Polycyclic Aromatic Hydrocarbons Degradation Potential Research Articles

New insights in the biodegradation of high-cyclic polycyclic aromatic hydrocarbons with crude enzymes of Trametes versicolor

ABSTRACT High-cyclic polycyclic aromatic hydrocarbons (PAHs), with complex fused aromatic structures, are widespread, refractory and harmful in soil, but the current remediation technologies for high-cyclic PAHs are often inefficient and costly. This study focused on the biodegradation process of high-cyclic benzo[a]pyrene by Trametes versicolor crude enzymes. The crude enzymes exhibited high laccase activity (22112 U/L) and benzo[a]pyrene degradation efficiency (42.21%) within a short reaction time. Through the actual degradation and degradation kinetics, the degradation efficiency of PAHs decreased with the increase of aromatic rings. And the degradation conditions (temperature, pH, Cu2+ concentration, mediator) were systematically optimised. The optimum degradation conditions (1.5 mM Cu2+, 28℃ and pH 6) showed significant degradation efficiency for the low and medium concentrations of benzo[a]pyrene. In addition, complete degradation of benzo[a]pyrene could be achieved using only 0.2 mM of HBT mediator compared with crude enzymes alone. Collectively, these results showed the high-cyclic PAHs degradation potential of Trametes versicolor crude enzymes, and provided references to evaluate applicable prospects of white rot fungus crude enzymes in PAHs-contaminated soils.

Phylogeny and polycyclic aromatic hydrocarbons degradation potential of bacteria isolated from crude oil-contaminated soil in Diyarbakir, in the southeast of Turkey

In the present study, four indigenous bacteria designed as OACR6-OACR9 capable of degrading Polycyclic Aromatic Hydrocarbons (PAHs) were isolated from oil-contaminated soils in Diyarbakir city, in Turkey. 16S rRNA gene analysis revealed that strain OACR6 indicated 99.78% homology to Bacillus megaterium NBRC 15308 = ATCC 14581. OACR7, OACR8 and OACR9 strains were found to be members of the Sphingobacterium genus according to genetic analysis. It was observed that the OACR7 and OACR8 strains were 96.63% and 96.94% similar to Sphingobacterium multivorum strain IAM 14316, respectively. On the other hand, strain OACR9 indicated 96.79% homology to Sphingobacterium siyangense strain SY1 16S. GC-MS analyzing revealed that strain OACR6 was able to degrade 68.7% of fluorene and 69.8% of phenanthrene compared to the controls, strain OACR7 was able to degrade 67.5% of fluorene and 65.9% of phenanthrene, strain OACR8 was able to degrade 74.4% of fluorene and 76.4% of phenanthrene and strain OACR9 was found to be able to degrade 67.9% of fluorene and 69.8% of phenanthrene. The findings of this study indicate that the strains investigated have bioremediation potential at oil-contaminated sites and to our knowledge, this is the first study on the biodegradation of PAHs in the oil-contaminated areas in Diyarbakir.

Effects of Comamonas testosteroni on PAHs degradation and bacterial community structure in Leymus chinensis rhizosphere soil

To investigate the degradation of polycyclic aromatic hydrocarbons (PAHs) and the changes of rhizosphere microorganisms in the rhizosphere soil of Leymus chinensis during the remediation of PAHs contaminated soil by Comamonas testosteroni (C.t)-assisted Leymus chinensis, we evaluated the removal of PAHs in the rhizosphere of Leymus chinensis using gas chromatography-mass spectrometry (GC-MS), analyzed the bacterial community and the diversity in Leymus chinensis rhizosphere soil by high-throughput sequencing technology, characterized the correlation among PAHs degradation and bacterial community components performing redundancy analysis (RDA) and network analysis, and predicted PAHs degradation potential via PICRUSt software in this paper. The degradation of PAHs in the rhizosphere of Leymus chinensis was promoted, the abundance and diversity of bacteria and the correlation among bacteria and PAHs were changed, and the degradation potential of PAHs in Leymus chinensis rhizosphere soil was enhanced in the later stage of phytoremediation (60-120 d) due to the incorporation of C.t. The accelerated degradation of three PAHs (Nap, Phe, BaP) was accompanied by the differ abundance and correlation of Proteobacteria (Sphingomonas, MND1, Nordella), Actinomycetes (Rubrobacter, Gaiella), Acidobacteria (RB41) and Bacteroides (Flavobacterium) affected by C.t. The results provide new insight into the microorganism choices for microbial assisted plant remediation of soil PAHs and the mechanisms of enhanced PAHs degradation via the combination of Comamonas testosteroni engineering bacteria and plants.

Assessment of PAH degradation potential of native species from a coking plant through identifying of the beneficial bacterial community within the rhizosphere soil

Understanding the mechanisms underlying plant–rhizobacteria interactions in field-contaminated soils is crucial for designing effective rhizoremediation strategies. This study aimed to test the ability of four native herb species to remove polycyclic aromatic hydrocarbons (PAHs) and to analyze their associated bacterial community structures and functional genes within the rhizosphere from the abandoned site of a former Shenyang coking plant in China; the bulk soil was collected as control. All four species removed PAHs, of which the rhizosphere of Kochia scoparia had the highest PAH removal rate (almost 30.2%). Although the composition of the bacterial community within the rhizosphere varied among plant species, all plant species could promote the growth of Sphingomonas, Pedomicrobium, Rhodoplanes, Blastoccus, Mycobacterium, Devosia, and Pseudomonas, and their relative abundance positively correlated with the removal rates of PAHs, soil moisture, and total carbon/total nitrogen in the rhizosphere. Moreover, the activities of 1-aminocyclopropane-1 -carboxylic deaminase gene and Gram-negative ring-hydroxylating dioxygenase gene significantly (P < 0.05) increased compared with those in the control, and these activities had a strong positive correlation with the removal rates of PAHs [r = 0.759 (P < 0.01) and 0.87 (P < 0.01), respectively]. The findings of this study indicated that PAHs were the main factor driving the composition of beneficial bacteria in PAH rhizodegradation, and the PAH rhizoremediation of native plants grown in coking plant can be controlled though altering soil properties.

Hydroponic approach to assess rhizodegradation by sudangrass (Sorghum x drummondii) reveals pH- and plant age-dependent variability in bacterial degradation of polycyclic aromatic hydrocarbons (PAHs)

Rhizodegradation of polycyclic aromatic hydrocarbons (PAHs) is a product of complex interactions between plant and bacteria. In this study, hydroponic culture of sudangrass was established in order to investigate the effects of the plant on PAHs degradation and vice versa through changes in rhizosphere bacterial community. Results showed a plant-induced variability in PAHs degradation dependent on a characteristic shift in bacterial community, with pH and plant age as driving factors. Moreover, bacterial communities with high diversity seemed to abate the phytotoxic effects of PAHs degradation as observed in the plant’s gross health. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing revealed that regardless of plant age and culture conditions, the increase or decrease of Sphingobium sp. could dictate the PAHs degradation potential of the bacterial consortium. Overall, this study utilized hydroponic culture of sudangrass to show that plant even of same species can suppress, support, or enhance PAHs degradation of bacteria depending on specific factors.

Biodegradation of polycyclic aromatic hydrocarbons by native Ganoderma sp. strains: identification of metabolites and proposed degradation pathways.

Since polycyclic aromatic hydrocarbons (PAHs) are mutagenic, teratogenic, and carcinogenic, they are of considerable environmental concern. A biotechnological approach to remove such compounds from polluted ecosystems could be based on the use of white-rot fungi (WRF). The potential of well-adapted indigenous Ganoderma strains to degrade PAHs remains underexplored. Seven native Ganoderma sp. strains with capacity to produce high levels of laccase enzymes and to degrade synthetic dyes were investigated for their degradation potential of PAHs. The crude enzymatic extracts produced by Ganoderma strains differentially degraded the PAHs assayed (naphthalene 34-73%, phenanthrene 9-67%, fluorene 11-64%). Ganoderma sp. UH-M was the most promising strain for the degradation of PAHs without the addition of redox mediators. The PAH oxidation performed by the extracellular enzymes produced more polar and soluble metabolites such as benzoic acid, catechol, phthalic and protocatechuic acids, allowing us to propose degradation pathways of these PAHs. This is the first study in which breakdown intermediates and degradation pathways of PAHs by a native strain of Ganoderma genus were determined. The treatment of PAHs with the biomass of this fungal strain enhanced the degradation of the three PAHs. The laccase enzymes played an important role in the degradation of these compounds; however, the role of peroxidases cannot be excluded. Ganoderma sp. UH-M is a promising candidate for the bioremediation of ecosystems polluted with PAHs.

Linking initial soil bacterial diversity and polycyclic aromatic hydrocarbons (PAHs) degradation potential.

The aim of this study was to understand the role of indigenous soil microbial communities on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) and to determine whether PAHs degradation potential in soils may be evaluated by analysis of bacterial diversity and potential metabolisms using a metagenomics approach. Five different soils were artificially contaminated with seven selected PAHs and the most abundant bacterial taxa were assessed by sequencing the 16S rRNA gene, and linking them to PAH biodegradation efficiencies. A PICRUSt approach was then led to estimate the degradation potentials by metagenomics inference. Although the role of bacteria in PAHs degradation is not directly established here, the presence of a large number of bacteria belonging to the Betaproteobacteria class correlated to a higher degradation of LMW PAHs. A link with specific bacterial taxa was more difficult to establish concerning HMW PAHs, which seemed to require more complex mechanisms as shown by PICRUSt.

N-Hexadecane and pyrene biodegradation and metabolization by Rhodococcus sp. T1 isolated from oil contaminated soil

Abstract The high-molecular weight polycyclic aromatic hydrocarbons (PAHs) pyrene and typical long chain alkane n -hexadecane are both difficult to degrade. In this study, n -hexadecane and pyrene degrading strain Rhodococcus sp. T1 was isolated from oil contaminated soil. Strain T1 could remove 90.81% n -hexadecane (2 vol%) and 42.79% pyrene (200 mg·L − 1 ) as a single carbon within 5 days, respectively. Comparatively, the degradation of pyrene increased to 60.63%, but the degradation of n -hexadecane decreased to 87.55% when these compounds were mixed. Additionally, identification and analysis of degradation metabolites of Rhodococcus sp. T1 in the above experiments showed that there were significant changes in alanine, methylamine, citric acid and heptadecanoic acid between sole and dual substrate degradation. The optimal conditions for degradation were then determined based on analysis of the pH, salinity, additional nutrient sources and liquid surface activity. Under the optimal conditions of pH 7.0, 35 °C, 0.5% NaCl, 5 mg·L − 1 of yeast extract and 90 mg·L − 1 of surfactant, the degradation increased in single or dual carbon sources. To our knowledge, this is the first study to discuss metabolite changes in Rhodococcus sp. T1 using sole substrate and dual substrate to enhance the long-chain alkanes and PAHs degradation potential.

Phylogeny and polycyclic aromatic hydrocarbons degradation potential of bacteria isolated from crude oil-contaminated site

ABSTRACTThis study employed the use of 16S rRNA gene sequence analysis to identify three of four native bacterial strains isolated from crude oil-contaminated site in Poza Rica, Veracruz, Mexico. The identified bacteria were Ochrobactrum intermedium, Pandoraea pnomenusa and Ochrobactrum sp., but SA2-09 strain was not identified. The ability of the isolates to degrade polycyclic aromatic hydrocarbons (PAHs) was evaluated at 31.61 and 54.52 mg/kg PAHs in soil, when used as crude oil in soil microcosm during 80 days of incubation at 30°C. The results demonstrated that O. intermedium biodegraded many PAHs, including the high molecular weight (HMW) PAHs fluoranthene (100% equivalent 0.24 mg/kg), benzo [b] fluoranthene (81.8% equal 0.18 mg/kg), Benzo[a]pyrene (87.0%, 0.20 mg/kg) and Benzo[g,h,i]perylene (52.7%, 0.39 mg/kg). P. pnomenusa had a degradation profile of HMW PAHs, which was similar to O. intermedium, while Ochrobactrum sp. and the strain SA-09 exhibited lower degradation rates of HMW.

Reconstructed metagenomes reveal changes of microbial functional profiling during PAHs degradation along a rice (Oryza sativa) rhizosphere gradient.

The response of microbial metagenome to polycyclic aromatic hydrocarbons (PAHs) degradation in the rice rhizosphere remains poorly understood. We investigated the spatial and temporal variations of microbial communities and reconstructed metagenomes along the rice rhizosphere gradient during PAHs degradation. The experiment was performed in rhizoboxes, in which the rhizosphere region was divided into five 1-mm thick layers. Based on denaturant gradient gel electrophoresis profiling and sequencing of bacterial and archaeal 16S rRNA genes, predicted metagenomes were reconstructed. The microbial communities in the rice rhizosphere were influenced by the PAHs concentration and distance from the root surface during PAHs degradation. Correlation network analysis showed that archaea played an important role in PAHs degradation. Predicted metagenomes can be clustered into two groups with high and low PAHs degrading potential, respectively. The relative abundance of genes for defense mechanisms, replication, recombination and reparation was significantly higher in samples with high PAHs degrading potentials. The relative abundance of the dioxygenase gene was greater near the root surface of the rice. However, the abundance of aldolase and dehydrogenase was constant in rhizosphere soils at different distances from the root surface. Distance from root surface and PAH concentrations affected the microbial communities and metagenomes in rice rhizosphere. The abundance of dioxygenase genes relating to PAH degradation in metagenomes mirrored the PAH degradation potential in rice rhizosphere. Our findings suggested that the predicted metagenomes reconstructed from 16S rRNA marker gene sequences provide further insights into the spatial variation and dynamics of microbial functioning that occur during bioremediation.

On the Suitability of a Bacterial Consortium To Implement a Continuous PAHs Biodegradation Process in a Stirred Tank Bioreactor

A new microbial consortium made up with two bacterial strains phylogenetically identified as Bacillus pumilus and Staphylococcus warneri was obtained from lab soils polluted with polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Its PAH degradation potential has been demonstrated recently by culturing the consortium in the presence of phenanthrene (PHE), pyrene (PYR), and benzoanthracene (BaA). The efficiency of the proposed degradation process was evaluated at flask and bioreactor scale, operating in fed-batch mode, as a prior step to achieve an effective biodegradation process in continuous mode. An acclimation of the consortium to the selected PAHs has been evidenced in fed-batch cultures after 6 batches (90% of degradation in less than one day). The effect of the dilution rate was analyzed in a continuous stirred tank bioreactor operating for 2 months, observing that some of the dilution rates employed allowed achieving degradation rates higher than 90% per day for all the contaminants.

Anaerobic PAH degradation in soil by a mixed bacterial consortium under denitrifying conditions

Polycyclic aromatic hydrocarbons (PAHs) are one of the main classes of contaminants in the terrestrial environment. Concentrations of biphenyl, fluorene, phenanthrene and pyrene were added to soil samples in order to investigate the anaerobic degradation potential of PAHs under denitrifying conditions. A mixed population of microorganisms obtained from a paddy soil was incubated for 20 days in anaerobic conditions in the presence of soil alone or with nitrate, adding, as electron donors, PAHs and, in some samples, glucose or acetate. At regular time intervals oxidation–reduction potential, PAHs concentration, microbial ATP and nitrate concentration into the solution were measured. Degradation trends for each hydrocarbon are similar under all conditions, indicating that the molecular conformation prevails over other parameters in controlling the degradation. Poor degradation results were obtained when PAHs were the only organic matter available for the inoculum, thus confirming the recalcitrance to degradation of these compounds. Biodegradation was influenced by the addition of other carbon sources. As better degradation results were generally obtained when acetate or glucose were added, the hypothesis of a co-metabolic enhancement of PAH biodegradation seems likely. Thus, anaerobic biodegradation of PAHs studied, biphenyl, fluorene, phenanthrene and pyrene, seems to be possible both through fermentative and respiratory metabolism, provided that low molecular weight co-metabolites and suitable electron acceptors (nitrate) are present.

CHARACTERISTICS OF PAHS INTRINSIC DEGRADATION IN TWO COKE FACTORY SOILS

Polycyclic aromatic hydrocarbons (PAHs) are the most commonly found pollutants in former coke site grounds. These organic pollutants are particularly a concern because of their possible toxic, carcinogenic or mutagenic properties. Biodegradation is one possible pathway for PAHs elimination from soils. This study aims to evaluate intrinsic degradation potential of PAHs in soils taken from two former coke sites, differing by their contamination levels and by their physico-chemical characteristics (organic carbon and metal contents).PAHs biodegradation kinetics as observed in both soil types distinguishes between two steps: a first step showing a rapid but short PAHs abiotic degradation, followed by a second step which is characterized by a much slower PAHs decrease pattern, progressively smoothing along time. These patterns lead to a significant decrease in the bulk PAHs content of 35% and 46% respectively for site 1 and site 2 soils after 12 months. In this experiment, PAHs degradation seems to be altered neither by the conditions of the medium (availability of carbon, phosphorus, nitrogen, moisture, oxygen …), nor by any decrease in bacterial degrading activity, but rather by lack of PAHs' bioavailability and recalcitrance of some degradation products. If the occurrence of metals and organic carbon does not alter the bulk yield of PAHs' degradation, it does modify the degradation pattern, insofar as bacterial processes seem to need longer to set when metals and organic carbon are present in higher amounts.