate that structures and functions of bacterial communities are significantly different among four root-associated niches, and bacterial diversities gradually decline along bulk soil - rhizosphere - rhizoplane - endosphere. DEHP stress significantly reduces bacterial community diversities in both rhizosphere and rhizoplane, and changes their composition, enrichment and depleting process. DEHP stress led to the enrichment of some specific bacterial taxa like phthalate-degrading bacteria (e.g., Rhizobium and Agromyces) and functional genes involving in phthalate degradation (e.g., pht3 and pcaG). Notably, rhizoplane bacterial community is more sensitive to DEHP stress by enriching stress-resistant bacteria and more complex microbial network on rhizoplane than in rhizosphere. DEHP stress also disturbs the colonization and biofilm forming of root-associated bacteria on rhizoplane. Rhizoplane bacterial community is significantly correlated with maize growth while negatively influenced by DEHP stress. DEHP stress negatively influences plant-microbe interaction and inhibits maize growth. This study provides deep and comprehensive understanding for root-associated bacterial community in response to organic pollution.