An environmentally-relevant mixture of organochlorines and its vehicle control, dimethylsulfoxide, induce ultrastructural alterations in porcine oocytes

Organochlorine chemicals accumulate in the environment, particularly in the Arctic, and constitute potential developmental hazards to wildlife and human health. Although some of their harmful effects are recognized, their mechanisms of action within the target cells need to be better understood. This study was designed to test the hypothesis that an environmentally-relevant organochlorine mixture alters oocyte ultrastructure in the porcine model. Immature cumulus-oocyte complexes (COCs), partially cultured (18 hr) COCs without treatment or exposed to the organochlorine mixture or its vehicle (0.1% dimethysulfoxide; DMSO) during culture were processed for light and transmission electronic microscopy (TEM). The organochlorines induced major ultrastructural changes in the COCs: decreased density of the lipid droplets, increased smooth endoplasmic reticulum (SER) volume and increased interactions among SER, mitochondria, lipid droplets and vesicles. We suggest that these ultrastructural changes facilitate energy formation necessary to produce metabolizing enzymes. Other ultrastructural changes may reflect some degree of organochlorine toxicity: fewer gap junctions and decreased electron density of the cortical granules. Unexpectedly, the DMSO control treatment also induced similar ultrastructural changes, but to a lesser degree than the organochlorine mixture. This study is the first to demonstrate the effect of environmental contaminants on mammalian oocyte ultrastructure.     

Stable isotope probing reveals the dominant role of Burkholderia species in aerobic degradation of PCBs

The active bacteria of a biofilm community grown directly on polychlorinated biphenyl (PCB) droplets were analyzed by 16S rRNA fingerprinting, identified by their 16S rRNA gene sequences and fatty acid profiling, and compared with isolates from the biofilm. Although, the multi-species biofilm degraded di- and trichlorinated PCB-congeners these substrates were not attacked by its individual isolated members, which suggests that a metabolic network is responsible for PCB degradation in the biofilm. The community metabolized [U-13C]-2,2'-dichlorobiphenyl incorporating the label into certain phospholipid fatty acids matching those found in Burkholderia species. In contrast, abundant biofilm community members, like Methylobacterium species, did not incorporate the label. These results provide prima faciae evidence for Burkholderia species as the main degraders of PCBs in this type of aerobic soils.     

Catabolic characteristics of biphenyl-utilizing isolates which cometabolize PCBs

As there are at least three types of bacteria involved in the aerobic mineralization of polychlorinated biphenyls (PCBs), this study was undertaken to determine what catabolic features are lacking in biphenyl-degraders and to determine if chlorobenzoate- and chloroacetate-utilizing bacteria are as indigenous to soil as biphenyl-degraders. Bacteria were tested for their ability to utilize chlorinated acids and to cometabolize Aroclor 1254 and dibenzo-p-dioxane (dioxin). The broad and variable substrate specificity of the biphenyl dioxygenase among strains was noted by the range of <1 to 53% cometabolism of total PCB congeners and by the oxidation of dioxin, which was not a growth substrate. Growth on chloroalkanoic acids was more frequent with 2-chloropropionate (87% of all strains), 3-chloropropionate (72%), 4-chlorobutyrate (66%), and less frequent (28%) withtrans-3-chlorocrotonate. However, only one strain,Pseudomonas fluorescens K3, could utilize chloroacetate. No biphenyl-utilizers grew on 2- or 4-chlorobenzoate, and only five strains grew on 3-chlorobenzoate. Acetate and benzoate-utilizers were found in all three soils tested at levels near 10⁶/g, whereas chloroacetate- or chlorobenzoate-utilizers were not detected. The inability of biphenyl-degraders to dehalogenate the products of PCB cometabolism is clearly unrelated to metabolism of saturated chloroaliphatic acids, with the notable exception of chloroacetate, since most strains grew on them. Thus, the inability to utilize chloroacetate, a central intermediate in the meta fission pathway, may be relevant to the incomplete catabolism of PCBs by biphenyl-utilizers.     

Role of receptors in human and rodent hepatocarcinogenesis

The liver is a major target organ in rodent carcinogenicity assays. Amongst the agents that are effective in producing rodent liver tumours are many chemicals which are not mutagenic, but are believed to mediate their effects by promoting the clonal outgrowth of initiated cells. Some of these chemicals, such as dibenzo-p-dioxins and certain PCBs, have been demonstrated to interact with specific cellular receptors and receptor binding appears crucial for their tumourigenic activity. Enzyme-altered foci in rat liver may serve as a sensitive means to estimate the promoting activity of these agents in rodents. Mechanistic considerations are of relevance when extrapolating these date from rodents to humans.     

The effect of chemical pretreatment on the aerobic microbial degradation of PCB congeners in aqueous systems

A series of experiments was conducted to examine the effects of chemical pretreatment on biodegradation of¹⁴C-labeled PCB congeners in aqueous systems. Fenton's reagent was used to generate hydroxyl radicals (OH) which were successful in partially oxidizing/transforming otherwise recalcitrant molecules of tetrachlorinated PCB, but had little or no impact on the biodegradation of a monochlorinated congener. Application of Fenton's reagent (1% H₂O₂, 1 mM FeSO₄) followed by inoculation with pure culturesPseudomonas sp, strain LB 400 andAlcaligenes eutrophus, strain H850 resulted in the removal of approximately 38% of 2-chlorobiphenyl and 51% of 2,2, 4,4-tetrachlorobiphenyl in the form of¹⁴CO₂. Comparison of the rate and extent of biodegradation of 2,2, 4,4-tetrachlorobiphenyl after the application of Fenton's reagent with the dynamic and final level of radioactivity in the aqueous phase of experimental system suggests two possible means of microbial utilization of tetrachlorinated PCB congener altered by chemical oxidation: (a) consumption of the partially oxidized chemical dissolved in the aqueous phase, and (b) direct microbial attack on the transformed compound, which may still be adhered to the solid surface.     

Different molecular capacity in the induction of apoptosis by polychlorinated biphenyl congeners in rat renal tubular cell cultures

The effects of a commercial polychlorinated biphenyl (PCB) mixture (Aroclor 1248) and two individual PCB congeners were evaluated on rat renal proximal tubule culture cell viability and internucleosomal DNA fragmentation (DNA ladder) characteristic of apoptosis. Treatment with Aroclor 1248 caused the loss of cell viability and promoted apoptosis in a concentration- and time-dependent manner. The two PCB congeners assessed can also induce apoptosis. However, the extent of apoptosis generated was greater for the non-ortho-substituted planar congener (3,3,4,4-tetrachlorobiphenyl) than for the di-ortho-substituted nonplanar congener (2,2,4,4,5,5-hexachlorobiphenyl). This correlated with the loss of cell viability since the planar compound is much more cytotoxic. The results suggest a different molecular mechanism in the induction of apoptosis by planar or nonplanar PCB congeners.     

多氯联苯降解菌Burkholderia xenovorans LB400研究进展

Burkholderia xenovorans LB400是一株多氯联苯(polychlorinated biphenyls,PCBs)降解菌,可以氧化含有1?6个氯取代基的多氯联苯。近年来,由于其广泛的底物谱和优异的降解性能,菌株LB400已成为研究原核生物降解多氯联苯的生物化学和分子生物学方面的模式生物。目前关于PCBs的微生物降解研究已不再局限于对微生物资源的挖掘,而是更多地聚焦在LB400等降解菌的PCBs降解基因、降解酶的酶学特性以及酶的人工分子进化等方面。同时,LB400作为早期发现的降解菌,其对多氯联苯的降解途径、底物范围及相关机制也被广泛探讨;但是对于PCBs降解相关基因的调控研究较少。因此,本文以Burkholderia xenovorans LB400对多氯联苯降解为核心,通过综述其代谢途径、代谢相关基因和酶系以及降解应用等方面的研究进展,以期为深入探讨Burkholderia xenovorans LB400的应用以及进一步在遗传、分子和生化水平研究其他多氯联苯降解菌株提供借鉴。     

Resonance light scattering technique for determination of polychlorinated biphenyls with silver nanoparticles

In this paper, a simple and novel method for the determination of polychlorinated biphenyls (PCBs), using silver nanoparticles (AgNPs) as a resonance light scattering (RLS) probe, is proposed. Under optimized conditions, there existed linear relationships between the enhancing RLS intensity of the system and the concentrations of PCBs in the range 8.0 × 10^?8?1.0 × 10^?6 g mL^?1 for 2,4,4′‐trichlorbiphenyl (PCB28), 9.0 × 10^?8?1.0 × 10^?6 g mL^?1 for 2,2′,5,5′‐tetrachlorbiphenyl (PCB52) and 4.0 × 10^?8?1.0 × 10^?6 g mL^?1 for 3,3′,4,4′‐tetrachlorobiphenyl (PCB77). The corresponding detection limits (S/N = 3) were 2.6 × 10^?8 g mL^?1 for PCB28, 3.3 × 10^?8 g mL^?1 for PCB52 and 6.3 × 10^?9 g mL^?1 for PCB77, respectively. Finally, the mechanism of RLS enhancement was also studied. The results indicated that PCBs were adsorbed on the surface of AgNPs to form larger AgNP–PCB aggregates, resulting in the RLS enhancement of the system. Copyright © 2011 John Wiley & Sons, Ltd.     

Isolation and characterization of a thermophilic Bacillus sp. JF8 capable of degrading polychlorinated biphenyls and naphthalene

Bacillus sp. strain JF8, which was isolated from compost, utilizes naphthalene and biphenyl as carbon sources at 60 degrees C. Biphenyl grown cells of strain JF8 barely degraded naphthalene while naphthalene grown cells did not degrade p-chlorobiphenyl, suggesting the existince of two independent degradation pathways. Isolation of JF8N, a mutant strain which can not utilize biphenyl as a carbon source while retaining the ability to utilize naphthalene, supports this hypothesis. Biphenyl grown cells of strain JF8 can degrade several polychlorinated biphenyl congeners including tetra- and pentachlorobiphenyl. bph and nah probes from mesophilic organisms failed to hybridize to strain JF8 DNA.