Early-Life Exposure to Polycyclic Aromatic Hydrocarbons and ADHD Behavior Problems

Importance

Polycyclic aromatic hydrocarbons are widespread urban air pollutants from combustion of fossil fuel and other organic material shown previously to be neurotoxic.

Objective

In a prospective cohort study, we evaluated the relationship between Attention Deficit Hyperactivity Disorder behavior problems and prenatal polycyclic aromatic hydrocarbon exposure, adjusting for postnatal exposure.

Materials and Methods

Children of nonsmoking African-American and Dominican women in New York City were followed from in utero to 9 years. Prenatal polycyclic aromatic hydrocarbon exposure was estimated by levels of polycyclic aromatic hydrocarbon- DNA adducts in maternal and cord blood collected at delivery. Postnatal exposure was estimated by the concentration of urinary polycyclic aromatic hydrocarbon metabolites at ages 3 or 5. Attention Deficit Hyperactivity Disorder behavior problems were assessed using the Child Behavior Checklist and the Conners Parent Rating Scale- Revised.

Results

High prenatal adduct exposure, measured by elevated maternal adducts was significantly associated with all Conners Parent Rating Scale-Revised subscales when the raw scores were analyzed continuously (N = 233). After dichotomizing at the threshold for moderately to markedly atypical symptoms, high maternal adducts were significantly associated with the Conners Parent Rating Scale-Revised DSM-IV Inattentive (OR = 5.06, 95% CI [1.43, 17.93]) and DSM-IV Total (OR = 3.37, 95% CI [1.10, 10.34]) subscales. High maternal adducts were positivity associated with the DSM-oriented Attention Deficit/Hyperactivity Problems scale on the Child Behavior Checklist, albeit not significant. In the smaller sample with cord adducts, the associations between outcomes and high cord adduct exposure were not statistically significant (N = 162).

Conclusion

The results suggest that exposure to polycyclic aromatic hydrocarbons encountered in New York City air may play a role in childhood Attention Deficit Hyperactivity Disorder behavior problems.     

Resistance to Nucleotide Excision Repair of Bulky Guanine Adducts Opposite Abasic Sites in DNA Duplexes and Relationships between Structure and Function

The nucleotide excision repair of certain bulky DNA lesions is abrogated in some specific non-canonical DNA base sequence contexts, while the removal of the same lesions by the nucleotide excision repair mechanism is efficient in duplexes in which all base pairs are complementary. Here we show that the nucleotide excision repair activity in human cell extracts is moderate-to-high in the case of two stereoisomeric DNA lesions derived from the pro-carcinogen benzo[a]pyrene (cis- and trans-B[a]P-N ²-dG adducts) in a normal DNA duplex. By contrast, the nucleotide excision repair activity is completely abrogated when the canonical cytosine base opposite the B[a]P-dG adducts is replaced by an abasic site in duplex DNA. However, base excision repair of the abasic site persists. In order to understand the structural origins of these striking phenomena, we used NMR and molecular spectroscopy techniques to evaluate the conformational features of 11mer DNA duplexes containing these B[a]P-dG lesions opposite abasic sites. Our results show that in these duplexes containing the clustered lesions, both B[a]P-dG adducts adopt base-displaced intercalated conformations, with the B[a]P aromatic rings intercalated into the DNA helix. To explain the persistence of base excision repair in the face of the opposed bulky B[a]P ring system, molecular modeling results suggest how the APE1 base excision repair endonuclease, that excises abasic lesions, can bind productively even with the trans-B[a]P-dG positioned opposite the abasic site. We hypothesize that the nucleotide excision repair resistance is fostered by local B[a]P residue—DNA base stacking interactions at the abasic sites, that are facilitated by the absence of the cytosine partner base in the complementary strand. More broadly, this study sets the stage for elucidating the interplay between base excision and nucleotide excision repair in processing different types of clustered DNA lesions that are substrates of nucleotide excision repair or base excision repair mechanisms.     

Oxidative DNA Base Modifications and Polycyclic Aromatic Hydrocarbon DNA Adducts in Squamous Cell Carcinoma of Larynx

Tobacco smoke, recognized as a major etiological factor for cancers of the upper aerodigestive tract, represents an abundant source of reactive oxygen species (ROS), which are believed to play a significant role in mutagenesis and carcinogenesis. An additional source of ROS in tissues exposed to tobacco smoke may be metabolic oxidation of polycyclic aromatic hydrocarbons (PAH). To investigate the relationships between oxidative DNA lesions and aromatic DNA adducts, six modified DNA bases 5-hydroxyuracil, 5-hydroxycytosine, 7,8-dihydro-8-oxoguanine, 7,8-dihydro-8-oxoadenine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine and 4,6-diamino-5-formamidopyrimidine and the total level of PAH-related DNA adducts were measured in cancerous and the surrounding normal larynx tissues (68 subjects), using gas chromatography/isotope-dilution mass spectroscopy with selected ion monitoring and the 32 P-postlabeling-HPLC assay, respectively. The levels of oxidative DNA lesions in cancerous and adjacent tissue were comparable; the differences between the two types of tissue were significant only for 5-hydroxypyrimidines (slightly higher levels were observed in the adjacent tissue). Comparable levels of DNA lesions in cancerous and the surrounding normal tissues observed in the larynx tumors support a field cancerization theory. The surrounding tissues may still be recognized as normal by histological criteria. However, molecular alterations resulting from the chronic tobacco smoke exposure, which equally affects larynx epithelia, may lead to multiple premalignant lesions. Thus, a demonstration of similar levels of DNA damage in cancerous and the adjacent tissue could explain a frequent formation of secondary tumors in the larynx and the frequent recurrence in this type of cancer. A weak, but distinct effect of tumor grading and metastatic status was observed in both kinds of tissue in the case of 5-hydroxyuracil, 5-hydroxycytosine, 7,8-dihydro-8-oxoguanine, 7,8-dihydro-8-oxoadenine. This effect was displayed as a gradual shift in the data distribution toward high values from G1 through G2-G3 and from non-metastatic to metastatic tumors. Since the levels of oxidative DNA base modifications tended to increase with the tumor aggressiveness, we postulate that the oxidative DNA lesions increase genetic instability and thus contribute to tumor progression in laryngeal cancer. No associations between aromatic adduct levels and oxidative DNA lesions were present, suggesting that the metabolism of PAH does not contribute significantly to the oxidative stress in larynx tissues, remaining the tobacco smoke ROS as a major source of oxidative DNA damage in the exposed tissue.     

Rad18-mediated Translesion Synthesis of Bulky DNA Adducts Is Coupled to Activation of the Fanconi Anemia DNA Repair Pathway

Fanconi anemia (FA) is a cancer susceptibility syndrome characterized by sensitivity to DNA-damaging agents. The FA proteins (FANCs) are implicated in DNA repair, although the precise mechanisms by which FANCs process DNA lesions are not fully understood. An epistatic relationship between the FA pathway and translesion synthesis (TLS, a post-replication DNA repair mechanism) has been suggested, but the basis for cross-talk between the FA and TLS pathways is poorly understood. We show here that ectopic overexpression of the E3 ubiquitin ligase Rad18 (a central regulator of TLS) induces DNA damage-independent mono-ubiquitination of proliferating cell nuclear antigen (PCNA) (a known Rad18 substrate) and FANCD2. Conversely, DNA damage-induced mono-ubiquitination of both PCNA and FANCD2 is attenuated in Rad18-deficient cells, demonstrating that Rad18 contributes to activation of the FA pathway. WT Rad18 but not an E3 ubiquitin ligase-deficient Rad18 C28F mutant fully complements both PCNA ubiquitination and FANCD2 activation in Rad18-depleted cells. Rad18-induced mono-ubiquitination of FANCD2 is not observed in FA core complex-deficient cells, demonstrating that Rad18 E3 ligase activity alone is insufficient for FANCD2 ubiquitylation. Instead, Rad18 promotes FA core complex-dependent FANCD2 ubiquitination in a manner that is secondary to PCNA mono-ubiquitination. Taken together, these results demonstrate a novel Rad18-dependent mechanism that couples activation of the FA pathway with TLS.     

Analysis of Intervention Strategies for Inhalation Exposure to Polycyclic Aromatic Hydrocarbons and Associated Lung Cancer Risk Based on a Monte Carlo Population Exposure Assessment Model

It is difficult to evaluate and compare interventions for reducing exposure to air pollutants, including polycyclic aromatic hydrocarbons (PAHs), a widely found air pollutant in both indoor and outdoor air. This study presents the first application of the Monte Carlo population exposure assessment model to quantify the effects of different intervention strategies on inhalation exposure to PAHs and the associated lung cancer risk. The method was applied to the population in Beijing, China, in the year 2006. Several intervention strategies were designed and studied, including atmospheric cleaning, smoking prohibition indoors, use of clean fuel for cooking, enhancing ventilation while cooking and use of indoor cleaners. Their performances were quantified by population attributable fraction (PAF) and potential impact fraction (PIF) of lung cancer risk, and the changes in indoor PAH concentrations and annual inhalation doses were also calculated and compared. The results showed that atmospheric cleaning and use of indoor cleaners were the two most effective interventions. The sensitivity analysis showed that several input parameters had major influence on the modeled PAH inhalation exposure and the rankings of different interventions. The ranking was reasonably robust for the remaining majority of parameters. The method itself can be extended to other pollutants and in different places. It enables the quantitative comparison of different intervention strategies and would benefit intervention design and relevant policy making.     

Microbial Transformation of Polycyclic Aromatic Hydrocarbons in Pristine and Petroleum-Contaminated Sediments

To determine rates of microbial transformation of polycyclic aromatic hydrocarbons (PAH) in freshwater sediments, ¹⁴C-labeled PAH were incubated with samples from both pristine and petroleum-contaminated streams. Evolved ¹⁴CO₂ was trapped in KOH, unaltered PAH and polar metabolic intermediate fractions were quantitated after sediment extraction and column chromatography, and bound cellular ¹⁴C was measured in sediment residues. Large fractions of ¹⁴C were incorporated into microbial cellular material; therefore, measurement of rates of ¹⁴CO₂ evolution alone would seriously underestimate transformation rates of [¹⁴C]naphthalene and [¹⁴C]anthracene. PAH compound turnover times in petroleum-contaminated sediment increased from 7.1 h for naphthalene to 400 h for anthracene, 10,000 h for benz(a)anthracene, and more than 30,000 h for benz(a)pyrene. Turnover times in uncontaminated stream sediment were 10 to 400 times greater than in contaminated samples, while absolute rates of PAH transformation (micrograms of PAH per gram of sediment per hour) were 3,000 to 125,000 times greater in contaminated sediment. The data indicate that four- and five-ring PAH compounds, several of which are carcinogenic, may persist even in sediments that have received chronic PAH inputs and that support microbial populations capable of transforming two- and three-ring PAH compounds.     

Influence of Nonionic Surfactants on Bioavailability and Biodegradation of Polycyclic Aromatic Hydrocarbons

The presence of the synthetic nonionic surfactants Triton X-100, Tergitol NPX, Brij 35, and Igepal CA-720 resulted not only in increased apparent solubilities but also in increased maximal rates of dissolution of crystalline naphthalene and phenanthrene. A model based on the assumption that surfactant micelles are formed and act as a separate phase underestimated the dissolution rates; this led to the conclusion that surfactants present at concentrations higher than the critical micelle concentration affect the dissolution process. This conclusion was confirmed by the results of batch growth experiments, which showed that the rates of biodegradation of naphthalene and phenanthrene in the dissolution-limited growth phase were increased by the addition of surfactant, indicating that the dissolution rates were higher than the rates in the absence of surfactant. In activity and growth experiments, no toxic effects of the surfactants at concentrations up to 10 g liter(sup-1) were observed. Substrate present in the micellar phase was shown to be not readily available for degradation by the microorganisms. This finding has important consequences for the application of (bio)surfactants in biological soil remediation.     

Screening Level Assessment of Risks Associated with Dietary Exposure to Selected Heavy Metals,Polycyclic Aromatic Hydrocarbons,and Radionuclides in Kuwait

To assess the health risks associated with dietary exposure of the Kuwait population, two market baskets comprising 146 food items, which represented the diets of various age groups of the Kuwaiti population, were collected twice, once in the winter of 1997 and again in the summer of 1998, to account for seasonal variation. These food items were analyzed for their heavy metals, polycyclic aromatic hydrocarbons (PAHs) and selected radionuclides contents. Probabilistic risk assessments using the Monte Carlo simulation technique were conducted for Cd, Pb, PAHs, ¹³⁷Cs, ⁹⁰Sr, and ²²⁶Ra. The data obtained showed that high Cd and Pb exposures, which exceeded the World Health Organization's (WHO's) standards are encountered among young children. Exposures to PAHs of the different age groups of the Kuwaiti population were not unusually high at the higher percentiles. On the other hand, dietary exposures to ⁹⁰Sr were all below WHO standards for all percentile and age groups. Exposures to ¹³⁷Cs were slightly above the WHO standard at the 90^th percentile for most age groups, and ²²⁶Ra exposures were all well above WHO standards at the upper percentiles for all age groups, but still below the United States Food and Drug Administration's (USFDA's) intervention levels.     

叶片涂施多环芳烃在黄瓜体内的积累效应及对其生理特性的影响

以黄瓜品种 ‘秀川701’ 为材料,采用叶片涂施试验,考察了不同浓度的多环芳香烃(PAHs)萘、菲、荧蒽、苯并(a)蒽、苯并(a)芘混合液胁迫处理对黄瓜生长、生理和品质的影响及PAHs在黄瓜植株体内的积累特征,探究PAHs对蔬菜作物的生长影响及毒害机理。结果表明：(1)黄瓜7个部位(根、茎、叶片、叶柄、果皮、果肉、果瓤)中总PAHs含量随着叶片涂施浓度的升高呈先增加后降低的趋势,营养器官中以叶片含量最高、叶柄含量最低,果实中果皮含量最高、果瓤含量最低。(2)外源PAHs胁迫对黄瓜株高、茎粗、根长、叶长、叶宽、果实纵径、果实横径、单果重的影响均为低浓度促进中高浓度抑制。(3)外源PAHs处理使叶片SOD、CAT活性下降,MDA含量先提高后降低,尤其是中浓度胁迫下POD活性、叶绿素含量均显著提高。(4)外源PAHs对黄瓜果实维生素C、可溶性蛋白、可滴定酸含量的影响表现为低浓度促进中高浓度抑制,而对可溶性糖、可溶性固形物含量均具有抑制作用。研究认为,5种PAHs在黄瓜体内呈现出了特定的分布规律,直接暴露于大气环境的部位更容易吸收、积累PAHs;PAHs作为典型有机污染物,给黄瓜生长发育带来伤害的同时也起到了正向促进作用,且叶片对PAHs的吸收以及PAHs对黄瓜生理特性的促进或抑制作用都有一定阈值。     

Effects of Crude Oil Exposure on Bioaccumulation of Polycyclic Aromatic Hydrocarbons and Survival of Adult and Larval Stages of Gelatinous Zooplankton

Gelatinous zooplankton play an important role in marine food webs both as major consumers of metazooplankton and as prey of apex predators (e.g., tuna, sunfish, sea turtles). However, little is known about the effects of crude oil spills on these important components of planktonic communities. We determined the effects of Louisiana light sweet crude oil exposure on survival and bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in adult stages of the scyphozoans Pelagia noctiluca and Aurelia aurita and the ctenophore Mnemiopsis leidyi, and on survival of ephyra larvae of A. aurita and cydippid larvae of M. leidyi, in the laboratory. Adult P. noctiluca showed 100% mortality at oil concentration ≥20 µL L⁻¹ after 16 h. In contrast, low or non-lethal effects were observed on adult stages of A. aurita and M. leidyi exposed at oil concentration ≤25 µL L⁻¹ after 6 days. Survival of ephyra and cydippid larva decreased with increasing crude oil concentration and exposition time. The median lethal concentration (LC₅₀) for ephyra larvae ranged from 14.41 to 0.15 µL L⁻¹ after 1 and 3 days, respectively. LC₅₀ for cydippid larvae ranged from 14.52 to 8.94 µL L⁻¹ after 3 and 6 days, respectively. We observed selective bioaccumulation of chrysene, phenanthrene and pyrene in A. aurita and chrysene, pyrene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[a]anthracene in M. leidyi. Overall, our results indicate that (1) A. aurita and M. leidyi adults had a high tolerance to crude oil exposure compared to other zooplankton, whereas P. noctiluca was highly sensitive to crude oil, (2) larval stages of gelatinous zooplankton were more sensitive to crude oil than adult stages, and (3) some of the most toxic PAHs of crude oil can be bioaccumulated in gelatinous zooplankton and potentially be transferred up the food web and contaminate apex predators.     

Comparison of Photocatalytic Oxidation and Ozonation in Degrading of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are hazardous pollutants. Photocatalytic oxidation (PCO) was used to degrade individual PAHs dissolved in aqueous solution and results were compared to those used for ozonation treatment of PAHs in aqueous phase and adsorbed on soil reported previously. Both PCO and ozonation showed high effectiveness and efficiency in degrading PAHs within only minutes of time. Ozonation showed higher performance in the degradation of PAHs in aqueous solution than in soil, whereas the treatment efficiency of PCO was higher than that of ozonation in degrading PAHs in aqueous solution. Both methods have advantages over each other but they have their own limitation(s) in practical application.     

Effects of Alkylphosphates and Nitrous Oxide on Microbial Degradation of Polycyclic Aromatic Hydrocarbons

We conducted a series of liquid-culture experiments to begin to evaluate the abilities of gaseous sources of nitrogen and phosphorus to support biodegradation of polycyclic aromatic hydrocarbons (PAHs). Nutrients examined included nitrous oxide, as well as triethylphosphate (TEP) and tributylphosphate (TBP). Cultures were established using the indigenous microbial populations from one manufactured gas plant (MGP) site and one crude oil-contaminated drilling field site. Mineralization of phenanthrene was measured under alternative nutrient regimes and was compared to that seen with ammoniacal nitrogen and PO₄. Parallel cultures were used to assess removal of a suite of three- to five-ring PAHs. In summary, the abilities of the different communities to degrade PAH when supplemented with N₂O, TEP, and TBP were highly variable. For example, in the MGP soil, organic P sources, especially TBP, supported a considerably higher degree of removal of low-molecular-weight PAHs than did PO₄; however, loss of high-molecular-weight compounds was impaired under these conditions. The disappearance of most PAHs was significantly less in the oil field soil when organophosphates were used. These results indicate that the utility of gaseous nutrients for PAH bioremediation in situ may be limited and will very likely have to be assessed on a case-by-case basis.     

Haplotype Analyses of DNA Repair Gene Polymorphisms and Their Role in Ulcerative Colitis

Ulcerative colitis (UC) is a major clinical form of inflammatory bowel disease. UC is characterized by mucosal inflammation limited to the colon, always involving the rectum and a variable extent of the more proximal colon in a continuous manner. Genetic variations in DNA repair genes may influence the extent of repair functions, DNA damage, and thus the manifestations of UC. This study thus evaluated the role of polymorphisms of the genes involved in DNA repair mechanisms. A total of 171 patients and 213 controls were included. Genotyping was carried out by ARMS PCR and PCR-RFLP analyses for RAD51, XRCC3 and hMSH2 gene polymorphisms. Allelic and genotypic frequencies were computed in both control & patient groups and data was analyzed using appropriate statistical tests. The frequency of ‘A’ allele of hMSH2 in the UC group caused statistically significant increased risk for UC compared to controls (OR 1.64, 95% CI 1.16–2.31, p = 0.004). Similarly, the CT genotype of XRCC3 gene was predominant in the UC group and increased the risk for UC by 1.75 fold compared to controls (OR 1.75, 95% CI 1.15–2.67, p = 0.03), further confirming the risk of ‘T’ allele in UC. The GC genotype frequency of RAD51 gene was significantly increased (p = 0.02) in the UC group (50.3%) compared to controls (38%). The GC genotype significantly increased the risk for UC compared to GG genotype by 1.73 fold (OR 1.73, 95% CI 1.14–2.62, p = 0.02) confirming the strong association of ‘C’ allele with UC. Among the controls, the SNP loci combination of hMSH2:XRCC3 were in perfect linkage. The GTC and ACC haplotypes were found to be predominant in UC than controls with a 2.28 and 2.93 fold significant increase risk of UC.     

4种城市绿化树种叶片PAHs含量特征与叶面结构的关系

用气质联用仪测定了长沙市樟树(Cinnamomu camphora)、广玉兰(Magnolia grandiflora)、桂花(Opsmanthus fragrans)和红檵木(Redrlowered loropetalum)4个主要绿化树种叶片中PAHs含量,同时测定了叶片的气孔密度、气孔长宽比、叶片的宽长比和叶面积等叶面结构特征值,探讨了叶面结构与叶片中PAHs含量的关系。结果表明:红檵木叶片的PAHs含量最高,为11.13mg·kg-1,16种PAHs在4树种叶片中均有不同程度的检出,其中以3环和4环为主,菲的浓度最高。除桂花外,在气温较低的秋冬季节,其余3种植物叶片气孔密度大PAHs含量高。叶面宽长比、气孔长宽比均与叶片PAHs含量呈极显著正相关,而叶面积与PAHs含量呈极显著负相关。表明叶面结构是影响叶片PAHs含量的重要因素。研究结果可为城市绿化树种合理选择与配置提供科学依据。     

Polycyclic Aromatic Hydrocarbons in Road-Deposited Sediments and Roadside Soil in Tijuana,Mexico

Road-deposited sediment and roadside soil in the urban area of the city of Tijuana were collected and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs). The ΣPAH concentration for road-deposited sediment (RDS) ranged between 460 and 2027 µg/kg with an average of 933 µg/kg. The ΣPAH concentration in roadside soil was lower than in RDS, with a range between 54 and 1863 µg/kg and a mean value of 308 µg/kg. The diagnostic ratios showed that the PAHs originated mostly from pyrogenic sources such as gasoline and diesel combustion. The results show that PAH concentration in RDS and roadside soils is low when compared with other published studies. The low PAH levels found in this study are possibly related to differences in climate, urban features, and anthropogenic activities conducted in the studied areas. The toxicity equivalent concentrations (TEQ) of PAH calculated were also low in comparison with other studies. This is probably due to the lower concentration of total PAHs and the highly toxic high-molecular-weight PAHs.     

Growth of Various Bacteria on Polycyclic Aromatic Hydrocarbons and N-2–Fluorenylacetamide

Several heterotrophic bacteria grew in nutrient broth medium containing high concentrations (10⁻⁵ M) of the potent carcinogenic compounds, benz[a]pyrene, 3-methylcholanthrene or N-2–fluorenylacetamide. They were capable of metabolizing the polycyclic aromatic hydrocarbons to smaller molecules and utilized these compounds as the sole source of carbon and energy. Identification of the metabolites formed from benz[a]pyrene revealed that the major metabolite (3-hydroxybenz[a]pyrene) of mammalian systems did not accumulate in any of these cultures when the standard fluorometric assay was used. Benz[a]pyrene metabolism profiles with high-pressure liquid chromatography also exhibited no accumulation of any metabolites (hydroxy, quinone and diol derivatives).     

Determination of Polycyclic Aromatic Hydrocarbons and Trace Metals in New Orleans Soils and Sediments

Soil and sediment samples from New Orleans have been collected and analyzed for contamination by 16 polycyclic aromatic hydrocarbons (PAHs) and 8 trace metals. Total PAH contents were found to vary from 40 μ g/kg to 40,000 μ g/kg, and concentrations of total metals varied in the range of 80 mg/kg and 7600 mg/kg. Source analysis of PAHs using diagnostic concentration ratios such as phenanthrene/anthracene and fluoranthene/ pyrene indicated that PAHs found at elevated concentrations in New Orleans soils and sediments were of pyrolytic origins. Spearman rank bivariate correlation analysis revealed significant correlations between soil PAHs and metals (r = 0.80, p < 0.0001) and between sediment PAHs and metals (r = 0.62, p < 0.05), suggesting common pollution sources for the two groups of environmental pollutants. Strong correlations were also found between Pb and Zn in soils (r = 0.93, p < 0.0001) as well as in sediments (r = 0.65, p < 0.05).     

Synthesis of Polycyclic Aromatic Hydrocarbons and Acetylene Polymers in Ice: A Prebiotic Scenario

The recent evidences of presence of subsurface oceans of liquid water and ice on Saturn's moons, and the possible presence and astrobiological importance of polycyclic aromatic hydrocarbons (PAHs) in these environments, provide strong motivation for the exploration of the prebiotic chemistry in ice and to test if PAHs could be experimentally synthesized in ice surfaces under atmospheres containing methane as carbon source. In this work, we present a new design for prebiotic‐chemistry experiments in ice matrix. Using this design, a mixture of products including PAHs, polar aromatic compounds, and hydrophilic acetylene‐based polymers was obtained. We propose that acetylene generation in a methane/nitrogen atmosphere and subsequent polymerization to PAHs and polyynes could be a favored pathway in the presence of water freeze–melt cycles. These results shed light on the processes involved in PAH synthesis in icy environments and on the physical factors that drive the different competing pathways in methane/nitrogen atmospheres.     

Occurrence and Phylogenetic Diversity of Sphingomonas Strains in Soils Contaminated with Polycyclic Aromatic Hydrocarbons

Bacterial strains of the genus Sphingomonas are often isolated from contaminated soils for their ability to use polycyclic aromatic hydrocarbons (PAH) as the sole source of carbon and energy. The direct detection of Sphingomonas strains in contaminated soils, either indigenous or inoculated, is, as such, of interest for bioremediation purposes. In this study, a culture-independent PCR-based detection method using specific primers targeting the Sphingomonas 16S rRNA gene combined with denaturing gradient gel electrophoresis (DGGE) was developed to assess Sphingomonas diversity in PAH-contaminated soils. PCR using the new primer pair on a set of template DNAs of different bacterial genera showed that the method was selective for bacteria belonging to the family Sphingomonadaceae. Single-band DGGE profiles were obtained for most Sphingomonas strains tested. Strains belonging to the same species had identical DGGE fingerprints, and in most cases, these fingerprints were typical for one species. Inoculated strains could be detected at a cell concentration of 10⁴ CFU g of soil⁻¹. The analysis of Sphingomonas population structures of several PAH-contaminated soils by the new PCR-DGGE method revealed that soils containing the highest phenanthrene concentrations showed the lowest Sphingomonas diversity. Sequence analysis of cloned PCR products amplified from soil DNA revealed new 16S rRNA gene Sphingomonas sequences significantly different from sequences from known cultivated isolates (i.e., sequences from environmental clones grouped phylogenetically with other environmental clone sequences available on the web and that possibly originated from several potential new species). In conclusion, the newly designed Sphingomonas-specific PCR-DGGE detection technique successfully analyzed the Sphingomonas communities from polluted soils at the species level and revealed different Sphingomonas members not previously detected by culture-dependent detection techniques.