PCB Degradation Research Articles

Integrated transcriptomics and metabolomics analyses reveal the aerobic biodegradation and molecular mechanisms of 2,3′,4,4′,5-pentachlorodiphenyl (PCB 118) in Methylorubrum sp. ZY-1

2,3′,4,4′,5-pentachlorodiphenyl (PCB 118), a highly representative PCB congener, has been frequently detected in various environments, garnering much attention across the scientific community. The degradation of highly chlorinated PCBs by aerobic microorganisms is challenging due to their hydrophobicity and persistence. Herein, the biodegradation and adaptation mechanisms of Methylorubrum sp. ZY-1 to PCB 118 were comprehensively investigated using an integrative approach that combined degradation performance, product identification, metabolomic and transcriptomic analyses. The results indicated that the highest degradation efficiency of 0.5 mg L−1 PCB 118 reached 75.66% after seven days of inoculation when the bacteria dosage was 1.0 g L−1 at pH 7.0. A total of eleven products were identified during the degradation process, including low chlorinated PCBs, hydroxylated PCBs, and ring-opening products, suggesting that strain ZY-1 degraded PCB 118 through dechlorination, hydroxylation, and ring-opening pathways. Metabolomic analysis demonstrated that the energy supply and redox metabolism of strain ZY-1 was disturbed with exposure to PCB 118. To counteract this environmental stress, strain ZY-1 adjusted both the fatty acid synthesis and purine metabolism. The analysis of transcriptomics disclosed that multiple intracellular and extracellular oxidoreductases (e.g., monooxygenase, alpha/beta hydrolase and cytochrome P450) participated in the degradation of PCB 118. Besides, active efflux of PCB 118 and its degradation intermediates mediated by multiple transporters (e.g., MFS transporter and ABC transporter ATP-binding protein) might enhance bacterial resistance against these substances. These discoveries provided the inaugural insights into the biotransformation of strain ZY-1 to PCB 118 stress, illustrating its potential in the remediation of contaminated environments.

Environmental fate of sulfonated-PCBs: Soil partitioning properties, bioaccumulation, persistence, and mobility

Two new classes of PCB metabolites were recently discovered: sulfonated-polychlorinated biphenyls (sulfonated-PCBs) and hydroxy-sulfonated-polychlorinated biphenyls (OH-sulfonated-PCBs). These metabolites, originating from PCB degradation, seem to possess more polar characteristics than their parent compounds. However, no other information, such as their chemical identity (CAS number) or their ecotoxicity or toxicity, is available so far, although more than about one hundred different chemicals were observed in soil samples. In addition, their physico-chemical properties are still uncertain since only estimations are available. Here we show the first evidence on the fate of these new classes of contaminants in the environment, producing results from several experiments, to evaluate sulfonated-PCBs and OH-sulfonated-PCBs soil partition coefficients, degradation in soil after 18 months of rhizoremediation, uptake into plant roots and earthworms, as well as a preliminary analytical method to extract and concentrate these chemicals from water. The results give an overview of the expected environmental fate of these chemicals and open questions for further studies.

Endogenous biohydrogen from a rhizobium-legume association drives microbial biodegradation of polychlorinated biphenyl in contaminated soil

Endogenous hydrogen (H2) is produced through rhizobium-legume associations in terrestrial ecosystems worldwide through dinitrogen fixation. In turn, this gas may alter rhizosphere microbial community structure and modulate biogeochemical cycles. However, very little is understood about the role that this H2 leaking to the rhizosphere plays in shaping the persistent organic pollutants degrading microbes in contaminated soils. Here, we combined DNA-stable isotope probing (DNA-SIP) with metagenomics to explore how endogenous H2 from the symbiotic rhizobium-alfalfa association drives the microbial biodegradation of tetrachlorobiphenyl PCB 77 in a contaminated soil. The results showed that PCB77 biodegradation efficiency increased significantly in soils treated with endogenous H2. Based on metagenomes of 13C-enriched DNA fractions, endogenous H2 selected bacteria harboring PCB degradation genes. Functional gene annotation allowed the reconstruction of several complete pathways for PCB catabolism, with different taxa conducting successive metabolic steps of PCB metabolism. The enrichment through endogenous H2 of hydrogenotrophic Pseudomonas and Magnetospirillum encoding biphenyl oxidation genes drove PCB biodegradation. This study proves that endogenous H2 is a significant energy source for active PCB-degrading communities and suggests that elevated H2 can influence the microbial ecology and biogeochemistry of the legume rhizosphere.

The evaluation of Hudson River sediment as a growth substrate – Microbial activity, PCB-degradation potential and risk assessment

The potential use of growth substrates prepared with an admixture of 10% to 75% Hudson River sediments was evaluated by analysis of changes in microbial activity (measured using Biolog Ecoplates) and molecular markers (presence of degradative tceA1 and bphA genes) as well as potential risks toward humans and the environment (health and environmental risk quotients). The highest microbial activity was found in growth substrate with 25% Hudson River sediments compared to unamended control soil. Significant differences were observed between samples amended with lower (0–10%) and higher (25–75%) proportion of sediment. Microbial activity increased with the proportion of sediment amendment (≥25% sediment); however, this increase in microbial activity was not affected by increasing pollutant concentrations (PCBs, Pb, Cr Ni and Zn) nor decreasing TOC content. The growth substrate amended with Hudson River sediments demonstrated a potential for PCB degradation, as evidenced by the presence of tceA1 and bphA genes responsible, respectively, for reductive dehalogenation and oxidation of a range of aromatic organic compounds including PCBs. An assessment of risk quotients showed that the growth substrates containing lower doses of Hudson River sediments (10–50%) meet the international requirements for use in agriculture/horticulture for the production of non-food crops. Nevertheless, due to the elevated content of some toxic metals and PCBs, the growth substrate prepared with the highest proportion of sediments (75%) was not suitable for agricultural/horticultural use.

Mechanistic Aspects Regarding the Ultraviolet Degradation of Polychlorinated Biphenyls in Different Media: Insights from Carbon and Chlorine Isotope Fractionation.

In this study, the carbon and chlorine isotope fractionation during ultraviolet-photolysis of polychlorinated biphenyls (PCBs, including PCB18, PCB77, PCB110, and PCB138) in n-hexane (Hex), methanol/water (MeOH/H2O), and silica gel was first investigated to explore their mechanistic processes. We observed a significant variation in ΛCl-C (εCl/εC) for the same PCBs in different photochemical systems, implying that PCB degradation processes in various photoreaction systems could differ. Although all substrates showed normal apparent carbon/chlorine kinetic isotope effects (C-/Cl-AKIE >1), the putative inverse C-AKIE of nondechlorinated pathways was suggested by 13C depletion of the average carbon isotope composition of PCB138 and corresponding dechlorinated products in MeOH/H2O, which might originate from the magnetic isotope effect. Significant negative correlations were found between C-AKIE and relative disappearance quantum yields ("Φ") of ortho-dechlorinated substrates (PCB18, PCB110, and PCB138) in Hex and MeOH/H2O. However, the C-AKIE and "Φ" of PCB77 (meta/para-dechlorinated congener) obviously deviated from the above correlations. Furthermore, significantly different product-related carbon isotope enrichment factors of PCB77 in Hex were found. These results demonstrated the existence of dechlorination position-specific and masking effects in carbon isotope fractionations.

Enhanced bioremediation of 2,3′,4,4′,5-pentachlorodiphenyl by consortium GYB1 immobilized on sodium alginate-biochar

2,3′,4,4′,5-pentachlorodiphenyl (PCB 118), a dioxin-like PCB, is often detected in the environment and is difficult to be aerobically biodegraded. In this study, a novel polychlorinated biphenyl degrading consortium GYB1 that can metabolize PCB 118 was successfully obtained by acclimatization process. To enhance the application performance of free bacterial cells, consortium GYB1 was immobilized with sodium alginate and biochar to prepare SC-GYB1 beads. Orthogonal experiments indicated that the optimal composition of the beads (0.2 g) was 2.0% sodium alginate (SA) content, 2.0% wet weight of cells and 1.5% biochar content, which can degrade 50.50% PCB 118 in 5 d. Immobilization shortened the degradation half-life of 1 mg/L PCB 118 by consortium GYB1 from 8.14 d to 3.79 d and made the beads more robust to respond to environmental stress. The SC-GYB1 beads could even keep considerable PCB degradation ability under 200 mg/L Cd2+ stress. According to 16S rRNA gene analysis, Pseudomonas and Stenotrophomonas played the dominant role in consortium GYB1. And embedding obviously altered the community structure and the key bacterial genera during the PCB removal process. Therefore, the immobilization of bacteria consortium by sodium alginate-biochar enhanced the biodegradation of PCB 118, which will provide new insights into functional microorganisms' actual application for PCB restoration.

Selective pressure of biphenyl/polychlorinated biphenyls on the formation of aerobic bacterial associations and their biodegradative potential.

Unique bacterial associations were formed in the polluted soils from territory of the industrial factories Open Joint Stock Company "The Middle Volga Chemical Plant," Chapaevsk, Russia and Open Joint Stock Company "Lubricant Producing Plant," Perm, Russia. This study evaluates the influence of the biphenyl/polychlorinated biphenyls (PCB) on the formation of aerobic bacterial associations and their biodegradative potential. Enrichment cultivation of the soil samples from the territories of these industrial factories with PCB (commercial mixture Sovol) was lead for forming aerobic bacterial enrichment cultures showing a unique composition. The dominating in these bacterial cultures was the phylum Proteobacteria (Beta- and Gammaproteobacteria). Using biphenyl as a carbon source led to decrease of biodiversity in the final stable bacterial associations. Periodic cultivation experiments demonstrated that the association PN2-B has a high degradative potential among the six studied bacterial associations. PN2-B degraded 100% mono-chlorobiphenyls (94.5mg/L), 86.2% di-chlorobiphenyls (22.3mg/L), 50.9% Sovol, and 38.4% Delor 103 (13.8mg/L). Qualitative analysis of metabolites showed that association performed transformation of chlorobenzoic acids (PCB degradation intermediates) into metabolites of citrate cycle. Twelve individual strain-destructors were isolated. The strains were found to degrade 17.7-100% PCB1, 36.2-100% PCB2, 18.8-100% PCB3 (94.5mg/L), and 15.7-78.2% PCB8 (22.3mg/L). The strains were shown to metabolize chlorobenzoic acids formed during degradation of chlorobiphenyls. A unique ability of strains Micrococcus sp. PNS1 and Stenotrophomonas sp. PNS6 to degrade ortho-, meta-, and para-monosubstituted chlorobenzoic acids was revealed. Our results suggest that PN2-B and individual bacterial strains will be perspective for cleaning of the environment from polychlorinated biphenyls.

Thermoresponsive PNIPAm–PMMA-Functionalized PVDF Membranes with Reactive Fe–Pd Nanoparticles for PCB Degradation

Fe–Pd nanoparticles are immobilized in stimuli-responsive poly-N-isopropylacrylamide (PNIPAm)- and poly-methyl methacrylate-functionalized polyvinylidene fluoride membranes using ion exchange for 2...

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.

Bioremediation vs. Nanoremediation: Degradation of Polychlorinated Biphenyls (PCBS) Using Integrated Remediation Approaches

Integration of physicochemical and biological approach represented by sequential application of nanoscale zerovalent iron (nZVI dispersion) and bioaugmentation by bacterial strains isolated from the PCB-contaminated site seems to be an innovative way to remove the PCB contamination, which still persists in the environment. First, nanoremediation of the minimal mineral medium artificially contaminated with Delor 103 and of historically contaminated sediment was performed in 70% and 46% PCB removal efficiency. Integrated remediation was carried out as bionanoremediation initiated by addition of bacterial strains and finished by addition of nZVI dispersion Nanofer 25S. Nanobioremediation initiated by nZVI and followed by the addition of bacterial strains A. xylosoxidans, S. maltophilia, and O. anthropi was more effective and led to the increase of PCB degradation to 75%, 85%, and 99%. The bacterial mixed culture (BMC) consisted of 7 bacterial strains with PCB-degrading activity was used for integrated remediation, as well. By the nanobioremediation of the historically contaminated sediment, 78% degradation of PCBs was achieved by combining the nZVI and BMC, with the addition of non-ionic surfactant Triton X-100. The sediment was periodically reinoculated with fresh nZVI dispersion and BMC inoculum. The possible toxic effects of nZVI in concentration used in integrated remediation 2 g l−1 were evaluated on bacterial strains used for integrated remediation. The cell concentrations of the bacterial strains A. xylosoxidans, S. maltophilia, and O. anthropi, expressed as CFU ml−1, decreased in the presence of nZVI by 75%, 52%, and 61%, respectively.

Whole gene transcriptomic analysis of PCB/biphenyl degrading Rhodococcus jostii RHA1.

This study gives the first picture of whole RNA-Sequencing analysis of a PCB-degrading microbe, Rhodococcus jostii RHA1. Genes that were highly expressed in biphenyl-grown cells, compared with pyruvate-grown cells, were chosen based on the Reads Per Kilobase Million (RPKM) value and were summarized based on the criteria of RPKM ≥100 and fold change ≥2.0. Consequently, 266 total genes were identified as genes expressed particularly for the degradation of biphenyl. After comparison with previous microarray data that identified highly-expressed genes, based on a fold change ≥2.0 and p-value ≤0.05, 62 highly-expressed genes from biphenyl-grown cells were determined from both analytical platforms. As these 62 genes involve known PCB degradation genes, such as bph, etb, and ebd, the genes identified in this study can be considered as essential genes for PCB/biphenyl degradation. In the 62 genes, eleven genes encoding hypothetical proteins were highly expressed in the biphenyl-grown cells. Meanwhile, we identified several highly-expressed unannotated DNA regions on the opposite strand. In order to verify the encoded proteins, two regions were cloned into an expression vector. A protein was successfully obtained from one region at approximately 25 kDa from the unannotated strand. Thus, the genome sequence with transcriptomic analysis gives new insight, considering re-annotation of the genome of R. jostii RHA1, and provides a clearer picture of PCB/biphenyl degradation in this strain.

POTENSI BAKTERI LAUT UNTUK BIOREMEDIASI

POTENCY OF MARINE BACTERIA FOR BIOREMEDIATION. Marine bacteria have a high abundance on variation as well as the qenes, so it can be used in variousaspects, including the prevention of marine pollution through bioremediation. High genetic variations provide a source of marine bacteria which has decompose-various substances capability. Various studies have been conducted to determine the potential of marine bacteria in degrading pollutants, including degradation of hydrocarbons, PAH, plastic, PCB and removal of heavy metal. Recombination through the insertion of the marine bacteria’s gene coding enzyme has been also performed on indigenous actinomycetes on soil.

Ferrate(VI) based chemical oxidation for the remediation of aged PCB contaminated soil: Comparison with conventional oxidants and study of limiting factors

Ferrate (Fe(VI)) has emerged as an efficient oxidant to treat organic pollutants in aqueous solution. However, its application has never been assessed to remediate the contaminated soils. Here, we report the first study to use Fe(VI) for chemical oxidation of PCBs in historically contaminated soils obtained from an industrial wasteland. The first part of this study explores the efficiency of ferrate(VI) to degrade PCBs under various experimental conditions (liquid/solid ratio, oxidant dose, temperature and reaction time). Integrated application of Fe(VI) with conventional oxidants (hydrogen peroxide H2O2, persulfate S2O82− and peroxymonosulfate HSO5−) was also tested. Conventional oxidants resulted in only 2–12% PCB degradation while Fe(VI) removed 30% of PCBs. Integrated use of Fe(VI) and conventional oxidants improved the degradation efficiency which was the highest (40% removal) by Fe(VI)/HSO5−. This could be attributed to two-step degradation proceeding firstly by electron transfer with Fe(VI) followed by radical attack of conventional oxidants. To evaluate if PCB degradation is limited by soil factors, role of carbonate content, overall soil matrix, and PCB availability were assessed as a second part of this study. Negative role of soil matrix was highly prominent for conventional oxidants than Fe(VI). An increase in PCB availability improved the treatment efficiency (45% removal by Fe(VI) alone) highlighting the role of soil factors. All these results indicate the higher suitability and efficiency of Fe(VI) as compared to the conventional oxidants for soil remediation. Since use of Fe(VI) is innovative for both soil remediation and PCB oxidation, degradation mechanisms are also proposed.

EDDS enhanced PCB degradation and heavy metals stabilization in co-contaminated soils by ZVI under aerobic condition

In the present study, biodegradable ligand EDDS was employed to assist ZVI on simultaneous remediation of PCB and heavy metals co-contaminated soils under aerobic condition. With addition of 4 mmol L−1 EDDS and 5 g L−1 ZVI, the total removal ratio of PCB reached 75.3%, and the stabilization ratio of Pb and Cu attained 97.1% and 91.9% respectively. EDDS played two key roles during the process. Firstly, the addition of EDDS could enhance hydroxyl radical generation by ZVI and oxygen for the oxidation of PCB including distribution in the soil phase and dissolved form in the aqueous phase. Secondly, free EDDS could accelerate the release of Cu and Pb from the soil phase to the aqueous phase. As the oxidation of EDDS and the increase of pH value during the process, the dissolved Cu and Pb could be efficiently stabilized by iron oxyhydroxide through coprecipitation. Compared with ZVI/Air, ZVI/EDDS/Air treatment could significantly enhance the stabilization of Pb and Cu. The reason was the dissolution of Cu and Pb by EDDS extraction could reduce the mass transfer limitations between heavy metals and iron oxyhydroxide. Therefore, our study suggests a promising alternative for remediation of organic compounds and heavy metals co-contaminated soil.

Role of membrane pore polymerization conditions for pH responsive behavior, catalytic metal nanoparticle synthesis, and PCB degradation

This article describes the effects of changing monomer and cross-linker concentrations on the mass gain, water permeability, Pd-Fe nanoparticle (NP) loading, and the rate of degradation of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) of pore functionalized polyvinylidene fluoride (PVDF) membranes. In this study, monomer (acrylic acid (AA)) and cross-linker (N, N′- methylene-bis (acrylamide)) concentrations were varied from 10 to 20 wt% of polymer solution and 0.5–2 mol% of monomer concentration, respectively. Results showed that responsive behavior of membrane could be tuned in terms of water permeability over a range of 270–1 L m−2 h−1 bar−1, which is a function of water pH. The NP size on the membrane surface was found in the range of 16–23 nm. With increasing cross-linker density the percentage of smaller NPs (< 10 nm) increases due to smaller mesh size formation during in-situ polymerization of membrane. NP loading was found to vary from 0.21 to 0.94 mg per cm2 of membrane area depending on the variation of available carboxyl groups in membrane pore domain. The NPs functionalized membranes were then tested for use as a platform for the degradation of PCB 126. The observed batch reaction rate (Kobs) for PCB 126 degradation for per mg of catalyst loading was found 0.08–0.1 h−1. Degradation study in convective flow mode shows 98.6% PCB 126 is degraded at a residence time of 46.2 s. The corresponding surface area normalized reaction rate (Ksa) is found about two times higher than Ksa of batch degradation; suggesting elimination of the effect of diffusion resistance for degradation of PCB 126 in convective flow mode operation. These Pd-Fe-PAA-PVDF membranes and nanoparticles are characterized by TGA, contact angle measurement, surface zeta potential, XRD, SEM, XPS, FIB, TEM and other techniques reveal the details about the membrane surface, pores and nanoparticles size, shape and size-distribution. Statistical analysis based on experimental results allows us to depict responsive behavior of functionalized membrane. In our best knowledge this paper first time reports detail study on responsive behavior of pore functionalized membrane in terms of permeability, NPs size, metal loading and its effect on PCB 126 degradation in a quantified approach.

Zero-valent iron particles for PCB degradation and an evaluation of their effects on bacteria, plants, and soil organisms.

Two types of nano-scale zero-valent iron (nZVI-B prepared by borohydride reduction and nZVI-T produced by thermal reduction of iron oxide nanoparticles in H2) and a micro-scale ZVI (mZVI) were compared for PCB degradation efficiency in water and soil. In addition, the ecotoxicity of nZVI-B and nZVI-T particles in treated water and soil was evaluated on bacteria, plants, earthworms, and ostracods. All types of nZVI and mZVI were highly efficient in degradation of PCBs in water, but had little degradation effect on PCBs in soil. Although nZVI-B had a significant negative impact on the organisms tested, treatment with nZVI-T showed no negative effect, probably due to surface passivation through controlled oxidation of the nanoparticles.

Influence of activated-carbon-supported transition metals on the decomposition of polychlorobiphenyls. Part I: Catalytic decomposition and kinetic analysis

In this study, the synergism between activated carbon (AC) as a catalyst support and transition metals (TMs) is used to destroy low concentrations of PCBs. AC-supported TM catalysts were prepared according to two different methods: impregnation and ion exchange. Thermal reactions between 2,2′,4,4′,5,5’-hexachlorobiphenyl (PCB-153) and catalysts generated using AC-supported Ni or Cu ion exchange were conducted under a N2 atmosphere and resulted in a decomposition efficiency > 99.0%. Decomposition efficiency of PCB-153, the residual PCB-153 distribution, and the fingerprint characteristics of the decomposition products are investigated. Important findings include: (i) establishing a ranking of TM reactivities with respect to PCB decomposition of: Ni > Cu > Zn > Fe, (ii) PCB degradation reactions proceed via adsorption, reaction, and desorption, (iii) for ion-exchange-type catalysts, the activation energy order was IRNi-C < IRCu-C < IRZn-C < IRFe-C, which matches the order of the catalytic effects of the catalyst.

Dynamics of changes in coplanar and indicator PCB in sewage sludge during mesophilic methane digestion

Research was conducted, which aim was to evaluate the influence of mesophilic methane digestion on degradation of coplanar and indicator PCB in sewage sludge, and on dynamics of changes of these congeners during the process. For the research, sewage sludge from a municipal wastewater treatment plant were used. Mesophilic digestion was conducted at the temperature of 36°C±1°C. The anaerobic stabilization processes of sewage sludge occurred correctly what was confirmed by appropriate values of pH, content of volatile fatty acids (VFA) and ratio of VFA to alkalinity. Biodegradation of organic compounds in sewage sludge was confirmed by the decrease in total solids (by 26%) and volatile solids (by 36%). Up to the 3rd day of the digestion process no statistically significant differences in concentration of both coplanar and indicator PCB was observed. During the following days of the process, an increase in lower chlorinated PCB concentration was demonstrated and a decrease in concentration of higher chlorinated congeners (penta-, hexa-, and heptachlorobiphenyls). After the digestion, a decrease in higher chlorinated congener concentration was found. Significant degradation was demonstrated for coplanar PCB 169 (from 77.8 to 80.5%), and indicator PCB 180 (from 57.1 to 90.3%) and PCB 153 (from 60.4 to 79.2%).

Improvement of thermal stability and reduction of LiBH4/polymer host interaction of nanoconfined LiBH4 for reversible hydrogen storage

Addition of multi-wall carbon nanotube (MWCNT) and NaAlH4 into nanoconfined LiBH4–PcB (poly (methyl methacrylate)–co–butyl methacrylate) for improving thermal stability and reducing LiBH4/PcB interaction is proposed. The greater the amount of gases desorbed due to polymer (PcB) degradation, the less the thermal stability of polymer host. During dehydrogenation of nanoconfined LiBH4–PcB, combination of gases due to PcB degradation is 64.3% with respect to H2 content, while those of nanoconfined samples doped with MWCNT and NaAlH4 are only 9 and 7.9%, respectively. The LiBH4/PcB (i.e., B⋯OCH3) interaction is quantitatively evaluated by FTIR technique. The more the ratio of peak area between υ(B–H) (from LiBH4) and υ(CO) (from PcB), the lower the LiBH4/PcB interaction. It is found that by adding small amount of MWCNT and NaAlH4, this ratio significantly increases up to 78%. This is in agreement with B 1s XPS results, where the relative amount of BxOy (x/y = 3) to LiBH4 decreases after adding MWCNT and NaAlH4 into nanoconfined LiBH4–PcB. It should be remarked that significant improvement of thermal stability and decrease of LiBH4/PcB interaction after adding MWCNT and NaAlH4 into nanoconfined LiBH4–PcB result in considerable amount of hydrogen release and uptake as well as hydrogen reproducibility during cycling. However, the dispersion of MWCNT is still one of the most critical factors to be concerned due to probably its hindrance for hydrogen diffusion.

Structural insights into broad substrate range of biphenyl dioxygenases &amp; dehydrogenase

Biphenyl dioxygenase(BphAE) &amp; biphenyl dehydrogenase(BphB) catalyze first two steps of aerobic degradation of biphenyl &amp; various polychlorinated biphenyls,PCBs. These enzymes are of interest for their potential to oxidize toxic pollutants &amp; manufacture of fine chemicals. We have determined the crystal structures of two variants of BphAE from B. xenovorans LB400, viz BphAERR41 &amp; BphAEp4, evolved by site directed mutagenesis. We have compared the structures of wild type BphAELB400 &amp; BphAEp4. Biochemical properties of BphAELB400 variants with single substitutions, T335A or F336M shows that residue 336 contacts biphenyl &amp; influences regiospecificity of the reaction, but do not enhance enzyme's reactivity toward 2,6-dichlorobiphenyl. However, residue 335 does not contact biphenyl but contributes significantly to expand enzyme's substrate range. Crystal structure of variant BphAERR41 explains the transformation of dibenzofuran &amp; 2-chlorodibenzofuran. This study provides structural insight for expanded substrate range of Rieske-type oxygenases through mutations that enhance the plasticity and/or mobility of enzyme segments lining the catalytic site. Enzyme, BphB catalyze 2nd step of PCB degradation pathway. We have determined the crystal structure of apoenzyme, binary complex with NAD+ &amp; ternary complexes with NAD+2,3-dihydroxybiphenyl from P. pnomenusa B356. A crystal structure representing an intermediate state of the enzyme was also obtained where the substrate binding loop was ordered in comparison with apo &amp; binary forms but was displaced significantly w.r.t ternary structure. These structures reveal that the substrate binding loop is highly mobile &amp; changes conformation during ligand binding, starting from a disorganized loop in apo state to a well organized loop in ligand-bound form. Conformational changes are induced during ligand binding; forming a well defined cavity to accommodate wide range of substrates. For the 1st time, a combination of structural, biochemical, &amp; molecular docking studies of BphBB356 elucidate the unique ability of enzyme to transform the cis-dihydrodiols of double meta-, para-, &amp; ortho-substituted chlorobiphenyls.