Biological dehalogenation and halogenation reactions

Determining the abundance, composition and spatial distribution of organohalogens in marine sediments using combustion-ion chromatography

Understanding the distribution of halogenated organic compounds (HOCs) in marine sediments is essential for understanding the marine carbon and halogen cycling, and also important for assessing the ecosystem health. In this study, a method based on combustion-ion chromatography was developed for determination of the composition and abundance of HOCs in marine sediments. The method showed high accuracy, precision and reproducibility in determining the content of adsorbable organic halogens (AOX), including fluorine, chlorine and bromine (AOF, AOCl, AOBr) and the corresponding insoluble organic halogens (IOF, IOCl, IOBr, IOX), as well as total organic halogen contents (TOX). Application of the method in coastal and deep-sea sediments revealed high ratios of organic halogens in the organic carbon pool of marine sediments, suggesting that organic halogen compounds represent an important yet previously overlooked stock of carbon and energy in marine sediments. Both the TOX and the proportion of organohalogens in organic carbon (X:C ratio) showed an increasing trend from the coast to the deep-sea sediments, indicating an increased significance of HOCs in deep-sea environments. The developed method and the findings of this study lay the foundation for further studies on biogeochemical cycling of HOCs in the ocean.

Microbial Nanotechnology for Precision Nanobiosynthesis: Innovations, Current Opportunities and Future Perspectives for Industrial Sustainability

A new area of biotechnology is nanotechnology. Nanotechnology is an emerging field that aims to develope various substances with nano-dimensions that have utilization in the various sectors of pharmaceuticals, bio prospecting, human activities and biomedical applications. An essential stage in the development of nanotechnology is the creation of nanoparticles. To increase their biological uses, eco-friendly material synthesis processes are becoming increasingly important. Recent years have shown a lot of interest in nanostructured materials due to their beneficial and unique characteristics compared to their polycrystalline counterparts. The fascinating performance of nanomaterials in electronics, optics, and photonics has generated a lot of interest. An eco-friendly approach of creating nanoparticles has emerged in order to get around the drawbacks of conventional techniques. Today, a wide range of nanoparticles have been created by employing various microbes, and their potential in numerous cutting-edge technological fields have been investigated. These particles have well-defined chemical compositions, sizes, and morphologies. The green production of nanoparticles mostly uses plants and microbes. Hence, the use of microbial nanotechnology in agriculture and plant science is the main emphasis of this review. The present review highlights the methods of biological synthesis of nanoparticles available with a major focus on microbially synthesized nanoparticles, parameters and biochemistry involved. Further, it takes into account the genetic engineering and synthetic biology involved in microbial nanobiosynthesis to the construction of microbial nanofactories.

Integration of molecular and computational approaches paints a holistic portrait of obscure metabolisms

Microorganisms are essential drivers of earth's geochemical cycles. However, the significance of elemental redox cycling mediated by microorganisms is often underestimated beyond the most well-studied nutrient cycles. Phosphite, (per)chlorate, and iodate are each considered esoteric substrates metabolized by microorganisms. However, recent investigations have indicated that these metabolisms are widespread and ubiquitous, affirming a need to continue studying the underlying microbiology to understand their biogeochemical effects and their interface with each other and our biosphere. This review focuses on combining canonical techniques of culturing microorganisms with modern omic approaches to further our understanding of obscure metabolic pathways and elucidate their importance in global biogeochemical cycles. Using these approaches, marker genes of interest have already been identified for phosphite, (per)chlorate, and iodate using traditional microbial physiology and genetics. Subsequently, their presence was queried to reveal the distribution of metabolic pathways in the environment using publicly available databases. In conjunction with each other, computational and experimental techniques provide a more comprehensive understanding of the location of these microorganisms, their underlying biochemistry and genetics, and how they tie into our planet's geochemical cycles.

Fungal Biotransformation of Hazardous Organic Compounds in Wood Waste

A diverse spectrum of organisms, such as fungi, bacteria, and actinomycetes, can degrade and transform organic matter, including wood, into valuable nutrients. A sustainable economy has the goal of efficiently using waste as raw materials, and in this optic, it uses biological preparations more and more often, supporting the decomposition of lignocellulosic waste. With reference to wood wastes, which are produced in a substantial amount by the forest and wood industry, one of the possibilities to biodegrade such lignocellulosic material is the composting process. In particular, microbiological inoculum containing dedicated fungi can contribute to the biodegradation of wood waste, as well as the biotransformation of substances from the protection of wood, such as pentachlorophenol (PCP), lindane (hexachlorobenzene) and polycyclic aromatic hydrocarbons (PAHs). The purpose of this research was to produce a literature review in terms of the selection of decay fungi that could potentially be used in toxic biotransformation unions. The findings of the literature review highlighted how fungi such as Bjerkandera adusta, Phanerochaete chrysosporium, and Trametes versicolor might be ingredients of biological consortia that can be effectively applied in composting wood waste containing substances such as pentachlorophenol, lindane, and polycyclic aromatic hydrocarbons (PAHs).

Probing the mechanism of flavin action in the oxidative decarboxylation catalyzed by salicylate hydroxylase

Salicylate hydroxylase (NahG) is a FAD-dependent monooxygenase in which the reduced flavin activates O₂ coupled to the oxidative decarboxylation of salicylate to catechol or uncoupled from substrate oxidation to afford H₂O₂. This chapter presents different methodologies in equilibrium studies, steady-state kinetics, and identification of reaction products, which were important to understand the S_EAr mechanism of catalysis in NahG, the role of the different FAD parts for ligand binding, the extent of uncoupled reaction, and the catalysis of salicylate's oxidative decarboxylation. These features are likely familiar to many other FAD-dependent monooxygenases and offer a potential asset for developing new tools and strategies in catalysis.

Phylogenetic Analyses of Microbial Hydrolytic Dehalogenases Reveal Polyphyletic Origin

Hydrolytic dehalogenases form an important class of dehalogenases that include haloacid dehalogenase, haloalkane dehalogenase, haloacetate dehalogenase, and atrazine chlorohydrolase. These enzymes are involved in biodegradation of various environmental pollutants and therefore it is important to understand their phylogeny. In the present study, it was found that the enzymes haloalkane and haloacetate dehalogenases share a common ancestry with enzymes such as carboxyesterase, epoxide hydrolase, and lipases, which can be traced to ancestral α/β hydrolase fold enzyme. Haloacid dehalogenases and atrazine chlorohydrolases have probabaly evolved from ancestral enzymes with phosphatase and deaminases activity, respectively. These findings were supported by the similarities in the secondary structure, key catalytic motifs and placement of catalytic residues. The phylogeny of haloalkane dehalogenases and haloacid dehalogenases differs from 16S rRNA gene phylogeny, suggesting spread through horizontal gene transfer. Hydrolytic dehalogenases are polyphyletic and do not share a common evolutionay history, the functional similarities are due to convergent evolution. The present study also identifies key functional residues, mutating which, can help in generating better enzymes for clean up of the persistent environmental pollutants using enzymatic bioremediation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-022-01043-8.

Impact of abiotic and biogeochemical processes on halogen concentrations (Cl, Br, F, I) in mineral soil along a climatic gradient

In contrast to earlier ideas that halogens behave inertly in soil, extensive biogeochemical cycling of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) has been shown for temperate forests. To further advance our understanding of halogen behaviour in soil beyond humid temperate forests, we sampled soil profiles in protected areas along the Chilean Coastal Cordillera, representing a pronounced climatic gradient spanning from arid to humid. Halogen concentrations in soil were analysed by combustion ion chromatography. Highest average total halogen concentrations occurred at the arid site (Cl, F: 4270 and 897 mg kg^-1) as well as the humid end of the climatic gradient (Br, I: 42.6 and 9.8 mg kg^-1). Vertical distribution patterns of halogens were most pronounced at the humid end of the gradient and became less distinct under drier climate. The climatic gradient demonstrates the important role of biotic processes (e.g. the halogenation of organic matter) on the retention of halogens in the soil. However, this climate-specific role may be overridden by mainly abiotic processes within a given climate zone (e.g. weathering, leaching, sorption to secondary soil minerals, evaporative enrichment), resulting in vertical relocation of halogens in the soil. Since some of these processes oppose each other, complex interactions and depth distributions of F, Cl, Br and I occur in the soil. In summary, our findings provide new insights into the fate of halogens in mineral soil of different climatic zones, which is important, for example, when radiohalogens are deposited on a large scale after nuclear accidents.

Oxidation of p-[125I]Iodobenzoic Acid and p-[211At]Astatobenzoic Acid Derivatives and Evaluation In Vivo

The alpha particle-emitting radionuclide astatine-211 (²¹¹At) is of interest for targeted radiotherapy; however, low in vivo stability of many ²¹¹At-labeled cancer-targeting molecules has limited its potential. As an alternative labeling method, we evaluated whether a specific type of astatinated aryl compound that has the At atom in a higher oxidation state might be stable to in vivo deastatination. In the research effort, para-iodobenzoic acid methyl ester and dPEG₄-amino acid methyl ester derivatives were prepared as HPLC standards. The corresponding para-stannylbenzoic acid derivatives were also prepared and labeled with ¹²⁵I and ²¹¹At. Oxidization of the [¹²⁵I]iodo- and [²¹¹At]astato-benzamidyl-dPEG₄-acid methyl ester derivatives provided materials for in vivo evaluation. A biodistribution was conducted in mice with coinjected oxidized ¹²⁵I- and ²¹¹At-labeled compounds. The oxidized radioiodinated derivative was stable to in vivo deiodination, but unfortunately the oxidized [²¹¹At]astatinated benzamide derivative was found to be unstable under the conditions of isolation by radio-HPLC (post animal injection). Another biodistribution study in mice evaluated the tissue concentrations of coinjected [²¹¹At]NaAtO₃ and [¹²⁵I]NaIO₃. Comparison of the tissue concentrations of the isolated material from the oxidized [²¹¹At]benzamide derivative with those of [²¹¹At]astatate indicated the species obtained after isolation was likely [²¹¹At]astatate.

Palladium-Catalyzed Cross Haloalkynylation of Haloalkynes

Herein, we have developed a robust Pd-catalyzed haloalkynylation of haloalkynes for the synthesis of dihaloalkenyne derivatives. This cross-haloalkynylation reaction proceeds in a highly chemo- and regioselective manner under mild conditions in the presence of two slightly structurally different haloalkynes and shows strong functional group tolerance under ligand- and base-free conditions.

The role of remote flavin adenine dinucleotide pieces in the oxidative decarboxylation catalyzed by salicylate hydroxylase

Salicylate hydroxylase (NahG) has a single redox site in which FAD is reduced by NADH, the O₂ is activated by the reduced flavin, and salicylate undergoes an oxidative decarboxylation by a C(4a)-hydroperoxyflavin intermediate to give catechol. We report experimental results that show the contribution of individual pieces of the FAD cofactor to the observed enzymatic activity for turnover of the whole cofactor. A comparison of the kinetic parameters and products for the NahG-catalyzed reactions of FMN and riboflavin cofactor fragments reveal that the adenosine monophosphate (AMP) and ribitol phosphate pieces of FAD act to anchor the flavin to the enzyme and to direct the partitioning of the C(4a)-hydroperoxyflavin reaction intermediate towards hydroxylation of salicylate. The addition of AMP or ribitol phosphate pieces to solutions of the truncated flavins results in a partial restoration of the enzymatic activity lost upon truncation of FAD, and the pieces direct the reaction of the C(4a)-hydroperoxyflavin intermediate towards hydroxylation of salicylate.

Chlorination of soil organic matter: The role of humus type and land use

The levels of natural organic chlorine (Cl_org) typically exceed levels of chloride in most soils and is therefore clearly of high importance for continental chlorine cycling. The high spatial variability raises questions on soil organic matter (SOM) chlorination rates among topsoils with different types of organic matter. We measured Cl_org formation rates along depth profiles in six French temperate soils with similar Cl deposition using ³⁶Cl tracer experiments. Three forest sites with different humus types and soils from grassland and arable land were studied. The highest specific chlorination rates (fraction of chlorine pool transformed to Cl_org per time unit) among the forest soils were found in the humus layers. Comparing the forest sites, specific chlorination was highest in mull-type humus, characterized by high microbial activity and fast degradation of the organic matter. Considering non-humus soil layers, grassland and forest soils had similar specific chlorination rates in the uppermost layer (0-10 cm below humus layer). Below this depth the specific chlorination rate decreased slightly in forests, and drastically in the grassland soil. The agricultural soil exhibited the lowest specific chlorination rates, similar along the depth profile. Across all sites, specific chlorination rates were correlated with soil moisture and in combination with the patterns on organic matter types, the results suggest an extensive Cl cycling where humus types and soil moisture provided best conditions for microbial activity. Cl_org accumulation and theoretical residence times were not clearly linked to chlorination rates. This indicates intensive Cl cycling between organic and inorganic forms in forest humus layers, regulated by humic matter reactivity and soil moisture, while long-term Cl_org accumulation seems more linked with overall deep soil organic carbon stabilization. Thus, humus types and factors affecting soil carbon storage, including vegetation land use, could be used as indicators of potential Cl_org formation and accumulation in soils.

Cyanobacteria blooms potentially enhance volatile organic compound (VOC) emissions from a eutrophic lake: Field and experimental evidence

Eutrophication promotes massive cyanobacteria blooms (CBBs), leading to the release of volatile organic compounds (VOCs). To investigate the effects of cyanobacteria on VOC emissions, field campaigns were carried out in eutrophic Chaohu Lake at six sites with different microalgae densities during CBBs in summer 2019, and incubation experiments were performed in the laboratory. The results showed that the lake water was the primary source of VOCs at six sampling sites in Chaohu Lake during CBBs, with an average total VOC flux of 81.2 ± 20.6 μg m^-2 h^-1. Alkanes were the most abundantly emitted VOCs, with a share of 23.1-63.7% of total emitted VOCs, followed by aromatics (16.6-46.3%). The fluxes of total VOCs were significantly greater at sites B and/or C than at site A in July, and at site B' and/or C' than at site A' in August in Chaohu Lake. The fluxes of total VOCs from living and decayed cyanobacteria in the experimental treatments were two orders of magnitude higher than the corresponding values in the control treatments in the laboratory incubation. Taken together, these results suggested that CBBs potentially enhanced VOC emissions from the eutrophic lake, and that cyanobacteria acted as an important source of VOCs. Additionally, non-methane hydrocarbons (i.e., alkanes, alkenes, and aromatics) predominated among the released VOCs during the stabilization and senescence stages, while oxygenated volatile organic compounds (i.e. alcohols, aldehydes, ketones, esters, and furans) prevailed during the apoptosis stage and aromatics and volatile organic sulfur compounds predominated during the decomposition stage, suggesting that VOC emissions varied markedly at different life stages.

Chlorine cycling and the fate of Cl in terrestrial environments

Chlorine (Cl) in the terrestrial environment is of interest from multiple perspectives, including the use of chloride as a tracer for water flow and contaminant transport, organochlorine pollutants, Cl cycling, radioactive waste (radioecology; 36Cl is of large concern) and plant science (Cl as essential element for living plants). During the past decades, there has been a rapid development towards improved understanding of the terrestrial Cl cycle. There is a ubiquitous and extensive natural chlorination of organic matter in terrestrial ecosystems where naturally formed chlorinated organic compounds (Clorg) in soil frequently exceed the abundance of chloride. Chloride dominates import and export from terrestrial ecosystems while soil Clorg and biomass Cl can dominate the standing stock Cl. This has important implications for Cl transport, as chloride will enter the Cl pools resulting in prolonged residence times. Clearly, these pools must be considered separately in future monitoring programs addressing Cl cycling. Moreover, there are indications that (1) large amounts of Cl can accumulate in biomass, in some cases representing the main Cl pool; (2) emissions of volatile organic chlorines could be a significant export pathway of Cl and (3) that there is a production of Clorg in tissues of, e.g. plants and animals and that Cl can accumulate as, e.g. chlorinated fatty acids in organisms. Yet, data focusing on ecosystem perspectives and combined spatiotemporal variability regarding various Cl pools are still scarce, and the processes and ecological roles of the extensive biological Cl cycling are still poorly understood.

Organohalide-Respiring Bacteria at the Heart of Anaerobic Metabolism in Arctic Wet Tundra Soils

Recent work revealed an active biological chlorine cycle in coastal Arctic tundra of northern Alaska. This raised the question of whether chlorine cycling was restricted to coastal areas or if these processes extended to inland tundra. The anaerobic process of organohalide respiration, carried out by specialized bacteria like Dehalococcoides, consumes hydrogen gas and acetate using halogenated organic compounds as terminal electron acceptors, potentially competing with methanogens that produce the greenhouse gas methane. We measured microbial community composition and soil chemistry along an ∼262-km coastal-inland transect to test for the potential of organohalide respiration across the Arctic Coastal Plain and studied the microbial community associated with Dehalococcoides to explore the ecology of this group and its potential to impact C cycling in the Arctic. Concentrations of brominated organic compounds declined sharply with distance from the coast, but the decrease in organic chlorine pools was more subtle. The relative abundances of Dehalococcoides were similar across the transect, except for being lower at the most inland site. Dehalococcoides correlated with other strictly anaerobic genera, plus some facultative ones, that had the genetic potential to provide essential resources (hydrogen, acetate, corrinoids, or organic chlorine). This community included iron reducers, sulfate reducers, syntrophic bacteria, acetogens, and methanogens, some of which might also compete with Dehalococcoides for hydrogen and acetate. Throughout the Arctic Coastal Plain, Dehalococcoides is associated with the dominant anaerobes that control fluxes of hydrogen, acetate, methane, and carbon dioxide. Depending on seasonal electron acceptor availability, organohalide-respiring bacteria could impact carbon cycling in Arctic wet tundra soils.IMPORTANCE Once considered relevant only in contaminated sites, it is now recognized that biological chlorine cycling is widespread in natural environments. However, linkages between chlorine cycling and other ecosystem processes are not well established. Species in the genus Dehalococcoides are highly specialized, using hydrogen, acetate, vitamin B₁₂-like compounds, and organic chlorine produced by the surrounding community. We studied which neighbors might produce these essential resources for Dehalococcoides species. We found that Dehalococcoides species are ubiquitous across the Arctic Coastal Plain and are closely associated with a network of microbes that produce or consume hydrogen or acetate, including the most abundant anaerobic bacteria and methanogenic archaea. We also found organic chlorine and microbes that can produce these compounds throughout the study area. Therefore, Dehalococcoides could control the balance between carbon dioxide and methane (a more potent greenhouse gas) when suitable organic chlorine compounds are available to drive hydrogen and acetate uptake.

Direct C-H bond halogenation and pseudohalogenation of hydrocarbons mediated by high-valent 3d metal-oxo species

Late-stage direct functionalization of the C-H bond is synthetically desirable. Metalloenzymes having metal-oxo active sites are well known to selectively catalyze hydroxylation and halogenation reactions with high efficiency. This review highlights the recent developments in the field of direct C-H halogenation and pseudohalogenation reactions catalyzed by the functional models of metalloenzymes.

Overview of flavin-dependent enzymes

Flavin-dependent enzymes catalyze a wide variety of biological reactions that are important for all types of living organisms. Knowledge gained from studying the chemistry and biological functions of flavins and flavin-dependent enzymes has continuously made significant contributions to the development of the fields of enzymology and metabolism from the 1970s until now. The enzymes have been applied in various applications such as use as biocatalysts in synthetic processes for the chemical and pharmaceutical industries or in the biodetoxification and bioremediation of toxic or unwanted compounds, and as biosensors or biodetection tools for quantifying various agents of interest. Many flavin-dependent enzymes are also prime targets for drug development. Based on their reaction mechanisms, they can be classified into five categories: oxidase, dehydrogenase, monooxygenase, reductase, and redox neutral flavin-dependent enzymes. In this chapter, the general properties of flavin-dependent enzymes and the nature of their chemical reactions are discussed, along with their practical applications.

Intersecting Xenobiology and Neometabolism To Bring Novel Chemistries to Life

The diversity of life relies on a handful of chemical elements (carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus) as part of essential building blocks; some other atoms are needed to a lesser extent, but most of the remaining elements are excluded from biology. This circumstance limits the scope of biochemical reactions in extant metabolism - yet it offers a phenomenal playground for synthetic biology. Xenobiology aims to bring novel bricks to life that could be exploited for (xeno)metabolite synthesis. In particular, the assembly of novel pathways engineered to handle nonbiological elements (neometabolism) will broaden chemical space beyond the reach of natural evolution. In this review, xeno-elements that could be blended into nature's biosynthetic portfolio are discussed together with their physicochemical properties and tools and strategies to incorporate them into biochemistry. We argue that current bioproduction methods can be revolutionized by bridging xenobiology and neometabolism for the synthesis of new-to-nature molecules, such as organohalides.

Biotransformation of Tris(2-chloroethyl) Phosphate (TCEP) in Sediment Microcosms and the Adaptation of Microbial Communities to TCEP

Tris(2-chloroethyl) phosphate (TCEP), a typical chlorinated organophosphate ester (OPE), is an emerging contaminant of global concern because of its frequent occurrence, potential toxic effects, and persistence in the environment. In this study, we investigated the microbial TCEP biotransformation and the development of microbial communities in sediment microcosms with repeated TCEP amendments. The TCEP degradation fitted pseudo-zero-order kinetics, with reaction rates of 0.068 mg/(L h) after the first spike of 5 mg/L and 1.85 mg/(L h) after the second spike of 50 mg/L. TCEP was mainly degraded via phosphoester bond hydrolysis, evidenced by the production of bis(2-chloroethyl) phosphate (BCEP) and mono-chloroethyl phosphate (MCEP). Bis(2-chloroethyl) 2-hydroxyethyl phosphate (TCEP-OH), phosphoric bis(2-chloroethyl) (2-oxoethyl) ester (TCEP-CHO), phosphoric acid bis(2-chloroethyl)(carboxymethyl) ester (TCEP-COOH), and 2-chloroethyl 2-hydroxyethyl hydrogen phosphate (BCEP-OH) were also identified as microbial TCEP transformation products, indicating that TCEP degradation may follow hydrolytic dechlorination and oxidation pathways. Microbial community compositions in TCEP-amended microcosms shifted away from control microcosms after the second TCEP spike. Burkholderiales and Rhizobiales were two prevalent bacterial guilds enriched in TCEP-amended microcosms and were linked to the higher abundances of alkaline and acid phosphatase genes and genes involved in the metabolism of 2-chloroethanol, a side product of TCEP hydrolysis, indicating their importance in degrading TCEP and its metabolites.

Cometabolic degradation of p-chloroaniline by the genus Brevibacillus bacteria with extra carbon sources

In this study, we discovered and isolated a new genus Brevibacillus strain from effluent of dyeing and finishing factory containing highly toxic p-chloroanilines (PCA). Based on the morphological, physiological and biochemical characteristics, as well as 16S rDNA sequence, the strain was identified and denominated as Brevibacillus S-618. Co-metabolism effect was found with extra carbon sources including sodium succinate, sodium citrate, ammonium chloride and glucose which can efficiently promote the biodegradation process of PCA. Under the optimal growth conditions at temperature of 30 °C, pH˜7 and air-water ratio of 0.3 m³/m³·min, the degradation rate of PCA in a 2 L pilot bioreactor with high concentration of 180 mg/L increased from 86.7% to 100% within 72 h after adding sodium succinate. The release of chloride ions during the growth process of the strain was equivalent to the degradation amount of PCA. Meanwhile, the cleavage pathway of PCA degradation by Brevibacillus S-618 was proposed by analysis of enzyme activities of microorganism and intermediate products in the reaction. Benefiting from excellent degradation ability and unique characters in high pollutant contents, high efficient bioreactor can easily be scale up for industrial application. Our study provides a facile route for cost-effectively and environmental-friendly degrading hazardous chemicals.

An Overview of Synthetic Methods for the Preparation of Halolactones

Halolactones are used both in chemical synthesis as intermediates as well as in various industries. These compounds may be secondary metabolites of living organisms, although they are mainly obtained by chemical synthesis. The substrates for the synthesis of chloro-, bromo- and iodolactones are often unsaturated carboxylic acids, and sometimes they are unsaturated esters. The article presents a number of different methods for the production of halolactones, both racemic mixtures and enantiomerically enriched compounds.

Emergence and fate of volatile iodinated organic compounds during biological treatment of oil and gas produced water

Oil and gas (O&G) production in the United States is expected to grow at a substantial rate over the coming decades. Environmental sustainability related to water consumption during O&G extraction can be addressed through treatment and reuse of water returning to the surface after well completion. Water quality is an important factor in reuse applications, and specific treatment technologies must be utilized to remove different contaminants. Among others, biological active filtration can remove dissolved organic matter as a pre-treatment for surface discharge or to facilitate reuse in such applications as hydraulic fracturing, dust suppression, road stabilization, and crop irrigation. Yet, the formation of byproducts during treatment of O&G wastewater remains a concern when evaluating reuse applications. In this study, we investigated the previously unnoticed biotic formation of iodinated organic compounds (IOCs) such as triiodomethane during biological treatment of O&G wastewater for beneficial reuse. Iodide and several IOCs were quantified in O&G produced water before and after treatment in biological active filters filled with different media types over 13 weeks of operation. While iodide and total IOCs were measured at concentrations <53 mg/L and 147 μg/L, respectively, before biological treatment, total IOCs were measured at concentrations close to 4 mg/L after biological treatment. Triiodomethane was the IOC that was predominantly present. IOC formation had a negative strong correlation (r = -0.7 to -0.8, p < 0.05, n = 9) with iodide concentration in the treated O&G wastewater, indicating that iodide introduced to the biological active filter system was utilized in various reactions, including biologically mediated halogenation of organic matter. Additionally, iodide-oxidizing bacteria augmented in the treated produced water pointed towards potential negative environmental implications when releasing biologically treated halide-rich wastewater effluents to the aquatic environment.

Nature-driven approaches to non-natural terpene analogues

The reactions catalysed by terpene synthases belong to the most complex and fascinating cascade-type transformations in Nature.

Aerobic degradation of 2- and 3-fluoroaniline in mixed culture systems and microbial community analysis

Among three monofluoroanilines, 2-fluoroaniline (2-FA) and 3-fluoroaniline (3-FA) exhibit relatively poor biodegradability. This work examined their degradation characteristics in a mixed culture system and also analyzed the microorganism community. After acclimation for 58 d and 43 d, the high removal efficiency of 100% of 2-FA and 95.3% of 3-FA was obtained by adding 25 mg L^-1 of 2-FA or 3-FA to the two reactors, respectively. In addition, the high defluorination rates of 2-FA and 3-FA were observed to be 87.0% and 89.3%, respectively. The degradation kinetics showed that the maximum specific degradation rates of 2-FA and 3-FA were (21.23 ± 0.91) mg FA (g•VSS·h)^-1, and (11.75 ± 0.99) mg FA (g•VSS·h)^-1, respectively. PCR-DGGE analysis revealed that the unique bacteria degrading 2-FA were mainly composed of six genera (Novosphingobium, Bradyrhizobium, Aquaspirillum, Aminobacter, Ochrobactrum, and Labrys), and five genera that degraded 3-FA (Ochrobactrum, Aquaspirillum, Lachnobacterium, Bradyrhizobium, and Variovorax). Analysis of the key catabolic enzyme activities indicated that the simultaneous hydroxylation and dehalogenation were involved in monooxygenase elimination of 2-FA and conversion of 3-FA to 4-fluorocatechol by dioxygenase, indicating that enriched mixed cultures were effective to metabolize 2-FA or 3-FA by unconventional pathways to prevent the accumulation of toxic metabolites.

Diversity of tryptophan halogenases in sponges of the genus Aplysina

Marine sponges are a prolific source of novel enzymes with promising biotechnological potential. Especially halogenases, which are key enzymes in the biosynthesis of brominated and chlorinated secondary metabolites, possess interesting properties towards the production of pharmaceuticals that are often halogenated. In this study we used a polymerase chain reaction (PCR)-based screening to simultaneously examine and compare the richness and diversity of putative tryptophan halogenase protein sequences and bacterial community structures of six Aplysina species from the Mediterranean and Caribbean seas. At the phylum level, bacterial community composition was similar amongst all investigated species and predominated by Actinobacteria, Chloroflexi, Cyanobacteria, Gemmatimonadetes, and Proteobacteria. We detected four phylogenetically diverse clades of putative tryptophan halogenase protein sequences, which were only distantly related to previously reported halogenases. The Mediterranean species Aplysina aerophoba harbored unique halogenase sequences, of which the most predominant was related to a sponge-associated Psychrobacter-derived sequence. In contrast, the Caribbean species shared numerous novel halogenase sequence variants and exhibited a highly similar bacterial community composition at the operational taxonomic unit (OTU) level. Correlations of relative abundances of halogenases with those of bacterial taxa suggest that prominent sponge symbiotic bacteria, including Chloroflexi and Actinobacteria, are putative producers of the detected enzymes and may thus contribute to the chemical defense of their host.

Substitution Reactions on Iodine and Bromine: Mechanisms for Facile Halogenations of Heterocycles

Gas-phase techniques were used to examine the halogenation of deprotonated heterocycles by perfluoroaryl and perfluoroalkyl halides. The results indicate that S_N2@Br and S_N2@I reactions can be very facile and are effective means of halogenating heterocycles. 2-Iodoheptafluoropropane is exceptionally selective for S_N2@I reactions with yields upward of 90%. The results also provide evidence counter to the recent suggestion that t-butoxide-induced halogenations of heterocycles proceed via a radical mechanism.

Biogenic Iodine and Iodine-Containing Metabolites

This review is intended as a comprehensive survey of iodinated metabolites possessing carbon–iodine covalent bond, which have been obtained from living organisms. Generally thought to be minor components produced by many different organisms these interesting compounds now number more than 110. Many from isolated and identified iodine-containing metabolites showed high biological activities. Recent research, especially in the marine area, indicates this number will increase in the future. Sources of iodinated metabolites include microorganisms, algae, marine invertebrates, and some animals. Their origin and possible biological significance have also been discussed.

Microbial Synthesis and Transformation of Inorganic and Organic Chlorine Compounds

Organic and inorganic chlorine compounds are formed by a broad range of natural geochemical, photochemical and biological processes. In addition, chlorine compounds are produced in large quantities for industrial, agricultural and pharmaceutical purposes, which has led to widespread environmental pollution. Abiotic transformations and microbial metabolism of inorganic and organic chlorine compounds combined with human activities constitute the chlorine cycle on Earth. Naturally occurring organochlorines compounds are synthesized and transformed by diverse groups of (micro)organisms in the presence or absence of oxygen. In turn, anthropogenic chlorine contaminants may be degraded under natural or stimulated conditions. Here, we review phylogeny, biochemistry and ecology of microorganisms mediating chlorination and dechlorination processes. In addition, the co-occurrence and potential interdependency of catabolic and anabolic transformations of natural and synthetic chlorine compounds are discussed for selected microorganisms and particular ecosystems.

Occurrence of halogenated natural products in highly consumed fish from polluted and unpolluted tropical bays in SE Brazil

Natural compounds from the metabolism of marine organisms have been detected at high concentrations in environmental samples which are not the producers of these compounds. These natural substances are known as halogenated natural products (HNPs). HNPs are possibly toxic halogenated compounds analogous to POPs that may bioaccumulate and biomagnify along the food web and pose a further risk to human and environmental health. The present study analyzed the occurrence of HNPs in the edible muscle of the three most consumed commercial fish species in the state of Rio de Janeiro: sardine (Sardinella brasiliensis), whitemouth croaker (Micropogonias furnieri) and mullet (Mugil liza) from the highly polluted Guanabara Bay (GB) and the less polluted Ilha Grande Bay (IGB). The analytical steps included Soxhlet extraction, clean-up step and injection in a gas chromatography system coupled to a mass spectrometer operated in the electron-capture negative ion mode (GC/ECNI-MS). The compounds 2,4,6-TBP, 2,4,6-TBA, MHC-1, Q1, 6-MeO-BDE 47 and 2'-MeO-BDE 68 were found in the analyzed fish from both studied areas. Q1, 6-MeO-BDE 47 and 2'-MeO-BDE 68 showed the highest concentrations in samples. Q1 concentrations in the sardines from IGB were higher than the sardines from GB (p < 0.05) and higher than the other IGB species (p < 0.05). The differences found among the species may be related to their characteristic habitat and diet. It is noteworthy that most of these compounds do not have any toxicological reference value. Moreover, the HNPs are being detected in species of low trophic level and since this study has worked only with commercial species, these fish may be considered as a source for human exposure to these natural compounds.

Roles of Two Glutathione-Dependent 3,6-Dichlorogentisate Dehalogenases in Rhizorhabdus dicambivorans Ndbn-20 in the Catabolism of the Herbicide Dicamba

The herbicide dicamba is initially demethylated to 3,6-dichlorosalicylate (3,6-DCSA) in Rhizorhabdus dicambivorans Ndbn-20 and is subsequently 5-hydroxylated to 3,6-dichlorogentisate (3,6-DCGA). In the present study, two glutathione-dependent 3,6-DCGA dehalogenases, DsmH1 and DsmH2, were identified in strain Ndbn-20. DsmH2 shared a low identity (only 31%) with the tetrachlorohydroquinone (TCHQ) dehalogenase PcpC from Sphingobium chlorophenolicum ATCC 39723, while DsmH1 shared a high identity (79%) with PcpC. In the phylogenetic tree of related glutathione S-transferases (GSTs), DsmH1 and DsmH2, together with PcpC and the 2,5-dichlorohydroquinone dehalogenase LinD, formed a separate clade. DsmH1 and DsmH2 were synthesized in Escherichia coli BL21 and purified as His-tagged enzymes. Both enzymes required glutathione (GSH) as a cofactor and could 6-dechlorinate 3,6-DCGA to 3-chlorogentisate in vitro DsmH2 had a significantly higher catalytic efficiency toward 3,6-DCGA than DsmH1. Transcription and disruption analysis revealed that DsmH2 but not DsmH1 was responsible for the 6-dechlorination of 3,6-DCGA in strain Ndbn-20 in vivo Furthermore, we propose a novel eta class of GSTs to accommodate the four bacterial dehalogenases PcpC, LinD, DsmH1, and DsmH2.IMPORTANCE Dicamba is an important herbicide, and its use and leakage into the environment have dramatically increased since the large-scale planting of genetically modified (GM) dicamba-resistant crops in 2015. However, the complete catabolic pathway of dicamba has remained unknown, which limits ecotoxicological studies of this herbicide. Our previous study revealed that 3,6-DCGA was an intermediate of dicamba degradation in strain Ndbn-20. In this study, we identified two glutathione-dependent 3,6-DCGA dehalogenases, DsmH1 and DsmH2, and demonstrated that DsmH2 is physiologically responsible for the 6-dechlorination of 3,6-DCGA in strain Ndbn-20. GSTs play an important role in the detoxification and degradation of a variety of endogenous and exogenous toxic compounds. On the basis of their sequence identities, phylogenetic status, and functions, the four bacterial GSH-dependent dehalogenases (PcpC, LinD, DsmH1, and DsmH2) were reclassified as a new eta class of GSTs. This study helps us to elucidate the microbial catabolism of dicamba and enhances our understanding of the diversity and functions of GSTs.

Two-Component FAD-Dependent Monooxygenases: Current Knowledge and Biotechnological Opportunities

Flavoprotein monooxygenases create valuable compounds that are of high interest for the chemical, pharmaceutical, and agrochemical industries, among others. Monooxygenases that use flavin as cofactor are either single- or two-component systems. Here we summarize the current knowledge about two-component flavin adenine dinucleotide (FAD)-dependent monooxygenases and describe their biotechnological relevance. Two-component FAD-dependent monooxygenases catalyze hydroxylation, epoxidation, and halogenation reactions and are physiologically involved in amino acid metabolism, mineralization of aromatic compounds, and biosynthesis of secondary metabolites. The monooxygenase component of these enzymes is strictly dependent on reduced FAD, which is supplied by the reductase component. More and more representatives of two-component FAD-dependent monooxygenases have been discovered and characterized in recent years, which has resulted in the identification of novel physiological roles, functional properties, and a variety of biocatalytic opportunities.

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.

Coupling between Nitrogen Fixation and Tetrachlorobiphenyl Dechlorination in a Rhizobium-Legume Symbiosis

Legume-rhizobium symbioses have the potential to remediate soils contaminated with chlorinated organic compounds. Here, the model symbiosis between Medicago sativa and Sinorhizobium meliloti was used to explore the relationships between symbiotic nitrogen fixation and transformation of tetrachlorobiphenyl PCB 77 within this association. 45-day-old seedlings in vermiculite were pretreated with 5 mg L^-1 PCB 77 for 5 days. In PCB-supplemented nodules, addition of the nitrogenase enhancer molybdate significantly stimulated dechlorination by 7.2-fold and reduced tissue accumulation of PCB 77 (roots by 96% and nodules by 93%). Conversely, dechlorination decreased in plants exposed to a nitrogenase inhibitor (nitrate) or harboring nitrogenase-deficient symbionts (nifA mutant) by 29% and 72%, respectively. A range of dechlorinated products (biphenyl, methylbiphenyls, hydroxylbiphenyls, and trichlorobiphenyl derivatives) were detected within nodules and roots under nitrogen-fixing conditions. Levels of nitrogenase-derived hydrogen and leghemoglobin expression correlated positively with nodular dechlorination rates, suggesting a more reducing environment promotes PCB dechlorination. Our findings demonstrate for the first time that symbiotic nitrogen fixation acts as a driving force for tetrachlorobiphenyl dechlorination. In turn, this opens new possibilities for using rhizobia to enhance phytoremediation of halogenated organic compounds.

Thermodynamics of aqueous perfluorooctanoic acid (PFOA) and 4,8-dioxa-3H-perfluorononanoic acid (DONA) from DFT calculations: Insights into degradation initiation

Modern fluorosurfactants introduced during and after perfluoroalkyl carboxylates/sulfonates phase-out present chemical features designed to facilitate abatement, hence reducing persistence. However, the implications of such features on environmental partitioning and stability are yet to be fully appreciated, partly due to experimental difficulties inherent to the handling of their (diluted) aqueous solutions. In this work, rigorous quantum chemistry calculations were carried out in order to provide theoretical insights into the thermodynamics of hydroperfluorosurfactants in aqueous medium. Estimates of acid dissociation constant (pK_a), standard reduction potential (E⁰), and bond dissociation enthalpy (BDE) and free energy (BDFE) were computed for perfluorooctanoic acid (PFOA), 4,8-dioxa-3H-perfluorononanoic acid (DONA) and their anionic forms via ensemble averaging at density functional theory level with implicit solvent models. A ‹pK_a› in the neighborhood of zero and a E⁰ of about 2.2 V were obtained for PFOA. Predictions for the acidic function of DONA compare well with PFOA's, with a pK_a of 0.8-1.5 and a E⁰ of 2.07-2.15 V. Deprotonation thus represents the dominant phenomenon at environmental conditions. Calculations indicate that H-abstraction of the aliphatic proton of DONA by a hydroxyl radical is the thermodynamically favored reaction path in oxidative media, whereas hydrolysis is not a realistic scenario due to the high dissociation constant. Short intramolecular interactions available to the peculiar hydrophobic tail of DONA were also reviewed, and the relevance of the full conformational space of the fluorinated side chain discussed.

Influence of Multiple Environmental Factors on Organic Matter Chlorination in Podsol Soil

Natural chlorination of organic matter is common in soils. The abundance of chlorinated organic compounds frequently exceeds chloride in surface soils, and the ability to chlorinate soil organic matter (SOM) appears widespread among microorganisms. Yet, the environmental control of chlorination is unclear. Laboratory incubations with ³⁶Cl as a Cl tracer were performed to test how combinations of environmental factors, including levels of soil moisture, nitrate, chloride, and labile organic carbon, influenced chlorination of SOM from a boreal forest. Total chlorination was hampered by addition of nitrate or by nitrate in combination with water but enhanced by addition of chloride or most additions including labile organic matter (glucose and maltose). The greatest chlorination was observed after 15 days when nitrate and water were added together with labile organic matter. The effect that labile organic matter strongly stimulated the chlorination rates was confirmed by a second independent experiment showing higher stimulation at increased availability of labile organic matter. Our results highlight cause-effect links between chlorination and the studied environmental variables in podsol soil-with consistent stimulation by labile organic matter that did overrule the negative effects of nitrate.

Organohalide respiration in pristine environments: implications for the natural halogen cycle

Halogenated organic compounds, also termed organohalogens, were initially considered to be of almost exclusively anthropogenic origin. However, over 5000 naturally synthesized organohalogens are known today. This has also fuelled the hypothesis that the natural and ancient origin of organohalogens could have primed development of metabolic machineries for their degradation, especially in microorganisms. Among these, a special group of anaerobic microorganisms was discovered that could conserve energy by reducing organohalogens as terminal electron acceptor in a process termed organohalide respiration. Originally discovered in a quest for biodegradation of anthropogenic organohalogens, these organohalide-respiring bacteria (OHRB) were soon found to reside in pristine environments, such as the deep subseafloor and Arctic tundra soil with limited/no connections to anthropogenic activities. As such, accumulating evidence suggests an important role of OHRB in local natural halogen cycles, presumably taking advantage of natural organohalogens. In this minireview, we integrate current knowledge regarding the natural origin and occurrence of industrially important organohalogens and the evolution and spread of OHRB, and describe potential implications for natural halogen and carbon cycles.

Perinatal exposure to 2,2',4'4' -Tetrabromodiphenyl ether induces testicular toxicity in adult rats

Since 1965, polybrominated diphenyl ethers (PBDEs) have been used internationally as flame-retardant additives. PBDEs were recently withdrawn from commerce in North America and Europe due to their environmental persistence, bioaccumulative properties and endocrine-disrupting effects. Generations exposed perinatally to the highest environmental doses of PBDE account for one-fifth of the total United States population. While, toxicity of PBDE for the male reproductive system has been demonstrated in several human and animal studies, the long-lasting effects of perinatal exposures on male reproduction are still poorly understood. In this study, pregnant Wistar rats were exposed to 0.2mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. Male reproductive outcomes were analyzed on postnatal day 120 in offspring. Exposed animals had significantly smaller testes, displayed decreased sperm production per testis weight, had significantly increased percentage of morphologically abnormal spermatozoa, and showed an increase in spermatozoa head size. Perinatal BDE-47 exposure led to significant changes in testes transcriptome, including suppression of genes essential for spermatogenesis and activation of immune response genes. In particular, we observed a 4-fold average decrease in expression of protamine and transition protein genes in testes, suggesting that histone-protamine exchange may be dysregulated during spermatogenesis, resulting in an aberrant sperm epigenome. The possibility of long-lasting effects of developmental PBDE exposures calls for additional studies to build a foundation for the development of preventive and protective interventions against the environmentally-induced decline in fertility.

Metagenome-derived haloalkane dehalogenases with novel catalytic properties

Haloalkane dehalogenases (HLDs) are environmentally relevant enzymes cleaving a carbon-halogen bond in a wide range of halogenated pollutants. PCR with degenerate primers and genome-walking was used for the retrieval of four HLD-encoding genes from groundwater-derived environmental DNA. Using specific primers and the environmental DNA as a template, we succeeded in generating additional amplicons, resulting altogether in three clusters of sequences with each cluster comprising 8-13 closely related putative HLD-encoding genes. A phylogenetic analysis of the translated genes revealed that three HLDs are members of the HLD-I subfamily, whereas one gene encodes an enzyme from the subfamily HLD-II. Two metagenome-derived HLDs, eHLD-B and eHLD-C, each from a different subfamily, were heterologously produced in active form, purified and characterized in terms of their thermostability, pH and temperature optimum, quaternary structure, substrate specificity towards 30 halogenated compounds, and enantioselectivity. eHLD-B and eHLD-C showed striking differences in their activities, substrate preferences, and tolerance to temperature. Profound differences were also determined in the enantiopreference and enantioselectivity of these enzymes towards selected substrates. Comparing our data with those of known HLDs revealed that eHLD-C exhibits a unique combination of high thermostability, high activity, and an unusually broad pH optimum, which covers the entire range of pH 5.5-8.9. Moreover, a so far unreported high thermostability for HLDs was determined for this enzyme at pH values lower than 6.0. Thus, eHLD-C represents an attractive and novel biocatalyst for biotechnological applications.

Rapid degradation of 2,4-dichlorophenoxyacetic acid facilitated by acetate under methanogenic condition

Acetate can be used as an electron donor to stimulate 2,4-dichlorophenoxyacetic acid (2,4-D), which has not been determined under methanogenic condition. This study applied high-throughput sequencing and methanogenic inhibition approaches to investigate the 2,4-D degradation process using the enrichments obtained from paddy soil. Acetate addition significantly promoted 2,4-D degradation, which was 5-fold higher than in the acetate-unsupplemented enrichments in terms of the 2,4-D degradation rate constant. Dechloromonas and Pseudomonas were the dominant 2,4-D degraders. Methanogenic inhibition experiments indicated that the 2,4-D degradation was independent of methanogenesis. It was proposed that the accelerated 2,4-D degradation in the acetate-supplemented enrichment involved an unusual interaction, where members of the acetate oxidizers primarily oxidized acetate and produced H₂. H₂ was utilized by the 2,4-D degraders to degrade 2,4-D, but also partially consumed by the hydrogenotrophic methanogens to produce methane. The findings presented here provide a new strategy for the remediation of 2,4-D-polluted soils.

Enzymatic Halogenation and Dehalogenation Reactions: Pervasive and Mechanistically Diverse

Naturally produced halogenated compounds are ubiquitous across all domains of life where they perform a multitude of biological functions and adopt a diversity of chemical structures. Accordingly, a diverse collection of enzyme catalysts to install and remove halogens from organic scaffolds has evolved in nature. Accounting for the different chemical properties of the four halogen atoms (fluorine, chlorine, bromine, and iodine) and the diversity and chemical reactivity of their organic substrates, enzymes performing biosynthetic and degradative halogenation chemistry utilize numerous mechanistic strategies involving oxidation, reduction, and substitution. Biosynthetic halogenation reactions range from simple aromatic substitutions to stereoselective C-H functionalizations on remote carbon centers and can initiate the formation of simple to complex ring structures. Dehalogenating enzymes, on the other hand, are best known for removing halogen atoms from man-made organohalogens, yet also function naturally, albeit rarely, in metabolic pathways. This review details the scope and mechanism of nature's halogenation and dehalogenation enzymatic strategies, highlights gaps in our understanding, and posits where new advances in the field might arise in the near future.

Isolation and Molecular Characterization of Novel Chlorpyrifos and 3,5,6-trichloro-2-pyridinol-degrading Bacteria from Sugarcane Farm Soils

Chlorpyrifos (CP) is one of the most widely used organophosphate pesticides in agriculture worldwide, but its extensive use has led to the contamination of various soil and water systems. Microbial bioremediation is considered to be one of the most viable options for the removal of CP from the environment; however, little is known about the soil bacterial diversity that degrade CP. Sequential soil and liquid culture enrichments enabled the isolation of bacterial CP degraders with sequence homologies to Xanthomonas sp., Pseudomonas sp., and Rhizobium sp. The efficacy of the three isolated strains: Xanthomonas sp. 4R3-M1, Pseudomonas sp. 4H1-M3, and Rhizobium sp. 4H1-M1 was further investigated for biodegradation of CP and its primary metabolic product, 3,5,6-trichloro-2-pyridinol (TCP). The results indicate that all three bacterial strains almost completely metabolized CP (10 mg/L) and TCP, occurring as a metabolic degradation product, in mineral salt media as a sole source of carbon and nitrogen. The isolated bacterial strains Xanthomonas sp. 4R3-M1 and Pseudomonas sp. 4H1-M3 could also degrade TCP (10 mg/L) as a sole carbon and nitrogen source, when provided externally. Thus, these bacterial strains may be effective in practical application of bioremediation of both CP and TCP.

AOX contamination status and genotoxicity of AOX-bearing pharmaceutical wastewater

Adsorbable organic halogens (AOX) are a general indicator for the total amount of compounds containing organically bonded halogens. AOX concentrations and components were investigated along the wastewater treatment process in four large-scale pharmaceutical factories of China, and genotoxicity based on the SOS/umu test was also evaluated. The results showed that AOX concentrations in wastewater of four factories ranged from 4.6 to 619.4mg/L, which were high but greatly different owing to differences in the raw materials and products. The wastewater treatment process removed 50.0%-89.9% of AOX, leaving 1.3-302.5mg/L AOX in the effluents. Genotoxicity levels ranged between 2.1 and 68.0μg 4-NQO/L in the raw wastewater and decreased to 1.2-41.2μg 4-NQO/L in the effluents of the wastewater treatment plants (WWTPs). One of the main products of factory I, ciprofloxacin, was identified as the predominant contributor to its genotoxicity. However, for the other three factories, no significant relationship was observed between genotoxicity and detected AOX compounds.