Microbial transformation of chiral organohalides: Distribution, microorganisms and mechanisms

Understanding the sources, function, and irreplaceable role of cobamides in organohalide-respiring bacteria

Halogenated organic compounds are persistent pollutants that pose a serious threat to human health and the safety of ecosystems. Cobamides are essential cofactors for reductive dehalogenases (RDase) in organohalide-respiring bacteria (OHRB), which catalyze the dehalogenation process. This review systematically summarizes the impact of cobamides on organohalide respiration. The catalytic processes of cobamide in dehalogenation processes are also discussed. Additionally, we examine OHRB, which cannot synthesize cobamide and must obtain it from the environment through a salvage pathway; the co-culture with cobamide producer is more beneficial and possible. This review aims to help readers better understand the importance and function of cobamides in reductive dehalogenation. The presented information can aid in the development of bioremediation strategies.

Expanding the Role of Chiral Drugs and Chiral Nanomaterials as a Potential Therapeutic Tool

Chirality, the property of molecules having mirror-image forms, plays a crucial role in pharmaceutical and biomedical research. This review highlights its growing importance, emphasizing how chiral drugs and nanomaterials impact drug effectiveness, safety, and diagnostics. Chiral molecules serve as precise diagnostic tools, aiding in accurate disease detection through unique biomolecule interactions. The article extensively covers chiral drug applications in treating cardiovascular diseases, CNS disorders, local anesthesia, anti-inflammatories, antimicrobials, and anticancer drugs. Additionally, it explores the emerging field of chiral nanomaterials, highlighting their suitability for biomedical applications in diagnostics and therapeutics, enhancing medical treatments.

Comprehensive exploration of the anaerobic biotransformation of polychlorinated biphenyls in Dehalococcoides mccartyi CG1: Kinetics, enantioselectivity, and isotope fractionation

Anaerobic microbial transformation is a key pathway in the natural attenuation of polychlorinated biphenyls (PCBs). Much less is known about the transformation behaviors induced by pure organohalide-respiring bacteria, especially kinetic isotope effects. Therefore, the kinetics, pathways, enantioselectivity, and carbon and chlorine isotope fractionation of PCBs transformation by Dehalococcoides mccartyi CG1 were comprehensively explored. The results indicated that the PCBs were mainly dechlorinated via removing their double-flanked meta-chlorine, with their first-order kinetic constants following the order of PCB132 > PCB174 > PCB85 > PCB183 > PCB138. However, PCBs occurred great loss of stoichiometric mass balance during microbial transformation, suggesting the generation of other non-dehalogenation products and/or stable intermediates. The preferential transformation of (-)-atropisomers and generation of (+)-atropisomers were observed during PCB132 and PCB174 biotransformation with the enantiomeric enrichment factors of -0.8609 ± 0.1077 and -0.4503 ± 0.1334 (first half incubation times)/-0.1888 ± 0.1354 (second half incubation times), respectively, whereas no enantioselectivity occurred during PCB183 biotransformation. More importantly, although there was no carbon and chlorine isotope fractionation occurring for studied substrates, the δ13C values of dechlorination products, including PCB47 (-28.15 ± 0.35‰ ∼ -27.77 ± 0.20‰), PCB91 (-36.36 ± 0.09‰ ∼ -34.71 ± 0.49‰), and PCB149 (-28.08 ± 0.26‰ ∼ -26.83 ± 0.10‰), were all significantly different from those of their corresponding substrates (PCB85: -30.81 ± 0.02‰ ∼ -30.22 ± 0.21‰, PCB132: -33.57 ± 0.15‰ ∼ -33.13 ± 0.14‰, and PCB174: -26.30 ± 0.09‰ ∼ -26.01 ± 0.07‰), which further supported the generation of other non-dehalogenation products and/or stable intermediates with enrichment or depletion of 13C. These findings provide deeper insights into the anaerobic microbial transformation behaviors of PCBs.

Enantioselective transformation of phytoplankton-derived dihydroxypropanesulfonate by marine bacteria

Chirality, a fundamental property of matter, is often overlooked in the studies of marine organic matter cycles. Dihydroxypropanesulfonate (DHPS), a globally abundant organosulfur compound, serves as an ecologically important currency for nutrient and energy transfer from phytoplankton to bacteria in the ocean. However, the chirality of DHPS in nature and its transformation remain unclear. Here, we developed a novel approach using chiral phosphorus-reagent labeling to separate DHPS enantiomers. Our findings demonstrated that at least one enantiomer of DHPS is present in marine diatoms and coccolithophores, and that both enantiomers are widespread in marine environments. A novel chiral-selective DHPS catabolic pathway was identified in marine Roseobacteraceae strains, where HpsO and HpsP dehydrogenases at the gateway to DHPS catabolism act specifically on R-DHPS and S-DHPS, respectively. R-DHPS is also a substrate for the dehydrogenase HpsN. All three dehydrogenases generate stable hydrogen bonds between the chirality-center hydroxyls of DHPS and highly conserved residues, and HpsP also form coordinate-covalent bonds between the chirality-center hydroxyls and Zn2+, which determines the mechanistic basis of strict stereoselectivity. We further illustrated the role of enzymatic promiscuity in the evolution of DHPS metabolism in Roseobacteraceae and SAR11. This study provides the first evidence of chirality's involvement in phytoplankton-bacteria metabolic currencies, opening a new avenue for understanding the ocean organosulfur cycle.

Metabolism of natural and synthetic bioactive compounds in Cunninghamella fungi and their applications in drug discovery

Investigation of xenobiotic metabolism is a key step for drug discovery. Since the in vivo investigations may be associated with harmful effects attributed to production of toxic metabolites, it is deemed necessary to predict their structure especially at the preliminary clinical studies. Furthermore, the application of microorganisms that are capable of metabolizing drugs mimic human metabolism and consequently may predict possible metabolites. The genus Cunninghamella has been proven to be a potential candidate, which mimics xenobiotic metabolism occurring inside the human body, including phase I and II metabolic reactions. Moreover, biotransformation with Cunninghamella showed chemical diversity, where a lot of products were detected in relation to the initial substrates after being modified by oxidation, hydroxylation, and conjugation reactions. Some of these products are more bioactive than the parent compounds. The current review presents a comprehensive literature overview regarding the Cunninghamella organisms as biocatalysts, which simulate mammalian metabolism of natural secondary and synthetic compounds.

Enantioselective Behaviors of Chiral Pesticides and Enantiomeric Signatures in Foods and the Environment

Unreasonable application of pesticides may result in residues in the environment and foods. Chiral pesticides consist of two or more enantiomers, which may exhibit different behaviors. This Review intends to provide progress on the enantioselective residues of chiral pesticides in foods. Among the main chiral analytical methods, high performance liquid chromatography (HPLC) is the most frequently utilized. Most chiral pesticides are utilized as racemates; however, due to enantioselective dissipation, bioaccumulation, biodegradation, and chiral conversion, enantiospecific residues have been found in the environment and foods. Some chiral pesticides exhibit strong enantioselectivity, highlighting the importance of evaluation on an enantiomeric level. However, the occurrence characteristics of chiral pesticides in foods and specific enzymes or transport proteins involved in enantioselectivity needs to be further investigated. This Review could help the production of some chiral pesticides to single-enantiomer formulations, thereby reducing pesticide consumption as well as increasing food production and finally reducing human health risks.

Microbial Detoxification of Residual Pesticides in Fermented Foods: Current Status and Prospects

The treatment of agricultural areas with pesticides is an indispensable approach to improve crop yields and cannot be avoided in the coming decades. At the same time, significant amounts of pesticides remain in food and their ingestion causes serious damage such as neurological, gastrointestinal, and allergic reactions; cancer; and even death. However, during the fermentation processing of foods, residual amounts of pesticides are significantly reduced thanks to enzymatic degradation by the starter and accompanying microflora. This review concentrates on foods with the highest levels of pesticide residues, such as milk, yogurt, fermented vegetables (pickles, kimchi, and olives), fruit juices, grains, sourdough, and wines. The focus is on the molecular mechanisms of pesticide degradation due to the presence of specific microbial species. They contain a unique genetic pool that confers an appropriate enzymological profile to act as pesticide detoxifiers. The prospects of developing more effective biodetoxification strategies by engaging probiotic lactic acid bacteria are also discussed.

The profiles of chiral pesticides in peri-urban areas near Yangtze River: Enantioselective distribution characteristics and correlations with surface sediments

Chiral pesticides account for 30% of pesticides. Pesticides are inevitably leached into the groundwater by runoff. At the watershed level, the distribution characteristics of enantiomers in sediments collected from the river network of an agricultural area near the middle and lower reaches of the Yangtze River were tested, and their potential correlations with the physicochemical properties and microbial communities of the sediments were analyzed. The sediment pollution was serious at sites 8 and 9, with their pollution source possibly being agricultural or industrial sewage. Moreover, there were higher cumulative contents of pesticide residues at sites 4, 8, and 9. Specifically, Cycloxaprid was the most detected chiral pesticide in the study area, followed by Dinotefuran and Diclofop-methyl. Additionally, Ethiprole and Difenoconazole had strong enantioselectivity in the study area. Interestingly, the enantiomers of some chiral pesticides, such as Tebuconazole, had completely different distributions at different sites. Pearson correlation analysis showed that sediment catalase and microbial biomass carbon were important factors for enantioselectivity of chiral pesticides. The effect of sediment physicochemical properties on enantioselective distribution was achieved by influencing the microorganisms in the sediment. Furthermore, the enantioselective distribution of Tebuconazole was closely related to the genus Arenimonas. Overall, the enantioselective distribution of most of the chiral pesticides was positively correlated with the prokaryotic microbial community. This study provides empirical support for agricultural non-point source pollution caused by chiral pesticides, and also lays a research foundation for exploring the factors that affect the fate of chiral pesticides in the environment.

Mechanistic insight into co-metabolic dechlorination of hexachloro-1,3-butadiene in Dehalococcoides

Hexachloro-1,3-butadiene (HCBD) as one of emerging persistent organic pollutants (POPs) poses potential risk to human health and ecosystems. Organohalide-respiring bacteria (OHRB)-mediated reductive dehalogenation represents a promising strategy to remediate HCBD-contaminated sites. Nonetheless, information on the HCBD-dechlorinating OHRB and their dechlorination pathways remain unknown. In this study, both in vivo and in vitro experiments, as well as quantum chemical calculation, were employed to successfully identify and characterize the reductive dechlorination of HCBD by Dehalococcoides. Results showed that some Dehalococcoides extensively dechlorinated HCBD to (E)-1,2,3-tri-CBD via (E)-1,1,2,3,4-penta-CBD and (Z,E)-1,2,3,4-tetra-CBD in a co-metabolic way. Both qPCR and 16S rRNA gene amplicon sequencing analyses suggested that the HCBD-dechlorinating Dehalococcoides coupled their cell growth with dechlorination of perchloroethene (PCE), rather than HCBD. The in vivo and in vitro ATPase assays indicated ≥78.89% decrease in ATPase activity upon HCBD addition, which suggested HCBD inhibition on ATPase-mediated energy harvest and provided rationality on the Dehalococcoides-mediated co-metabolic dechlorination of HCBD. Interestingly, dehalogenation screening of organohalides with the HCBD-dechlorinating enrichment cultures showed that debromination of bromodichloromethane (BDCM) was active in the in vitro RDase assays but non-active in the in vivo experiments. Further in vitro assays of hydrogenase activity suggested that significant inhibition of BDCM on the hydrogenase activity could block electron derivation from H₂ for consequent reduction of organohalides in the in vivo experiments. Therefore, our results provided unprecedented insight into metabolic, co-metabolic and RDase-active-only dehalogenation of varied organohalides by specific OHRB, which could guide future screening of OHRB for remediation of sites contaminated by HCBD and other POPs.

Long-Term Dechlorination of Polychlorinated Biphenyls (PCBs) in Taihu Lake Sediment Microcosms: Identification of New Pathways, PCB-Driven Shifts of Microbial Communities, and Insights into Dechlorination Potential

Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) is regarded as an alternative approach for in situ remediation and detoxification in the environment. To better understand the process of PCB dechlorination in freshwater lake sediment, a long-term (108 weeks) dechlorination study was performed in Taihu Lake sediment microcosms with nine parent PCB congeners (PCB5, 12, 64, 71, 105, 114, 149, 153, and 170). Within 108 weeks, the total PCBs declined by 32.8%, while parent PCBs declined by 84.8%. PCB dechlorinators preferred to attack meta- and para-chlorines, principally para-flanked meta and single-flanked para chlorines. A total of 58 dechlorination pathways were observed, and 20 of them were not in 8 processes, suggesting the broad spectrum of PCB dechlorination in the environment. Rare ortho dechlorination was confirmed to target the unflanked ortho chlorine, indicating a potential for complete dechlorination. PCBs drove the shifts of the microbial community structures, and putative dechlorinating bacteria were growth-linked to PCB dechlorination. The distinct jump of RDase genes ardA, rdh12, pcbA4, and pcbA5 was found to be consistent with the commencement of dechlorination. The maintained high level of putative dechlorinating phylum Chloroflexi (including Dehalococcoides and o-17/DF-1), genus Dehalococcoides, and four RDase genes at the end of incubation revealed the long-term dechlorination potential. This work provided insights into dechlorination potential for long-term remediation strategies at PCB-contaminated sites.

Environmental occurrence and remediation of emerging organohalides: A review

As replacements for "old" organohalides, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), "new" organohalides have been developed, including decabromodiphenyl ethane (DBDPE), short-chain chlorinated paraffins (SCCPs), and perfluorobutyrate (PFBA). In the past decade, these emerging organohalides (EOHs) have been extensively produced as industrial and consumer products, resulting in their widespread environmental distribution. This review comprehensively summarizes the environmental occurrence and remediation methods for typical EOHs. Based on the data collected from 2015 to 2021, these EOHs are widespread in both abiotic (e.g., dust, air, soil, sediment, and water) and biotic (e.g., bird, fish, and human serum) matrices. A significant positive correlation was found between the estimated annual production amounts of EOHs and their environmental contamination levels, suggesting the prohibition of both production and usage of EOHs as a critical pollution-source control strategy. The strengths and weaknesses, as well as the future prospects of up-to-date remediation techniques, such as photodegradation, chemical oxidation, and biodegradation, are critically discussed. Of these remediation techniques, microbial reductive dehalogenation represents a promising in situ remediation method for removal of EOHs, such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) and halogenated flame retardants (HFRs).

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in Pacific salmon from the Kamchatka Peninsula and Sakhalin Island, Northwest Pacific

The purpose of the present study was to determine levels of POPs (dieldrin, endrin, HCH isomers, DDT metabolites, and PCB congeners) in organs of chum (Oncorhynchus keta), pink (O. gorbuscha), sockeye (O. nerka), masu (O. masou), and Chinook salmon (O. tshawytscha), and to identify the patterns of toxicants' distribution in organisms and the environment of the northwestern Pacific. Principal component factor analysis showed that all the salmon species typically exhibit relationships between the PCB congeners and are characterized by a similar pattern of entry of PCBs 101, 118, and 153. The OCPs levels in the organs of Pacific salmon are decreasing from 2012 to 2018, which suggests the elimination of these toxicants from the northwestern Pacific Ocean.

Spatial Distribution, Bioconversion and Ecological Risk of PCBs and PBDEs in the Surface Sediment of Contaminated Urban Rivers: A Nationwide Study in China

Surface sediments of polluted urban rivers can be a reservoir of hydrophobic persistent organic pollutants (POPs). In this study, we comprehensively assessed the contamination of two groups of POPs, that is, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), in 173 black-odorous urban rivers in China. Spatial distribution of PCBs and PBDEs showed similar patterns but very different contamination levels in surface sediments, that is, average concentrations of 10.73 and 401.16 ng/g dw for the ∑PCBs and ∑PBDEs, respectively. Tetra-/di-CBs and deca-BDE are major PCBs and PBDEs and accounted for 59.11 and 95.11 wt % of the ∑PCBs and ∑PBDEs, respectively. Compared with the persistence of PBDEs, the EF changes of chiral PCBs together with previous cultivation evidence indicated indigenous bioconversion of PCBs in black-odorous urban rivers, particularly the involvement of uncharacterized Dehalococcoidia in PCB dechlorination. Major PCB sources (and their relative contributions) included pigment/painting (25.36%), e-waste (22.92%), metallurgical industry (13.25%), and e-waste/biological degradation process (10.95%). A risk assessment indicated that exposure of resident organisms in urban river sediments to deca-/penta-BDEs could pose a high ecological risk. This study provides the first insight into the contamination, conversion and ecological risk of PCBs and PBDEs in nationwide polluted urban rivers in China.

Lake Superior Has Lost over 90% of Its Pesticide HCH Load since 1986

The time trend of α- and γ-hexachlorocyclohexane (HCH) isomers in Lake Superior water was followed from 1986 to 2016, the longest record for any persistent organic pollutant (POP) in Great Lakes water. Dissipation of α-HCH and γ-HCHs was first order, with halving times (t1/2) of 5.7 and 8.5 y, respectively. Loss rates were not significantly different starting a decade later (1996-2016). Concentrations of β-HCH were followed from 1996-2016 and dissipated more slowly (t1/2 = 16 y). In 1986, the lake contained an estimated 98.8 tonnes of α-HCH and 13.2 tonnes of γ-HCH; by 2016, only 2.7% and 7.9% of 1986 quantities remained. Halving times of both isomers in water were longer than those reported in air, and for γ-HCH, they were longer in water than those reported in lake trout. Microbial degradation was evident by enantioselective depletion of (+)α-HCH, which increased from 1996 to 2011. Volatilization was the main removal process for both isomers, followed by degradation (hydrolytic and microbial) and outflow through the St. Mary's River. Sedimentation was minor. Major uncertainties in quantifying removal processes were in the two-film model for predicting volatilization and in microbial degradation rates. The study highlights the value of long-term monitoring of chemicals in water to interpreting removal processes and trends in biota.

Enhanced mineralization of chlorpyrifos bound residues in soil through inoculation of two synergistic degrading strains

Bioaugmentation methods are frequently employed for pesticide pollution remediation; however, it is not clear whether the introduced bacteria affect the pesticide bound residue (BRs) composition and whether the BRs can be catabolized by the introduced strains. This study aimed at answering these questions by using ¹⁴C-chlorpyrifos (¹⁴C-CPF) and two CPF-degrading strains (Pseudomonas sp. DSP-1 and Cupriavidus sp. P2). The results showed that the BRs can be up to 83.0%, and that the CPF-BRs formed can be further transformed into ¹⁴CO₂ by the strains. Indeed, the microbial inoculation can increase the CPF mineralization by 1.0-22.1 times and can decrease the BRs by up to ~50% of the control (on day 20). Compared with the control without bioaugmentation, microbial inoculation enhanced the release of BRs by 2.2-18.0 times. Adding biochar to the soil can greatly inhibit CPF mineralization and maintain the BR content at a relatively stable level. The CPF residue can affect the composition of the indigenous soil microbial community, but the introduction of bacteria for remediation did not have a significant effect. The results indicate that Pseudomonas sp. DSP-1 and Cupriavidus sp. P2 are useful for remediating both CPF extractable and bound residues.

Flounders as indicators of environmental contamination by persistent organic pollutants and health risk

The purpose of this study was to elucidate the potential of using flounders as bioindicators of accumulation and transformation of POPs and to assess the possible environmental risk to the health of the population of the Russian coastal regions. The mean levels of HCH, DDT, and PCBs in the flounders were as follows: in the eastern Sea of Okhotsk, 49 ± 51, 62 ± 89, and 106 ± 83 ng/g lipid weight; in the southern Sea of Okhotsk, 36 ± 37, 15 ± 16, and 97 ± 41 ng/g lipid wt; in the Sea of Japan/East Sea, 62 ± 36, 39 ± 28, and 1616 ± 1177 ng/g lipid wt, respectively. In the Tatar Strait, OCPs were represented mainly by β-HCH with a concentration of 221 ± 182 ng/g lipid wt; the PCB level was 455 ± 317 ng/g lipid wt. Values of ILCR = 2.1·10^-5 due to the consumption of flounder from the Sea of Japan/East Sea at a rate of 29 kg/yr indicate a probability of developing cancer during a lifetime.

Analysis of pyrethroids in cereals by HPLC with a deep eutectic solvent-based dispersive liquid-liquid microextraction with solidification of floating organic droplets

This work presents a novel and green analytical procedure involving a deep eutectic solvent-based dispersive liquid-liquid microextraction with solidification of floating organic droplets (DES-DLLME-SFOD) followed by HPLC to measure three pyrethroids (bifenthrin, β-cypermethrin, and deltamethrin) in cereal samples. Firstly, a low-density hydrophobic DES was synthesized from thymol and octanoic acid in the molar ratio of 1/4 and this was applied as a green extraction solvent in the DLLME procedure to avoid the use of a toxic extractant. After centrifugation and placing it on an ice bath, it is transformed into a solid phase on the top of the sample solution to reduce the loss of extractant, conducive to convenient collection thereafter. This procedure required the optimal conditions (including the type, proportion, and amount of DES as the extractant, the volume of the dispersant acetonitrile, the amount of salt, and the pH value) to be evaluated. Under optimized variates, the proposed method provided good linearity with a correlation coefficient greater than 0.997 and limits of quantification within the range of 6.6-8.9 μg kg^-1. The recoveries of pyrethroids in corn, wheat, barley, and oats were 75.6-87.2%, and the relative standard deviation was less than 3.6%. The method, therefore, offers a green, efficient, and convenient approach for the determination of pesticides in cereals.

Microbial catabolism of lindane in distinct layers of acidic paddy soils combinedly affected by different water managements and bioremediation strategies

The environmental fate of the recalcitrant organic chlorine insecticide lindane and its removal from contaminated soils are still of great concern. However, the key factors influencing microbial removal of lindane from paddy soils with intermittent flooding and draining remain largely unknown. Here, we conducted laboratory experiments to investigated lindane biodegradation in different layers of typical acidic paddy soils under different water managements and bioremediation strategies, together with the changes of functional bacterial consortium, key genes and metabolic pathways. It was found that under flooded conditions, lindane spiking significantly stimulated the growth of some bacterial genera with potential anaerobic catabolic functions in both top- (0-20 cm depth) and subsoil (20-40 cm depth), leading to the shortest half-life of lindane with 7.6-9.0 d in the topsoil. In contrary, lindane spiking dramatically stimulated the growth of bacterial members with aerobic catabolic functions under drained conditions, exhibiting half-lives of lindane with 85-131 d and 18-23 d in the top- and subsoil, respectively. Overall, biostimulation coupled with flooding management would be the better combination for increased lindane bioremediation. Functional genes involved in lindane degradation and retrieved from metagenomic data further supported the anaerobic and aerobic biodegradation of lindane under flooded and drained conditions, respectively. Moreover, the integrated network analysis suggested water management and organic matter were the primary factors shaped the assembly of functional bacteria in lindane degradation, among which Clostridium and Rhodanobacter were the key anaerobic and aerobic functional genera, respectively. Taken together, our study provides a comprehensive understanding of lindane biodegradation in distinct layers of acidic paddy soils that were combinedly affected by different water managements and bioremediation strategies.

Tracing the sources and microbial degradation of PCBs in field sediments by a multiple-line-of-evidence approach including compound-specific stable isotope analysis

Comprehensive monitoring is crucial for tracing micropollutants in the natural environment. To better evaluate the sources and natural attenuation of polychlorinated biphenyls (PCBs), three composite sediment cores were sampled from a closed pond near e-waste recycling plants, and a multiple-line-of-evidence approach (MLEA) including quantification, enantiomer analysis, microbial community profiling, and compound-specific isotope analysis (CSIA) was used to investigate the fate of PCBs in sediment cores. The difference in the maximum PCB concentrations and associated depths between sites 1/2 and 3 and the corresponding significant (p < 0.01) difference in δ¹³C values strongly indicated two different PCB inputs at sites 1/2 and 3. A significant (p < 0.01) negative correlation between the variation in chlorine per biphenyl (CPB) and Log the abundance of Dehalococcoides/total molar concentration of PCBs (Log Dhc/TPCB) along the cores suggested that different degrees of PCB degradation occurred and that Dehalococcoides likely participated in PCB degradation in these sediments. Nonracemic compositions and pronounced stable carbon isotope fractionation (Δδ¹³C > 1‰) of PCB congeners were observed, confirming that in situ degradation occurred in the sediment cores. The progressive enrichment in ¹³C with increasing core depth suggested strengthened microbial degradation of the residual congener pools. The results of this study suggested that MLEA analysis of PCBs can provide reliable information to better monitor the sources and fate of these compounds in the environment.

Stereoselective environmental behavior and biological effects of the chiral bitertanol

Bitertanol is a widely used chiral triazole fungicide. The stereoselective environmental behavior and biological effects of bitertanol are not clear. The present study evaluated the stereoselectivity of bitertanol, including its degradation in five typical soils (under laboratory controlled aerobic, anaerobic and sterilization conditions), metabolism in rat liver microsomes (RLM; in vitro), and the endocrine disruption effects on the estrogen receptor (ER) and thyroid hormone receptor (TR) using reporter gene assays. The results indicated that (1S,2R)-bitertanol and (1R,2S)-bitertanol had faster degradation rates in soil than the other stereoisomers. The half-lives of four bitertanol stereoisomers ranged from 9.1 d to 86.6 d in different soils under different conditions. (1S,2R)-bitertanol was preferentially metabolized in RLM. The molecular docking results confirmed the in vitro experiments that (1S,2R)-bitertanol had shortest binding distances and lowest energies with cytochrome P450 enzymes (CYPs). Four bitertanol stereoisomers showed stereoselective antagonistic effects on ER. Additionally, (1S,2R)-bitertanol and (1R,2S)-bitertanol exhibited antagonistic effects on TR. These results suggest that the use of pure (1S,2R)-bitertanol instead of the commercial stereoisomer mix, may help reduce environmental pollution and biological toxicity.

Microbial degradation of halogenated aromatics: molecular mechanisms and enzymatic reactions

Halogenated aromatics are used widely in various industrial, agricultural and household applications. However, due to their stability, most of these compounds persist for a long time, leading to accumulation in the environment. Biological degradation of halogenated aromatics provides sustainable, low-cost and environmentally friendly technologies for removing these toxicants from the environment. This minireview discusses the molecular mechanisms of the enzymatic reactions for degrading halogenated aromatics which naturally occur in various microorganisms. In general, the biodegradation process (especially for aerobic degradation) can be divided into three main steps: upper, middle and lower metabolic pathways which successively convert the toxic halogenated aromatics to common metabolites in cells. The most difficult step in the degradation of halogenated aromatics is the dehalogenation step in the middle pathway. Although a variety of enzymes are involved in the degradation of halogenated aromatics, these various pathways all share the common feature of eventually generating metabolites for utilizing in the energy-producing metabolic pathways in cells. An in-depth understanding of how microbes employ various enzymes in biodegradation can lead to the development of new biotechnologies via enzyme/cell/metabolic engineering or synthetic biology for sustainable biodegradation processes.

Preparation and Evaluation of a Cholesterol Derivatized β-Cyclodextrin-bonded Phase for Achiral and Chiral HPLC

A cholesterol mono-derivatized β-cyclodextrin was synthesized and bonded onto silica gel (SBA-15) to obtain a cholesterol mono-derivatized β-cyclodextrin-bonded stationary phase (CHCDP). The chemical structures of mono-derivatized β-cyclodextrin and CHCDP were characterized by infrared spectroscopy, mass spectrometry, elemental analysis and thermogravimetric analysis, correspondingly. Furthermore, the separation ability of CHCDP in terms of achiral compounds was systematically evaluated by separating benzene homologs, polycyclic aromatic hydrocarbons (PAHs) and some positional isomers. As a result, CHCDP completely separated five benzene homologs and nine PAHs within 30 min under the reversed-phase. In addition, the chiral chromatographic property of CHCDP was also evaluated by separating some racemic compounds including flavanones, triazoles, β-blockers, etc. The results showed that the CHCDP exhibited high enantioselectivities towards most of selected analytes. The enantioresolutions were in the range from 1.43 to 2.51 on CHCDP. Especially the resolutions of 2'-hydroxyflavanone, hexaconazole, Dns-serine and atenolol were as high as 1.94, 1.91, 2.15 and 1.57, respectively. Obviously, the CHCDP was a versatile stationary phase with chiral and achiral separation capabilities in multi-mode chromatography, which was related to the introduction of cholesterol to the port of cyclodextrin, enhancing the hydrophobic interaction of cyclodextrin with achiral compounds, while maintaining the inclusion complexation of it with chiral compounds as well.