Biotransformation of 6:2 fluorotelomer sulfonate and microbial community dynamics in water-saturated one-dimensional flow-through columns

Nearly all per- and polyfluoroalkyl substances (PFAS) biotransformation studies reported to date have been limited to laboratory-scale batch reactors. The fate and transport of PFAS in systems that more closely represent field conditions, i.e., in saturated porous media under flowing conditions, remain largely unexplored. This study investigated the biotransformation of 6:2 fluorotelomer sulfonate (6:2 FTS), a representative PFAS of widespread environmental occurrence, in one-dimensional water-saturated flow-through columns packed with soil obtained from a PFAS-contaminated site. The 305-day column experiments demonstrated that 6:2 FTS biotransformation was rate-limited, where a decrease in pore-water velocity from 3.7 to 2.4 cm/day, resulted in a 21.7-26.1 % decrease in effluent concentrations of 6:2 FTS and higher yields (1.0-1.4 mol% vs. 0.3 mol%) of late-stage biotransformation products (C4C7 perfluoroalkyl carboxylates). Flow interruptions (2 and 7 days) were found to enhance 6:2 FTS biotransformation during the 6-7 pore volumes following flow resumption. Model-fitted 6:2 FTS column biotransformation rates (0.039-0.041 cmw3/gs/d) were ∼3.5 times smaller than those observed in microcosms (0.137 cmw3/gs/d). Additionally, during column experiments, planktonic microbial communities remained relatively stable, whereas the composition of the attached microbial communities shifted along the flow path, which may have been attributed to oxygen availability and the toxicity of 6:2 FTS and associated biotransformation products. Genus Pseudomonas dominated in planktonic microbial communities, while in the attached microbial communities, Rhodococcus decreased and Pelotomaculum increased along the flow path, suggesting their potential involvement in early- and late-stage 6:2 FTS biotransformation, respectively. Overall, this study highlights the importance of incorporating realistic environmental conditions into experimental systems to obtain a more representative assessment of in-situ PFAS biotransformation.

Aerobic biotransformation of 6:2 fluorotelomer sulfonate in soils from two aqueous film-forming foam (AFFF)-impacted sites

Although 6:2 fluorotelomer sulfonate (6:2 FTS) is a common ingredient in aqueous film-forming foam (AFFF) formulations, its environmental fate at AFFF-impacted sites remains poorly understood. This study investigated the biotransformation of 6:2 FTS in microcosms prepared with soils collected from two AFFF-impacted sites; the former Loring Air Force Base (AFB) and Robins AFB. The half-life of 6:2 FTS in Loring soil was 43.3 days; while >60 mol% of initially spiked 6:2 FTS remained in Robins soil microcosms after a 224-day incubation. Differences in initial sulfate concentrations and the depletion of sulfate over the incubation likely contributed to the different 6:2 FTS biotransformation rates between the two soils. At day 224, stable transformation products, i.e., C4C7 perfluoroalkyl carboxylates, were formed with combined molar yields of 13.8 mol% and 1.2 mol% in Loring and Robins soils, respectively. Based on all detected transformation products, the biotransformation pathways of 6:2 FTS in the two soils were proposed. Microbial community analysis suggests that Desulfobacterota microorganisms may promote 6:2 FTS biotransformation via more efficient desulfonation. In addition, species from the genus Sphingomonas, which exhibited higher tolerance to elevated concentrations of 6:2 FTS and its biotransformation products, are likely to have contributed to 6:2 FTS biotransformation. This study demonstrates the potential role of biotransformation processes on the fate of 6:2 FTS at AFFF-impacted sites and highlights the need to characterize site biogeochemical properties for improved assessment of 6:2 FTS biotransformation behavior.

Comparative Toxicological Effects of Perfluorooctane Sulfonate and Its Alternative 6:2 Chlorinated Polyfluorinated Ether Sulfonate on Earthworms

High levels of 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), which is a substitute for perfluorooctane sulfonate (PFOS), are detected in various environmental matrices, wildlife, and humans. Chlorinated polyfluorinated ether sulfonate has received increased attention due to its potential risk to ecosystems. However, its toxicity in the soil organisms remains unclear. In the present study, a comparative investigation was conducted on the toxicities of 6:2 Chlorinated polyfluorinated ether sulfonate (F-53B) and PFOS to the earthworm Eisenia. fetida. F-53B was significantly more acutely toxic to earthworms than PFOS, with median lethal concentrations of 1.43 and 1.83 mmol/kg dry soil (~816 and 984 mg/kg dry soil), respectively. Although both F-53B and PFOS, at 0.4 mmol/kg dry soil (=228 and 215 mg/kg dry soil) caused oxidative stress in earthworms, as evidenced by increased superoxide dismutase, peroxidase, and catalase activities as well as malondialdehyde level, the stress caused by F-53B was higher than that caused by PFOS. In transcriptomic and metabolomic studies, negative effects of PFOS and F-53B were observed on several metabolic processes in earthworms, including protein digestion and amino acid absorption, lipid metabolism, and the immune response. Compared with PFOS, F-53B exhibited a weaker disruption of lipid metabolism, comparable potency for toxicity to the immune response, and a stronger potency in extracellular matrix destruction along with apoptosis and ferroptosis induction. Hence, our data suggest that F-53B is more toxic than PFOS to earthworms. The findings provide some new insights into the potential toxicity of F-53B to soil organisms. Environ Toxicol Chem 2024;43:170-181. © 2023 SETAC.

Evaluating the Effect of Gestational Exposure to Perfluorohexane Sulfonate on Placental Development in Mice Combining Alternative Splicing and Gene Expression Analyses

BACKGROUND

Perfluorohexane sulfonate (PFHxS) is a frequently detected per- and polyfluoroalkyl substance in most populations, including in individuals who are pregnant, a period critical for early life development. Despite epidemiological evidence of exposure, developmental toxicity, particularly at realistic human exposures, remains understudied.

OBJECTIVES

We evaluated the effect of gestational exposure to human-relevant body burden of PFHxS on fetal and placental development and explored mechanisms of action combining alternative splicing (AS) and gene expression (GE) analyses.

METHODS

Pregnant ICR mice were exposed to 0, 0.03, and 0.3 μ g / kg / day  from gestational day 7 to day 17 via oral gavage. Upon euthanasia, PFHxS distribution was measured using liquid chromatography-tandem mass spectrometry. Maternal and fetal phenotypes were recorded, and histopathology was examined for placenta impairment. Multiomics was adopted by combining AS and GE analyses to unveil disruptions in mRNA quality and quantity. The key metabolite transporters were validated by quantitative real-time PCR (qRT-PCR) for quantification and three-dimensional (3D) structural simulation by AlphaFold2. Targeted metabolomics based on liquid chromatography-tandem mass spectrometry was used to detect amino acid and amides levels in the placenta.

RESULTS

Pups developmentally exposed to PFHxS exhibited signs of intrauterine growth restriction (IUGR), characterized by smaller fetal weight and body length (p < 0.01 ) compared to control mice. PFHxS concentration in maternal plasma was 5.01 ± 0.54  ng / mL . PFHxS trans-placenta distribution suggested dose-dependent transfer through placental barrier. Histopathology of placenta of exposed dams showed placental dysplasia, manifested with an attenuated labyrinthine layer area and deescalated blood sinus counts and placental vascular development index marker CD34. Combined GE and AS analyses pinpointed differences in genes associated with key biological processes of placental development, proliferation, metabolism, and transport in placenta of exposed dams compared to that of control dams. Further detection of placental key transporter gene expression, protein structure simulation, and amino acid and amide metabolites levels suggested that PFHxS exposure during pregnancy led to impairment of placental amino acid transportation.

DISCUSSION

The findings from this study suggest that exposure to human-relevant very-low-dose PFHxS during pregnancy in mice caused IUGR, likely via downregulating of placental amino acid transporters, thereby impairing placental amino acid transportation, resulting in impairment of placental development. Our findings confirm epidemiological findings and call for future attention on the health risk of this persistent yet ubiquitous chemical in the early developmental stage and provide a new approach for understanding gene expression from both quantitative and qualitative omics approaches in toxicological studies. https://doi.org/10.1289/EHP13217.

Isethionate is an intermediate in the degradation of sulfoacetate by the human gut pathobiont Bilophila wadsworthia

The obligately anaerobic sulfite-reducing bacterium Bilophila wadsworthia is a common human pathobiont inhabiting the distal intestinal tract. It has a unique ability to utilize a diverse range of food- and host-derived sulfonates to generate sulfite as a terminal electron acceptor (TEA) for anaerobic respiration, converting the sulfonate sulfur to H2S, implicated in inflammatory conditions and colon cancer. The biochemical pathways involved in the metabolism of the C2 sulfonates isethionate and taurine by B. wadsworthia were recently reported. However, its mechanism for metabolizing sulfoacetate, another prevalent C2 sulfonate, remained unknown. Here, we report bioinformatics investigations and in vitro biochemical assays that uncover the molecular basis for the utilization of sulfoacetate as a source of TEA (STEA) for B. wadsworthia, involving conversion to sulfoacetyl-CoA by an ADP-forming sulfoacetate-CoA ligase (SauCD), and stepwise reduction to isethionate by NAD(P)H-dependent enzymes sulfoacetaldehyde dehydrogenase (SauS) and sulfoacetaldehyde reductase (TauF). Isethionate is then cleaved by the O2-sensitive isethionate sulfolyase (IseG), releasing sulfite for dissimilatory reduction to H2S. Sulfoacetate in different environments originates from anthropogenic sources such as detergents, and natural sources such as bacterial metabolism of the highly abundant organosulfonates sulfoquinovose and taurine. Identification of enzymes for anaerobic degradation of this relatively inert and electron-deficient C2 sulfonate provides further insights into sulfur recycling in the anaerobic biosphere, including the human gut microbiome.

Structural and molecular changes in the rat myocardium following perfluoroctane sulfonate (PFOS) exposure are mitigated by quercetin via modulating HSP 70 and SERCA 2

Perfluorooctane sulfonate (PFOS) is a man-made fluorinated compound employed in a variety of industrial and civilian applications. Due to its long elimination half-life and promotion of oxidative stress and inflammation, it is one of the most abundant organic contaminants. The present study was designed to determine the cytotoxic effect of PFOS on adult male rat cardiac tissue and to assess the cardioprotective role of the flavonoid quercetin (Que), which possesses antioxidant, anti-inflammatory, and anti-apoptotic properties. Twenty-four adult male Sprague-Dawley rats were randomly divided into four equal groups: Group I (Control). Group II (Que) received Que (75 mg/kg/day for 4 weeks) by oral gavage. Group III (PFOS group): supplemented orally with PFOS (20 mg/kg/day for 4 weeks) and Group IV (PF OS/Que). The rat heart was processed for histological, immunohistochemical, and gene expression studies. The PFOS group showed histological alterations in the myocardium that were partially reversed by the administration of Que. The inflammatory biomarkers (TNF, IL-6, and IL-1), lipid profile, TSH, MDA, and serum cardiac enzymes (LDH and CK-MB) were all altered. These findings collectively suggest that PFOS had adverse effects on the cardiac muscle structure, and these effects were alleviated by quercetin, which is a promising cardioprotective flavonoid.

A Variant of the Sulfoglycolytic Transketolase Pathway for the Degradation of Sulfoquinovose into Sulfoacetate

Sulfoquinovose (SQ, 6-deoxy-6-sulfo-glucose) constitutes the polar head group of plant sulfolipids and is one of the most abundantly produced organosulfur compounds in nature. Degradation of SQ by bacterial communities contributes to sulfur recycling in many environments. Bacteria have evolved at least four mechanisms for glycolytic degradation of SQ, termed sulfoglycolysis, producing C3 sulfonate (dihydroxypropanesulfonate and sulfolactate) and C2 sulfonate (isethionate) by-products. These sulfonates are further degraded by other bacteria, leading to the mineralization of the sulfonate sulfur. The C2 sulfonate sulfoacetate is widespread in the environment and is also thought to be a product of sulfoglycolysis, although the mechanistic details are yet unknown. Here, we describe a gene cluster in an Acholeplasma sp., from a metagenome derived from deeply circulating subsurface aquifer fluids (GenBank accession no. QZKD01000037), encoding a variant of the recently discovered sulfoglycolytic transketolase (sulfo-TK) pathway that produces sulfoacetate instead of isethionate as a by-product. We report the biochemical characterization of a coenzyme A (CoA)-acylating sulfoacetaldehyde dehydrogenase (SqwD) and an ADP-forming sulfoacetate-CoA ligase (SqwKL), which collectively catalyze the oxidation of the transketolase product sulfoacetaldehyde into sulfoacetate, coupled with ATP formation. A bioinformatics study revealed the presence of this sulfo-TK variant in phylogenetically diverse bacteria, adding to the variety of mechanisms by which bacteria metabolize this ubiquitous sulfo-sugar. IMPORTANCE Many bacteria utilize environmentally widespread C2 sulfonate sulfoacetate as a sulfur source, and the disease-linked human gut sulfate- and sulfite-reducing bacteria can use it as a terminal electron receptor for anaerobic respiration generating toxic H2S. However, the mechanism of sulfoacetate formation is unknown, although it has been proposed that sulfoacetate originates from bacterial degradation of sulfoquinovose (SQ), the polar head group of sulfolipids present in all green plants. Here, we describe a variant of the recently discovered sulfoglycolytic transketolase (sulfo-TK) pathway. Unlike the regular sulfo-TK pathway that produces isethionate, our biochemical assays with recombinant proteins demonstrated that a CoA-acylating sulfoacetaldehyde dehydrogenase (SqwD) and an ADP-forming sulfoacetate-CoA ligase (SqwKL) in this variant pathway collectively catalyze the oxidation of the transketolase product sulfoacetaldehyde into sulfoacetate, coupled with ATP formation. A bioinformatics study revealed the presence of this sulfo-TK variant in phylogenetically diverse bacteria and interpreted the widespread existence of sulfoacetate.

Effect of substrate concentrations on aerobic biotransformation of 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate

Biotransformation of 6:2 fluorotelomer sulfonate (FTS) results in the formation of short-chain (C4 - C6) perfluorocarboxylic acids (PFCAs) in landfill leachate. Although leachate substrate concentrations (i.e., organic carbon, ammonia) vary widely, their effects on 6:2 FTS biotransformation and PFCAs formation are unknown. This study investigated the effect of organic carbon and ammonia concentration in 6:2 FTS aerobic biotransformation and PFCA formation in leachate. Biotransformation experiments were conducted with sediment collected from a landfill leachate ditch, to which deionized (DI) water and various amounts of leachate were added. Microbial community analysis using 16S rRNA indicated that while phylum Proteobacteria dominated the bacterial composition throughout the 60 days, Actinobacteria increased with time. Many genera from Proteobacteria and Actinobacteria can synthesize a wide array of enzymes, indicating that these phyla are likely to play an important role in 6:2 FTS biotransformation. Higher biotransformation of 6:2 FTS was observed in leachate-added microcosms (∼21%), compared to DI water microcosm (∼14%), likely reflecting the substrate dependency of 6:2 FTS biotransformation. Substrate limiting conditions in DI water microcosm resulted in slightly greater formation of ∑(C4 - C6) PFCAs (∼14 mol%), compared with leachate added microcosms (10-13 mol%). The findings suggest that dilution of landfill leachate, (e.g., during wet seasons), likely results in reduced 6:2 FTS biotransformation and increased PFCAs formation compared to dry conditions. Observed formation of C7 - C8 PFCAs in the live microcosms suggested that landfills act as secondary sources of legacy PFCAs (e.g., perfluorooctanoic acid) in the environment.

Polystyrene microplastics decrease F-53B bioaccumulation but induce inflammatory stress in larval zebrafish

There is growing concern that microplastics (MPs), which act as carriers of other organic contaminants, are mistakenly ingested by aquatic organisms, consequently causing unpredictable adverse effects. In this study, zebrafish larvae (6 d post fertilization) were exposed to either 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), polystyrene microplastics (PS-MPs) or their combination for 7 d to evaluate the effects of the presence of PS-MPs on the bioaccumulation and immunomodulation of F-53B. PS-MPs greatly promoted the sorption of F-53B, which reduced the bioavailability and bioaccumulation of F-53B in zebrafish larvae. F-53B, PS-MPs, or their mixture significantly reduced the body weight of zebrafish larvae. Combined exposure of PS-MPs and F-53B resulted in a significant reduction in superoxide dismutase (SOD) and lysozyme activity, indicating the occurrence of oxidative stress and inflammatory response in zebrafish larvae. The content of malondialdehyde (MDA) and immunoglobulin M (IgM) was not affected by F-53B or PS-MPs, but significantly increased in their combined exposure. Furthermore, co-exposure of F-53B and PS-MPs significantly upregulated the transcripts of pro-inflammatory cxcl-clc and il-1β genes and increased the levels of iNOS protein in zebrafish larvae. In addition, enhanced protein expression of NF-κB paralleled the upregulation in the expression of most immune-related genes, suggesting NF-κB pathway was mechanistically involved in these responses. Collectively, the presence of MPs decreased F-53B bioaccumulation, but induced inflammatory stress in larval zebrafish. These findings highlight the health risks of co-contamination of MPs and F-53B in aquatic environments.

Legacy and emerging per- and polyfluoroalkyl substances (PFASs) in the coastal environment of Korea: Occurrence, spatial distribution, and bioaccumulation potential

Contamination by per- and polyfluoroalkyl substances (PFASs) is of great concern in global environments. Due to strong regulation of legacy PFASs, emerging PFASs including alternatives and precursors have been introduced to the industrial market. In this study, legacy and emerging PFASs were measured in seawater, sediment, and bivalves collected along the Korean coast to investigate the occurrence, distribution, contamination sources, and bioaccumulation potential of PFASs. Wide concentration ranges of legacy PFASs were detected in multiple environmental samples, indicating widespread contamination. C8-based PFASs (e.g., PFOA and PFOS) were still major contaminants in all of the environmental samples. Some precursors, such as 8:2 fluorotelomer sulfonate (8:2 FTS) and N-ethyl-perfluorooctane sulfonamidoacetic acid (N-EtFOSAA), and perfluoro-2-propoxypropanoic potassium 9-chlorohexadecafluoro-3-oxanonane-1-sulfonate (F-53B), an alternative to PFOS, were detected in sediment or bivalve samples, implying a shift in consumption patterns from legacy to emerging PFASs. The highest concentrations of PFASs in environmental samples were found at the locations near industrial complexes, such as those for the semi-conductor, paper mill, automobile, and metal-plating industry. This result indicates that PFAS contamination is associated with intensive industrial activities in the coastal environment. Matrix-dependent contamination and profiles of PFASs were observed. Seawater was dominated by short-chained PFASs as a prompt reflection of regulation, while the sediment and bivalves were dominated by long-chained PFASs. Carbon-chain length was a major factor governing environmental behavior and bioaccumulation of PFASs. This was the first nation-wide survey on legacy and emerging PFASs in the coastal environment of Korea.

Formation of perfluorocarboxylic acids from 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate: Role of microbial communities

Fluorotelomer compounds in landfill leachate can undergo biotransformation under aerobic conditions and act as a secondary source of perfluorocarboxylic acids (PFCAs) to the environment. Very little is known about the role of various microbial communities towards fluorotelomer compounds biotransformation. Using an inoculum prepared from the sediment of a leachate collection ditch, 6:2 fluorotelomer sulfonate (6:2 FTS) biotransformation experiments were carried out. Specific substrates (i.e., glucose, ammonia) and ammonia-oxidizing inhibitor (allylthiourea) were used to produce two experimental runs with heterotrophic (HET) growth only and heterotrophic with ammonia-oxidizing and nitrite- oxidizing bacteria (HET + AOB + NOB). After 10 days, ∼20% of the spiked 6:2 FTS removal was observed in HET + AOB + NOB, compared to ∼7% under HET condition. Higher 6:2 FTS removal in HET + AOB + NOB likely resulted from ammonia monooxygenase enzyme that catalyzes the first step of ammonia oxidation. The HET + AOB + NOB condition also showed higher PFCA (C4-C6) formation (∼2% of initially spiked 6:2 FTS), possibly due to higher overall bioactivity. Microbial community analysis through 16s rRNA sequencing confirmed that Proteobacteria and Bacteroidetes were the most abundant phyla (>75% relative abundance) under all experimental conditions. High abundance of Actinobacteria (>17%) was observed under the HET + AOB + NOB condition on day 7. Since Actinobacteria can synthesize a wide range of enzymes including monooxygenases, they likely play an important role in 6:2 FTS biotransformation and PFCA production.

An Alkane Sulfonate Monooxygenase Is Required for Symbiotic Nitrogen Fixation by Bradyrhizobium diazoefficiens (syn. Bradyrhizobium japonicum) USDA110T

Sulfur (S)-containing molecules play an important role in symbiotic nitrogen fixation and are critical components of nitrogenase and other iron-S proteins. S deficiency inhibits symbiotic nitrogen fixation by rhizobia. However, despite its importance, little is known about the sources of S that rhizobia utilize during symbiosis. We previously showed that Bradyrhizobium diazoefficiens USDA110T can assimilate both inorganic and organic S and that genes involved in organic S utilization are expressed during symbiosis. Here, we show that a B. diazoefficiens USDA110T mutant with a sulfonate monooxygenase (ssuD) insertion is defective in nitrogen fixation. Microscopy analyses revealed that the ΔssuD mutant was defective in root hair infection and that ΔssuD mutant bacteroids showed degradation compared to the wild-type strain. Moreover, the ΔssuD mutant was significantly more sensitive to hydrogen peroxide-mediated oxidative stress than the wild-type strain. Taken together, these results show that the ability of rhizobia to utilize organic S plays an important role in symbiotic nitrogen fixation. Since nodules have been reported to be an important source of reduced S used during symbiosis and nitrogen fixation, further research will be needed to determine the mechanisms involved in the regulation of S assimilation by rhizobia.IMPORTANCE Rhizobia form symbiotic associations with legumes that lead to the formation of nitrogen-fixing nodules. Sulfur-containing molecules play a crucial role in nitrogen fixation; thus, the rhizobia inside nodules require large amounts of sulfur. Rhizobia can assimilate both inorganic (sulfate) and organic (sulfonates) sources of sulfur. However, very little is known about rhizobial sulfur metabolism during symbiosis. In this report, we show that sulfonate utilization by Bradyrhizobium diazoefficiens is important for symbiotic nitrogen fixation in both soybean and cowpea. The symbiotic defect is probably due to increased sensitivity to oxidative stress from sulfur deficiency in the mutant strain defective for sulfonate utilization. The results of this study can be extended to other rhizobium-legume symbioses, as sulfonate utilization genes are widespread in these bacteria.

Desolvation of the substrate-binding protein TauA dictates ligand specificity for the alkanesulfonate ABC importer TauABC

Under limiting sulfur availability, bacteria can assimilate sulfur from alkanesulfonates. Bacteria utilize ATP-binding cassette (ABC) transporters to internalise them for further processing to release sulfur. In gram-negative bacteria the TauABC and SsuABC ensure internalization, although, these two systems have common substrates, the former has been characterized as a taurine specific system. TauA and SsuA are substrate-binding proteins (SBPs) that bind and bring the alkanesulfonates to the ABC importer for transport. Here, we have determined the crystal structure of TauA and have characterized its thermodynamic binding parameters by isothermal titration calorimetry in complex with taurine and different alkanesulfonates. Our structures revealed that the coordination of the alkanesulfonates is conserved, with the exception of Asp205 that is absent from SsuA, but the thermodynamic parameters revealed a very high enthalpic penalty cost for binding of the other alkanesulfonates relative to taurine. Our molecular dynamic simulations indicated that the different levels of hydration of the binding site contributed to the selectivity for taurine over the other alkanesulfonates. Such selectivity mechanism is very likely to be employed by other SBPs of ABC transporters.

Elucidating the fate of perfluorooctanoate sulfonate using a rainbow trout (Oncorhynchus mykiss) physiologically-based toxicokinetic model

Per- and poly-fluorinated substances (PFAS) are widely found in freshwater ecosystems because of their resistance to degradation. Among them, several long-chain perfluoroalkyl acids bioaccumulate in aquatic vertebrates, but our understanding of the mechanisms of absorption, distribution and elimination is still limited in fish. For this purpose, we developed a 10-compartment physiologically-based toxicokinetic (PBTK) model to elucidate perfluorooctane sulfonate (PFOS) kinetics in adult rainbow trout. This PBTK model included various physiological characteristics: blood perfusion to each organ, plasmatic fraction, PFOS free fraction, and growth of individuals. The parameters were optimized using Bayesian inferences. First, only PFOS absorption by diet was considered in the model as well as its elimination by urine, bile and feces. Then two mechanistic hypotheses, assumed to govern PFOS toxicokinetics in fish, namely the enterohepatic cycle and the absorption and elimination though gills, were tested. Improvement of the model's fit to the data was studied in each organ by comparing predictions with observed data using relative error. The experimental data set was obtained from an exposure experiment, where adult rainbow trout were fed with a PFOS-spiked diet for 42 days, followed by a 35-day depuration period. In all cases, PFOS concentrations were accurately predicted in organs and feces by the model. The results of this PBTK model demonstrated that feces represented the major elimination route for PFOS while urine was a minor route. Also, PFOS branchial uptake can be substantial despite low concentrations of the compound in water, and elimination through gills should not be neglected. Finally, the enterohepatic cycle is likely to play a minor role in PFOS toxicokinetics. Overall, this PBTK model accurately described PFOS distribution in rainbow trout and provides information on the relative contribution of absorption and elimination pathways.

Biotransformation of polyfluoroalkyl substances by microbial consortia from constructed wetlands under aerobic and anoxic conditions

The wide application of 6:2 fluorotelomer sulfonate (6:2 FTS) and its precursors results in their ubiquitous occurrence in the environment. This study investigated the biotransformation of 6:2 FTS using fresh slurries collected from constructed wetland under aerobic and anoxic conditions. Biotransformation rates of 6:2 FTS was extremely slow under both aerobic and anoxic conditions. The analysis of transformation products showed that less than 0.7 mol% of initial concentration of 6:2 FTS was biotransformed under anoxic conditions. Effects of 6:2 FTS on the shifts in microbial community in wetland slurry during aerobic and anoxic transformation were evaluated using 16S rRNA gene amplicon sequencing. Under aerobic conditions, 6:2 FTS altered the microbial community structure, in which Methylocaldum (Gamma-proteobacteria) became the predominant genus after being exposed to 6:2 FTS. This means that Methylocaldum appears to have higher tolerance to 6:2 FTS and seems to be potential 6:2 FTS-degrading bacteria. Under anoxic transformation, only the genus Methanomethylovorans (Euryarchaeota) was increased remarkably in wetland slurry exposed to 6:2 FTS.

Probing mechanisms for bioaccumulation of perfluoroalkyl acids in carp (Cyprinus carpio): Impacts of protein binding affinities and elimination pathways

With regulations on the manufacture and usage of perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS) and related compounds, short-chain perfluoroalkyl acids (PFAAs) are increasingly being used as alternatives. However, there are limited studies on their bioaccumulation mechanisms, especially for short-chain PFAAs. In this study, we examined the binding affinity of PFAAs with fish serum proteins and tissue distributions of perfluoroalkyl carboxylates (C7-C11 PFCAs) and perfluoroalkyl sulfonates (C4, C6, and C8 PFSAs) in carp (Cyprinus carpio), including the isomers of PFOS and perfluorohexane sulfonate (PFHxS). For both PFCAs and PFSAs, the fish serum protein binding constant (K_A) and bioconcentration factor (BCF) increased with an increase in the carbon chain length. PFHxS (C6 PFSA) had a much higher K_A but displayed a much lower BCF than those of C7-C11 PFCAs. It indicated that not only fish blood proteins, but also other proteins in the liver and kidney, mediated the accumulation of PFAAs in fish. The lowest concentration ratios of PFHxS in liver to blood and in kidney to blood suggested that it could not be effectively transported to liver and kidney by fatty acid binding proteins and organic anion transporters. PFOS and PFHxS displayed different elimination pathways, although their linear (n-) isomers were accumulated more in fish than the corresponding branched (br-) isomers. The n-PFOS was eliminated more via the feces but br-PFOS was eliminated more via the urine; while the opposite trend was observed for PFHxS isomers.

Bioaccumulation and effects of novel chlorinated polyfluorinated ether sulfonate in freshwater alga Scenedesmus obliquus

Chlorinated polyfluorinated ether sulfonate (Cl-PFESA) is a novel alternative compound for perfluorooctane sulfonate (PFOS), with its environmental risk not well known. The bioaccumulation and toxic effects of Cl-PFESA in the freshwater alga is crucial for the understanding of its potential hazards to the aquatic environment. Scenedesmus obliquus was exposed to Cl-PFESA at ng L^-1 to mg L^-1, with the exposure regime beginning at the environmentally relevant level. The total log BAF of Cl-PFESA in S. obliquus was 4.66, higher than the reported log BAF of PFOS in the freshwater plankton (2.2-3.2). Cl-PFESA adsorbed to the cell surface accounted for 33.5-68.3% of the total concentrations. The IC50 of Cl-PFESA to algal growth was estimated to be 40.3 mg L^-1. Significant changes in algal growth rate and chlorophyll a/b contents were observed at 11.6 mg L^-1 and 13.4 mg L^-1 of Cl-PFESA, respectively. The sample cell membrane permeability, measured by the fluorescein diacetate hydrolyzation, was increased by Cl-PFESA at 5.42 mg L^-1. The mitochondrial membrane potential, measured by Rh123 staining, was also increased, indicating the hyperpolarization induced by Cl-PFESA. The increasing ROS and MDA contents, along with the enhanced SOD, CAT activity, and GSH contents, suggested that Cl-PFESA caused oxidative damage in the algal cells. It is less possible that current Cl-PFESA pollution in surface water posed obvious toxic effects on the green algae. However, the bioaccumulation of Cl-PFESA in algae would contribute to its biomagnification in the aquatic food chain and its effects on membrane property could potentially increase the accessibility and toxicity of other coexisting pollutants.

Ornamental plants for micropollutant removal in wetland systems

The objective of this paper was to evaluate the efficiency of micropollutant removal, such as Cu, Zn, carbamazepine, and linear alkylbenzene sulfonates (LAS), through the use of a subsurface vertical flow constructed wetland system with ornamental plants. Zantedeschia aethiopica, Canna indica, Carex hirta, Miscanthus sinensis, and Phragmites australis were selected and planted in lysimeters filled up with gravel. The lysimeters were completely saturated with synthetic wastewater (N 280 mg L(-1), P 30 mg L(-1), Cu 3.6 mg L(-1), Zn 9 mg L(-1), carbamazepine 5 μg L(-1), linear alkylbenzene sulfonates 14 mg L(-1)), and the leaching water was collected for analysis after 15, 30, and 60 days in winter-spring and spring-summer periods. Nutrients (N and P) and heavy metals decreased greatly due to both plant activity and adsorption. C. indica and P. australis showed the highest metal content in their tissues and also the greatest carbamazepine and LAS removal. In these plants, the adsorption/degradation processes led to particularly high oxidative stress, as evidenced by the significantly high levels of ascorbate peroxidase activity detected. Conversely, Z. aethiopica was the less efficient plant in metal and organic compound removal and was also less stressed in terms of ascorbate peroxidase activity.

First report of a Chinese PFOS alternative overlooked for 30 years: its toxicity, persistence, and presence in the environment

This is the first report on the environmental occurrence of a chlorinated polyfluorinated ether sulfonate (locally called F-53B, C8ClF16O4SK). It has been widely applied as a mist suppressant by the chrome plating industry in China for decades but has evaded the attention of environmental research and regulation. In this study, F-53B was found in high concentrations (43-78 and 65-112 μg/L for the effluent and influent, respectively) in wastewater from the chrome plating industry in the city of Wenzhou, China. F-53B was not successfully removed by the wastewater treatments in place. Consequently, it was detected in surface water that receives the treated wastewater at similar levels to PFOS (ca. 10-50 ng/L) and the concentration decreased with the increasing distance from the wastewater discharge point along the river. Initial data presented here suggest that F-53B is moderately toxic (Zebrafish LC50-96 h 15.5 mg/L) and is as resistant to degradation as PFOS. While current usage is limited to the chrome plating industry, the increasing demand for PFOS alternatives in other sectors may result in expanded usage. Collectively, the results of this work call for future assessments on the effects of this overlooked contaminant and its presence and fate in the environment.

First report of a Chinese PFOS alternative overlooked for 30 years: its toxicity, persistence, and presence in the environment

This is the first report on the environmental occurrence of a chlorinated polyfluorinated ether sulfonate (locally called F-53B, C8ClF16O4SK). It has been widely applied as a mist suppressant by the chrome plating industry in China for decades but has evaded the attention of environmental research and regulation. In this study, F-53B was found in high concentrations (43-78 and 65-112 μg/L for the effluent and influent, respectively) in wastewater from the chrome plating industry in the city of Wenzhou, China. F-53B was not successfully removed by the wastewater treatments in place. Consequently, it was detected in surface water that receives the treated wastewater at similar levels to PFOS (ca. 10-50 ng/L) and the concentration decreased with the increasing distance from the wastewater discharge point along the river. Initial data presented here suggest that F-53B is moderately toxic (Zebrafish LC50-96 h 15.5 mg/L) and is as resistant to degradation as PFOS. While current usage is limited to the chrome plating industry, the increasing demand for PFOS alternatives in other sectors may result in expanded usage. Collectively, the results of this work call for future assessments on the effects of this overlooked contaminant and its presence and fate in the environment.

Perfluoroalkyl acids in subarctic wild male mink (Neovison vison) in relation to age, season and geographical area

This study investigates the influence of biological and environmental factors on the concentrations of perfluoroalkyl acids (PFAAs) in a top predator; the American mink. Perfluorobutane sulfonate (PFBS), perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS) and perfluoroalkyl carboxylates (PFCAs) with C8-C13 perfluorinated carbon chains were analyzed in livers from wild male mink liver (n=101) from four areas in Sweden representing two inland environments (rural and highly anthropogenic, respectively) and two different coastal environments. Mean PFOS concentrations were 1250ng/g wet weight and some mink from the urban inland area had among the highest PFOS concentrations ever recorded in mink (up to 21 800ng/g wet weight). PFBS was detected in 89% of the samples, but in low concentrations (mean 0.6ng/g ww). There were significant differences in PFAA concentrations between the geographical areas (p<0.001-0.01). Age, body condition and body weight did not influence the concentrations significantly, but there was a seasonal influence on the concentrations of perfluorodecanoic acid (PFDA) and perfluoroundecanoic acid (PFUnDA) (p<0.01 and p<0.05, respectively), with lower concentrations in autumn samples than in samples taken in the winter and spring. It is thus recommended to take possible seasonal differences into account when using mink exposure data. The overall results suggest that the mink is a suitable sentinel species for assessing and monitoring environmental levels of PFAAs.

Testing for departures from additivity in mixtures of perfluoroalkyl acids (PFAAs)

This study is a follow-up to a paper by Carr et al. that determined a design structure to optimally test for departures from additivity in a fixed ratio mixture of four perfluoroalkyl acids (PFAAs) using an in vitro transiently-transfected COS-1 PPARα reporter model with a mixing ratio that is based on average serum levels in NHANES subjects. Availability of information regarding potential for additivity of PFAAs in mixtures is critically important for risk assessors who are concerned with the ability of the compounds to affect human health and impact ecological systems. It is clear that exposures are not to single compounds, but to mixtures of the PFAAs. This paper presents the results from the data collected using the design from Carr et al. along with subsequent analyses that were performed to classify the relationships among mixtures of PFAAs. A non-linear logistic additivity model was employed to predict relative luciferase units (RLU), an indicator of PPARα activation. The results indicated a less than additive relationship among the four PFAAs. To determine if the possible "antagonism" is from the competition among or between carboxylates and sulfonates, four different binary mixtures were also studied. There was a less than additive relationship in all four binary mixtures. These findings are generally similar to two other reports of interfering interactions between PFAAs in mixtures. The most conservative interpretation for our data would be an assumption of additivity (and lack of a greater than additive interaction), with a potential for antagonistic interactions.

Organic matter stabilization in reed bed systems: Danish and Italian examples

In this study, results about sludge stabilization in reed bed systems (RBSs) after the entire period of operation in two different systems situated in Denmark (Helsinge 42,000 population equivalent (p.e.) - 10 years) and in Italy (La Fontina, 30,000 p.e. - 6 years) were presented. In order to evaluate the process of sludge stabilization, parameters that highlighted the biochemical and chemico-structural properties of organic sludge matter have been determined. The level of total and soluble nutrients, and enzyme activities, parameters related to overall microbial activity, showed that stabilization of the sludge similarly occurred in both RBSs, even though in different landscape ecosystems. The chemical-structural characterization of sludge organic matter highlighted how the processes of stabilization have occurred satisfactorily in both RBSs; in fact, significant levels of pyrolytic indices for mineralization and humification were reached. The successful stabilization of organic matter occurred in both RBSs and was confirmed by the absence of Escherichia coli, and also by the results of organic compounds (polycyclic aromatic hydrocarbons, linear alkyl benzene sulfonates, nonylphenol ethoxylates, di-2-ethylhexyl-phthalate) and heavy metals.

Comparative tissue and body compartment accumulation and maternal transfer to eggs of perfluoroalkyl sulfonates and carboxylates in Great Lakes herring gulls

The comparative accumulation of C(4)-C(15) perfluorinated sulfonates (PFSAs) and carboxylates (PFCAs), and several precursors (e.g., perfluorooctane sulfonamide, N-methyl-FOSA, and fluorotelomer unsaturated acids and alcohols) was examined in tissues (liver, brain, muscle, and adipose), plasma/red blood cells (RBCs) and whole egg clutches (yolk and albumen) of female herring gulls collected in 2010 from Chantry Island, Lake Huron of the Laurentian Great Lakes. Highest mean ∑PFSA concentrations were in yolk, followed by adipose, liver, plasma, muscle, RBCs, and brain. Highest mean ∑PFCA concentrations were in yolk, followed by brain, plasma, liver, RBC, adipose and muscle. PFOS accounted for >88% of ∑PFSA in all samples; the liver, plasma/RBCs, muscle and adipose PFCA patterns were dominated by C(8)-C(11) PFCAs, whereas C(10)-C(15) PFCAs in brain and yolk. Among PFSAs and PFCAs there is tissue-specific accumulation, which could be due to a number of pharmacokinetic processes.

Highly elevated levels of perfluorooctane sulfonate and other perfluorinated acids found in biota and surface water downstream of an international airport, Hamilton, Ontario, Canada

Per- and poly-fluorinated compounds (PFCs), which include perfluorinated carboxylates (PFCAs) and sulfonates (PFSAs) and various precursors, are used in a wide variety of industrial, commercial and domestic products. This includes aqueous film forming foam (AFFF), which is used by military and commercial airports as fire suppressants. In a preliminary assessment prior to this study, very high concentrations (>1 ppm wet weight) of the PFSA, perfluorooctane sulfonate (PFOS), were discovered in the plasma of snapping turtles (Chelydra serpentina) collected in 2008 from Lake Niapenco in southern Ontario, Canada. We presently report on a suite of C(6) to C(15) PFCAs, C(4), C(6), C(8) and C(10) PFSAs, several PFC precursors (e.g. perfluorooctane sulfonamide, PFOSA), and a cyclic perfluorinated acid used in aircraft hydraulic fluid, perfluoroethylcyclohexane sulfonate (PFECHS) in surface water from the Welland River and Lake Niapenco, downstream of the John C. Munro International Airport, Hamilton, Ontario, Canada. Amphipods, shrimp, and water were sampled from the Welland River and Lake Niapenco, as well as local references. The same suite of PFCs in turtle plasma from Lake Niapenco was compared to those from other southern Ontario sites. PFOS dominated the sum PFCs in all substrates (e.g., >99% in plasma of turtles downstream the Hamilton Airport, and 72.1 to 94.1% at all other sites). PFOS averaged 2223(±247.1SE) ng/g in turtle plasma from Lake Niapenco, and ranged from 9.0 to 171.4 elsewhere. Mean PFOS in amphipods and in water were 518.1(±83.8)ng/g and 130.3(±43.6) ng/L downstream of the airport, and 19.1(±2.7) ng/g and 6.8(±0.5) ng/L at reference sites, respectively. Concentrations of selected PFCs declined with distance downstream from the airport. Although there was no known spill event or publicly reported use of AFFF associated with a fire event at the Hamilton airport, the airport is a likely major source of PFC contamination in the Welland River.

Perfluoroalkyl carboxylates and sulfonates and precursors in relation to dietary source tracers in the eggs of four species of gulls (Larids) from breeding sites spanning Atlantic to Pacific Canada

In the present study, we identified and examined the spatial trends, sources and dietary relationships of bioaccumulative perfluorinated sulfonate (PFSA; C(6), C(8), and C(10) chain lengths) and carboxylate (PFCA; C(6) to C(15) chain lengths) contaminants, as well as precursor compounds including several perfluorinated sulfonamides, and fluorotelomer acids and alcohols, in individual eggs (collected in 2008) from four gull species [glaucous-winged (Larus glaucescens), California (Larus californicus), ring-billed (Larus delawarensis) and herring (Larus argentatus) gulls] from 15 marine and freshwater colony sites in provinces across Canada. The pattern of PFSAs was dominated by perfluorooctane sulfonate (PFOS; >89% of ΣPFSA concentration) regardless of egg collection location. The highest ΣPFSA concentrations were found in the eggs collected in the urbanized areas in the Great Lakes and the St. Lawrence River area [Big Chicken Island 308 ng/g ww, Toronto Harbour 486 ng/g ww, and Ile Deslauriers (HG) 299 ng/g ww]. Also, eggs from all freshwater colony sites had higher ΣPFSA concentrations, which were significant (p<0.05) in many cases, compared to the marine sites with the exception of the Sable Island colony in Atlantic Canada off the coast of Nova Scotia. C(6) to C(15) chain length PFCAs were detected in the eggs, although the pattern was variable among the 15 sites, where PFUnA and PFTrA dominated the pattern for most colonies. Like the ΣPFSA, the highest concentrations of ΣPFCA were found in the eggs from Big Chicken Island, Toronto Harbour, Ile Deslauriers (HG), and Sable Island, although not all freshwater sites had higher concentrations compared to marine sites. Dietary tracers [δ(15)N and δ(13)C stable isotopes (SIs)] revealed that PFSA and PFCA exposure is colony dependent. SI signatures suggested that gulls from most marine colony sites were exposed to PFCs via marine prey. The exception was the Mandarte Island colony in Pacific British Columbia, where PFSA and PFCA exposure appeared to be via terrestrial and/or freshwater prey consumption. The same was true for the freshwater sites where egg SIs suggested both aquatic and terrestrial prey consumption as the source for PFC exposure depending on the colony. Both aquatic (marine and freshwater) and terrestrial prey are likely sources of PFC exposure to gulls but exposure scenarios are colony-specific.

Fluorinated alkyl compounds including long chain carboxylic acids in wild bird livers from Japan

A wide range of fluorinated alkyl compounds (FACs) has been reported in wildlife in various locations in the world. However, such information regarding Japanese wildlife is rarely found. In the present study, we investigated the occurrence of 21 FACs, including perfluorinated alkyl sulfonates (PFASs), perfluorinated carboxylates (PFCAs), and fluorotelomer acids, in the livers of 10 wild bird species from two regions in northern Japan. To avoid interferences, FACs were quantified by a recently developed method using acetonitrile and solid-phase extraction followed by an ion exchange HPLC column separation. Apart from perfluorooctane sulfonate (PFOS), which was found at the highest levels of all the compounds detected, several long chain perfluorinated carboxylates (PFCAs) from C8 to C16, particularly perfluorotetradecanoic acid (PFTeDA) and perfluorohexadecanoic acid (PFHxDA), were detected for the first time. Additionally, 7:3 FTCA, a fluorotelomer acid, was also detected in most swan livers from Miyagi prefecture and all the birds from Tochigi prefecture. However, none of the sulfonamides and unsaturated telomer acids were detected in any species. Swans seem to be the least exposed wild birds to FACs among the investigated birds, signifying that feeding habits may reflect FAC accumulation in wild birds. The highest total concentration of detected FACs was 405ngg(-1)wet wt., which was found in a Japanese sparrowhawk, indicating that the top predatory wild birds can accumulate several long chain carboxylic acids. However, the current FAC concentrations found in livers may suggest that these compounds alone would not cause a severe toxic effect in these species.

6:2 fluorotelomer sulfonate aerobic biotransformation in activated sludge of waste water treatment plants

The aerobic biotransformation of 6:2 FTS salt [F(CF2)6CH2CH2SO3- K+] was determined in closed bottles for 90d in diluted activated sludge from three waste water treatment plants (WWTPs) to compare its biotransformation potential with that of 6:2 FTOH [F(CF2)6CH2CH2OH]. The 6:2 FTS biotransformation was relatively slow, with 63.7% remaining at day 90 and all observed transformation products together accounting for 6.3% of the initial 6:2 FTS applied. The overall mass balance (6:2 FTS plus observed transformation products) at day 90 in live and sterile treatments averaged 70% and 94%, respectively. At day 90, the stable transformation products observed were 5:3 acid [F(CF2)5CH2CH2COOH, 0.12%], PFBA [F(CF2)3COOH, 0.14%], PFPeA [F(CF2)4COOH, 1.5%], and PFHxA [F(CF2)5COOH 1.1%]. In addition, 5:2 ketone [F(CF2)5C(O)CH3] and 5:2 sFTOH [F(CF2)5CH(OH)CH3] together accounted for 3.4% at day 90. The yield of all the stable transformation products noted above (2.9%) was 19 times lower than that of 6:2 FTOH in aerobic soil. Thus 6:2 FTS is not likely to be a major source of PFCAs and polyfluorinated acids in WWTPs. 6:2 FTOH, 6:2 FTA [F(CF2)6CH2COOH], and PFHpA [F(CF2)6COOH] were not observed during the 90-d incubation. 6:2 FTS primary biotransformation bypassed 6:2 FTOH to form 6:2 FTUA [F(CF2)5CF=CHCOOH], which was subsequently degraded via pathways similar to 6:2 FTOH biotransformation. A substantial fraction of initially dosed 6:2 FTS (24%) may be irreversibly bound to diluted activated sludge catalyzed by microbial enzymes. The relatively slow 6:2 FTS degradation in activated sludge may be due to microbial aerobic de-sulfonation of 6:2 FTS, required for 6:2 FTS further biotransformation, being a rate-limiting step in microorganisms of activated sludge in WWTPs.

Spatial distribution of polyfluoroalkyl compounds in dab (Limanda limanda) bile fluids from Iceland and the North Sea

The spatial distribution of polyfluoroalkyl compounds (PFCs) was investigated in dab (Limanda limanda) bile fluids collected from Iceland and the North Sea. Concentrations of various PFCs, including perfluorinated sulfonates (C(4)-C(6), C(8) PFSAs), perfluorinated carboxylic acids (C(9)-C(14) PFCAs) and n-methyl perfluorooctane sulfonamidoethanol (MeFOSE), were quantified. Perfluorooctane sulfonate (PFOS) was the predominant compound with highest concentrations along the Danish and German coast (mean 9.36ng/g wet weight (ww)). Significantly lower PFOS concentrations were found at the other sampling stations in the North Sea and Iceland (p<0.01, t-test). Conversely, the spatial distribution of the PFCAs in Iceland and the North Sea was more uniform. The most abundant PFCA was perfluorononanoic acid (PFNA), while the mean concentration decreased with increasing chain length from 4.7 ng/g ww for PFNA to 0.04 ng/g ww for perfluorotetradecanoic acid (PFTeDA). Overall, the different spatial distribution of PFCs indicates different origin of sources and different transportation mechanism.

omega-(Bis(trifluoromethyl)amino)alkane-1-sulfonates: synthesis and mass spectrometric study of the biotransformation products

In search of fluorinated functional groups which could undergo defluorination, and therefore be included in novel non-polluting fluorinated surfactants, omega-(bis(trifluoromethyl)amino)alkane-1-sulfonates (BTFMA-AS) with a homologue distribution from seven to thirteen methylene groups were synthesized and investigated for aerobic biodegradation applying both a standardized test and a fixed-bed bioreactor (FBBR). These compounds were prepared as part of a screening study for potentially mineralizable fluorinated endgroups.Application of hybrid triple quadrupole-linear ion trap mass spectrometry (QqQ(LIT)-MS) coupled to high-performance liquid chromatography (HPLC) allowed the tracking of primary degradation as well as the detection and structural elucidation of biotransformation intermediates. An understanding of the fragmentation pathway of the test compounds allowed selective precursor ion scans to reveal the presence of stable fluorinated metabolites. Structures were confirmed by enhanced product ion scans and MS(3) scans in the linear ion trap mode.The primary biodegradation rate and the extent of biodegradation were found to be chain-length dependent, with higher homologues being completely primarily degraded within 10 days. For the first time, two simultaneous metabolic pathways for substituted linear alkane-1-sulfonates were discovered: Desulfonation, oxidation to a carboxylic acid and subsequent chain-length shortening by beta-oxidation dominated the metabolism. This pathway resulted in the formation of 3-(bis(trifluoromethyl)amino)propionic acid and bis(trifluoromethyl)aminoacetic acid, which showed recalcitrance in this experiment. Oxidation of the alkyl chain to the respective carbonyl derivative represents the minor pathway. Only the long-chain homologues of these oxidized species were partially degraded; the short-chain homologues were not attacked.

Toxicity and biodegradation of the LAS surfactant 1-(p-sulfophenyl)nonane in presence of the ascidian Styela plicata

The main objective of this study, within development of engineering solutions for coastal areas depuration, was to establish the role of the benthic macro-organisms in the biodegradation of the detergents in marine environment and to estimate the toxicity of these substances for a particular marine species: the ascidian Styela plicata. The experimental studies undertaken in aquarium with seawater enriched in a pure lynear alkylbenzene sulfonate (LAS), the 1-(p-sulfophenyl)nonane (1C9-LAS), showed that the degradation was two times more fast in presence of the S. plicata, than of the only marine bacteria. The toxicity of this pollutant was also determined. This study demonstrates that the ascidia S. plicata can be a potential biomediator for the surfactant 1C9-LAS, and it can be used to design a pilot project, to bioremediate harbours and the coastal areas interested from the urban pollution.

The DUF81 protein TauE in Cupriavidus necator H16, a sulfite exporter in the metabolism of C2 sulfonates

The degradation of taurine, isethionate and sulfoacetate in Cupriavidus necator (Ralstonia eutropha) H16 was shown by enzyme assays to be inducible, and each pathway involved sulfoacetaldehyde, which was subject to phosphatolysis by a common sulfoacetaldehyde acetyltransferase (Xsc, H16_B1870) to yield acetyl phosphate and sulfite. The neighbouring genes encoded phosphate acetyltransferase (Pta, H16_B1871) and a hypothetical protein [domain of unknown function (DUF)81, H16_B1872], with eight derived transmembrane helices. RT-PCR showed inducible transcription of these three genes, and led to the hypothesis that H16_B1872 and orthologous proteins represent a sulfite exporter, which was named TauE.

Mechanism of flavin reduction in the alkanesulfonate monooxygenase system

The alkanesulfonate monooxygenase system from Escherichia coli is involved in scavenging sulfur from alkanesulfonates under sulfur starvation. An FMN reductase (SsuE) catalyzes the reduction of FMN by NADPH, and the reduced flavin is transferred to the monooxygenase (SsuD). Rapid reaction kinetic analyses were performed to define the microscopic steps involved in SsuE catalyzed flavin reduction. Results from single-wavelength analyses at 450 and 550 nm showed that reduction of FMN occurs in three distinct phases. Following a possible rapid equilibrium binding of FMN and NADPH to SsuE (MC-1) that occurs before the first detectable step, an initial fast phase (241 s(-1)) corresponds to the interaction of NADPH with FMN (CT-1). The second phase is a slow conversion (11 s(-1)) to form a charge-transfer complex of reduced FMNH(2) with NADP(+) (CT-2), and represents electron transfer from the pyridine nucleotide to the flavin. The third step (19 s(-1)) is the decay of the charge-transfer complex to SsuE with bound products (MC-2) or product release from the CT-2 complex. Results from isotope studies with [(4R)-(2)H]NADPH demonstrates a rate-limiting step in electron transfer from NADPH to FMN, and may imply a partial rate-limiting step from CT-2 to MC-2 or the direct release of products from CT-2. While the utilization of flavin as a substrate by the alkanesulfonate monooxygenase system is novel, the mechanism for flavin reduction follows an analogous reaction path as standard flavoproteins.

Regulation of sulfur assimilation pathways in Burkholderia cenocepacia: identification of transcription factors CysB and SsuR and their role in control of target genes

Two genes encoding transcriptional regulators involved in sulfur assimilation pathways in Burkholderia cenocepacia strain 715j have been identified and characterized functionally. Knockout mutations in each of the B. cenocepacia genes were constructed and introduced into the genome of 715j by allelic replacement. Studies on the utilization of various sulfur sources by 715j and the obtained mutants demonstrated that one of the B. cenocepacia regulators, designated CysB, is preferentially involved in the control of sulfate transport and reduction, while the other, designated SsuR, is required for aliphatic sulfonate utilization. Using transcriptional promoter-lacZ fusions and DNA-binding experiments, we identified several target promoters for positive control by CysB and/or SsuR--sbpp (preceding the sbp cysT cysW cysA ssuR cluster), cysIp (preceding the cysI cysD1 cysN cysH cysG cluster), cysD2p (preceding a separate cluster, cysD2 cysNC), and ssuDp (located upstream of the ssuDCB operon)--and we demonstrated overlapping functions of CysB and SsuR at particular promoters. We also demonstrated that the cysB gene is negatively controlled by both CysB and SsuR but the ssuR gene itself is not significantly regulated as a separate transcription unit. The function of B. cenocepacia CysB (in vivo and in vitro) appeared to be independent of the presence of acetylserine, the indispensable coinducer of the CysB regulators of Escherichia coli and Salmonella. The phylogenetic relationships among members of the "CysB family" in the gamma and beta subphyla are presented.

Proton exchange coupled to the specific binding of alkylsulfonates to serum albumins

We have applied isothermal titration calorimetry to investigate the linkage between ligand binding and the uptake or release of protons by human serum albumin (HSA) and bovine serum albumin (BSA). The ligands were sodium decyl sulfate (SDeS) and sodium dodecyl sulfate (SDS). Within a certain temperature range, the binding isotherm could be clearly resolved into two classes of sites (high affinity and low affinity) and modeled assuming independence and thermodynamic equivalence of the sites within each class. Measurements at pH 7.0 in different buffer systems revealed that the binding of SDS to the high affinity sites did not couple to any exchange of protons in either of the proteins. Saturation of the 6-8 low affinity sites for SDS, on the other hand, brought about the release of two protons from both HSA and BSA. In addition to elucidating the pH dependence of ligand binding, this analysis stressed that binding enthalpies for the low affinity sites measured by calorimetry must be corrected for effects due to the concomitant protonation of the buffer. The shorter ligand SDeS bound to HSA with a comparable stoichiometry but with four times lower affinity. Interestingly, no proton linkage was observed for the binding of SDeS. An empirical structural analysis suggested that His 242 in site 7 (of HSA) is a likely candidate for one of the proton donors.

Undecanesulfonate does not allosterically activate H+ uniport mediated by uncoupling protein-1 in brown adipose tissue mitochondria

Undecanesulfonate is transported by uncoupling protein-1. Its inability to induce H+ uniport with reconstituted uncoupling protein-1 supports fatty acid cycling hypothesis. Rial et al. [Rial, E., Aguirregoitia, E., Jimenez-Jimenez, J., & Ledesma, A. (2004). Alkylsulfonates activate the uncoupling protein UCP1: Implications for the transport mechanism. Biochimica et Biophysica Acta, 1608, 122-130], have challenged the fatty acid cycling by observing uncoupling of brown adipose tissue mitochondria due to undecanesulfonate, interpreted as allosteric activation of uncoupling protein-1. We have estimated undecanesulfonate effects after elimination of endogenous fatty acids by carnitine cycle in the presence or absence of bovine serum albumin. We show that the undecanesulfonate effect is partly due to fatty acid release from albumin when undecanesulfonate releases bound fatty acid and partly represents a non-specific uncoupling protein-independent acceleration of respiration, since it proceeds also in rat heart mitochondria lacking uncoupling protein-1 and membrane potential is not decreased upon addition of undecanesulfonate without albumin. When the net fatty acid-induced uncoupling was assayed, the addition of undecanesulfonate even slightly inhibited the uncoupled respiration. We conclude that undecanesulfonate does not allosterically activate uncoupling protein-1 and that fatty acid cycling cannot be excluded on a basis of its non-specific effects.

Tesaglitazar

AstraZeneca plc is developing tesaglitazar, an oral dual peroxisome proliferator-activated receptor alpha/gamma agonist, for the potential improvement of dyslipidemia and glycemic control in type 2 diabetic patients.

Crystallization and preliminary X-ray crystallographic studies of the alkanesulfonate FMN reductase from Escherichia coli

The alkanesulfonate FMN reductase (SsuE) from Escherichia coli catalyzes the reduction of FMN by NADPH to provide reduced flavin for the monooxygenase (SsuD) enzyme. The vapor-diffusion technique yielded single crystals that grow as hexagonal rods and diffract to 2.9 A resolution using synchrotron X-ray radiation. The protein crystallizes in the primitive hexagonal space group P622. The SsuE protein lacks any cysteine or methionine residues owing to the role of the SsuE enzyme in the acquisition of sulfur during sulfate starvation. Therefore, substitution of two leucine residues (Leu114 and Leu165) to methionine was performed to obtain selenomethionine-containing SsuE for MAD phasing. The selenomethionine derivative of SsuE has been expressed and purified and crystals of the protein have been obtained with and without bound FMN. These preliminary studies should lead to the structure solution of SsuE. It is anticipated that this new protein structure will provide detailed structural information on specific active-site regions of the protein and insight into the mechanism of flavin reduction and transfer of reduced flavin.

Steady-state and transient kinetic analyses of taurine/alpha-ketoglutarate dioxygenase: effects of oxygen concentration, alternative sulfonates, and active-site variants on the FeIV-oxo intermediate

Taurine/alpha-ketoglutarate (alphaKG) dioxygenase (TauD), an archetype alphaKG-dependent hydroxylase, is a non-heme mononuclear Fe(II) enzyme that couples the oxidative decarboxylation of alphaKG with the conversion of taurine to aminoacetaldehyde and sulfite. The crystal structure of taurine-alphaKG-Fe(II)TauD is known, and spectroscopic studies have kinetically defined the early steps in catalysis and identified a high-spin Fe(IV)-oxo reaction intermediate. The present analysis extends our understanding of TauD catalysis by investigating the steady-state and transient kinetics of wild-type and variant forms of the enzyme with taurine and alternative sulfonates. TauD proteins substituted at residues surrounding the active site were shown to fold properly based on their abilities to form a diagnostic chromophore associated with the anaerobic Fe(II)-alphaKG chelate complex and to generate a tyrosyl radical upon subsequent reaction with oxygen. Steady-state studies of mutant proteins confirmed the importance of His 70 and Arg 270 in binding the sulfonate moiety of taurine and indicated the participation of Asn 95 in recognizing the substrate amine group. The N97A and S158A variants are likely to undergo an increase in hydrophobicity and expansion of the substrate-binding pocket, thus accounting for their decreased K(m) toward pentanesulfonic acid compared to wild-type TauD. Stopped-flow UV-visible spectroscopic examination of the reaction of oxygen with taurine-alphaKG-Fe(II)TauD confirmed a minimal three-step sequence of reactions attributed to Fe(IV)-oxo formation (k(1)), bleaching to the Fe(II) state upon substrate hydroxylation (k(2)), rebinding of excess substrates (k(3)), and indicated that none of the steps exhibit detectable solvent k(H)/k(D) isotope effects. This demonstrates that no protons are involved in the rate-determining step of Fe(IV)-oxo formation, in contrast to heme iron oxygenases. The Fe(IV)-oxo species is likely to be utilized in conversion of the alternative substrates pentanesulfonic acid and 3-N-morpholinopropanesulfonic acid; however, this spectroscopic intermediate was not detected because of the decreased k(1)/k(2) ratio. With taurine, k(1) was shown to depend on the oxygen concentration allowing calculation of a second-order rate constant of 1.58 x 10(5) M(-)(1) s(-)(1) for this irreversible reaction. Stopped-flow analyses of TauD variants provided several insights into how the protein environment influences the rates of Fe(IV)-oxo formation and decay. The Fe(IV)-oxo species was not detected in the N95D or N95A variants because of a reduced k(1)/k(2) ratio, likely related to a decreased substrate-dependent conversion of the six-coordinate to five-coordinate metal site.

Pharmacokinetics and metabolism of tesaglitazar, a novel dual-acting peroxisome proliferator-activated receptor alpha/gamma agonist, after a single oral and intravenous dose in humans

The pharmacokinetics of tesaglitazar (GALIDA), a novel dual-acting peroxisome proliferator-activated receptor alpha and gamma agonist, were studied in eight healthy male subjects. The subjects initially received either a single oral or intravenous (i.v.) dose of 1 mg of [(14)C]tesaglitazar. After a washout period, they received 1 mg of nonlabeled tesaglitazar via the alternative administration route. Serial blood samples and complete urine and feces were collected until 336 h postdose. Tesaglitazar absorption was rapid, with maximum plasma concentration (C(max)) at approximately 1 h postdose, and the absolute bioavailability was approximately 100%, suggesting no, or negligible, first-pass metabolism. Mean plasma clearance was 0.16 l/h and the volume of distribution at steady state was 9.1 liters. After either route of administration, the plasma concentration-time profiles of radioactivity and tesaglitazar were virtually identical, indicating low systemic metabolite concentrations and formation rate limitation of metabolite elimination. The elimination half-life of radioactivity and tesaglitazar was approximately 45 h. Radioactivity recovery was complete in all subjects, with mean values of 99.9% (i.v.) and 99.6% (oral). Tesaglitazar was mainly metabolized before excretion, and most radioactivity (91%) was recovered in urine. Approximately 20% of the dose was recovered unchanged after either administration route, resulting in a renal clearance of 0.030 l/h. Most of the radioactivity in urine was identified as acyl glucuronide of tesaglitazar. Plasma protein binding of tesaglitazar was high ( approximately 99.9%), and the mean blood-plasma partitioning ratio was 0.66, suggesting low affinity for red blood cells. There was no indication of partial inversion of the (S)-enantiomer to the corresponding (R)-form. Tesaglitazar was well tolerated.

The stereoselectivity and catalytic properties of Xanthobacter autotrophicus 2-[(R)-2-Hydroxypropylthio]ethanesulfonate dehydrogenase are controlled by interactions between C-terminal arginine residues and the sulfonate of coenzyme M

2-[(R)-2-Hydroxypropylthio]ethanesulfonate (R-HPC) dehydrogenase (DH) catalyzes the reversible oxidation of R-HPC to 2-(2-ketopropylthio)ethanesulfonate (2-KPC) in a key reaction in the bacterial conversion of chiral epoxides to beta-keto acids. R-HPCDH is highly specific for the R-enantiomer of HPC, while a separate enzyme, S-HPCDH, catalyzes the oxidation of the corresponding S-enantiomer. In the present study, the features of substrate and enzyme imparting stereospecificity have been investigated for R-HPCDH. S-HPC was a substrate for R-HPCDH with a K(m) identical to that for R-HPC but with a k(cat) 600 times lower. Achiral 2-propanol and short-chain (R)- and (S)-2-alkanols were substrates for R-HPCDH. For (R)-alkanols, as the carbon chain length increased, K(m) decreased, with the K(m) for (R)-2-octanol being 1700 times lower than for 2-propanol. At the same time, k(cat) changed very little and was at least 90% lower than k(cat) for R-HPC and at least 22 times higher than k(cat) for S-HPC. (S)-2-Butanol and (S)-2-pentanol were substrates for R-HPCDH. The K(m) for (S)-2-butanol was identical to that for (R)-2-butanol, while the K(m) for (S)-2-pentanol was 7.5 times higher than for (R)-2-pentanol. Longer chain (S)-2-alkanols were sufficiently poor substrates for R-HPCDH that kinetic parameters could not be determined. Mutagenesis of C-terminal arginine residues of R-HPCDH revealed that R152 and R196 are essential for effective catalysis with the natural substrates R-HPC and 2-KPC but not for catalysis with 2-alkanols or ketones as substrates. Short-chain alkylsulfonates and coenzyme M (2-mercaptoethanesulfonate) were found to modify the kinetic parameters for 2-butanone reduction by R-HPCDH in a saturable fashion, with the general effect of increasing k(cat), decreasing K(m), and increasing the enantioselectivity of 2-butanone reduction to a theoretical value of 100% (S)-2-butanol. The modulating effects of ethanesulfonate and propanesulfonate provided thermodynamic binding constants close to K(m) for the natural substrates R-HPC and 2-KPC. The effects of alkylsulfonates on modulating the enantioselectivity and kinetic properties of R-HPCDH were abolished in R152A and R196A mutants but not in mutants of other C-terminal arginine residues. Collectively, the results suggest that interactions between the sulfonate of CoM and specific arginine residues are key to the enantioselectivity and catalytic efficiency of R-HPCDH. A model is proposed wherein sulfonate-arginine interactions within an alkylsulfonate binding pocket control the catalytic properties of R-HPCDH.

Gelatin–alpha olefin sulfonate interactions studied by dynamic light scattering

Dynamic light scattering (DLS) measurements were performed to study the binding of anionic surfactant alpha olefin sulfonate (AOS) to gelatin chains at various NaCl concentrations at 30 degrees C in aqueous sodium phosphate buffer (pH = 6.8) solutions. The surfactant concentration was varied from 0 to 80 mM and the NaCl concentrations chosen were 0.025, 0.05, and 0.1 M. AOS exhibited electrostatic binding to the positively charged sites of the polypeptide chain resulting in considerable reduction in its hydrodynamic radius up to critical micellar concentration (cmc = 8 mM for no salt, 0.01 and 0.025 M, and 5 mM for 0.05 M and 2 mM for 0.1 M solutions). The correlation function revealed the presence of two types of structures above cmc; namely the micelles of AOS and gelatin-AOS micelle complexes. The micellar radii (Rm), the effective gelatin-surfactant complex radii (Rc), have been determined as a function of salt concentration. No critical aggregation concentration (cac) was observed. The inter-gelatin-surfactant complex (kD1) and inter-micellar interactions (kD2), were determined by fitting the concentration dependence of Rm and Rc to a virial expansion in reduced concentration (c - cmc), which are compared. While kD1 showed strong ionic strength dependence, kD2 remained invariant of the same. The protein to surfactant binding ratio was found to be smaller than normal. Results have been discussed within the framework of the necklace-bead model of polymer-surfactant interactions.

Fibronectin fibrillogenesis on sulfonated polystyrene surfaces

Extracellular matrix (ECM) protein adsorption and organization serves as a critical first step in the development and organization of tissues. Advances in tissue engineering, therefore, will depend on the ability to control the rate and pattern of ECM formation. Fibronectin is a prominent component of the ECM, which undergoes fibrillogenesis in the presence of cells. Using sulfonated polysyrene surfaces, we showed that fibronectin undergoes a transition from monolayer to multilayer adsorption at calculated surface charge densities above 0.03 Coulombs (C)/m(2). At charge densities above approximately 0.08 C/m(2), distinct fibronectin fibrillar networks are observed to form with a fibril morphology similar to those observed to form in situ on cell surfaces. This self-organization process is time dependent, with the fibrils achieving dimensions of 30-40 microm in length and 1 microm in height after 72 h of incubation. We suggest that the polarization of charge domains on the polyampholytic fibronectin molecules near high charge density surfaces is sufficient to initiate the multilayer adsorption and the organization of these fibrillar structures. These results suggest that the nonlinear dependence of adsorption on surface charge density may play an important role in the self-organization of many matrix components.

Dissimilation of the C2 sulfonates

Organosulfonates are widespread in the environment, both as natural products and as xenobiotics; and they generally share the property of chemical stability. A wide range of phenomena has evolved in microorganisms able to utilize the sulfur or the carbon moiety of these compounds; and recent work has centered on bacteria. This Mini-Review centers on bacterial catabolism of the carbon moiety in the C2-sulfonates and the fate of the sulfonate group. Five of the six compounds examined are subject to catabolism, but information on the molecular nature of transport and regulation is based solely on sequencing data. Two mechanisms of desulfonation have been established. First, there is the specific monooxygenation of ethanesulfonate or ethane-1,2-disulfonate. Second, the oxidative, reductive and fermentative modes of catabolism tend to yield the intermediate sulfoacetaldehyde, which is now known to be desulfonated to acetyl phosphate by a thiamin-diphosphate-dependent acetyltransferase. This enzyme is widespread and at least three subgroups can be recognized, some of them in genomic sequencing projects. These data emphasize the importance of acetyl phosphate in bacterial metabolism. A third mechanism of desulfonation is suggested: the hydrolysis of sulfoacetate.

Hepatobiliary excretion of dipyrrinone sulfonates in Mrp2-deficient (TR(-)) rats

The biliary excretion of the sodium salts of 8-(2-ethanesulfonic acid)-3-ethyl-2,7,9-trimethyl-1,10-dihydro-11H-dipyrrin-1-one (xanthosulfonic acid) and a fluorescent analogue (8-desethyl-N,N'-carbonyl-kryptopyrromethenone-8-sulfonic acid) was compared in Mrp2-deficient (TR(-)) and normal rats. Both organic anions were excreted rapidly in bile in Mrp2-deficient rats, but the biliary excretion of the fluorescent sulfonate was impaired relative to normal controls. The rat clearly has efficient Mrp2-independent mechanisms for biliary efflux of these anions that are not used by bilirubin or its mono- and diglucuronides.

Escherichia coli utilizes methanesulfonate and L-cysteate as sole sulfur sources for growth

Twenty-three Escherichia coli strains were tested for their ability to use taurine, methanesulfonate, L-cysteate and other alkanesulfonates as sole sulfur sources for growth. One strain was unable to use any of the alkanesulfonates offered as sole sulfur sources for growth but grew with sulfate. Seven strains (class I) used alkanesulfonates for this purpose, but not methanesulfonate or L-cysteate. A further seven strains (class II) grew with all compounds tested, except with L-cysteate, and eight strains (class III) utilized all compounds tested as sulfur sources. Sulfur assimilation from methanesulfonate and L-cysteate was absolutely dependent on the ssuEADCB operon that encodes an alkanesulfonate uptake system (SsuABC) and a two-component monooxygenase (SsuDE) involved in the release of sulfite from alkanesulfonates. Long-term exposure of class I strains to methanesulfonate and of class II strains to L-cysteate selected for derivatives that utilized these two sulfur sources as efficiently as sulfate. The nucleotide sequence of the ssuEADCB operon in the methanesulfonate- and L-cysteate-utilizing derivative EC1250Me+ was identical to that in the class I wild-type EC1250. Gain of the ability to utilize methanesulfonate and L-cysteate as sulfur sources thus appears to result from increased expression of ssu genes rather than from a change in the quality of one or several of the Ssu proteins.

Alkanesulfonate degradation by novel strains of Achromobacter xylosoxidans, Tsukamurella wratislaviensis and Rhodococcus sp., and evidence for an ethanesulfonate monooxygenase in A. xylosoxidans strain AE4

Novel isolates of Achromobacter xylosoxidans, Tsukamurella wratislaviensis and a Rhodococcus sp. are described. These grew with short-chain alkanesulfonates as their sole source of carbon and energy. T. wratislaviensis strain SB2 grew well with C(3)-C(6) linear alkanesulfonates, isethionate and taurine, Rhodococcus sp. strain CB1 used C(3)-C(10) linear alkanesulfonates, taurine and cysteate, but neither strain grew with ethanesulfonate. In contrast, A. xylosoxidans strain AE4 grew well with ethanesulfonate, making it the first bacterium to be described which can grow with this compound. It also grew with unsubstituted C(3)-C(5) alkanesulfonates and isethionate. Hydrolysis was excluded as a mechanism for alkanesulfonate metabolism in these strains; and evidence is given for a diversity of uptake and desulfonatase systems. We provide evidence for an initial monooxygenase-dependent desulfonation in the metabolism of ethanesulfonate and propanesulfonate by A. xylosoxidans strain AE4.

[Electron microscopic study of the colonies of an alkylsulfonate-utilizing bacterial consortium]

The light- and electron-microscopic analysis of the colonies of a bacterial consortium capable of utilizing alkylsulfonates, which are the main ingredients of sewage from the synthetic rubber industry, revealed the presence of eight types of cells. All types of cells were gram-negative and differed in shape, size, and the presence of capsule and cytoplasmic inclusions. Three types of cells were present in all the colonies that were studied. The presence of the other types of cells depended on the inoculum used and on the composition of the growth medium.

Ethanedisulfonate is degraded via sulfoacetaldehyde in Ralstonia sp. strain EDS1

Aerobic enrichment cultures (11) yielded three cultures able to utilise ethane-1,2-disulfonate as sole source of carbon and energy in salts medium. Two pure cultures were obtained and we worked with strain EDS1, which was assigned to the genus Ralstonia on the basis of its 16S rDNA sequence and simple taxonomic tests. Strain EDS1 utilised at least seven alkane(di)sulfonates, ethane-1,2-disulfonate, taurine, isethionate, sulfoacetate, sulfoacetaldehyde and propane-1,3-disulfonate, as well as methanesulfonate and formate. Growth with ethanedisulfonate was concomitant with substrate disappearance and the formation of 2 mol sulfate per mol substrate. The growth yield, 7 g protein (mol C)(-1), indicated quantitative utilisation of the substrate. Ethanedisulfonate-dependent oxygen uptake of whole cells during growth rose to a maximum before the end of growth and then sank rapidly; this was interpreted as evidence for an inducible desulfonative oxygenase that was not active in cell extracts. Inducible sulfoacetaldehyde sulfo-lyase was detected at high activity. Inducible degradation of taurine or isethionate or sulfoacetate via sulfoacetaldehyde sulfo-lyase is interpreted from the data.

Sulfonate-sulfur metabolism and its regulation in Escherichia coli

In the absence of sulfate and cysteine, Escherichia coli can use aliphatic sulfonates as a source of sulfur for growth. Starvation for sulfate leads to the expression of the tauABCD and ssuEADCB genes. Each of these gene clusters encodes an ABC-type transport system required for uptake of aliphatic sulfonates and a desulfonation enzyme. The TauD protein is an alpha-ketoglutarate-dependent dioxygenase that preferentially liberates sulfite from taurine (2-aminoethanesulfonic acid). SsuD is a monooxygenase that catalyzes the oxygenolytic desulfonation of a range of aliphatic sulfonates other than taurine. Its cosubstrate is FMNH2, which is provided by SsuE, an NAD(P)H-dependent FMN reductase. In contrast to many other bacteria, E. coli is unable to grow with arylsulfonates or with sulfate esters as sulfur source. The tau and ssu systems thus provide all genes for the utilization of known organosulfur sources by this organism, except the as yet unidentified gene(s) that enable some E. coli strains to grow with methanesulfonate or cysteate as a sulfur source. Expression of the tau and ssu genes requires the LysR-type transcriptional regulatory proteins CysB and Cbl. Synthesis of Cbl itself is under control of the CysB protein, and the CysB protein may therefore be regarded as the master regulator for sulfur assimilation in E. coli, while the Cbl protein functions as an accessory element specific for utilization of sulfur from organosulfur sources.