Biodegradation Of Polychlorinated Biphenyls Research Articles

A comparison of microbial diversity, distribution patterns, and halogenated aromatics biodegrading genes in sediments of two urban rivers

Urban river sediments often serve as reservoirs of halogenated aromatic pollutants, such as polychlorinated biphenyls (PCBs), leading to significantly alterations in the biological characteristics of this ecosystem. Various microbes can degrade halogenated aromatics, serving as a crucial detoxification mechanism that converts toxic pollutants into common metabolites to complete the carbon cycle. However, the impact of PCBs on the diversity and structure of microbial communities in urban rivers has remained largely unexplored. Understanding the dynamics of microbial community structure and function is essential for unraveling biodegradation pathways and interactions of these microbial degraders in PCB-contaminated urban river sediments. In this study, a thorough analysis of microbial diversity and distribution patterns was conducted using 16S rRNA gene-based sequencing in the sediments of two urban rivers, the Dasha River and Maozhou River. Our results unveiled distinct community variances between the two rivers, primarily influenced by environmental factors. The detailed composition and abundance of halogenated aromatic biodegradation related genes were elucidated using metagenomics, mainly contributed by Proteobacteria, Desulfobacterota, and Chloroflexi. Network analysis revealed close interactions among these microbes within each river, indicating a cooperative propensity for PCBs biodegradation, which underscores the interactions as the mode of metabolism and common survival strategy in contaminated rivers.

Black Carbon Impacts on Paraburkholderia xenovorans Strain LB400 Cell Enrichment and Activity: Implications toward Lower-Chlorinated Polychlorinated Biphenyls Biodegradation Potential.

Volatilization of lower-chlorinated polychlorinated biphenyls (LC-PCBs) from sediment poses health threats to nearby communities and ecosystems. Biodegradation combined with black carbon (BC) materials is an emerging bioaugmentation approach to remove PCBs from sediment, but development of aerobic biofilms on BC for long-term, sustained LC-PCBs remediation is poorly understood. This work aimed to characterize the cell enrichment and activity of biphenyl- and benzoate-grown Paraburkholderia xenovorans strain LB400 on various BCs. Biphenyl dioxygenase gene (bphA) abundance on four BC types demonstrated corn kernel biochar hosted at least 4 orders of magnitude more attached cells per gram than other feedstocks, and microscopic imaging revealed the attached live cell fraction was >1.5× more on corn kernel biochar than GAC. BC characteristics (i.e., sorption potential, pore size, pH) appear to contribute to cell attachment differences. Reverse transcription qPCR indicated that BC feedstocks significantly influenced bphA expression in attached cells. The bphA transcript-per-gene ratio of attached cells was >10-fold more than suspended cells, confirmed by transcriptomics. RNA-seq also demonstrated significant upregulation of biphenyl and benzoate degradation pathways on attached cells, as well as revealing biofilm formation potential/cell-cell communication pathways. These novel findings demonstrate aerobic PCB-degrading cell abundance and activity could be tuned by adjusting BC feedstocks/attributes to improve LC-PCBs biodegradation potential.

Unveiling the PCB biodegradation potential and stress survival strategies of resuscitated strain Pseudomonas sp. HR1

The exploration of resuscitated strains, facilitated by the resuscitation promoting factor (Rpf), has substantially expanded the pool of cultivated degraders, enhancing the screening of bio-inoculants for bioremediation applications. However, it remains unknown whether these resuscitated strains can re-enter the viable but non-culturable (VBNC) state and the specific stress conditions that trigger such a transition. In this work, the whole genome, and polychlorinated biphenyl (PCB)-degrading capabilities of a resuscitated strain HR1, were investigated. Notably, the focus of this exploration was on elucidating whether HR1 would undergo a transition into the VBNC state when exposed to low temperature and PCBs, with and without the presence of heavy metals (HMs). The results suggested that the resuscitated strain Pseudomonas sp. HR1 harbored various functional genes related to xenobiotic biodegradation, demonstrating remarkable efficiency in Aroclor 1242 degradation and strong resistance against stress induced by low temperature and PCBs. Nevertheless, when exposed to the combined stress of low temperature, PCBs, and HMs, HR1 underwent a transition into the VBNC state. This transition was characterized by significant decreases in enzyme activities and notable changes in both morphological and physiological traits when compared to normal cells. Gene expression analysis revealed molecular shifts underlying the VBNC state, with down-regulated genes showed differential expression across multiple pathways and functions, including oxidative phosphorylation, glycolysis, tricarboxylic acid cycle, amino acid metabolism, translation and cytoplasm, while up-regulated genes predominantly associated with transcription regulation, membrane function, quorum sensing, and transporter activity. These findings highlighted the great potential of resuscitated strains as bio-inoculants in bioaugmentation and shed light on the survival mechanisms of functional strains under stressful conditions, which should be carefully considered during bioremediation processes.

Strategy for Remediation of Polychlorinated Biphenyls-Contaminated Soil Through Redox Management Based on Electronegativity of the Contaminants.

Literature review reveals that Persistent Organic Pollutants (POPs), such as polychlorinated biphenyls (PCBs), are electron deficient compounds due to the presence of highly electronegative groups. Hence, they are more amenable to anaerobic biodegradation rather than oxidative metabolism. However, the studies on PCBs bioremediation are more inclined towards aerobic treatment. Besides, the past studies are mainly centered on screening and application of PCB-degrading microorganisms. In our opinion the degradative capacity is already present in the native microflora, and choice of electron donor is of paramount importance for faster reductive metabolism of PCBs. In this study, the use of methanol as electron donor with cow dung as the general microbial inoculum resulted in high specific rate of degradation (0.0542-0.0637 /day) for high-chlorinated biphenyls. The % removal of PCBs ranged between 67.7 and 71.7%. It may be the first study on the application of methanol as a cheap electron donor for PCBs biodegradation without bioaugmentation with specifically selected microorganisms.

Lab-scale biodegradation assay using passive samplers to determine microorganisms’ ability to reduce polychlorinated biphenyl (PCB) volatilization from contaminated sediment

Many PCB-degrading aerobes have been identified which may serve as bioaugmentation strains for aerobic, in situ bioremediation or in combination with dredging operations. The present work describes a lab-scale PCB biodegradation assay which can be used to screen potential bioaugmentation strains or consortia for their ability to decrease PCB mass flux from contaminated sediment to air through biodegradation of freely dissolved PCBs that have desorbed from sediment particles. The assay uses two types of passive samplers to simultaneously measure PCB mass that is freely dissolved in aqueous solution and PCB mass that has volatilized to the headspace of the bioreactor. Using this approach, relative comparisons of PCB mass accumulated in passive samplers between bioaugmented treatments and controls allow for practical assessment of a microbial strain's ability to reduce both freely dissolved and vapor phase PCB concentrations. The method is designed to be conducted using aliquots of homogenized, well-characterized, PCB-contaminated sediment gathered from a field site. This work details the experimental design methodology, required materials, bioreactor set-up, passive sampling, PCB-extraction, sample cleanup, and quantification protocols such that the biodegradation assay can be conducted or replicated. A step-by-step protocol is also included and annotated with photos, tips, and tricks from experienced analysts.•Relative comparisons of PCB mass accumulated in passive samplers between experimental treatments and controls allow for practical assessment of bioaugmentation strain's ability to reduce both freely dissolved and vapor phase PCB concentrations•Passive sampler preparation, deployment, PCB-extraction, cleanup procedures, and quantification are detailed step-by-step and annotated by experienced analysts

Myco- and phyco-remediation of polychlorinated biphenyls in the environment: a review.

Polychlorinated biphenyls (PCBs) are toxic organic compounds and pose serious threats to environment and public health. PCBs still exist in different environments such as air, water, soil, and sediments even on ban. This review summarizes the phyco- and myco-remediation technologies developed to detoxify the PCB-polluted sites. It was found that algae mostly use bioaccumulation to biodegradation strategies to reclaim the environment. As bio-accumulator, Ulva rigida C. Agardh has been best at 25ng/g dry wt to remove PCBs. Evidently, Anabaena PD-1 is the only known PCB degrading alga and efficiently degrade Aroclor 1254 and dioxin-like PCBs up to 84.4% and 37.4% to 68.4%, respectively. The review suggested that factors such as choice of algal strains, response of microalgae, biomass, the rate of growth, and cost-effective cultivation conditions significantly influence the remediation of PCBs. Furthermore, the Anabaena sp. linA gene of Pseudomonas paucimobilis Holmes UT26 showed enhanced efficiency. Pleurotus ostreatus (Jacq.) P. Kumm is the most efficient PCB degrading fungus, degrading up to 98.4% and 99.6% of PCB in complex and mineral media, respectively. Combine metabolic activities of bacteria and yeast led to the higher detoxification of PCBs. Fungi-algae consortia would be a promising approach in remediation of PCBs. A critical analysis on potentials and limits of PCB treatment through fungal and algal biosystems have been reviewed, and thus, new insights have emerged for possible bioremediation, bioaccumulation, and biodegradation of PCBs.

DNA stable isotope probing on soil treated by plant biostimulation and flooding revealed the bacterial communities involved in PCB degradation

Polychlorinated biphenyl (PCB)-contaminated soils represent a major treat for ecosystems health. Plant biostimulation of autochthonous microbial PCB degraders is a way to restore polluted sites where traditional remediation techniques are not sustainable, though its success requires the understanding of site-specific plant–microbe interactions. In an historical PCB contaminated soil, we applied DNA stable isotope probing (SIP) using 13C-labeled 4-chlorobiphenyl (4-CB) and 16S rRNA MiSeq amplicon sequencing to determine how the structure of total and PCB-degrading bacterial populations were affected by different treatments: biostimulation with Phalaris arundinacea subjected (PhalRed) or not (Phal) to a redox cycle and the non-planted controls (Bulk and BulkRed). Phal soils hosted the most diverse community and plant biostimulation induced an enrichment of Actinobacteria. Mineralization of 4-CB in SIP microcosms varied between 10% in Bulk and 39% in PhalRed soil. The most abundant taxa deriving carbon from PCB were Betaproteobacteria and Actinobacteria. Comamonadaceae was the family most represented in Phal soils, Rhodocyclaceae and Nocardiaceae in non-planted soils. Planted soils subjected to redox cycle enriched PCB degraders affiliated to Pseudonocardiaceae, Micromonosporaceae and Nocardioidaceae. Overall, we demonstrated different responses of soil bacterial taxa to specific rhizoremediation treatments and we provided new insights into the populations active in PCB biodegradation.

Aerobic Bioaugmentation to Decrease Polychlorinated Biphenyl (PCB) Emissions from Contaminated Sediments to Air.

We conducted experiments to determine whether bioaugmentation with aerobic, polychlorinated biphenyl (PCB)-degrading microorganisms can mitigate polychlorinated biphenyl (PCB) emissions from contaminated sediment to air. Paraburkholderia xenovorans strain LB400 was added to bioreactors containing PCB-contaminated site sediment. PCB mass in both the headspace and aqueous bioreactor compartments was measured using passive samplers over 35 days. Time-series measurements of all 209 PCB congeners revealed a 57% decrease in total PCB mass accumulated in the vapor phase of bioaugmented treatments relative to non-bioaugmented controls, on average. A comparative congener-specific analysis revealed preferential biodegradation of lower-chlorinated PCBs (LC-PCBs) by LB400. Release of the most abundant congener (PCB 4 [2,2′-dichlorobiphenyl]) decreased by over 90%. Simulations with a PCB reactive transport model closely aligned with experimental observations. We also evaluated the effect of the phytogenic biosurfactant, saponin, on PCB bioavailability and biodegradation by LB400. Time-series qPCR measurements of biphenyl dioxygenase (bphA) genes showed that saponin better maintained bphA abundance, compared to the saponin-free treatment. These findings indicate that an active population of bioaugmented, aerobic PCB-degrading microorganisms can effectively lower PCB emissions and may therefore contribute to minimizing PCB inhalation exposure in communities surrounding PCB-contaminated sites.

PCB-77 biodegradation potential of biosurfactant producing bacterial isolates recovered from contaminated soil.

Polychlorinated biphenyls (PCBs) are persistent organic pollutants widely distributed in the environment and possess deleterious health effects. The main objective of the study was to obtain bacterial isolates from PCB-contaminated soil for enhanced biodegradation of PCB-77. Selective enrichment resulted in the isolation of 33 strains of PCB-contaminated soil nearby Bhilai steel plant, Chhattisgarh, India. Based on the prominent growth using biphenyl as the sole carbon source and the confirmation of its degradation by GC-MS/MS analysis, four isolates were selected for further study. The isolates identified by 16S rRNA gene sequencing were Pseudomonas aeruginosa MAPB-2, Pseudomonas plecoglossicida MAPB-6, Brucella anthropi MAPB-9, and Priestia megaterium MAPB-27. The isolate MAPB-9 showed a degradation of 66.15% biphenyl, while MAPB-2, MAPB-6, and MAPB-27 showed a degradation of 62.06, 57.02, and 56.55%, respectively in 48 h. Additionally, the degradation ability of these strains was enhanced with addition of co-metabolite glucose (0.2%) in the culture medium. Addition of glucose showed 100% degradation of biphenyl by MAPB-9, in 48 h, while MAPB-6, MAPB-2, and MAPB-27 showed 97.1, 67.5, and 53.3% degradation, respectively as analyzed by GC-MS/MS. Furthermore, in the presence of inducer, PCB-77 was found to be 59.89, 30.49, 27.19, and 4.43% degraded by MAPB-6, MAPB-9, MAPB-2, and MAPB-27, respectively in 7 d. The production of biosurfactants that aid in biodegradation process were observed in all the isolates. This was confirmed by ATR-FTIR analysis that showed the presence of major functional groups (CH2, CH3, CH, = CH2, C–O–C, C-O) of the biosurfactant. The biosurfactants were further identified by HPTLC and GC-MS/MS analysis. Present study is the first to report PCB-77 degradation potential of Pseudomonas aeruginosa, B. anthropi, Pseudomonas plecoglossicida, and Priestia megaterium. Similarly, this is the first report on Pseudomonas plecoglossicida and Priestia megaterium for PCB biodegradation. Our results suggest that the above isolates can be used for the biodegradation of biphenyl and PCB-77 in PCB-contaminated soil.

Metagenomes, Metagenome-Assembled Genomes, and Metatranscriptomes from Polychlorinated Biphenyl-Contaminated Sediment Microcosms.

ABSTRACTWe present a comprehensive data set that describes an anaerobic microbial consortium native to polychlorinated biphenyl (PCB)-contaminated sediments. Obtained from sediment microcosms incubated for 200 days, the data set includes 4 metagenomes, 4 metatranscriptomes (in duplicate), and 62 metagenome-assembled genomes and captures microbial community interactions, structure, and function relevant to anaerobic PCB biodegradation.

Isolation and genomic characterization of Klebsiella Lw3 with polychlorinated biphenyl degradability

ABSTRACT Bioremediation of sediment organic pollution has been intensely investigated, but the degradation of complex organic compounds, pesticide residues, and polychlorinated biphenyls (PCBs) remains poorly studied. In this study, sediments were collected from Zhanjiang Mangrove Reserve and inoculated in an inorganic salt medium using only biphenyl (BP) and PCBs as the carbon sources to obtain a PCB-degrading strain. A gram-negative bacterium that metabolized PCBs was isolated and identified as Klebsiella Lw3 by 16S rDNA phylogenetic analysis. Genomic sequencing showed that this bacterium possessed genes related to BP/PCB degradation, and its GC content was 58.2%; we identified 3326 cellular pathways. Gas chromatography–mass spectrometry was employed to test the PCB degrading ability; the results showed that the strain had a good degradation effect on PCB3 at concentrations of 5, 10, 20, 40, and 60 mg/L and that the final degradation rate was higher than 97% after 96 h. Interestingly, this strain showed good biodegradability of PCBs despite having no classical PCB degradation pathway, providing a new direction for Klebsiella research with practical significance for in situ bioremediation of PCB contamination. Overall, this study provides valuable insights into the genetic structure of PCB-degrading strains as well as eco-friendly and low-cost PCB degradation and lays a foundation for the discovery of new degradation pathways.

Microbial dechlorination of polychrolinated biphenyls

Polychlorinated biphenyls (PCBs) are organic xenobiotics contaminating environment for at least 50 years. They could be eventually eliminated by various organisms under different conditions. The degree of chlorine substitution per biphenyl molecule influences biodegradability which decreases with increasing chlorination. Our work is focused on the PCBs biodegradation under anaerobic conditions. The suitable high chlorinated biphenyls are converted via reductive dechlorination to the chlorinated biphenyls with lower extent of chlorine, which could be eventually fully mineralized by aerobic bacteria. Microbial consortium was isolated from sediment of Strážský Creek (located near by plant producing PCBs in the past). This consortium was able to dechlorinate polychlorinated biphenyls under anoxic conditions. The effectiveness of this process was tested under different cultivation condition – different energetic sources (Aroclor 1248 or Aroclor 1260 or Delor 103 or Delor 106), addition of potential electron donors (pyruvate, lactate or acetate with hydrogen) and further if there is necessary to add yeast extract into fresh low sulphur cultivation media.
 Our microbial consortia so far do not need supplementation by non-contaminated sediment to maintain dechlorination activity. Addition of yeast extract is non essential, but needs to be further proved in serial transfers. In all cases (except acetate without yeast extract) dechlorination proceeds at meta- and flanked paraposition.

Mechanism analysis of the phytotoxicity and phytodegradation of PCBs based on the 2D-QASR model and sensitivity analysis method

The phytotoxicity of polychlorinated biphenyls (PCBs) permanently affects the ability of plants to remediate contaminated soil. The biodegradability of PCBs in plants directly represents the effectiveness of plants to remediate contaminated soil. This paper investigates the mechanisms that affect the phytotoxicity and phytodegradation of PCBs. Besides, the corresponding improvement measures have been proposed here, which provides a theoretical basis for the research on enhanced phytoremediation of PCBs contaminated soil. The structural parameters that significantly affect the phytotoxicity and phytodegradation of PCBs have been screened by 2D-QASR models combined with sensitivity analysis method. Finally, the main parameters are regulated following a molecular dynamics approach to analyze the mitigation of the phytotoxicity of PCBs and enhancement measures of biodegradability in plants. The result shows that the 2D-QSAR model constructed in this paper meets the stability requirements. The structural parameters that significantly affect the phytotoxicity of PCBs include EHOMO, ELUMO and EG, respectively. The three structural parameters that significantly affect the biodegradability of PCBs in plants are logP, TE and IR-(C-CL)svf, respectively. According to the results of molecular dynamics verification, the addition of redox substances can mitigate the phytotoxicity of PCBs. The addition of substances that promote the affinity between PCBs and degradation enzymes can improve the biodegradability of PCBs in plants.

Comparative study of single cultures and a consortium of white rot fungi for polychlorinated biphenyls treatment.

To evaluate the mycoremediation of polychlorinated biphenyls (PCBs) by either single cultures or binary consortia of Pleurotus pulmonarius LBM 105 and Trametes sanguinea LBM 023. PCBs tolerance, removal capacity, toxicity reduction and ligninolytic enzyme expression were assessed when growing single culture and binary consortium of fungus in 217mgl-1 of a technical mixture of Aroclor 1242, 1254 and 1260 in transformer oil. A decrease in tolerance and variation in ligninolytic enzyme secretion were observed in PCB-amended solid media. Pleurotus pulmonarius LBM 105 mono-culture was able to remove up to 95·4% of PCBs, whereas binary consortium and T. sanguinea LBM 023 could biodegrade about 55% after 24days. Significant detoxification levels were detected in all treatments by biosorption mechanism. Pleurotus pulmonarius LBM 105 in single culture had the best performance regarding PCBs biodegradation and toxicity reduction. Ligninolytic enzyme secretion changed in co-culture. The evaluation of PCBs bioremediation effectiveness of basidiomycetes consortium in terms of PCB removal, toxicity and ligninolytic enzyme production to unravel the differences between using individual cultures or consortium has not been reported. The results from this study enable the selection of P. pulmonarius LBM 105 mono-culture to bioremediate PCBs as it showed higher efficiency compared to binary consortium with T. sanguinea LBM 023 for potential decontamination of PCB-contaminated transformer oil.

Potential use of Impatiens balsamina L. for bioremediation of lead and polychlorinated biphenyl contaminated soils

AbstractIn recent years, due to the improper dismantling of electronic waste (e‐waste) in China, high levels of lead (Pb) and polychlorinated biphenyls (PCBs) have been released into the environment, which posed potential health risks to residents, especially to children. A pot‐culture experiment was carried out to evaluate the phytoremediation potential of PCBs and Pb co‐contaminated soil by the use of Impatiens balsamina L. The results indicated that PCBs and Pb had negative effect on plant growth, while the presence of PCBs partially alleviated Pb toxicity to I. balsamina. The existence of PCBs showed nonsignificant effects on Pb uptake by I. balsamina. However, the presence of PCBs influenced the distribution of Pb among plant tissues. The order of Pb accumulation in tissues was roots > stems > leaves, indicating the plant may be suitable for the phytostabilization of Pb in soil. The degradation rates of PCB 18 (25–68%) and PCB 28 (14–61%) in the planted soil was significantly higher than that in the unplanted soil, which confirmed the vegetation is beneficial for the biodegradation of PCBs in soils. Plant–microbial consortia in the rhizosphere make a predominant contribution to PCBs dissipation in the co‐contaminated soil. Significant differences in microbial taxonomic composition between the contaminated soils and a blank control were observed. I. balsamina could have the potential for remediating PCBs and lead co‐contaminated soils, even though further field studies are still required.

Screening and metabolic potential of fungal strains isolated from contaminated soil and sediment in the polychlorinated biphenyl degradation

Polychlorinated biphenyls (PCBs) are widespread persistent pollutants deleterious for environment and very dangerous for human kind. As the bioremediation of PCB polluted sites by model white-rot fungi is still unsatisfactory, the use of efficient native strains which have the natural capacity to develop on polluted sites may constitute a relevant alternative strategy. In this study, we isolated 12 fungal strains from PCB contaminated soil and sediment, improved the screening method to obtain the most efficient ones in biodegradation and detoxification of PCBs and characterized potential underlying enzymatic activities. Four strains Penicillium chrysogenum, P. citreosulfuratum, P. canescens and Aspergillus jensenii, showed remarkable biodegradation capacities, greater than 70%. The remaining PCB-toxicity of their culture, including that of Trametes versicolor and Acremonium sclerotigenum, which present interesting ecological and metabolic properties, was studied. Only P. canescens was able to significantly reduce the toxicity related to PCBs and their metabolites. The enzymatic activities induced by PCBs were different according to the strains, namely laccases in T. versicolor and peroxidases in Ac. sclerotigenum. Our promising results show that the use of native fungal strains can constitute an effective strategy in the depollution of PCB polluted sites.

Enhancement of polychlorinated biphenyl biodegradation by resuscitation promoting factor (Rpf) and Rpf-responsive bacterial community

The activities of indigenous bacterial communities in polychlorinated biphenyls (PCBs) contaminated environments is closely related to the efficiency of bioremediation processes. Using resuscitation promoting factor (Rpf) from Micrococcus luteus is a promising method for resuscitation and stimulation of functional bacterial populations under stressful conditions. This study aims to use the Rpf to accelerate the biodegradation of Aroclor 1242, and explore putative PCB degraders which were resuscitated by Rpf addition. The Rpf-responsive bacterial populations were investigated using culture-dependent and culture-independent approaches, respectively. The results confirm that Rpf was capable of enhancing PCB degradation of enriched cultures from PCB-contaminated soils, and improving the activities of cultures with low tolerance to PCBs. High-throughput 16S rRNA analysis displays that the Rpf greatly altered the composition and abundance of bacterial populations in the phylum Proteobacteria. Identification of the resuscitated strains further suggests that the Rpf-responsive population was mostly represented by Sphingomonas and Pseudomonas, which are most likely the key PCB-degraders for enhanced biodegradation of PCBs.

Recent advances in the biodegradation of polychlorinated biphenyls.

Polychlorinated biphenyls (PCBs) are typical lasting organic pollutants. Persistence and recalcitrance to biodegradation of PCBs have hampered the transformation of PCB congeners from the environment. Biological transformation of polychlorinated biphenyls could take place through anaerobic dechlorination, aerobic microbial degradation, and a combination of transformation of anaerobic dechlorination and aerobic degradation. Under anaerobic conditions, microbial dechlorination is an important degradation mode for PCBs, especially high-chlorinated congeners. The low-chlorinated compounds formed after reductive dechlorination could be further aerobically degraded and completely mineralized. This paper reviews the recent advances in biological degradation of PCBs, introduces the functional bacteria and enzymes involved in the anaerobic and aerobic degradation of PCBs, and discusses the synergistic action of anaerobic reduction and aerobic degradation. In addition, the different ways to the microbial remediation of PCBs-contaminated environments are discussed. This review provides a theoretical foundation and practical basis to use PCBs-degrading microorganisms for bioremediation.

A new dataset of PCB half-lives in soil: Effect of plant species and organic carbon addition on biodegradation rates in a weathered contaminated soil

This paper presents a new dataset of Polychlorinated Biphenyls (PCBs) half-lives in soil. Data were obtained from a greenhouse experiment performed with an aged contaminated soil under semi-field conditions, collected from a National Relevance Site (SIN) located in Northern Italy (SIN Brescia-Caffaro). Ten different treatments (combination of seven plant species and different soil conditions) were considered together with the respective controls (soil without plants). PCB concentration reduction in soil was measured over a period of 18 months to evaluate the ability of plants to stimulate the biodegradation of these compounds. Tall fescue, tall fescue cultivated together with pumpkin and tall fescue amended with compost reduced more than the 50% of the 79 measured PCB congeners, including the most chlorinated ones (octa to deca-PCBs). However, the data obtained showed that no plant species was uniquely responsible for the effective degradation of all isomeric classes and congeners. The obtained half-lives ranged from 1.3 to 5.6 years and were up to a factor of 8 lower compared to generic HL values reported in literature. This highlighted the importance of cultivation and plant-microbe interactions in speeding up the PCB biodegradation. This new dataset could contribute to substantially improve the predictions of soil remediation time, multimedia fate and the long-range transport of PCBs. Additionally, the half-lives obtained here can also be used in the evaluation of the food chain transfer of these chemicals, and finally the exposure and potential for effects on ecosystems.

Exploring bacterial community structure and function associated with polychlorinated biphenyl biodegradation in two hydrogen-amended soils

Hydrogen (H2) is a universal energy source supplying survival energy for numerous microbial functions. Diffusive fluxes of H2 released by rhizobacterial symbiont nodules in which H2 is an obligate by-product of dinitrogen fixation may act as an additional energy input shaping microbial community structure and function in soils. However, the effects of H2 at the soil-nodule interface on soil contaminant degradation processes are poorly understood. Here, we mimicked the hydrogen conditions present at the soil-nodule interface (10,000 ppmv) to test the impact of elevated H2 concentrations on soil microbial removal of 3, 3′, 4, 4′-tetrachlorobiphenyl (PCB77) and examined the associated bacterial communities and their functions by conducting a microcosm experiment using two different soil types at three PCB contamination levels (0.5, 1.0 and 5.0 mg kg−1). After incubation for 84 days the PCB77 removal rates in the elevated H2 treatments in the Paddy soil were significantly promoted (by 4.88 to 6.41%) compared with the control (0.5 ppmv H2) but no significant effect was observed in a Fluvo-aquic soil. This is consistent with changes in the abundance of functional genes for PCB-degraders as shown by quantitative real-time PCR (Q-PCR) and phylogenetic investigation of bacterial communities by reconstruction of unobserved states (PICRUSt). 16S amplicon sequencing was conducted to explore bacterial community structure and correlate the genera to potential PCB degradation. The abundance of a total of four potentially PCB-degrading bacterial genera (Bacillus, Streptomyces, Ramlibacter and Paenibacillus) increased with increasing H2 level. In addition, the abundance of hydrogenase in the elevated H2 treatments was higher than in the control across different contamination levels in both soil types. Thus, elevated H2 stimulated soil PCB degradation with direct effects (aerobic PCB-degrading bacteria directly utilized H2 as an energy source for growth and thus enhanced PCB degradation efficiency) and indirect effects (aerobic PCB-degrading bacteria acted synergistically with other hydrogenotrophs to enhance PCB degradation efficiency by exchange of substances and energy). These results help to further understand the role of elevated hydrogen amendment in the PCB biodegradation process and provide evidence that H2 supports metabolic and energetic flexibility in microorganisms supplying a range of ecosystem services.