Degradation Of High Molecular Weight Polycyclic Aromatic Hydrocarbons Research Articles

Ligninolytic enzyme involved in removal of high molecular weight polycyclic aromatic hydrocarbons by Fusarium strain ZH-H2.

The capacity of Fusarium sp. strain ZH-H2 to secret lignin peroxidase (LiP), laccase (Lac), and manganese peroxidase (MnP) and degrade high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) was studied. When the fungus was grown in control mineral salt medium for 4days, LiP and Lac activities were detected at 8871UL-1 and 5123UL-1, respectively. In the presence of HMW-PAHs as the sole carbon source, only LiP activity was detectable, and LiP activity had significantly reduced HMW-PAHs at day 7, with a maximum decrease of 85.9%. A strong correlation between LiP activity and HMW-PAHs removal efficiency could be fit into various models, with the highest correlation coefficients obtained for quadratic functions (P < 0.01). When a specific enzyme inhibitor was added, the ability of Fusarium to remove HMW-PAHs was reduced from 85.9 to 66.7%, depending on the inhibitor's concentration. Meanwhile, the determined activity of LiP was reduced from 11.4 to 48.6%. We conclude that in the presence of HMW-PAHs as the only carbon source to support growth, Fusarium ZH-H2 mainly produces LiP but not Lac or MnP for HMW-PAHs degradation. To our knowledge, it was the first time to propose a metabolic lignin peroxidase characterization of HMW-PAHs degradation by Fusarium sp. strains.

A Dibenz[a,h]Anthracene-Degrading Strain Amycolatopsis sp. Y1-2 from Soils in the Coal Mining Areas

It is well-known that the high-molecular-weight polycyclic aromatic hydrocarbons (HMW-PAHs) are difficult to degrade, and they can cause tremendous damaging effects in environment. In this article, a novel dibenz[a,h]anthracene (DBA)-degrading strain Amycolatopsis sp. Y1-2 was isolated and identified from the contaminated soils in the coal mining areas. The degradation of HMW-PAHs by strain Y1-2 could be improved by adopting DBA, benzo(a)anthracene, benzo(b)fluoranthene, benzo(a)pyrene, and benzo(g,hi)perylene as the sole carbon and energy sources. The co-metabolism substrates test revealed that the HMW-PAHs degradation efficiency of strain Y1-2 could be significantly improved under co-metabolism substrates, especially glucose (increased by 34.70%) and cyclodextrin. The optimization results of DBA-degrading conditions obtained from response surface analysis are as follows: pH 7.6, concentration of DBA 10.71 mg L−1, inoculum amount 1.58 g 100 mL−1 medium, concentration of glucose 9.98 g L−1, and concentration of cyclodextrin 2.05 g L−1. The predicted value of degradation percentage in the optimized conditions was 99.03% (very similar with the actual value of 97.84%). Based on the above results, the strain Y1-2 can degrade HMW-PAHs effectively and will be applied in treating PAHs-containing soils and industrial wastewater.

ENHANCED BIODEGRADATION OF HIGH MOLECULAR WEIGHT PAHS USING YEAST CONSORTIA IMMOBILIZED ON MODIFIED BIOWASTE MATERIAL

The degradation of high molecular weight (HMW) polycyclic aromatic hydrocarbons (PAHs) viz. benzo[a]pyrene, perylene and benzo[ghi]perylene in soil was studied using yeast consortia immobilized on various conventional matrices and biowaste materials. Enhanced biodegradation was noted using yeast consortia immobilized in sawdust powder (SDP) which was chemically modified (M-SDP). The chemical modification destroyed the benzene rings in the cellulose and improved the porosity of SDP by decreasing the crystallinity of the biomass. The physicochemical properties of M-SDP were characterized with SEM, EDAX analysis, FTIR analysis, X-ray diffraction and TGA analysis. Application of M-SDP showed enhanced degradation of benzo[a]pyrene (82.5%) followed by perylene (75.1%) and benzo[ghi]perylene (63.4%) after 40 days of incubation. The results of kinetic study demonstrated that HMW PAHs degradation in soil fitted the first order kinetic model. It can be concluded that chemically modified SDP can serve as potential immobilization matrix for supporting pollutant-degrading yeast consortia which can be employed for effective degradation of HMW PAHs.

Comparison of plants with C3 and C4 carbon fixation pathways for remediation of polycyclic aromatic hydrocarbon contaminated soils

The phytoremediation technique has been demonstrated to be a viable option for the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study evaluated the potential applicability of plants with C3 and C4 carbon fixation pathways for the phytoremediation of recalcitrant high molecular weight (HMW) PAHs contaminated soil. A 60 and 120-day greenhouse study was conducted which showed higher degradation of HMW PAHs in soil grown with C4 plants when compared to C3 plants. Also, no PAHs were detected in the maize cobs, sunflower, wallaby, and Sudan grass seeds at the end of the experiment. The effect of plants in modifying the microbial community and dynamics in the rhizosphere was also examined by measuring soil biochemical properties such as dehydrogenase activity and water-soluble phenols. The results demonstrate a substantial difference in the microbial populations between planted and unplanted soils, which in turn facilitate the degradation of PAHs. To the best of our knowledge, this study for the first time evaluated the phytoremediation efficacy through the A. cepa cyto- and genotoxicity assay which should be considered as an integral part of all remediation experiments.

Role of a halothermophilic bacterial consortium for the biodegradation of PAHs and the treatment of petroleum wastewater at extreme conditions

Petroleum hydrocarbons are major pollutants in marine environments. The present study describes the potential of a halothermophilic bacterial consortium capable of degrading polycyclic aromatic hydrocarbons (PAHs) in petroleum wastewater under extreme conditions. The consortium was enriched from brine originating from a desalination plant. The consortium efficiently degraded both the low molecular weight (LMW) PAHs-naphthalene (NAP), phenanthrene (PHN), anthracene (AN) and fluorene (FLU) as well as the high molecular weight (HMW) PAHs-pyrene (PY), benzo(e)pyrene (B(e)P) and benzo(k)fluoranthene (B(k)F), respectively. A nearly quantitative release of carbon dioxide (85 ± 1.2%) in conjunction with significant reduction of PAH concentration and an increase in bacterial cell count (from 104 to 109 cfu/mL) pointed at mineralization of PHN. The consortium was able degrade 86± 2.7% and 58± 4.1% of PHN (200 ppm) at 20% and 30% NaCl concentration respectively. Co-metabolism with PHN thereby enhanced the degradation of HMW PAHs. In petroleum refinery wastewater the PAHs were potently degraded by the bacterial consortium with 94 ± 3.8% COD removal in a continuous stirred tank reactor. Ochrobactrum halosaudia strain AJH1, Ochrobactrum halosaudia strain AJH2 and Pseudomonas aeruginosa strain AJH3 were present in the PAH-degrading halothermophilic consortium.

Effective remediation of aged HMW-PAHs polluted agricultural soil by the combination of Fusarium sp. and smooth bromegrass (Bromus inermis Leyss.)

Fusarium sp. strain ZH-H2 is capable to degrade high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs), smooth bromegrass (Bromus inermis Leyss.) can also degrade 4- to 6-ring PAHs. Pot experiments were conducted to investigate how bromegrass and different inoculum sizes of ZH-H2 clean up HMW-PAHs in agricultural soil derived from a coal mine area. The results showed that, compared with control, different sizes of inocula of ZH-H2 effectively degraded HMW-PAHs, with removal rates of 19.01, 34.25 and 29.26% for 4-, 5- and 6-ring PAHs in the treatment with 1.0 g kg−1 ZH-H2 incubation after 90 d. After 5 mon of cultivation, bromegrass reached degradation rate of these compounds by 12.66, 36.26 and 36.24%, respectively. By adding strain ZH-H2 to bromegrass, HMW-PAHs degradation was further improved up to 4.24 times greater than bromegrass (W), in addition to the degradation rate of Bbf decrease. For removal rates of both 5- and 6-ring PAHs, addition of 0.5 g kg−1Fusarium ZH-H2 to pots with bromegrass performed better than addition of 0.1 g kg−1, while the highest concentration of 1.0 g kg−1Fusarium ZH-H2 did not further improve degradation. Degradation of 4-ring PAHs showed no significant difference among different ZH-H2 incubations with bromegrass treatments. We found that the degradation rates of 4-, 5- and 6-ring PAHs in all treatments are significantly correlated in a positive, linear manner with activity of lignin peroxidase (LiP) (r=0.8065, 0.9350 and 0.9165, respectively), while degradation of 5- and 6-ring PAHs is correlated to polyphenoloxidase (PPO) activity (r=0.7577 and 07806). Our findings suggest that the combination of Fusarium sp. ZH-H2 and bromegrass offers a suitable alternative for phytoremediation of aged PAH-contaminated soil in coal mining areas, with a recommended inoculation size of 0.5 g Fusarium sp. ZH-H2 per kg soil.

Biofilm and Planktonic Bacterial and Fungal Communities Transforming High-Molecular-Weight Polycyclic Aromatic Hydrocarbons.

High-molecular-weight polycyclic aromatic hydrocarbons (HMW-PAHs) are natural components of fossil fuels that are carcinogenic and persistent in the environment, particularly in oil sands process-affected water (OSPW). Their hydrophobicity and tendency to adsorb to organic matter result in low bioavailability and high recalcitrance to degradation. Despite the importance of microbes for environmental remediation, little is known about those involved in HMW-PAH transformations. Here, we investigated the transformation of HMW-PAHs using samples of OSPW and compared the bacterial and fungal community compositions attached to hydrophobic filters and in suspension. It was anticipated that the hydrophobic filters with sorbed HMW-PAHs would select for microbes that specialize in adhesion. Over 33 days, more pyrene was removed (75% ± 11.7%) than the five-ring PAHs benzo[a]pyrene (44% ± 13.6%) and benzo[b]fluoranthene (41% ± 12.6%). For both bacteria and fungi, the addition of PAHs led to a shift in community composition, but thereafter the major factor determining the fungal community composition was whether it was in the planktonic phase or attached to filters. In contrast, the major determinant of the bacterial community composition was the nature of the PAH serving as the carbon source. The main bacteria enriched by HMW-PAHs were Pseudomonas, Bacillus, and Microbacterium species. This report demonstrates that OSPW harbors microbial communities with the capacity to transform HMW-PAHs. Furthermore, the provision of suitable surfaces that encourage PAH sorption and microbial adhesion select for different fungal and bacterial species with the potential for HMW-PAH degradation.

Isolation and Investigation of Biodegradation Potential of Multiple Polycyclic Aromatic Hydrocarbons (PAHs) Degrading Marine Bacteria near Bhavnagar Coast, India

Present work deals with modified isolation methods for indigenous microorganisms with a capability to use both low molecular weight (LMW) and high molecular weight (HMW)PAHs, which are pervasive recalcitrant pollutants. Methods such as biphasic enrichment, and specific isolation methods has resulted in the isolation of organisms such as Sphingomonas, Pseudomonas, Mycobacterium, Achromobacter, and Streptomyces species with efficacy to degrade majority of LMW PAHs up to 85% after four days of experiments, which is substantially rapid rate of degradation attributed by microorganisms. Moreover, the organisms had shown up to 30% degradation of HMW PAHs within the same time frame, making the isolation strategies more credible. The study thus, holds prime importance of conquering the difficulties in the isolation of multiple hydrocarbons degrading microorganisms, which can be further applied for the successful application for bioremediation of hydrocarbon impacted environments.

Anaerobic biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons by a facultative anaerobe Pseudomonas sp. JP1.

Polycyclic aromatic hydrocarbons (PAHs) are harmful persistent organic pollutants, while the high-molecular-weight (HMW) PAHs are even more detrimental to the environment and human health. However, microbial anaerobic degradation of HMW PAHs has rarely been reported. One facultative anaerobe Pseudomonas sp. JP1 was isolated from Shantou Bay, Shantou, China, which could degrade a variety of HMW PAHs. After 40 days cultivation with strain JP1, anaerobic biodegradation rate of benzo[a]pyrene (BaP), fluoranthene, and phenanthrene was 30, 47, and 5 %, respectively. Consumption of nitrate as the electron acceptor was confirmed by N-(1-naphthyl) ethylenediamine spectrophotometry. Supplementation of sodium sulfite, maltose, or glycine, and in a salinity of 0-20 ‰ significantly stimulated anaerobic degradation of BaP. Lastly, the anaerobic degradation metabolites of BaP by strain JP1 were investigated using GC/MS, and the degradation pathway was proposed. This study is helpful for further studies on the mechanism of anaerobic biodegradation of PAHs.

Enhanced biodegradation of total polycyclic aromatic hydrocarbons (TPAHs) by marine halotolerant Achromobacter xylosoxidans using Triton X-100 and β-cyclodextrin – A microcosm approach

Ability of Achromobacter xylosoxidans, a chrysene degrading marine halotolerant bacterium to degrade polycyclic aromatic hydrocarbons (PAHs) using a cost effective laboratory microcosm approach, was investigated. Effect of variables as chrysene, glucose as a co-substrate, Triton X-100 as a non-ionic surfactant and β-cyclodextrin as a PAHs solubilizer was examined on degradation of low molecular weight (LMW) and high molecular weight (HMW) PAHs. A total of eleven PAHs detected from polluted saline soil were found to be degraded. Glucose, in combination with Triton X-100 and β-cyclodextrin resulted in 2.8 and 1.4-fold increase in degradation of LMW PAHs and 7.59 and 2.23-fold increase in degradation of HMW PAHs, respectively. Enhanced biodegradation of total PAHs (TPAHs) by amendments with Triton X-100 and β-cyclodextrin using Achromobacter xylosoxidans can prove to be promising approach for in situ bioremediation of marine sites contaminated with PAHs.

A novel P450-initiated biphasic process for sustainable biodegradation of benzo[a]pyrene in soil under nutrient-sufficient conditions by the white rot fungus Phanerochaete chrysosporium

High molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) such as benzo[a]pyrene (BaP) are resistant to biodegradation in soil. Conventionally, white rot fungus Phanerochaete chrysosporium has been investigated for HMW-PAH degradation in soil primarily using nutrient-deficient (ligninolytic) conditions, albeit with limited and non-sustainable biodegradation outcomes. In this study, we report development of an alternative novel biphasic process initiated under nutrient-sufficient (non-ligninolytic) culture conditions, by employing an advanced experimental design strategy. During the initial nutrient-sufficient non-ligninolytic phase (16 days), the process showed upregulation (3.6- and 22.3-fold, respectively) of two key PAH-oxidizing P450 monooxygenases pc2 (CYP63A2) and pah4 (CYP5136A3) and formation of typical P450-hydroxylated metabolite. This along with abrogation (84.9%) of BaP degradation activity in response to a P450-specific inhibitor implied key role of these monooxygenases. The subsequent phase triggered on continued incubation (to 25 days) switched the process from non-ligninolytic to ligninolytic resulting in a significantly higher net degradation (91.6% as against 67.4% in the control nutrient-limited set) of BaP with concomitant de novo ligninolytic enzyme expression making it a biphasic process yielding improved sustainable bioremediation of PAH-contaminated soil. To our knowledge this is the first report on development of such biphasic process for bioremediation application of a white rot fungus.

Substrate Specificity and Structural Characteristics of the Novel Rieske Nonheme Iron Aromatic Ring-Hydroxylating Oxygenases NidAB and NidA3B3 from Mycobacterium vanbaalenii PYR-1

The Rieske nonheme iron aromatic ring-hydroxylating oxygenases (RHOs) NidAB and NidA3B3 from Mycobacterium vanbaalenii PYR-1 have been implicated in the initial oxidation of high-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs), forming cis-dihydrodiols. To clarify how these two RHOs are functionally different with respect to the degradation of HMW PAHs, we investigated their substrate specificities to 13 representative aromatic substrates (toluene, m-xylene, phthalate, biphenyl, naphthalene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, benzo[a]pyrene, carbazole, and dibenzothiophene) by enzyme reconstitution studies of Escherichia coli. Both Nid systems were identified to be compatible with type V electron transport chain (ETC) components, consisting of a [3Fe-4S]-type ferredoxin and a glutathione reductase (GR)-type reductase. Metabolite profiles indicated that the Nid systems oxidize a wide range of aromatic hydrocarbon compounds, producing various isomeric dihydrodiol and phenolic compounds. NidAB and NidA3B3 showed the highest conversion rates for pyrene and fluoranthene, respectively, with high product regiospecificity, whereas other aromatic substrates were converted at relatively low regiospecificity. Structural characteristics of the active sites of the Nid systems were investigated and compared to those of other RHOs. The NidAB and NidA3B3 systems showed the largest substrate-binding pockets in the active sites, which satisfies spatial requirements for accepting HMW PAHs. Spatially conserved aromatic amino acids, Phe-Phe-Phe, in the substrate-binding pockets of the Nid systems appeared to play an important role in keeping aromatic substrates within the reactive distance from the iron atom, which allows each oxygen to attack the neighboring carbons.

Effects of enrichment with phthalate on polycyclic aromatic hydrocarbon biodegradation in contaminated soil

The effect of enrichment with phthalate on the biodegradation of polycyclic aromatic hydrocarbons (PAH) was tested with bioreactor-treated and untreated contaminated soil from a former manufactured gas plant (MGP) site. Soil samples that had been treated in a bioreactor and enriched with phthalate mineralized (14)C-labeled phenanthrene and pyrene to a greater extent than unenriched samples over a 22.5-h incubation, but did not stimulate benzo[a]pyrene mineralization. In contrast to the positive effects on (14)C-labeled phenanthrene and pyrene, no significant differences were found in the extent of biodegradation of native PAH when untreated contaminated soil was incubated with and without phthalate amendment. Denaturing-gradient gel electrophoresis (DGGE) profiles of bacterial 16S rRNA genes from unenriched and phthalate-enriched soil samples were substantially different, and clonal sequences matched to prominent DGGE bands revealed that beta-Proteobacteria related to Ralstonia were most highly enriched by phthalate addition. Quantitative real-time PCR analyses confirmed that, of previously determined PAH-degraders in the bioreactor, only Ralstonia-type organisms increased in response to enrichment, accounting for 89% of the additional bacterial 16S rRNA genes resulting from phthalate enrichment. These findings indicate that phthalate amendment of this particular PAH-contaminated soil did not significantly enrich for organisms associated with high molecular weight PAH degradation or have any significant effect on overall degradation of native PAH in the soil.

Initial characterization of new bacteria degrading high-molecular weight polycyclic aromatic hydrocarbons isolated from a 2-year enrichment in a two-liquid-phase culture system.

To characterize some polycyclic aromatic hydrocarbons (PAH)-degrading microorganisms isolated from an enriched consortium degrading high molecular weight (HMW) PAHs in a two-liquid-phase (TLP) soil slurry bioreactor, and to determine the effect of low molecular weight (LMW) PAH on their growth and HMW PAH-degrading activity. Several microorganisms were isolated from a HMW-PAH (pyrene, chrysene, benzo[a]pyrene and perylene) degrading consortium enriched in TLP cultures using silicone oil as the organic phase. From 16S rRNA analysis, four isolates were identified as Mycobacterium gilvum B1 (99% identity),Bacillus pumilus B44 (99% identity), Microbacterium esteraromaticum B21 (98% identity), and to the genus Porphyrobacter B51 (96% identity). The two latter isolates have not previously been associated with PAH degradation. Isolate B51 grew strongly in the interfacial fraction in the presence of naphthalene vapours and phenanthrene compared with cultures without LMW PAHs. Benzo[a]pyrene was degraded in cultures containing a HMW PAH mixture but pyrene had no effect on its degradation. The growth of isolates B1 and B21 was improved in the aqueous phase than in the interfacial fraction for cultures with naphthalene vapours. Pyrene was required for benzo[a]pyrene degradation by isolate B1. For isolate B21, pyrene and chrysene were degraded only in cultures without naphthalene vapours. Consortium enriched in a TLP culture is composed of microorganisms with different abilities to grow at the interface or in the aqueous phase according to the culture conditions and the PAH that are present. Naphthalene vapours increased the growth of the microorganisms in TLP cultures but did not stimulate the HMW PAH degradation. New HMW PAH-degrading microorganisms and a better understanding of the mechanisms involved in HMW PAH degradation in TLP cultures.