Biodegradation of dimethyl phthalate by Sphingomonas sp. isolated from phthalic-acid-degrading aerobic granules

Mechanisms and high-value applications of phthalate isomers degradation pathways in bacteria

Phthalate isomers are key intermediates in the biodegradation of pollutants including waste polyethylene terephthalate (PET) plastics and plasticizers. So far, an increasing number of phthalate isomer-degrading strains have been isolated, and their degradation pathways show significant diversity. In this paper, we comprehensively review the current status of research on the degrading bacteria, degradation characteristics, aerobic and anaerobic degradation pathways, and degradation genes (clusters) of phthalate isomers, and discuss the current shortcomings and challenges. Moreover, the degradation process of phthalate isomers produces many important aromatic precursor molecules, which can be used to produce higher-value derivative chemicals, and the modification of their degradation pathways holds good prospects. Therefore, this review also highlights the current progress made in modifying the phthalate isomer degradation pathway and explores its potential for high-value applications.

Process optimization and kinetic study of biodegradation of dimethyl phthalate by KS2, a novel strain of Micrococcus sp

The present study elucidates identification and characterization of dimethyl phthalate (DMP) degrading novel bacterial strain, Micrococcus sp. KS2, isolated from soil contaminated with municipal wastewater. Statistical designs were exercised to achieve optimum values of process parameters for DMP degradation by Micrococcus sp. KS2. The screening of the ten important parameters was performed by applying Plackett-Burman design, and it delivered three significant factors (pH, temperature, and DMP concentration). Further, response surface methodology involving central composite design (CCD) was implemented to examine mutual interactions among variables and achieve their optimal response. The predicted response indicated that maximum DMP degradation (99.67%) could be attained at pH 7.05, temperature 31.5 °C and DMP 289.19 mg/l. The strain KS2 was capable of degrading up to 1250 mg/l of DMP in batch mode and it was observed that oxygen was limiting factor in the DMP degradation. Kinetic modeling of DMP biodegradation indicated that Haldane model fitted well with the experimental data. During DMP degradation, monomethyl phthalate (MMP) and phthalic acid (PA) were identified as degradation metabolites. This study provides insight into DMP biodegradation process and proposes that Micrococcus sp. KS2 is a potential bacterial candidate to treat effluent containing DMP.

Mitigation of tobacco bacteria wilt with microbial degradation of phenolic allelochemicals

Long-term continuous monoculture cropping of tobacco leads to high incidence of tobacco bacterial wilt (TBW) caused by Ralstonia solanacearum, which threatening world tobacco production and causing great economy loss. In this study, a safe and effective way to control TBW by microbial degradation of phenolic allelochemicals (PAs) was explored. Eleven kinds of PAs were identified from continuous tobacco cropping soil. These PAs exhibited various effects on the growth, chemotaxis and biofilm formation of R. solanacearum. Then we isolated eight strains of Bacillus, one strain of Brucella, one strain of Enterobacter and one strain of Stenotrophomonas capable of degrading these PAs. The results of degradation assay showed that these isolated strains could degrade PAs both in culture solutions and soil. Besides, the incidence of TBW caused by R. solanacearum and deteriorated by PAs were significantly decreased by treating with these degrading strains. Furthermore, six out of eleven isolated strains were combined to degrade all the identified PAs and ultimately sharply reduced the incidence of TBW by 61.44% in pot experiment. In addition, the combined degrading bacteria could promote the plant growth and defense response. This study will provide a promising strategy for TBW control in tobacco production.

Impacts of dibutyl phthalate on biological municipal wastewater treatment in a pilot-scale A2/O-MBR system

Dibutyl phthalate (DBP) is a typical contaminant in pharmaceutical wastewater with strong bio-depressive properties which potentially affects the operation of municipal wastewater treatment systems. Based on a year-round monitoring of the quality of influent and effluent of a full-scale pharmaceutical wastewater treatment plant in Northeast China, the DBP was found to be the representative pollutant and its concentration in the effluent ranged 4.28 ± 0.93 mg/L. In this study, the negative effects of DBP on a pilot-scale A²/O-MBR system was investigated. When the influent DBP concentration reached 8.0 mg/L, the removals of chemical oxygen demand (COD) and total nitrogen (TN) were significantly inhabited (P < 0.01), with the effluent concentration of 54.7 ± 2.6 mg/L and 22.8 ± 3.7 mg/L, respectively. The analysis of pollutant removal characteristics of each process unit showed that DBP had the most significant effects on the removals of COD and TN in the anoxic tank. The α- and β-diversity in the system decreased significantly when the influent DBP concentration reached 8.0 mg/L. The impacts of DBP on known nitrifying bacteria, such as Nitrospira, and phosphorus accumulating organisms (PAOs), such as Cadidatus Accumulibacter, were not remarkable. Whereas, DBP negatively affected the proliferation of key denitrifying bacteria, represented by Simplicispira, Dechloromonas and Acinetobacter. This study systematically revealed the impacts of DBP on the pollutants removal performance and the bacterial community structure of the biological municipal wastewater treatment process, which would provide insights for understanding the potential impacts of residues in treated pharmaceutical wastewater on biological municipal wastewater treatment.

The Dynamic Shift of Bacterial Communities in Hybrid Anaerobic Baffled Reactor (ABR)—Aerobic Granules Process for Berberine Pharmaceutical Wastewater Treatment

Because of its anticancer, anti-inflammatory, and antibiotic properties, berberine has been used extensively in medication. The extensive production of berberine results in the generation of wastewater containing concentrated residual berberine. However, to date, limited related studies on the biological treatment of berberine wastewaters have been carried out. A lab-scale anaerobic baffled reactor (ABR)–aerobic granular sludge (AGS) process was developed for berberine removal from synthetic wastewater. The system showed effective removal of the berberine. In order to better understand the roles of the bacterial community, the ABR–aerobic granular sludge system was operated in the state with the highest BBR removal rate in this study. The bacterial community dynamics were studied using the 16S rDNA clone library. The results showed that the hybrid ABR-AGS process achieved 92.2% and 94.8% overall removals of berberine and COD, respectively. Bacterium was dominant species in ABR, while the CFB group bacteria and Betaproteobacteria were dominant species in AGS process. The uncultured bacterium clone B135, Bacillus endophyticus strain a125, uncultured bacterium mle1-42, uncultured bacterium clone OP10D15, and uncultured bacterium clone B21.29F54 in ABR, and uncultured bacterium clone F54, uncultured bacterium clone ZBAF1-105, uncultured bacterium clone SS-9, and uncultured bacterium clone B13 in AGS process were identified as functional species in the biodegradation of berberine and/or its metabolites. Both anaerobic and aerobic bacterial communities could adapt appropriately to different berberine selection pressures because the functional species’ identical functions ensured comparable pollutant removal performances. The information provided in this study may help with future research in gaining a better understanding of berberine biodegradation.

The Impact of Berberine Pharmaceutical Wastewater on Aerobic Granules Formation: Change of Granules’ Size

As important parameters in the characterization of aerobic granulation, the shape and average diameter were related to substrates. The previous studies disclosed that the morphology change in aerobic granules was the result of growth and the relatively strong hydrodynamic shear force. No further exploration of the size distribution of the aerobic granules has been conducted. To better understand the impact of toxic compounds on aerobic granules’ growth during their formation, the properties of aerobic granules were traced over 81 days in 3 sequencing batch reactors fed with acetate and berberine wastewater, especially the particle size and size distribution. The results showed that the aerobic granules were cultivated by the simulated acetate wastewater (R1), simulated berberine wastewater (R2), and effluent from an anaerobic baffled reactor (ABR) reactor which was fed with industrial berberine wastewater (R3). The reactors exhibited different COD removal efficiencies, and the MLSS and MLVSS values affected by the different substrates which were in an order of R1 > R2 > R3. However, the SVI and SOUR, which were affected by several factors, showed more complicated results. The aerobic granules had the lowest microbial activity (SOUR), while the aerobic granules in R3 had the lowest settling ability among the three kinds of granules. For the three reactors with different influent compositions, the aerobic granulation process displayed a three-stage process separately. Compared with the granules fed with berberine wastewater, the granules fed with acetate in a stable operation period showed more independence from other periods.The size distribution was affected by substrates. The aerobic granules with a range of 0.3–1.0 µm occupied 77.0%, 67.0%, and 35.7% of the volume for R1, R2, and R3, respectively. The biomass less than 0.3 µm occupied 59.1% volume in R3. The components of the substrate had a great influence on the growth of aerobic granules, not only on the diameter but also on the size distribution.

Isolation of Dibutyl Phthalate-Degrading Bacteria and Its Coculture with Citrobacter freundii CD-9 to Degrade Fenvalerate

Continued fenvalerate use has caused serious environmental pollution and requires large-scale remediation. Dibutyl phthalate (DBP) was discovered in fenvalerate metabolites degraded by Citrobacter freundii CD-9. Coculturing is an effective method for bioremediation, but few studies have analyzed the degradation pathways and potential mechanisms of cocultures. Here, a DBP-degrading strain (BDBP 071) was isolated from soil contaminated with pyrethroid pesticides (PPs) and identified as Stenotrophomonas acidaminiphila. The optimum conditions for DBP degradation were determined by response surface methodology (RSM) analysis to be 30.9 mg/l DBP concentration, pH 7.5, at a culture temperature of 37.2°C. Under the optimized conditions, approximately 88% of DBP was degraded within 48 h and five metabolites were detected. Coculturing C. freundii CD-9 and S. acidaminiphila BDBP 071 promoted fenvalerate degradation. When CD-9 was cultured for 16 h before adding BDBP 071, the strain inoculation ratio was 5:5 (v/v), fenvalerate concentration was 75.0 mg/l, fenvalerate was degraded to 84.37 ± 1.25%, and DBP level was reduced by 5.21 mg/l. In addition, 12 fenvalerate metabolites were identified and a pathway for fenvalerate degradation by the cocultured strains was proposed. These results provide theoretical data for further exploration of the mechanisms used by this coculture system to degrade fenvalerate and DBP, and also offer a promising method for effective bioremediation of PPs and their related metabolites in polluted environments.

Biodegradation of di-(2-ethylhexyl) phthalate by novel Rhodococcus sp. PFS1 strain isolated from paddy field soil

Di-(2-ethylhexyl)-phthalate (DEHP) is the phthalate ester frequently utilized as a plasticizer, commonly found in cosmetics, packaging materials; moreover, it has carcinogenic and mutagenic effects on humans. In the current study, we isolated the soil bacterium Rhodococcus sp. PFS1 and to assess its DEHP degradation ability in various environmental conditions. The strain PFS1 was isolated from paddy field soil and identified by the 16S rRNA sequencing analyses. The strain PFS1 was examined for its biodegradation ability of DEHP at various pH, temperature, salt concentration, glucose concentration, and high and low concentrations of DEHP. Moreover, the biodegradation of DEHP at a contaminated soil environment by strain PFS1 was assessed. Further, the metabolic pathway of DEHP degradation by PFS1 was analyzed by HPLC-MS analysis. The results showed that the strain PFS1 effectively degraded the DEHP at neutral pH and temperature 30 °C; moreover, expressed excellent DEHP degradation at the high salt concentration (up to 50 g/L). The strain PFS1 was efficiently degraded the different tested phthalate esters (PAEs) up to 90%, significantly removed the DEHP contamination in soil along with native organisms which are present in soil up to 94.66%; nevertheless, the PFS1 alone degraded the DEHP up to 87.665% in sterilized soil. According to HPLC-MS analysis, DEHP was degraded into phthalate (PA) by PFS1 strain via mono(2-ethylehxyl) phthalate (MEHP); then PA was utilized for cell growth. These results suggest that Rhodococcus sp. PFS1 has excellent potential to degrade DEHP at various environmental conditions especially in contaminated paddy field soil.

Contrasting impacts of drying-rewetting cycles on the dissipation of di-(2-ethylhexyl) phthalate in two typical agricultural soils

Di-(2-ethylhexyl) phthalate (DEHP) pollution has become a growing problem in farmlands of China. Drying-rewetting (DW) cycle is one of frequent environmental changes that agricultural production is confronted with, and also a convenient and practical agronomic regulation measure. In this study, in order to explore the effects of DW cycles on the dissipation of DEHP and their driving mechanisms in different types of soils, we performed a 45-day microcosm culture experiment with two typical agricultural soils, Lou soil (LS) and Red soil (RS). High-throughput sequencing was applied to study the response of soil microbial communities in the process of DEHP dissipation under DW cycles. The results showed that the DW cycles considerably inhibited the dissipation of DEHP in LS while promoted that in RS. The DW cycles obviously decreased the diversity, the relative abundance of significantly differential bacteria, and the total abundance of potential degrading bacterial groups in LS, whereas have little effect on bacterial community in RS, except at the initial cultivation stage when the corresponding parameters were promoted. The inhibition of the DW cycles on DEHP dissipation in LS was mainly derived from microbial degradation, but the interplay between microbial functions and soil attributes contributed to the promotion of DEHP dissipation in RS under the DW cycles. This comprehensive understanding of the contrasting impacts and underlying driving mechanisms may provide crucial implications for the prevention and control of DEHP pollution in regional soils.

Isolation, identification and characterization of phenolic acid-degrading bacteria from soil

AIMS

To isolate, identify and characterize phenolic acid-degrading bacteria and reduce plant growth inhibition caused by phenolic acids.

METHODS AND RESULTS

A total of 11 bacterial isolates with high phthalic acid (PA)-degrading ability were obtained using mineral salt medium (MSM) medium containing PA as sole carbon source. These isolates were identified as Arthrobacter globiformis, Pseudomonas putida and Pseudomonas hunanensis by sequence analyses of the 16S rRNA gene. Among them, five Pseudomonas strains could also effectively degrade ferulic acid (FA), p-hydroxybenzoic acid (PHBA) and syringic acid (SA) in MSM solution. P. putida strain 7 and P. hunanensis strain 10 showed highly efficient degradation of PA, SA, FA and PHBA, and could reduce their inhibition of lily, watermelon, poplar and strawberry seedling growth in soils respectively. These two strains could promote plant growth in soil with phenolic acids.

CONCLUSIONS

In this study, bacterial strains with highly efficient phenolic acid-degrading abilities could not only effectively reduce the autotoxicity of phenolic acids on plants but also were able to promote plant growth in soil with phenolic acids.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, Pseudomonas can promote plant growth while degrading phenolic acids. Our results provide new choices for the biological removal of autotoxins.

High-effectively degrade the di-(2-ethylhexyl) phthalate via biochemical system: Resistant bacterial flora and persulfate oxidation activated by BC@Fe3O4

Di-(2-ethylhexyl) phthalate (DEHP) has been classified as a priority pollutant which increased the healthy risk to human and animals dramatically. Hence, a novel biochemical system combined by DEHP-resistant bacterial flora (B) and a green oxidant of persulfate (PS) activated by Nano-Fe₃O₄ was applied to degrade DEHP in contaminated soil. In this study, the resistant bacterial flora was screened from activated sludge and immobilized by sodium alginate (SAB). Nano-Fe₃O₄ was coated on biochar (BC@Fe₃O₄) to prevent agglomerating in soil. X-ray diffraction (XRD) and scanning electron microscope (SEM) were utilized to characterize BC@Fe₃O₄. Results demonstrated that the treatment of biochemical system (SAB + BC@Fe₃O₄ + PS) presented the maximum degradation rate about 92.56% within 24 days of incubation and improved soil microecology. The 16S rDNA sequences analysis of soil microorganisms showed a significantly different abundance and a similar diversity among different treatments. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional genes difference analysis showed that some metabolic pathways, such as metabolism of cofactors and vitamins, energy metabolism, cell growth and death, replication and repair, were associated with the biodegradation of DEHP. Besides, DEHP was converted to MEHP and PA by biodegradation, while DEHP was converted to DBP and PA by persulfate and BC@Fe₃O₄, and then ultimately degraded to CO₂ and H₂O.

Enhanced biodegradation of an endocrine disrupting micro-pollutant: Di (2-ethylhexyl) phthalate using biogenic self-assembled monolayer of silver nanoparticles

Di (2-ethylhexyl) phthalate (DEHP) is one of the predominant plasticizer and an endocrine disrupting chemical occurring almost in all partitions of the environment. Though DEHP occur at lower concentration, reluctance arises due to their ability to disrupt endocrine system even lower concentration. In the present study, DEHP was assessed for degradation at minimal level (1-100 μg L^-1) by a novel bacterial strain, Rhodococcus jostii PEVJ9. In the experimental design, significant variables were concentration of silver nitrate and DEHP, pH, temperature, time and agitation. Degradation without SAM-silver nanoparticles was 30-66% (predicted value = 30.8-66.8%, R² = 99.7%) while, degradation in the presence of SAM-silver nanoparticles onto bacterial cells was 100% (predicted value = 98.4-102.1%, R² = 99.6%) within 72 h. In short, this is the first report illustrating the experimental designs in biogenic synthesis of SAM-silver nanoparticles and enhanced degradation of DEHP at minimal level. The study overcomes poor bioavailability and assimilation of DEHP at lower concentration by the microbial population present in the environment. Thus, an efficient clean-up would prevent or minimize DEHP exposure at all trophic levels ranging from feminization of fishes to reproductive disorders in humans.

Degradation of dibutyl phthalate (DBP) by a bacterial consortium and characterization of two novel esterases capable of hydrolyzing PAEs sequentially

Phthalate esters (PAEs), a class of toxic anthropogenic compounds, have been predominantly used as additives or plasticizers, and great concern and interests have been raised regarding its environmental behavior and degradation mechanism. In the present study, a bacterial consortium consisting of Microbacterium sp. PAE-1 and Pandoraea sp. PAE-2 was isolated by the enrichment method, which could degrade dibutyl phthalate (DBP) completely by biochemical cooperation. DBP was converted to phthalic acid (PA) via monobutyl phthalate (MBP) by two sequential hydrolysis steps in strain PAE-1, and then PA was further degraded by strain PAE-2. Strain PAE-1 could hydrolyze many dialkyl Phthalate esters (PAEs) including dimethyl, diethyl, dibutyl, dipentyl, benzyl butyl, dihexyl, di-(2-ethyhexyl) and their corresponding monoalkyl PAEs. Two esterase genes named dpeH and mpeH, located in the same transcription unit, were cloned from strain PAE-1 by the shotgun method and heterologously expressed in Escherichia. coli (DE3). The Km and kcat values of DpeH for DBP were 9.60 ± 0.97 μM and (2.72 ± 0.06) × 10⁶ s^-1, while those of MpeH for MBP were 18.61 ± 2.00 μM and (5.83 ± 1.00) × 10⁵ s^-1, respectively. DpeH could only hydrolyze dialkyl PAEs to the corresponding monoalkyl PAEs, which were then hydrolyzed to PA by MpeH. DpeH shares the highest similarity (53%) with an alpha/beta hydrolase from Microbacterium sp. MED-G48 and MpeH shows only 25% identity with a secreted lipase from Trichophyton benhamiae CBS 112371, indicating that DpeH and MpeH are two novel hydrolases against PAEs.

Isolation and Characterization of a Bacterial Strain Capable of Efficient Berberine Degradation

Background: Berberine (BBR) is a pharmaceutical chemical with a broad antibacterial spectrum, and its biological treatment has been of research and practical interest. In this study, a pure bacterial strain B16 was isolated from the activated sludge in a pharmaceutical wastewater treatment plant. The aim of the study is to characterize the properties of the strain B16, especially its BBR degradation capability. Methods: The identification of strain B16 was conducted by visual observation, as well as biochemical and phylogenetic analysis. The degradation kinetics of strain B16 was tentatively described by Haldane model. Results: The strain B16 was 100% determined as a Sphingopyxis sp. The kinetic parameters of BBR degradation by strain B16 were as follows: Vmax 54.73 ± 5.54 mg (g MLSS · h)⁻¹, Km 66.68 ± 8.95 mg L⁻¹, and Ki 43.16 ± 5.92 mg L⁻¹, with an R² of 0.996. Stain B16 exhibited considerable capability of BBR degradation. BBR of initial concentration 40 mg L⁻¹ could be completely degraded in 48 h under optimal conditions. Conclusions: strain B16 was the first pure culture found with the ability to totally mineralize BBR, indicating the potential of B16 application in real industrial processes.

Excellent Degradation Performance of a Versatile Phthalic Acid Esters-Degrading Bacterium and Catalytic Mechanism of Monoalkyl Phthalate Hydrolase

Despites lots of characterized microorganisms that are capable of degrading phthalic acid esters (PAEs), there are few isolated strains with high activity towards PAEs under a broad range of environmental conditions. In this study, Gordonia sp. YC-JH1 had advantages over its counterparts in terms of di(2-ethylhexyl) phthalate (DEHP) degradation performance. It possessed an excellent degradation ability in the range of 20–50 °C, pH 5.0–12.0, or 0–8% NaCl with the optimal degradation condition 40 °C and pH 10.0. Therefore, strain YC-JH1 appeared suitable for bioremediation application at various conditions. Metabolites analysis revealed that DEHP was sequentially hydrolyzed by strain YC-JH1 to mono(2-ethylhexyl) phthalate (MEHP) and phthalic acid (PA). The hydrolase MphG1 from strain YC-JH1 hydrolyzed monoethyl phthalate (MEP), mono-n-butyl phthalate (MBP), mono-n-hexyl phthalate (MHP), and MEHP to PA. According to molecular docking and molecular dynamics simulation between MphG1 and monoalkyl phthalates (MAPs), some key residues were detected, including the catalytic triad (S125-H291-D259) and the residues R126 and F54 potentially binding substrates. The mutation of these residues accounted for the reduced activity. Together, the mechanism of MphG1 catalyzing MAPs was elucidated, and would shed insights into catalytic mechanism of more hydrolases.

Biodegradation of Di-(2-ethylhexyl) Phthalate by Rhodococcus ruber YC-YT1 in Contaminated Water and Soil

Di-(2-ethylehxyl) phthalate (DEHP) is one of the most broadly representative phthalic acid esters (PAEs) used as a plasticizer in polyvinyl chloride (PVC) production, and is considered to be an endocrine-disrupting chemical. DEHP and its monoester metabolites are responsible for adverse effects on human health. An efficient DEHP-degrading bacterial strain Rhodococcus ruber YC-YT1, with super salt tolerance (0⁻12% NaCl), is the first DEHP-degrader isolated from marine plastic debris found in coastal saline seawater. Strain YC-YT1 completely degraded 100 mg/L DEHP within three days (pH 7.0, 30 °C). According to high-performance liquid chromatography⁻mass spectrometry (HPLC-MS) analysis, DEHP was transformed by strain YC-YT1 into phthalate (PA) via mono (2-ethylehxyl) phthalate (MEHP), then PA was used for cell growth. Furthermore, YC-YT1 metabolized initial concentrations of DEHP ranging from 0.5 to 1000 mg/L. Especially, YC-YT1 degraded up to 60% of the 0.5 mg/L initial DEHP concentration. Moreover, compared with previous reports, strain YC-YT1 had the largest substrate spectrum, degrading up to 13 kinds of PAEs as well as diphenyl, p-nitrophenol, PA, benzoic acid, phenol, protocatechuic acid, salicylic acid, catechol, and 1,2,3,3-tetrachlorobenzene. The excellent environmental adaptability of strain YC-YT1 contributed to its ability to adjust its cell surface hydrophobicity (CSH) so that 79.7⁻95.9% of DEHP-contaminated agricultural soil, river water, coastal sediment, and coastal seawater were remedied. These results demonstrate that R. ruber YC-YT1 has vast potential to bioremediate various DEHP-contaminated environments, especially in saline environments.

Complete degradation of the endocrine disruptor di-(2-ethylhexyl) phthalate by a novel Agromyces sp. MT-O strain and its application to bioremediation of contaminated soil

A newly isolated strain Agromyces sp. MT-O could utilize various phthalates and efficiently degraded di-(2-ethylhexyl) phthalate (DEHP). Response surface methodology was successfully employed for the optimization of culture conditions including pH (7.2), temperature (29.6), and inoculum size (OD600 of 0.2), resulting in almost complete degradation of DEHP (200mgL(-1)) within 7days. At different initial concentrations (50-1000mgL(-1)), DEHP degradation curves were fitted well with the first-order kinetic model, and the half-life of DEHP degradation ranged from 0.83 to 2.92days. Meanwhile, the substrate inhibition model was used to describe the special degradation rate with qmax, Ks, and Ki of 0.6298day(-1), 86.78mgL(-1), and 714.3mgL(-1), respectively. The GC-MS analysis indicated that DEHP was degraded into mono-ethylhexyl phthalate and phthalate acid before its complete mineralization. Bioaugmentation of DEHP-contaminated soils with strain MT-O has greatly enhanced DEHP disappearance rate in soils, providing great potential for efficiently remediating DEHP-contaminated environment.

Biodegradation of phthalic acid esters by a newly isolated Mycobacterium sp. YC-RL4 and the bioprocess with environmental samples

Bacterial strain YC-RL4, capable of utilizing phthalic acid esters (PAEs) as the sole carbon source for growth, was isolated from petroleum-contaminated soil. Strain YC-RL4 was identified as Mycobacterium sp. by 16S rRNA gene analysis and Biolog tests. Mycobacterium sp. YC-RL4 could rapidly degrade dibutyl phthalate (DBP), diethyl phthalate (DEP), dimethyl phthalate (DMP), dicyclohexyl phthalate (DCHP), and di-(2-ethylhexyl) phthalate (DEHP) under both individual and mixed conditions, and all the degradation rates were above 85.0 % within 5 days. The effects of environmental factors which might affect the degrading process were optimized as 30 °C and pH 8.0. The DEHP metabolites were detected by HPLC-MS and the degradation pathway was deduced tentatively. DEHP was transformed into phthalic acid (PA) via mono (2-ethylhexyl) phthalate (MEHP) and PA was further utilized for growth via benzoic acid (BA) degradation pathway. Cell surface hydrophobicity (CSH) assays illuminated that the strain YC-RL4 was of higher hydrophobicity while grown on DEHP and CSH increased with the higher DEHP concentration. The degradation rates of DEHP by strain YC-RL4 in different environmental samples was around 62.0 to 83.3 % and strain YC-RL4 survived well in the soil sample. These results suggested that the strain YC-RL4 could be used as a potential and efficient PAE degrader for the bioremediation of contaminated sites.

Phthalate esters in the environment: A critical review of their occurrence, biodegradation, and removal during wastewater treatment processes

Phthalate esters are one of the most frequently detected persistent organic pollutants in the environment. A better understanding of their occurrence and degradation in the environment and during wastewater treatment processes will facilitate the development of strategies to reduce these pollutants and to bioremediate contaminated freshwater and soil. Phthalate esters occur at measurable levels in different environments worldwide. For example, the concentrations of dimethyl phthalate (DMP) in atmospheric particulate matter, fresh water and sediments, soil, and landfills are N.D.-10.4 ng/m(3), N.D.-31.7 μg/L, N.D.-316 μg/kg dry weight, and N.D.-200 μg/kg dry weight, N.D.-43.27 μg/L, respectively. Bis(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP) are primary phthalate ester pollutants. Urbanization has increased the discharge of phthalate esters to atmospheric and aquatic environments, and the use of agricultural plastics has exacerbated soil contamination by phthalate esters in rural areas. Aerobic biodegradation is the primary manner of phthalate ester mineralization in the environment, and this process has been widely studied. Phthalate esters can be removed during wastewater treatment processes. The combination of different wastewater treatment technologies showed greater efficiency in the removal of phthalate esters than individual treatment steps, such as the combination of anaerobic wastewater treatment with a membrane bioreactor would increase the efficiency of phthalate ester removal from 65%-71% to 95%-97%. This review provides a useful framework to identify future research objectives to achieve the mineralization and elimination of phthalate esters in the environment.

Achromobacter denitrificans strain SP1 efficiently remediates di(2-ethylhexyl)phthalate

This study describes how Achromobacter denitrificans strain SP1, a novel isolate from heavily plastics-contaminated sewage sludge efficiently consumed the hazardous plasticizer, di(2-ethylhexyl)phthalate (DEHP) as carbon source supplemented in a simple basal salt medium (BSM). Response surface methodology was employed for the statistical optimization of the process parameters such as temperature (32°C), agitation (200 rpm), DEHP concentration (10 mM), time (72 h) and pH (8.0). At these optimized conditions, experimentally observed DEHP degradation was 63%, while the predicted value was 59.2%; and the correlation coefficient between them was 0.998, i.e., highly significant and fit to the predicted model. Employing GC-MS analysis, the degradation pathway was partially deduced with intermediates such as mono(2-ethylhexyl)phthalate and 2-ethyl hexanol. Briefly, this first report describes A. denitrificans strain SP1 as a highly efficient bacterium for completely remediating the hazardous DEHP (10 mM) in 96 h in BSM (50% consumed in 60 h), which offers great potentials for efficiently cleaning the DEHP-contaminated environments such as soil, sediments and water upon its deployment.