Reductive dechlorination of methoxychlor and DDT by human intestinal bacterium Eubacterium limosum under anaerobic conditions

An inclusive outlook on the fate and persistence of pesticides in the environment and integrated eco-technologies for their degradation

Intensive and inefficient exploitation of pesticides through modernized agricultural practices has caused severe pesticide contamination problems to the environment and become a crucial problem over a few decades. Due to their highly toxic and persistent properties, they affect and get accumulated in non-target organisms, including microbes, algae, invertebrates, plants as well as humans, and cause severe issues. Considering pesticide problems as a significant issue, researchers have investigated several approaches to rectify the pesticide contamination problems. Several analyses have provided an extensive discussion on pesticide degradation but using specific technology for specific pesticides. However, in the middle of this time, cleaner techniques are essential for reducing pesticide contamination problems safely and environmentally friendly. As per the research findings, no single research finding provides concrete discussion on cleaner tactics for the remediation of contaminated sites. Therefore, in this review paper, we have critically discussed cleaner options for dealing with pesticide contamination problems as well as their advantages and disadvantages have also been reviewed. As evident from the literature, microbial remediation, phytoremediation, composting, and photocatalytic degradation methods are efficient and sustainable and can be used for treatment at a large scale in engineered systems and in situ. However, more study on the bio-integrated system is required which may be more effective than existing technologies.

Characterization of chlorinated paraffin-degrading bacteria from marine estuarine sediments

This study explored chlorinated paraffin (CP)-degrading bacteria from the marine environment. Aequorivita, Denitromonas, Parvibaculum, Pseudomonas and Ignavibacterium were selected as the dominant genera after enrichment with chlorinated paraffin 52 (CP52) as the sole carbon source. Eight strains were identified as CP degraders, including Pseudomonas sp. NG6 and NF2, Erythrobacter sp. NG3, Castellaniella sp. NF6, Kordiimonas sp. NE3, Zunongwangia sp. NF12, Zunongwangia sp. NH1 and Chryseoglobus sp. NF13, and their degradation efficiencies ranged from 6.4% to 19.0%. In addition to Pseudomonas, the other six genera of bacteria were first reported to have the degradation ability of CPs. Bacterial categories, carbon-chain lengths and chlorination degrees were three crucial factors affecting the degradation efficiencies of CPs, with their influential ability of chlorinated degrees > bacterial categories > carbon-chain lengths. CP degradation can be performed by producing chlorinated alcohols, chlorinated olefins, dechlorinated alcohols and lower chlorinated CPs. This study will provide valuable information on CP biotransformation and targeted bacterial resources for studying the transformation processes of specific CPs in marine environments.

Impact of "chemical cocktails" exposure in shaping mice gut microbiota and the role of selenium supplementation combining metallomics, metabolomics, and metataxonomics

Biological systems are exposed to a complex environment in which pollutants can interact through synergistic or antagonistic mechanisms, but limited information is available on the combined effects. To this end, conventional and antibiotic-treated (Abx) mice models were fed regular rodent or selenium (Se) supplemented diets and exposed to a "chemical cocktail" (CC) including metals and pharmaceuticals. Metallomics, metabolomics, and metataxomics were combined to delve into the impact on gut microbiota, plasma selenoproteome, metabolome, and arsenic metabolization. At the molecular level, Se decreased the concentration of the antioxidant glutathione peroxidase in plasma and increased the arsenic methylation rate, possibly favoring its excretion, but not in the Abx and also plasma metabolomes of Abx, and Abx-Se were not differentiated. Moreover, numerous associations were obtained between plasma selenoproteins and gut microbes. Se-supplementation partially antagonizes the gut microbiota alteration caused by Abx, and slightly by CC, but strongly altered profiles were observed in CC-Abx-Se, suggesting synergistic deleterious effects between pollutants, Abx and Se. Moreover, although CC and Abx changed gut microbiota, several common taxa were enriched in CC-Abx and control mice, indicating possible synergistic effects. Our results suggest a potential beneficial impact of supplementation, but mediated by gut microbes being reversed in their absence.

Persistent organic pollutants in foods, their interplay with gut microbiota and resultant toxicity

Persistent Organic Pollutants (POPs) have become immensely prevalent in the environment as a result of their unique chemical properties (persistent, semi-volatile and bioaccumulative nature). Their occurrence in the soil, water and subsequently in food has become a matter of concern. With food being one of the major sources of exposure, the detrimental impact of these chemicals on the gut microbiome is inevitable. The gut microbiome is considered as an important integrant for human health. It participates in various physiological, biochemical and immunological activities; thus, affects the metabolism and physiology of the host. A myriad of studies have corroborated an association between POP-induced gut microbial dysbiosis and prevalence of disorders. For instance, ingestion of polychlorinated biphenyls, polybrominated diphenyl ethers or organochlorine pesticides influenced bile acid metabolism via alteration of bile salt hydrolase activity of Lactobacillus, Clostridium or Bacteroides genus. At the same time, some chemicals such as DDE have the potential to elevate Proteobacteria and Firmicutes/Bacteriodetes ratio influencing their metabolic activity leading to enhanced short-chain fatty acid synthesis, ensuing obesity or a pre-diabetic state. This review highlights the impact of POPs exposure on the gut microbiota composition and metabolic activity, along with an account of its corresponding consequences on the host physiology. The critical role of gut microbiota in impeding the POPs excretion out of the body resulting in their prolonged exposure and consequently, enhanced degree of toxicity is also emphasized.

Influence of nitrate concentration on trichloroethylene reductive dechlorination in weak electric stimulation system

The co-existence of volatile chlorinated hydrocarbons (VCHs) and nitrate pollution in groundwater is prominent, but how nitrate exposure affects weak-electrical stimulated bio-dechlorination activity of VCH is largely unknown. Here, by establishing weak-electrical stimulated trichloroethylene (TCE) dechlorination systems, the influence on TCE dechlorination by exposure to the different concentrations (25-100 mg L^-1) of nitrate was investigated. The existence of nitrate in general decreased TCE dechlorination efficiency to varying degrees, and the higher nitrate concentration, the stronger the inhibitory effects, verified by the gradually decreased transcription levels of tceA. Although the TCE dechlorination kinetic rate constant decreased by 36% the most, under all nitrate concentration ranges, TCE could be completely removed within 32 h and no difference in generated metabolites was found, revealing the well-maintained dechlorination activity. This was due to the quickly enriched bio-denitrification activity, which removed nitrate completely within 9 h, and thus relieved the inhibition on TCE dechlorination. The obvious bacterial community structure succession was also observed, from dominating with dechlorination genera (e.g., Acetobacterium, Eubacterium) to dominating with both dechlorination and denitrification genera (e.g., Acidovorax and Brachymonas). The study proposed the great potential for the in situ simultaneous denitrification and dehalogenation in groundwater contaminated with both nitrate and VCHs.

Past, present, and future perspectives on the assessment of bioavailability/bioaccessibility of polycyclic aromatic hydrocarbons: A 20-year systemic review based on scientific econometrics

Bioaccessibility/bioavailability (bioac-bioav) is an important criterion in the risk assessment of polycyclic aromatic hydrocarbons (PAHs), especially in the restoration of contaminated sites. Although, the bioac-bioav concept is widely employed in PAH risk assessment for both humans and wildlife, their growth and integration in risk assessment models are seldom discussed. Consequently, the relevant literature listed on Web of Science (WOS)™ was retrieved and analyzed using the bibliometric software Citespace in order to gain a comprehensive understanding of this issue. Due to the limitations of the literature search software, we manually searched the articles about PAHs bioac-bioav that were published before 2000. This stage focuses on research on the distribution coefficient of PAHs between different environmental phases and laid the foundation for the adsorption-desorption of PAHs in subsequent studies of the bioac-bioav of PAHs. The research progress on PAH bioac-bioav from 2000 to the present was evaluated using the Citespace software based on country- and discipline-wise publication volumes and research hotspots. The development stages of PAH bioac-bioav after 2000 were divided into four time segments. The first three segments (2000-2005, 2006-2010, and 2011-2015) focused on the degradation of PAHs and their in vivo (bioavailability)-in vitro (bioaccessibility) evaluation method and risk assessment. Meanwhile, the current (2016-present) research focuses on the establishment of analytical methods for assessing PAH derivatives at environmental concentrations and the optimization of various in vitro digestion methods, including chemical optimization (sorptive sink) and biological optimization (Caco-2 cell). The contents are aimed at supplying researchers with a deeper understanding of the development of PAH bioac-bioav.

New challenges of marine ecotoxicology in a global change context

Currently, research agenda in marine ecotoxicology is facing new challenges with the emergence of newly and complex synthetized chemicals. The study of the fate and adverse effects of toxicants remains increasingly complicated with global change events. Ecotoxicology had provided for a decades, precious scientific data and knowledge but also technical and management tools for the environmental community. Regarding those, it is necessary to update methodologies dealing with these issues such as combined effect of conventional and emergent stressors and global changes. In this point of view article, we discuss one hand the new challenges of ecotoxicology in this context, and in the other hand, the need of updating agenda and methodologies currently used in monitoring programs and finally recommendations and future research needs. Among recommendations, it could be cited the necessity to perform long-term experiments, the standardization of sentinel species and taking benefit from baseline studies and omics technologies.

Anaerococcus urinimassiliensis sp. nov., a new bacterium isolated from human urine

To date there are thirteen species validly assigned to the genus Anaerococcus. Most of the species in this genus are anaerobic and of human origin. Anaerococcus urinimassiliensis sp. nov., strain Marseille-P2143^T is member of family Peptoniphilaceae, which was isolated from the urine of a 17-year-old boy affected by autoimmune hepatitis and membranoproliferative glomerulonephritis using the culturomic approach. In the current study, a taxono-genomics method was employed to describe this new species. The strain Marseille-P2143^T was gram positive cocci with translucent colonies on blood agar. Its genome was 2,189,509 bp long with a 33.5 mol% G + C content and exhibited 98.48% 16S rRNA similarity with Anaerococcus provencensis strain 9,402,080. When Anaerococcus urinomassiliensis strain Marseill-P2143^T is compared with closely related species, the values ranged from 71.23% with A. hydrogenalis strain DSM 7454^T (NZ_ABXA01000052.1) to 90.64% with A. provencensis strain 9402080^T (NZ_HG003688.1). This strain has implemented the repertoire of known bacteria of the human urinary tract.

Oxidative Stress in NAFLD: Role of Nutrients and Food Contaminants

Non-alcoholic fatty liver disease (NAFLD) is often the hepatic expression of metabolic syndrome and its comorbidities that comprise, among others, obesity and insulin-resistance. NAFLD involves a large spectrum of clinical conditions. These range from steatosis, a benign liver disorder characterized by the accumulation of fat in hepatocytes, to non-alcoholic steatohepatitis (NASH), which is characterized by inflammation, hepatocyte damage, and liver fibrosis. NASH can further progress to cirrhosis and hepatocellular carcinoma. The etiology of NAFLD involves both genetic and environmental factors, including an unhealthy lifestyle. Of note, unhealthy eating is clearly associated with NAFLD development and progression to NASH. Both macronutrients (sugars, lipids, proteins) and micronutrients (vitamins, phytoingredients, antioxidants) affect NAFLD pathogenesis. Furthermore, some evidence indicates disruption of metabolic homeostasis by food contaminants, some of which are risk factor candidates in NAFLD. At the molecular level, several models have been proposed for the pathogenesis of NAFLD. Most importantly, oxidative stress and mitochondrial damage have been reported to be causative in NAFLD initiation and progression. The aim of this review is to provide an overview of the contribution of nutrients and food contaminants, especially pesticides, to oxidative stress and how they may influence NAFLD pathogenesis.

Unlocking the potential of plant growth-promoting rhizobacteria on soil health and the sustainability of agricultural systems

The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.

Predicting the potential for organohalide respiration in wastewater: Comparison of intestinal and wastewater microbiomes

Halogenated compounds such as polychlorinated biphenyl (PCBs) and polybrominated diphenyl ethers (PBDEs) enter wastewater treatment plants (WWTPs) via the sewage system. These organic contaminants partition between the aqueous and the biosolid phase, where the former is discharged as wastewater effluent. Biosolids from a WWTP provide a hydrophobic surface for adsorption and thus the presence and potential growth of organohalide respiring (OHR) bacteria. In this study, the aim was to assess the potential organohalide respiration capacity in wastewater biosolids by investigating actively organohalide respiring bacteria with a focus on organohalide respiration of PCBs and PCE. The results of the biosolids analysis showed increased amounts of products from PCB respiration. Simultaneously, experiments with organohalide respiration of PCE in biosolids samples showed significant decreases PCE concentration after 46 days (28-92%). Subsequently, it was evaluated if the OHR microbial populations in biosolids were similar to those present in intestinal human biofilms by applying a bioinformatic approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The overall groups Proteobacteria, Bacteroides, Actinobacteria, and Firmicutes phyla dominated the microbiomes in all datasets. The OHR groups in biosolids and intestinal biofilms included Dehalogenimonas, Dehalobacter, Desulfitibacter, Desulfovibrio, Sulfurospirillum, Clostridium, and Comamonas. The results of this study showed that several OHR phyla were present in all samples independent of origin. Wastewater and intestinal microbiomes also contained OHR phyla. Overall, the results points towards using bacterial communities in biosolids as indicators of organohalide respiration in wastewater and intestinal microbiomes, which is related to ingestion or halogenated compounds.

Gut microbiota of aquatic organisms: A key endpoint for ecotoxicological studies

Gut microbial communities constitute a compartment of crucial importance in regulation of homeostasis of multiple host physiological functions as well as in resistance towards environmental pollutants. Many chemical contaminants were shown to constitute a major threat for gut bacteria. Changes in gut microbiome could lead to alteration of host health. The access to high-throughput sequencing platforms permitted a great expansion of this discipline in human health while data from ecotoxicological studies are scarce and particularly those related to aquatic pollution. The main purpose of this review is to summarize recent body of literature providing data obtained from microbial community surveys using high-throughput 16S rRNA sequencing technology applied to aquatic ecotoxicity. Effects of pesticides, PCBs, PBDEs, heavy metals, nanoparticles, PPCPs, microplastics and endocrine disruptors on gut microbial communities are presented and discussed. We pointed out difficulties and limits provided by actual methodologies. We also proposed ways to improve understanding of links between changes in gut bacterial communities and host fitness loss, along with further applications for this emerging discipline.

Effects of single and combined toxic exposures on the gut microbiome: Current knowledge and future directions

Human populations are chronically exposed to mixtures of toxic chemicals. Predicting the health effects of these mixtures require a large amount of information on the mode of action of their components. Xenobiotic metabolism by bacteria inhabiting the gastrointestinal tract has a major influence on human health. Our review aims to explore the literature for studies looking to characterize the different modes of action and outcomes of major chemical pollutants, and some components of cosmetics and food additives, on gut microbial communities in order to facilitate an estimation of their potential mixture effects. We identified good evidence that exposure to heavy metals, pesticides, nanoparticles, polycyclic aromatic hydrocarbons, dioxins, furans, polychlorinated biphenyls, and non-caloric artificial sweeteners affect the gut microbiome and which is associated with the development of metabolic, malignant, inflammatory, or immune diseases. Answering the question 'Who is there?' is not sufficient to define the mode of action of a toxicant in predictive modeling of mixture effects. Therefore, we recommend that new studies focus to simulate real-life exposure to diverse chemicals (toxicants, cosmetic/food additives), including as mixtures, and which combine metagenomics, metatranscriptomics and metabolomic analytical methods achieving in that way a comprehensive evaluation of effects on human health.

The Multifactorial Etiopathogeneses Interplay of Inflammatory Bowel Disease: An Overview

The gastrointestinal system where inflammatory bowel disease occurs is central to the immune system where the innate and the adaptive/acquired immune systems are balanced in interactions with gut microbes under homeostasis conditions. This article overviews the high-throughput research screening on multifactorial interplay between genetic risk factors, the intestinal microbiota, urbanization, modernization, Westernization, the environmental influences and immune responses in the etiopathogenesis of inflammatory bowel disease in humans. Inflammatory bowel disease is an expensive multifactorial debilitating disease that affects thousands new people annually worldwide with no known etiology or cure. The conservative therapeutics focus on the established pathology where the immune dysfunction and gut injury have already happened but do not preclude or delay the progression. Inflammatory bowel disease is evolving globally and has become a global emergence disease. It is largely known to be a disease in industrial-urbanized societies attributed to modernization and Westernized lifestyle associated with environmental factors to genetically susceptible individuals with determined failure to process certain commensal antigens. In the developing nations, increasing incidence and prevalence of inflammatory bowel disease (IBD) has been associated with rapid urbanization, modernization and Westernization of the population. In summary, there are identified multiple associations to host exposures potentiating the landscape risk hazards of inflammatory bowel disease trigger, that include: Western life-style and diet, host genetics, altered innate and/or acquired/adaptive host immune responses, early-life microbiota exposure, change in microbiome symbiotic relationship (dysbiosis/dysbacteriosis), pollution, changing hygiene status, socioeconomic status and several other environmental factors have long-standing effects/influence tolerance. The ongoing multipronged robotic studies on gut microbiota composition disparate patterns between the rural vs. urban locations may help elucidate and better understand the contribution of microbiome disciplines/ecology and evolutionary biology in potentially protecting against the development of inflammatory bowel disease.

Flux, Impact, and Fate of Halogenated Xenobiotic Compounds in the Gut

Humans and their associated microbiomes are exposed to numerous xenobiotics through drugs, dietary components, personal care products as well as environmental chemicals. Most of the reciprocal interactions between the microbiota and xenobiotics, such as halogenated compounds, occur within the human gut harboring diverse and dense microbial communities. Here, we provide an overview of the flux of halogenated compounds in the environment, and diverse exposure routes of human microbiota to these compounds. Subsequently, we review the impact of halogenated compounds in perturbing the structure and function of gut microbiota and host cells. In turn, cultivation-dependent and metagenomic surveys of dehalogenating genes revealed the potential of the gut microbiota to chemically alter halogenated xenobiotics and impact their fate. Finally, we provide an outlook for future research to draw attention and attract interest to study the bidirectional impact of halogenated and other xenobiotic compounds and the gut microbiota.

Urbanization and the gut microbiota in health and inflammatory bowel disease

In the 21st century, urbanization represents a major demographic shift in developed and developing countries. Rapid urbanization in the developing world has been associated with an increasing incidence of several autoimmune diseases, including IBD. Patients with IBD exhibit a decrease in the diversity and richness of the gut microbiota, while urbanization attenuates the gut microbial diversity and might have a role in the pathogenesis of IBD. Environmental exposures during urbanization, including Westernization of diet, increased antibiotic use, pollution, improved hygiene status and early-life microbial exposure, have been shown to affect the gut microbiota. The disparate patterns of the gut microbiota composition in rural and urban areas offer an opportunity to understand the contribution of a 'rural microbiome' in potentially protecting against the development of IBD. This Perspective discusses the effect of urbanization and its surrogates on the gut microbiome (bacteriome, virome, mycobiome and helminths) in both human health and IBD and how such changes might be associated with the development of IBD.

The Environmental Issues of DDT Pollution and Bioremediation: a Multidisciplinary Review

DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane) is probably the best known and most useful organochlorine insecticide in the world which was used since 1945 for agricultural purposes and also for vector-borne disease control such as malaria since 1955, until its banishment in most countries by the Stockholm convention for ecologic considerations. However, the World Health Organization allowed its reintroduction only for control of vector-borne diseases in some tropical countries in 2006. Due to its physicochemical properties and specially its persistence related with a half-life up to 30 years, DDT linked to several health and social problems which are due to its accumulation in the environment and its biomagnification properties in living organisms. This manuscript compiles a multidisciplinary review to evaluate primarily (i) the worldwide contamination of DDT and (ii) its (eco) toxicological impact onto living organisms. Secondly, several ways for DDT bioremediation from contaminated environment are discussed. For this, reports on DDT biodegradation capabilities by microorganisms and ways to enhance bioremediation strategies to remove DDT are presented. The different existing strategies for DDT bioremediation are evaluated with their efficiencies and limitations to struggle efficiently this contaminant. Finally, rising new approaches and technological bottlenecks to promote DDT bioremediation are discussed.

The gut microbiota: a major player in the toxicity of environmental pollutants?

Exposure to environmental chemicals has been linked to various health disorders, including obesity, type 2 diabetes, cancer and dysregulation of the immune and reproductive systems, whereas the gastrointestinal microbiota critically contributes to a variety of host metabolic and immune functions. We aimed to evaluate the bidirectional relationship between gut bacteria and environmental pollutants and to assess the toxicological relevance of the bacteria-xenobiotic interplay for the host. We examined studies using isolated bacteria, faecal or caecal suspensions-germ-free or antibiotic-treated animals-as well as animals reassociated with a microbiota exposed to environmental chemicals. The literature indicates that gut microbes have an extensive capacity to metabolise environmental chemicals that can be classified in five core enzymatic families (azoreductases, nitroreductases, β-glucuronidases, sulfatases and β-lyases) unequivocally involved in the metabolism of >30 environmental contaminants. There is clear evidence that bacteria-dependent metabolism of pollutants modulates the toxicity for the host. Conversely, environmental contaminants from various chemical families have been shown to alter the composition and/or the metabolic activity of the gastrointestinal bacteria, which may be an important factor contributing to shape an individual's microbiotype. The physiological consequences of these alterations have not been studied in details but pollutant-induced alterations of the gut bacteria are likely to contribute to their toxicity. In conclusion, there is a body of evidence suggesting that gut microbiota are a major, yet underestimated element that must be considered to fully evaluate the toxicity of environmental contaminants.

Advances in in vitro methods to evaluate oral bioaccessibility of PAHs and PBDEs in environmental matrices

Cleanup goals for sites contaminated with persistent organic pollutants (POPs) are often established based on total contaminant concentrations. However, mounting evidence suggests that understanding contaminant bioavailability in soils is necessary for accurate assessment of contaminant exposure to humans via oral ingestion pathway. Animal-based in vivo tests have been used to assess contaminant bioavailability in soils; however, due to ethical issues and cost, it is desirable to use in vitro assays as alternatives. Various in vitro methods have been developed, which simulate human gastrointestinal (GI) tract using different digestion fluids. These methods can be used to predict POP bioavailability in soils, foods, and indoor dust after showing good correlation with in vivo animal data. Here, five common in vitro methods are evaluated and compared using PAHs and PBDEs as an example of traditional and emerging POPs. Their applications and limitations are discussed while focusing on method improvements and future challenges to predict POP bioavailability in different matrices. The discussions should shed light for future research to accurately assess human exposure to POPs via oral ingestion pathway.

Enhanced biotransformation of DDTs by an iron- and humic-reducing bacteria Aeromonas hydrophila HS01 upon addition of goethite and anthraquinone-2,6-disulphonic disodium salt (AQDS)

A fermentative facultative anaerobe, strain HS01 isolated from subterranean sediment, was identified as Aeromonas hydrophila by 16S rRNA sequence analysis. The biotransformation of 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT), 1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene (DDD), and 1,1-dichloro-2,2-bis (4-chlorophenyl) ethane (DDE) by HS01 was investigated in the presence of goethite and anthraquinone-2,6-disulphonic disodium salt (AQDS). The results demonstrated that HS01 was capable of reducing DDTs, goethite and AQDS. And goethite can significantly enhance the reduction of DDT, DDD and DDE to some extent, while the addition of AQDS can further accelerate the reduction of Fe(III) and DDTs. The products of DDT transformation were identified as a large amount of dominant DDD, and small amounts of 1-chloro-2,2-bis-(p-chlorophenyl)ethane (DDMU), unsym-bis(p-chlorophenyl)-ethylene (DDNU), and 4,4'-dichlorobenzophenone (DBP). The results of cyclic voltammetry suggested that AQDS could increase the amounts of reactive biogenic Fe(II), resulting in the enhanced transformation of DDTs. This investigation gives some new insight in the fate of DDTs related to iron- and humic-reducing bacteria.

O-Demethylation and successive oxidative dechlorination of methoxychlor by Bradyrhizobium sp. strain 17-4, isolated from river sediment

O-Demethylation of insecticide methoxychlor is well known as a phase I metabolic reaction in various eukaryotic organisms. Regarding prokaryotic organisms, however, no individual species involved in such reaction have been specified and characterized so far. Here we successfully isolated a bacterium that mediates oxidative transformation of methoxychlor, including O-demethylation and dechlorination, from river sediment. The isolate was found to be closely related to Bradyrhizobium elkanii at the 16S rRNA gene sequence level (100% identical). However, based on some differences in the physiological properties of this bacterium, we determined that it was actually a different species, Bradyrhizobium sp. strain 17-4. The isolate mediated O-demethylation of methoxychlor to yield a monophenolic derivative [Mono-OH; 1,1,1-trichloro-2-(4-hydroxyphenyl)-2-(4-methoxyphenyl)ethane] as the primary degradation product. The chiral high-performance liquid chromatography (HPLC) analysis revealed that the isolate possesses high enantioselectivity favoring the formation of (S)-Mono-OH (nearly 100%). Accompanied by the sequential O-demethylation to form the bis-phenolic derivative Bis-OH [1,1,1-trichloro-2,2-bis(4-hydroxyphenyl)ethane], oxidative dechlorination of the side chain proceeded, and monophenolic carboxylic acid accumulated, followed by the formation of multiple unidentified polar degradation products. The breakdown proceeded more rapidly when reductively dechlorinated (dichloro-form) methoxychlor was applied as the initial substrate. The resultant carboxylic acids and polar degradation products are likely further biodegraded by ubiquitous bacteria. The isolate possibly plays an important role for complete degradation (mineralization) of methoxychlor by providing the readily biodegradable substrates.

Dechlorination of the dietary nona-chlorinated toxaphene congeners 62 and 50 into the octa-chlorinated toxaphene congeners 44 and 40 in zebrafish (Danio rerio) and Atlantic salmon (Salmo salar)

The relative feed-to-fish accumulation and possible biotransformation of the nona-chlorinated toxaphene congeners currently included in EU-legislation (CHB-50 and -62) and the octa-chlorinated congeners recommended by the European Food Safety Authority to be included in future surveillance of fish samples (CHB-40, 41, and 44) were investigated in the present study. Model fish Danio rerio were fed either (a) diets spiked with a combination as well as the pure individual toxaphene congeners CHB-50 or 62 or (b) diets spiked with the combination of CHB ∑50+62 and/or CHB ∑40+41+44. In addition, seawater adapted Atlantic salmon smolts were fed technical toxaphene enriched feeds for 62 days. Zebrafish fed a diet containing CHB-50 and CHB-62 accumulated newly formed CHB-40&41 and CHB-44, respectively. The biomagnifications factors (BMF) of the toxaphene congeners in Atlantic salmon muscle from the feeds spiked with technical toxaphene were significantly correlated with their relative lipophilicity (expressed as logK(ow)). An exception was CHB-44 which had a higher BMF than could be expected from its specific logK(ow), reflecting that CHB-44 is a metabolite formed under dietary exposure to CHB-62. This paper reports the in vivo dechlorination of nona-chlorinated toxaphene congeners into octa-chlorinated congeners in feeding trials with a model fish (zebrafish) and an oily food fish (Atlantic salmon).

Reductive dechlorination of methoxychlor by bacterial species of environmental origin: evidence for primary biodegradation of methoxychlor in submerged environments

Methoxychlor [1,1,1-trichloro-2,2-bis(4-methoxyphenyl)ethane] is an organochlorine insecticide that undergoes dechlorination in natural submerged environments. We investigated the ability to dechlorinate this compound in seven environmental bacterial species ( Aeromonas hydrophila , Enterobacter amnigenus , Klebsiella terrigena , Bacillus subtilis , Achromobacter xylosoxidans , Acinetobacter calcoaceticus , and Mycobacterium obuense ) and the enteric bacterium Escherichia coli as a positive control. In R2A broth at 25 °C under aerobic, static culture, all species except Ach. xylosoxidans were observed to convert methoxychlor to dechlorinated methoxychlor [1,1-dichloro-2,2-bis(4-methoxyphenyl)ethane]. The medium was aerobic at first, but bacterial growth resulted in the consumption of oxygen and generated microaerobic and weakly reductive conditions. Replacement of the headspace of the culture tubes with nitrogen gas was found to decrease the dechlorination rate. Our findings suggest that extensive bacterial species ubiquitously inhabiting the subsurface water environment play an important role in the primary dechlorination of methoxychlor.

Field validation of anaerobic degradation pathways for dichlorodiphenyltrichloroethane (DDT) and 13 metabolites in marine sediment cores from China

Although the production and use of dichlorodiphenyltrichloroethane (DDT), a legacy component of persistent organic pollutants, have been highly restricted worldwide, the environmental fate of DDT has remained a great concern as it is not only ubiquitous and bioaccumulative but can also be degraded to a series of metabolites that may be more hazardous ecologically. The present study, taking advantage of the abundant levels of DDT and its metabolites in a subtropical coastal region of China, investigated into the degradation pathways of DDT in natural coastal sediment. Sediment profiles indicated that degradation of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDT) to 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDD) mainly occurred in sediment of the top 20 cm layer. 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDE), aerobically transformed from p,p'-DDT prior to sedimentation, was likely to degrade to 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDMU) which was further converted to 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDNU). In addition, p,p'-DDNU could be transformed to 2,2-bis(p-chlorophenyl)ethane (p,p'-DDNS) and other high-order metabolites. On the other hand, the conversions of p,p'-DDD to p,p'-DDMU and 1-chloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDMS) to p,p'-DDNU were deemed slow in anaerobic sediment. Therefore, the present study confirmed all the degradation pathways involving reductive dechlorination and p,p'-DDE being a more important precursor for p,p'-DDMU than p,p'-DDD in anaerobic sediment, as proposed previously. On the other hand, the present study suggested that p,p'-DDMU instead of p,p'-DDMS was more likely the precursor for formation of high-order metabolites. Based on the current assessments, use of (DDD+DDE)/DDTs to indicate whether there is fresh DDT input may lead to large uncertainties if the concentrations of high-order metabolites are not negligible. Similarly, ecological risk assessment associated with DDT should be conducted with consideration of high-order DDT metabolites.

Enhanced reductive dechlorination of DDT in an anaerobic system of dissimilatory iron-reducing bacteria and iron oxide

The transformation of DDT was studied in an anaerobic system of dissimilatory iron-reducing bacteria (Shewanella decolorationis S12) and iron oxide (alpha-FeOOH). The results showed that S. decolorationis could reduce DDT into DDD, and DDT transformation rate was accelerated by the presence of alpha-FeOOH. DDD was observed as the primary transformation product, which was demonstrated to be transformed in the abiotic system of Fe(2+)+alpha-FeOOH and the system of DIRB+alpha-FeOOH. The intermediates of DDMS and DBP were detected after 9 months, likely suggesting that reductive dechlorination was the main dechlorination pathway of DDT in the iron-reducing system. The enhanced reductive dechlorination of DDT was mainly due to biogenic Fe(II) sorbed on the surface of alpha-FeOOH, which can serve as a mediator for the transformation of DDT. This study demonstrated the important role of DIRB and iron oxide on DDT and DDD transformation under anaerobic iron-reducing environments.

Monitoring abundance and expression of "Dehalococcoides" species chloroethene-reductive dehalogenases in a tetrachloroethene-dechlorinating flow column

We investigated the distribution and activity of chloroethene-degrading microorganisms and associated functional genes during reductive dehalogenation of tetrachloroethene to ethene in a laboratory continuous-flow column. Using real-time PCR, we quantified "Dehalococcoides" species 16S rRNA and chloroethene-reductive dehalogenase (RDase) genes (pceA, tceA, vcrA, and bvcA) in nucleic acid extracts from different sections of the column. Dehalococcoides 16S rRNA gene copies were highest at the inflow port [(3.6 +/- 0.6) x 10(6) (mean +/- standard deviation) per gram soil] where the electron donor and acceptor were introduced into the column. The highest transcript numbers for tceA, vcrA, and bvcA were detected 5 to 10 cm from the column inflow. bvcA was the most highly expressed of all RDase genes and the only vinyl chloride reductase-encoding transcript detectable close to the column outflow. Interestingly, no expression of pceA was detected in the column, despite the presence of the genes in the microbial community throughout the column. By comparing the 16S rRNA gene copy numbers to the sum of all four RDase genes, we found that 50% of the Dehalococcoides population in the first part of the column did not contain either one of the known chloroethene RDase genes. Analysis of 16S rRNA gene clone libraries from both ends of the flow column revealed a microbial community dominated by members of Firmicutes and Actinobacteria. Higher clone sequence diversity was observed near the column outflow. The results presented have implications for our understanding of the ecophysiology of reductively dehalogenating Dehalococcoides spp. and their role in bioremediation of chloroethenes.