The diversity of naturally produced organohalogens

Identification of a eukaryotic reductive dechlorinase and characterization of its mechanism of action on its natural substrate

Chlorinated compounds are important environmental pollutants whose biodegradation may be limited by inefficient dechlorinating enzymes. Dictyostelium amoebae produce a chlorinated alkyl phenone called DIF which induces stalk cell differentiation during their multicellular development. Here we describe the identification of DIF dechlorinase. DIF dechlorinase is active when expressed in bacteria, and activity is lost from Dictyostelium cells when its gene, drcA, is knocked out. It has a K_m for DIF of 88 nM and K_cat of 6.7 s⁻¹. DrcA is related to glutathione S-transferases, but with a key asparagine-to-cysteine substitution in the catalytic pocket. When this change is reversed, the enzyme reverts to a glutathione S-transferase, thus suggesting a catalytic mechanism. DrcA offers new possibilities for the rational design of bioremediation strategies.

Organic matter chlorination rates in different boreal soils: the role of soil organic matter content

Transformation of chloride (Cl(-)) to organic chlorine (Cl(org)) occurs naturally in soil but it is poorly understood how and why transformation rates vary among environments. There are still few measurements of chlorination rates in soils, even though formation of Cl(org) has been known for two decades. In the present study, we compare organic matter (OM) chlorination rates, measured by (36)Cl tracer experiments, in soils from eleven different locations (coniferous forest soils, pasture soils and agricultural soils) and discuss how various environmental factors effect chlorination. Chlorination rates were highest in the forest soils and strong correlations were seen with environmental variables such as soil OM content and Cl(-) concentration. Data presented support the hypothesis that OM levels give the framework for the soil chlorine cycling and that chlorination in more organic soils over time leads to a larger Cl(org) pool and in turn to a high internal supply of Cl(-) upon dechlorination. This provides unexpected indications that pore water Cl(-) levels may be controlled by supply from dechlorination processes and can explain why soil Cl(-) locally can be more closely related to soil OM content and the amount organically bound chlorine than to Cl(-) deposition.

Marine sponge: a potential source for methoxylated polybrominated diphenyl ethers in the Asia-Pacific food web

Marine sponges collected in Palau, Micronesia, were investigated for hydroxylated or methoxylated analogues of brominated diphenyl ethers (BDEs), brominated dibenzo-p-dioxin (BDD), and brominated biphenyls. The neutral fractions of Haliclona sp. and Callyspongia sp. contained 2'-methoxy-2,3',4,5'-tetraBDE, 6-methoxy-2,2',4,4'-tetraBDE, 2',6-dimethoxy-2,3',4,5-tetraBDE 2,2'-dimethoxy-3,3',5,5'-tetrabromobiphenyl, several methoxy-triBDEs, and dimethoxy-penta-/hexaBDEs. The methoxylated BDEs in sponges were strikingly similar to those of local fish living in the western Pacific Ocean. The total concentrations of these compounds (ΣMeO-PBDE) in both sponges were 63.5 μg/g extractable organic matter (EOM) for Haliclona sp. and 36.5 μg/g EOM for Callyspongia sp., which were about 2 orders of magnitude higher than the levels seen in tropical coral reef fish (unicornfish or surgeonfish) (280-290 ng/g lipid) and groupers (550 ng/g lipid) from Okinawan coastal waters. The phenolic fractions of both sponges contained hydroxy-methoxy tetra-/pentaBDEs as well as hydroxy-tetraBDD, in addition to the corresponding phenolic tetraBDE analogues. Although the total concentrations of phenolic products (27-80 μg/g EOM) in both sponges fell within a range comparable to the methoxylated products, ΣOH-PBDE in local fish were trace level (less than 10 ng/g lipid of) or undetectable. This survey indicates that marine sponges are a possible source of the MeO-PBDE analogues that biomagnify via the food chain to the higher trophic organisms in the western Pacific, whereas the distribution of the corresponding hydroxylated analogues is limited.

Enantioselective bromocycloetherification by Lewis base/chiral Brønsted acid cooperative catalysis

A binary catalyst system for the enantioselective bromocycloetherification of 5-arylpentenols is described. The combination of an achiral Lewis base and a chiral Brønsted acid affords good enantioselectivities for the cyclization of Z configured 5-arylpentenols to form bromomethyltetrahydrofurans. The constitutional site selectivity is highly dependent upon the aromatic substituent and the configuration of the double bond.

Variability of non-polar secondary metabolites in the red alga Portieria

Possible sources of variation in non-polar secondary metabolites of Portieria hornemannii, sampled from two distinct regions in the Philippines (Batanes and Visayas), resulting from different life-history stages, presence of cryptic species, and/or spatiotemporal factors, were investigated. PCA analyses demonstrated secondary metabolite variation between, as well as within, five cryptic Batanes species. Intraspecific variation was even more pronounced in the three cryptic Visayas species, which included samples from six sites. Neither species groupings, nor spatial or temporal based patterns, were observed in the PCA analysis, however, intraspecific variation in secondary metabolites was detected between life-history stages. Male gametophytes (102 metabolites detected) were strongly discriminated from the two other stages, whilst female gametophyte (202 metabolites detected) and tetrasporophyte (106 metabolites detected) samples were partially discriminated. These results suggest that life-history driven variations, and possibly other microscale factors, may influence the variation within Portieria species.

Natural niche for organohalide-respiring Chloroflexi

The phylum Chloroflexi contains several isolated bacteria that have been found to respire a diverse array of halogenated anthropogenic chemicals. The distribution and role of these Chloroflexi in uncontaminated terrestrial environments, where abundant natural organohalogens could function as potential electron acceptors, have not been studied. Soil samples (116 total, including 6 sectioned cores) from a range of uncontaminated sites were analyzed for the number of Dehalococcoides-like Chloroflexi 16S rRNA genes present. Dehalococcoides-like Chloroflexi populations were detected in all but 13 samples. The concentrations of organochlorine ([organochlorine]), inorganic chloride, and total organic carbon (TOC) were obtained for 67 soil core sections. The number of Dehalococcoides-like Chloroflexi 16S rRNA genes positively correlated with [organochlorine]/TOC while the number of Bacteria 16S rRNA genes did not. Dehalococcoides-like Chloroflexi were also observed to increase in number with a concomitant accumulation of chloride when cultured with an enzymatically produced mixture of organochlorines. This research provides evidence that organohalide-respiring Chloroflexi are widely distributed as part of uncontaminated terrestrial ecosystems, they are correlated with the fraction of TOC present as organochlorines, and they increase in abundance while dechlorinating organochlorines. These findings suggest that organohalide-respiring Chloroflexi may play an integral role in the biogeochemical chlorine cycle.

Identification of the natural product 2,3,4,5-tetrabromo-1-methylpyrrole in Pacific biota, passive samplers and seagrass from Queensland, Australia

Halogenated natural products (HNPs) are frequently detected in marine organisms. High HNP concentrations have previously been found in marine mammals from the Great Barrier Reef, Australia, including in the blubber of herbivorous dugongs (Dugong dugon). To identify the source of HNPs we initially focused on the analysis of Australian seagrass (Halophila ovalis) which serves as the principal food source for dugongs. GC/MS analysis of the seagrass indicated the presence of several organobromine compounds. One compound was identified as 2,3,4,5-tetrabromo-1-methylpyrrole (TBMP) by synthesis. Subsequent analysis of semipermeable membrane devices demonstrated that the photo-sensitive TBMP is widespread in the Great Barrier Reef (Queensland, Australia). The detection of larger TBMP concentrations in fish fillets from Chile and traces in mussels from New Zealand indicated that this potential HNP may be distributed throughout the Southern Pacific Ocean.

Substrate specificity of haloalkane dehalogenases

An enzyme's substrate specificity is one of its most important characteristics. The quantitative comparison of broad-specificity enzymes requires the selection of a homogenous set of substrates for experimental testing, determination of substrate-specificity data and analysis using multivariate statistics. We describe a systematic analysis of the substrate specificities of nine wild-type and four engineered haloalkane dehalogenases. The enzymes were characterized experimentally using a set of 30 substrates selected using statistical experimental design from a set of nearly 200 halogenated compounds. Analysis of the activity data showed that the most universally useful substrates in the assessment of haloalkane dehalogenase activity are 1-bromobutane, 1-iodopropane, 1-iodobutane, 1,2-dibromoethane and 4-bromobutanenitrile. Functional relationships among the enzymes were explored using principal component analysis. Analysis of the untransformed specific activity data revealed that the overall activity of wild-type haloalkane dehalogenases decreases in the following order: LinB~DbjA>DhlA~DhaA~DbeA~DmbA>DatA~DmbC~DrbA. After transforming the data, we were able to classify haloalkane dehalogenases into four SSGs (substrate-specificity groups). These functional groups are clearly distinct from the evolutionary subfamilies, suggesting that phylogenetic analysis cannot be used to predict the substrate specificity of individual haloalkane dehalogenases. Structural and functional comparisons of wild-type and mutant enzymes revealed that the architecture of the active site and the main access tunnel significantly influences the substrate specificity of these enzymes, but is not its only determinant. The identification of other structural determinants of the substrate specificity remains a challenge for further research on haloalkane dehalogenases.

Identification of volatile organic compounds in flowers of Astragalus lagopoides

Composition of volatile organic compounds (VOCs) in flowers of Astragalus lagopoides was studied using a hydrodistillation extraction procedure coupled with gas chromatography-mass spectrometry. The analyses allowed the identification of a number of 25 compounds, among which the presence of several bioactive aromatic derivatives such as guaiacol, eugenol, linalool, α- and 4-terpineol as well as nerol was attention-grabbing. Moreover, some other compounds like cyclohexane, 2-bromoethyl with repellent function also appeared to be present in the flower. As a result, the floral VOCs profile of A. lagopoides might reflect an adaptation to attract specialised pollinator insects. These findings provide important information for advances in understanding the ecological and evolutionary perspectives of pollination biology of the giant genus Astragalus.

Chloride and organic chlorine in forest soils: storage, residence times, and influence of ecological conditions

Recent studies have shown that extensive chlorination of natural organic matter significantly affects chlorine (Cl) residence time in soils. This natural biogeochemical process must be considered when developing the conceptual models used as the basis for safety assessments regarding the potential health impacts of 36-chlorine released from present and planned radioactive waste disposal facilities. In this study, we surveyed 51 French forested areas to determine the variability in chlorine speciation and storage in soils. Concentrations of total chlorine (Cl(tot)) and organic chlorine (Cl(org)) were determined in litterfall, forest floor and mineral soil samples. Cl(org) constituted 11-100% of Cl(tot), with the highest concentrations being found in the humus layer (34-689 mg Cl(org) kg(-1)). In terms of areal storage (53 - 400 kg Cl(org) ha(-1)) the mineral soil dominated due to its greater thickness (40 cm). Cl(org) concentrations and estimated retention of organochlorine in the humus layer were correlated with Cl input, total Cl concentration, organic carbon content, soil pH and the dominant tree species. Cl(org) concentration in mineral soil was not significantly influenced by the studied environmental factors, however increasing Cl:C ratios with depth could indicate selective preservation of chlorinated organic molecules. Litterfall contributions of Cl were significant but generally minor compared to other fluxes and stocks. Assuming steady-state conditions, known annual wet deposition and measured inventories in soil, the theoretical average residence time calculated for total chlorine (inorganic (Cl(in)) and organic) was 5-fold higher than that estimated for Cl(in) alone. Consideration of the Cl(org) pool is therefore clearly important in studies of overall Cl cycling in terrestrial ecosystems.

13-Desmethyl spirolide-C is neuroprotective and reduces intracellular Aβ and hyperphosphorylated tau in vitro

Spirolides are marine compounds of the cyclic imine group. Although the mechanism of action is not fully elucidated yet, cholinergic (muscarinic and nicotinic) receptors have been proposed as the main targets of these toxins. In this study we examined the effect of 13-desmethyl spirolide-C (SPX) on amyloid-beta (Aβ) accumulation and tau hyperphosphorylation in a neuronal model from triple transgenic mice (3xTg) for Alzheimer disease (AD). In vitro treatment of 3xTg cortical neurons with SPX reduced intracellular Aβ accumulation and the levels of phosphorylated tau. SPX treatment did not affect the steady-state levels of neither the M1 and M2 muscarinic nor the α7 nicotinic acetylcholine receptors (AChRs), while it decreased the amplitude of acetylcholine-evoked responses and increased ACh (acetylcholine) levels in 3xTg neurons. Additionally, SPX treatment decreased the levels of two protein kinases involved in tau phosphorylation, glycogen synthase kinase 3β (GSK-3β) and extracellular-regulated kinase (ERK). Also SPX abolished the glutamate-induced neurotoxicity in both control and 3xTg neurons. The results presented here constitute the first report indicating that exposure of 3xTg neurons to nontoxic concentrations of SPX produces a simultaneous reduction in the main pathological characteristics of AD. In spite of the few reports analyzing the mode of action of the toxin we suggest that SPX could ameliorate AD pathology increasing the intracellular ACh levels and simultaneously diminishing the levels of kinases involved in tau phosphorylation.

Oxidative intramolecular bromo-amination of N-alkenyl sulfonamides via umpolung of alkali metal bromides

The oxidative intramolecular bromo-amination of various N-alkenyl sulfonamides and N-alkenoxyl sulfonamides via umpolung of alkali metal bromides occurred exo-selectively to generate cyclic bromoamides in high yields with good diastereoselectivities. This method provided the desired products without elaborating the stoichiometric amount of corresponding organic waste.

Site-specific mobilization of vinyl chloride respiration islands by a mechanism common in Dehalococcoides

Background

Vinyl chloride is a widespread groundwater pollutant and Group 1 carcinogen. A previous comparative genomic analysis revealed that the vinyl chloride reductase operon, vcrABC, of Dehalococcoides sp. strain VS is embedded in a horizontally-acquired genomic island that integrated at the single-copy tmRNA gene, ssrA.

Results

We targeted conserved positions in available genomic islands to amplify and sequence four additional vcrABC -containing genomic islands from previously-unsequenced vinyl chloride respiring Dehalococcoides enrichments. We identified a total of 31 ssrA-specific genomic islands from Dehalococcoides genomic data, accounting for 47 reductive dehalogenase homologous genes and many other non-core genes. Sixteen of these genomic islands contain a syntenic module of integration-associated genes located adjacent to the predicted site of integration, and among these islands, eight contain vcrABC as genetic 'cargo'. These eight vcrABC -containing genomic islands are syntenic across their ~12 kbp length, but have two phylogenetically discordant segments that unambiguously differentiate the integration module from the vcrABC cargo. Using available Dehalococcoides phylogenomic data we estimate that these ssrA-specific genomic islands are at least as old as the Dehalococcoides group itself, which in turn is much older than human civilization.

Conclusions

The vcrABC -containing genomic islands are a recently-acquired subset of a diverse collection of ssrA-specific mobile elements that are a major contributor to strain-level diversity in Dehalococcoides, and may have been throughout its evolution. The high similarity between vcrABC sequences is quantitatively consistent with recent horizontal acquisition driven by ~100 years of industrial pollution with chlorinated ethenes.

Role of "Dehalococcoides" spp. in the anaerobic transformation of hexachlorobenzene in European rivers

The diffuse pollution by chlorinated organic compounds in river basins is a concern, due to their potential adverse effects on human health and the environment. Organohalides, like hexachlorobenzene (HCB), are recalcitrant to aerobic microbial degradation, and "Dehalococcoides" spp. are the only known microorganisms capable of anaerobic transformation of these compounds coupled to their growth. In this study, sediments from four European rivers were studied in order to determine their HCB dechlorination capacities and the role of Dehalococcoides spp. in this process. Only a weak correlation was observed between Dehalococcoides species abundance and HCB transformation rates from different locations. In one of these locations, in the Ebro River sediment, HCB dechlorination could be linked to Dehalococcoides species growth and activity by 16S rRNA-based molecular methods. Furthermore, HCB dechlorination activity in this sediment was found over the full range of ambient temperatures that this sediment can be exposed to during different seasons throughout the year. The sediment contained several reductive dehalogenase (rdh) genes, and analysis of their transcription revealed the dominance of cbrA, previously shown to encode a trichlorobenzene reductive dehalogenase. This study investigated the role of Dehalococcoides spp. in HCB dechlorination in river sediments and evaluated if the current knowledge of rdh genes could be used to assess HCB bioremediation potential.

Generation and analysis of mixed chlorinated/brominated homologs of the halogenated natural product heptachloro-1'-methyl-1,2'-bipyrrole

The 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (Q1, MBP-79) and further halogenated 1'-methyl-1,2'-bipyrroles (MBPs) are a class of marine natural products repeatedly detected in seafood and marine mammals from all over the world. Only Q1 is currently commercially available as reference standard and the full synthesis of mixed brominated-chlorinated compound is rather complicated. For this reason, synthetic Q1 (240 mg) was transferred into bromine-containing MBPs by UV-irradiation in the presence of bromine. Bromine, which rapidly vanished from the solutions, was renewed during the reaction in order to generate higher amounts of Br-containing MBPs. A total of ∼150 mg Q1 was transferred after ∼10 min irradiation with high amounts of Br(2) to give 30.5mg BrCl(6)-MBPs along with lower proportions of Br(2)Cl(5)-, Br(3)Cl(4)-, Br(4)Cl(3)- and traces of Br(5)Cl(2)-MBPs. Longer UV-irradiation in the presence of Br(2) even allowed for the detection of Br(6)Cl-MBPs and traces of Br(7)-MBP. However, this reaction also provided some unknown by-products. A sample stored in the dark and later in in-door light (no UV irradiation) also eliminated Q1 after 76 d in favour of heptahalogenated MBPs with up to three bromine substituents. The irradiation products were separated on silica, and fractions containing only Q1 and BrCl(6)-MBPs were then further fractionated by non-aqueous RP-HPLC. A pure isolate of the major BrCl(6)-MBP (∼1.5mg) was characterized by GC/MS and (13)C NMR to be 2-bromo-3,3',4,4',5,5'-hexachloro-1-methyl-1,2'-bipyrrole (Br-MBP-75). Partial GC enantioseparation of the axially chiral Br-MBP-75 was achieved on a β-PMCD column. A full enantioseparation was managed by enantioselective HPLC using a NUCLEOCEL DELTA S column. Low amounts of pure BrCl(6)-MBP enantiomers could be trapped.

Degradative fate of 3-chlorocarbazole and 3,6-dichlorocarbazole in soil

BACKGROUND, AIM, AND SCOPE

3-Chlorocarbazole and 3,6-dichlorocarbazole were isolated from Bavarian soils. The stereospecific formation of the isomers of these chlorinated carbazols can be explained by quantum mechanical calculations using the DFT method. It was shown that chlorination of carbazole and 3-chlorocarbazole respectively is preferred via the sigma-complexes 3-chlorocarbazole and 3,6-dichlorocarbazole as the most stable products. The dioxin-like toxicological potential of 3,6-dichlorocarbazole, determined by the Micro-EROD Test, is in the range of some picogram TCDD equivalents per milligram carbazole. The degradative fate of 3-chlorocarbazole and 3,6-dichlorocarbazole was analysed within a long-term study (57 days) in soil.

MATERIALS AND METHODS

The soil was extracted by ASE (accelerated solvent extraction) and a further clean-up procedure with column chromatography and chromatography with C18-SPE stationary phases. Quantification of 3-chlorocarbazole and 3,6-dichlorocarbazole was performed employing the isotope-dilution method. The samples were measured with high-resolution GC/MS.

RESULTS

The degradation (ln(c/c(0)) vs. time with best-fit line) showed in almost every storage condition a very small degradation (slopes (h(-1)) in -10(-4) range). However, the decay for the controls were two to three times (-28°C) and six times (with sodium azide) higher, than the decrease of 3-chlorocarbazole and 3,6-dichlorocarbazole in the samples of environmental conditions.

DISCUSSION

Especially because of the toxicological potential of 3-chlorocarbazole and 3,6-dichlorocarbazole the proven degradative fate is of large interest. The results show that the analysed carbazoles are not readily degradable in this time period.

CONCLUSIONS

The expected results of exponential decay behaviour could not be proven.

RECOMMENDATION AND PERSPECTIVES

Longer-lasting studies are expected to reveal more accurate half-lives, although it has been shown here, that the compounds are not readily degradable in their native soil environment.

Polybrominated diphenyl ethers and their hydroxylated/methoxylated analogs: environmental sources, metabolic relationships, and relative toxicities

Brominated compounds are ubiquitous in the aquatic environment. The polybrominated diphenyl ether (PBDE) flame retardants are anthropogenic compounds of concern. Studies suggest that PBDEs can be biotransformed to hydroxylated brominated diphenyl ethers (OH-BDE). However, the rate of OH-BDE formation observed has been extremely small. OH-BDEs have also been identified as natural compounds produced by some marine invertebrates. Another class of compounds, the methoxylated BDEs (MeO-BDEs), has also been identified as natural compounds in the marine environment. Both the OH-BDEs and MeO-BDEs bioaccumulate in higher marine organisms. Recent studies have demonstrated that MeO-BDEs can be biotransformed to OH-BDEs and this generates greater amounts of OH-BDEs than could be generated from PBDEs. Consequently, MeO-BDEs likely represent the primary source of metabolically derived OH-BDEs. Given that for some endpoints OH-BDEs often exhibit greater toxicity compared to PBDEs, it is prudent to consider OH-BDEs as chemicals of concern, despite their seemingly "natural" origins.

Trichloromethyl compounds--natural background concentrations and fates within and below coniferous forests

Pollution with organochlorines has received major attention due to various environmental effects, but it is now increasingly recognized, that they also take part in biogeochemical cycles and that natural background concentrations exist for several chlorinated compounds. We here report the natural occurrence and cycling of organic compounds with a trichloromethyl moiety in common. The study areas are temperate coniferous forests. Trichloromethyl compounds can be found in all compartments of the forests (groundwater, soil, vegetation and throughfall), but not all compounds in all compartments. The atmospheric input of trichloromethyl compounds is found to be minor, with significant contributions for trichloroacetic acid (TCAA), only. In top soil, where the formation of the compounds is expected to occur, there is a clear positive relationship between chloroform and trichloroacetyl containing compounds. Other positive relations occur, which in combination with chlorination experiments performed in the laboratory, point to the fact that all the trichloromethyl compounds may be formed concurrently in the soil, and their subsequent fates then differ due to different physical, chemical and biological properties. TCAA cannot be detected in soil and groundwater, but sorption and mineralization experiments performed in the laboratory in combination with analyses of vegetation, show that TCAA is probably formed in the top soil and then partly taken up by the vegetation and partly mineralized in the soil. Based on this and previous studies, a conceptual model for the natural cycling of trichloromethyl compounds in forests is proposed.

Integrating carbon-halogen bond formation into medicinal plant metabolism

Halogenation, once considered a rare occurrence in nature, has now been observed in many natural product biosynthetic pathways1. However, only a small fraction of halogenated compounds have been isolated from terrestrial plants2. Given the impact that halogenation can have on the biological activity of natural products1, we rationalized that introduction of halides into medicinal plant metabolism would provide the opportunity to rationally bioengineer a broad variety of novel plant products with altered, and perhaps improved, pharmacological properties. Here we report that chlorination biosynthetic machinery from soil bacteria can be successfully introduced into the medicinal plant Catharanthus roseus (Madagascar periwinkle). These prokaryotic halogenases function within the context of the plant cell to generate chlorinated tryptophan, which is then shuttled into monoterpene indole alkaloid metabolism to yield chlorinated alkaloids. A new functional group– a halide– is thereby introduced into the complex metabolism of C. roseus, and is incorporated in a predictable and regioselective manner onto the plant alkaloid products. Medicinal plants, despite their genetic and developmental complexity, therefore appear to be a viable platform for synthetic biology efforts.

2,4,6-Trichlorophenol mediated increases in extracellular peroxidase activity in three species of Lemnaceae

Chlorinated phenols, or chlorophenols, are persistent priority pollutants that are widespread in the environment. Class III peroxidases are well-characterised plant enzymes that can catalyse the oxidative dechlorination of chlorophenols. Expression of these enzymes by plants is commonly associated with plant stress, therefore limiting scope for phytoremediation. In this study, we have quantitatively compared peroxidase activity and phytotoxicity as a function of 2,4,6-trichlorophenol (TCP) concentration in three species of Lemnaceae; Lemna minor, Lemna gibba and Landoltia punctata. Effects of TCP on the growth rates of the three species differed considerably with L. punctata being the most tolerant species. TCP also affected photosynthetic parameters, causing a decrease in open photosystem II reaction centres (qP) and, in L. punctata only, a decrease in non-photochemical quenching (qN). In parallel, TCP exposure resulted in increased peroxidase activity in all three species. Peroxidase activity in L. minor and L. gibba displayed an inverse relationship with biomass accumulation, i.e. the more growth reduction the more peroxidase activity. In contrast, induction of peroxidase activity in L. punctata was bi-phasic, with a TCP-induced activity peak at concentrations that had no major effect on growth, and further induction under phytotoxic concentrations. The mechanism by which L. punctata recognises and responds to low concentrations of an anthropogenic compound, in the absence of wide-ranging stress, remains enigmatic. However, we conclude that this "window" of peroxidase production in the absence of major growth inhibition offers potential for the development of sustainable, peroxidise-mediated phytoremediation systems.

Contribution of combined sewer overflows to trace contaminant loads in urban streams

The present study examines the contribution of combined sewer overflows (CSO) to loads and concentrations of trace contaminants in receiving surface water. A simple method to assess the ratio of CSO to wastewater treatment plant (WWTP) effluents was applied to the urban River Spree in Berlin, Germany. The assessment indicated that annual loads are dominated by CSO for substances with removal in WWTP above approximately 95%. Moreover, it showed that substances with high removal in WWTP can lead to concentration peaks in the river during CSO events. The calculated results could be verified based on eight years of monitoring data from the River Spree, collected between 2000 and 2007. Substances that are well removed in WWTP such as NTA (nitrilotriacetic acid) were found to occur in significantly increased concentration during CSO, while the concentration of substances that are poorly removable in WWTP such as EDTA (ethylenediaminetetraacetic acid) decreased in CSO-influenced samples due to dilution effects. The overall results indicate the potential importance of the CSO pathway of well-removable sewage-based trace contaminants to rivers. In particular, high concentrations during CSO events may be relevant for aquatic organisms. Given the results, it is suggested to include well-removable, sewage-based trace contaminants, a substance group often neglected in the past, in future studies on urban rivers in case of combined sewer systems. The presented methodology is suggested for a first assessment, since it is based solely on urban drainage data, which is available in most cities.

Concentration of trace elements in blood and feed of homebred animals in Southern Serbia

BACKGROUND, AIM AND SCOPE

The paper presents concentrations of trace elements in blood of homebred animals (cows and sheep) from Southern Serbia (Bujanovac) and the contents of natural and anthropogenic radionuclides and some heavy metals in feed. The region of Southern Serbia was exposed to contamination by depleted uranium ammunition during NATO attacks in 1999 and therefore, is of great concern to environmental pollution and human and animal health.

MATERIALS AND METHODS

Conventional instrumental and epithermal neutron activation analyses are used to measure trace elements in cow and sheep blood samples collected randomly at six locations in the region of Bujanovac (village of Borovac) in the spring of 2005. Samples of feed (grass and crops: corn, wheat and oats), collected on the same locations (households), are analysed for the contents of radionuclides on an HPGe detector (Ortec, relative efficiency 23%) by standard gamma spectrometry. The content of Hg, Pb and Cd in feed is determined by standard atomic absorption spectrometry on the VarianSpectra220/ThermoSolar GFS97 spectrometer.

RESULTS

Concentrations of 29 elements (Na, Al (P), Cl, K, Sc, Cr, Mn, Ni, Fe, Co, Zn, Se, As, Br, Sr, Rb, Sb, In, I, Ba, Cs, La, Nd, Eu, Sm, Tb, Hf, Ta and Th) are determined in blood of the examined animals. In feeds, natural (40)K is found in all of the samples, cosmogenic (7)Be and fission product (137)Cs are detected only in the grass samples, while heavy metals Hg, Cd and Pb are found in the range of 0.01-0.02, 0.84-1.15 and 0.74-7.34 mg/kg, respectively. Calculated soil-to-blood transfer factors are in a wide range of 8 x 10(-6) to 64, as a result of varying significance of the elements in animal metabolism and feeding habits.

DISCUSSION

The results of trace elements' concentrations in animal blood are in good agreement with available data for K, Ni, Zn, Se and Rb. Higher Br concentrations in animal blood are most probably caused by large biomass burning events during blood sampling. Very low concentration of Fe in cows and sheep confirms the results of previous biochemical studies on animal anaemia in the region. High concentration of As correlates with geochemical peculiarities of the Balkans and is also likely influenced by the use of pesticides in the agricultural production. For some of the elements (La, Nd, Eu, Sm, Tb, Sb, Hf, Ta, Th, In, Ba, Sr, Sc and Cs), there are few or no literature data. Therefore, some of the presented data are significant not only for the country and the region, but on a wider scale. Activities of natural radionuclides in feeds are within the average values reported for the region, while the activities of (210)Pb and (235/238)U are below the limit of detection. This is in accordance with previous investigations showing no widespread contamination by depleted uranium in the area. Contents of Hg and Pb in feeds are below the nationally permissible levels, unlike the content of Cd which exceeds it, probably caused by the use of phosphate fertilisers and fossil fuel combustion in the area.

CONCLUSIONS

In general, the concentrations of trace elements in blood of homebred cows and sheep are in good agreement with reference materials, available literature data and the results of previous studies in the area. The exceptions are Fe, As and Br. The contents of natural and anthropogenic radionuclides in feeds are within the expected levels, and there are no signs of contamination by depleted uranium or other fission products. Apart from Cd, there are no signs of pollution by heavy metals in feeds. The highly sensitive method of instrumental neutron activation analysis provides data on the concentration of some elements in animal blood not previously reported for the region and elsewhere.

RECOMMENDATIONS AND PERSPECTIVES

The presented study is a part of the long term ongoing project on the health risk assessment on animals and humans in the region. The collected data is intended to provide a base for the animal and human risk assessment as well as an estimate of the general pollution status of the environment in the region. Since some of the investigated elements are classified as important trace elements for livestock, the results could also be used to balance and improve the animal diet and thus, improve the growth and reproduction rate.

Residue-specific global fluorination of Candida antarctica lipase B in Pichia pastoris

We report the in vivo fluorination of the tryptophan, tyrosine, and phenylalanine residues in a glycosylation-deficient mutant of Candida antarctica lipase B, CalB N74D, expressed in the methylotrophic yeast Pichia pastoris and subsequently segregated into the growth medium. To achieve this, a P. pastoris strain auxotrophic for all three aromatic amino acids was supplemented with 5-fluoro-L-tryptophan, meta-fluoro-(DL)-tyrosine, or para-fluoro-L-phenylalanine during expression of CalB N74D. The residue-specific replacement of the canonical amino acids by their fluorinated analogs was confirmed by mass analysis. Although global fluorination induced moderate changes in the secondary structure of CalB N74D, the fluorous variant proteins were still active lipases. However, their catalytic activity was lower than that of the non-fluorinated parent protein while their resistance to proteolytic degradation by proteinase K remained unchanged. Importantly, we observed that the global fluorination prolonged the shelf life of the lipase activity, which is an especially useful feature for the storage of, e.g., therapeutic proteins. Our study represents the first step on the road to the production of biotechnologically and pharmacologically relevant fluorous proteins in P. pastoris.

The halogenated metabolism of brown algae (Phaeophyta), its biological importance and its environmental significance

Brown algae represent a major component of littoral and sublittoral zones in temperate and subtropical ecosystems. An essential adaptive feature of this independent eukaryotic lineage is the ability to couple oxidative reactions resulting from exposure to sunlight and air with the halogenations of various substrates, thereby addressing various biotic and abiotic stresses i.e., defense against predators, tissue repair, holdfast adhesion, and protection against reactive species generated by oxidative processes. Whereas marine organisms mainly make use of bromine to increase the biological activity of secondary metabolites, some orders of brown algae such as Laminariales have also developed a striking capability to accumulate and to use iodine in physiological adaptations to stress. We review selected aspects of the halogenated metabolism of macrophytic brown algae in the light of the most recent results, which point toward novel functions for iodide accumulation in kelps and the importance of bromination in cell wall modifications and adhesion properties of brown algal propagules. The importance of halogen speciation processes ranges from microbiology to biogeochemistry, through enzymology, cellular biology and ecotoxicology.

Iodocionin, a cytotoxic iodinated metabolite from the Mediterranean ascidian Ciona edwardsii

Chemical investigation of the Mediterranean ascidian Ciona edwardsii has been performed, leading to the isolation of two halogenated compounds: a new tyrosineiodinated derivative iodocionin (1) and the relevant brominated analogue (2), previously isolated from a Caribbean sponge. The structure of the new compound 1 has been assigned on the basis of spectroscopic analysis. Both compounds were tested for cytotoxicity in vitro against two different cancer cell lines, L5178Y (mouse lymphoma) and PC-12 (rat pheochromocytoma). Iodocionin was shown to possess significant and selective activity against lymphoma cells with an IC₅₀ of 7.75 μg/mL.

Antitumour activity of 3-chlorodeoxylapachol, a naphthoquinone from Avicennia germinans collected from an experimental plot in southern Florida

As part of an ongoing collaborative effort to discover new anticancer agents from plants, an extract obtained from the leaves and twigs of Avicennia germinans, collected in a coastal area of southern Florida, was identified as possessing cytotoxic activity in a panel of human cancer cell lines. Fractionation of the petroleum ether partition, using cytotoxicity to guide the fractionation, led to the isolation of 3-chlorodeoxylapachol. The antitumour potential of 3-chlorodeoxylapachol was demonstrated with the in-vivo hollow fibre assay, a model of antitumour activity using human cancer cell-filled fibres implanted into mice. The possibility that this compound is an artefact of the isolation procedure was ruled out by liquid chromatography—mass spectrometry analysis of extracts prepared without the use of chlorinated solvent. In conclusion, 3-chlordeoxylapachol, a secondary metabolite obtained from the chloroform-soluble extract of a mangrove tree, was cytotoxic in a panel of human cancer cells, and active against KB human cancer cells in the murine hollow fibre antitumour model, with selectivity in KB cells for the intravenous site at lower doses, indicating possible metabolic activation.

Chloramphenicol biosynthesis: the structure of CmlS, a flavin-dependent halogenase showing a covalent flavin-aspartate bond

Chloramphenicol is a halogenated natural product bearing an unusual dichloroacetyl moiety that is critical for its antibiotic activity. The operon for chloramphenicol biosynthesis in Streptomyces venezuelae encodes the chloramphenicol halogenase CmlS, which belongs to the large and diverse family of flavin-dependent halogenases (FDH's). CmlS was previously shown to be essential for the formation of the dichloroacetyl group. Here we report the X-ray crystal structure of CmlS determined at 2.2 A resolution, revealing a flavin monooxygenase domain shared by all FDHs, but also a unique 'winged-helix' C-terminal domain that creates a T-shaped tunnel leading to the halogenation active site. Intriguingly, the C-terminal tail of this domain blocks access to the halogenation active site, suggesting a structurally dynamic role during catalysis. The halogenation active site is notably nonpolar and shares nearly identical residues with Chondromyces crocatus tyrosyl halogenase (CndH), including the conserved Lys (K71) that forms the reactive chloramine intermediate. The exception is Y350, which could be used to stabilize enolate formation during substrate halogenation. The strictly conserved residue E44, located near the isoalloxazine ring of the bound flavin adenine dinucleotide (FAD) cofactor, is optimally positioned to function as a remote general acid, through a water-mediated proton relay, which could accelerate the reaction of the chloramine intermediate during substrate halogenation, or the oxidation of chloride by the FAD(C4alpha)-OOH intermediate. Strikingly, the 8alpha carbon of the FAD cofactor is observed to be covalently attached to D277 of CmlS, a residue that is highly conserved in the FDH family. In addition to representing a new type of flavin modification, this has intriguing implications for the mechanism of FDHs. Based on the crystal structure and in analogy to known halogenases, we propose a reaction mechanism for CmlS.

Pyrrolomycins as potential anti-staphylococcal biofilms agents

With the goal of discovering new anti-infective agents active against microbial biofilms, this investigation focused on some natural pyrrolomycins, a family of halogenated pyrrole antibiotics. In this study the anti-staphylococcal biofilm activity of pyrrolomycins C, D, F1, F2a, F2b, F3 and of the synthesized related compounds I, II, III were investigated. The susceptibility of six staphylococcal biofilms was determined by methyltiazotetrazolium staining. Most of the compounds were active at concentrations of 1.5 microg ml(-1) with significant inhibition percentages. A few of the compounds were active at the lowest screening concentration of 0.045 microg ml(-1). The population log reduction of activity against the two best biofilm forming Staphylococcus aureus strains as determined by viable plate counts is also reported. In order to adequately assess the utility of these compounds, their toxicity against human cells was evaluated. It is concluded that pyrrolomycins and synthetic derivatives are promising compounds for developing novel effective chemical countermeasures against staphylococcal biofilms.

Organo-iodine formation in soils and aquifer sediments at ambient concentrations

One of the key risk drivers at radioactive waste disposal facilities is radioiodine, especially 129I. As iodine mobility varies greatly with iodine speciation, experiments with 129I-contaminated aquifer sediments from the Savannah River Site located in Aiken, SC, were carried out to test iodine interactions with soils and aquifer sediments. Using tracer 125I- and stable 127I- additions, it was shown that such interactions were highly dependent on I- concentrations added to sediment suspensions, contact time with the sediment, and organic carbon (OC) content, resulting in an empirical particle-water partition coefficient (Kd) that was an inverse power function of the added I- concentration. However, Kd values of organically bound 127I were 3 orders of magnitude higher than those determined after 1-2 weeks of tracer equilibration, approaching those of OC. Under ambient conditions, organo-iodine (OI) was a major fraction (67%) of the total iodine in the dissolved phase and by implication of the particulate phase. As the total concentration of amended I- increased, the fraction of detectable dissolved OI decreased. This trend, attributed to OC becoming the limiting factor in the aquifer sediment explains why at elevated I-concentrations OI is often not detected.

Application of lime and calcium hypochlorite in the dephenolisation and discolouration of olive mill wastewater

The application of hypochlorite for the removal of soluble COD, phenolic and polyphenolic like compounds, and other organic compounds responsible for the olive mill wastewater (OOWW) colour has been experimentally studied. After the OOWW filtration on a sand column, the effluent was subjected to a fast liming under optimal conditions. Lime application reduced polyphenols, COD and SS contents to half of their initial values but an important blackening of the treated OOWW was observed, especially when adding high concentrations of lime (10% (W/V) and 15% (W/V)). A second stage of treatment was applied using calcium hypochlorite. In this stage, removal of the studied compounds reached as much as 95% at higher concentrations, and particularly the colouring of OOWW which is generally difficult to eliminate was greatly reduced. The OOWW hypochloration acted through coagulation-flocculation and a rapid oxidation of the organic matter proceeded from the first 5min. The kinetic study of the degradation of the waste polluting compounds from liming showed that Ca(ClO)(2) reacts similarly in the elimination of organic compounds, polyphenols, SS and colouration. The analysis of the organochloride compounds generated by the reaction between hypochlorite and the organic compounds showed that DDD, DDT and the heptachlor contents exceeded the values recommended by the International and European drinking water standards.

The little bacteria that can - diversity, genomics and ecophysiology of 'Dehalococcoides' spp. in contaminated environments

The fate and persistence of chlorinated organics in the environment have been a concern for the past 50 years. Industrialization and extensive agricultural activities have led to the accumulation of these pollutants in the environment, while their adverse impact on various ecosystems and human health also became evident. This review provides an update on the current knowledge of specialized anaerobic bacteria, namely ‘Dehalococcoides’ spp., which are dedicated to the transformation of various chlorinated organic compounds via reductive dechlorination. Advances in microbiology and molecular techniques shed light into the diversity and functioning of Dehalococcoides spp. in several different locations. Recent genome sequencing projects revealed a large number of genes that are potentially involved in reductive dechlorination. Molecular approaches towards analysis of diversity and expression especially of reductive dehalogenase‐encoding genes are providing a growing body of knowledge on biodegradative pathways active in defined pure and mixed cultures as well as directly in the environment. Moreover, several successful field cases of bioremediation strengthen the notion of dedicated degraders such as Dehalococcoides spp. as key players in the restoration of contaminated environments.

Determination of halogenated natural products in passive samplers deployed along the Great Barrier Reef, Queensland/Australia

Halogenated natural products (HNPs) have been increasingly reported to occur in marine wild life from all oceans. Several HNPs, such as 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'-bipyrrole (1) and 4,6-dibromo-2-(2',4'-dibromo)phenoxyanisole (2'-MeO-BDE 68 or BC-2), were detected at particularly high concentrations in dolphins from Queensland/Australia. About half of the coastline of Queensland (approximately 2500 km) is covered by the Great Barrier Reef, a rich ecosystem hosting a huge variety of species, many of which are known to produce natural compounds. In this study, semipermeable membrane devices (SPMDs) were deployed as passive samplers for about 30 days at 12 marine and 2 nonmarine sites (i.e., rivers) along the Great Barrier Reef as part of a routine monitoring program during November 2007 and May 2008. Q1 and 2'-MeO-BDE 68 were detected at the marine sites with frequencies of about 65% but not in any sample from the two rivers. Further HNPs (2,4,6-tribromophenol, TBP; 2,4,6-tribromoanisole, TBA; 2,2'-dimethoxy-3,3'5,5'-tetrabromobiphenyl, 2,2'-diMeO-BB 80 or BC-1; 3,5-dibromo-2-(2',4'-dibromo)phenoxyanisole, 6-MeO-BDE 47 or BC-3; and 3,5-dibromo-2-(3',5'-dibromo,2'-methoxy)phenoxyanisole, 2',6-diMeO-BDE 68 or BC-11) were detected as well with frequencies of 18-97% in the marine samples, but no polybrominated flame retardants were detected. The highest amount of a single HNP, 2.3 microg/SPMD, was determined for TBP, which had a frequency of detection of only 46%. The maximum (average) amount in the SPMDs from marine sites was 44 ng (12 ng) for (1 and 115 ng (20 ng) for 2'-MeO-BDE 68. A first order kinetic model was used to estimate concentrations of the HNPs in the water phase. Based on the depuration of performance reference compounds obtained at one of the sites, we assumed a sampling rate of 16 L/day. We used this sampling rate to estimate that the highest and average available concentrations of Q1 in the water during the deployment of the SPMD were 97 and 25 pg/L, respectively. The estimated maximum water concentrations of 2'-MeO-BDE 68, 2,2'-diMeO-BB 80, 6-MeO-BDE 47, and 2',6-diMeO-BDE 68 were on average 2-5.5 fold higher than that of Q1. The results confirm that the HNPs are produced throughout the Great Barrier Reef, which appears to be a significant source of these compounds.

Natural abiotic formation of trihalomethanes in soil: results from laboratory studies and field samples

Trihalomethanes (THM), especially trichloromethane, play an important role in photochemical processes of the lower atmosphere, but the current knowledge of the known sources and sinks of trichloromethane is still incomplete. The trichloromethane flux through the environment is estimated at approximately 660 kt year(-1) and 90% of the emissions are of natural origin. Next to offshore seawater contributing approximately 360 kt year(-1) unknown soil processes are the most prominent source (approximately 220 kt year(-1)). This paper describes a new abiotic source of trichloromethane from the terrestrial environment induced by the oxidation of organic matter by iron(III) and hydrogen peroxide in the presence of chloride. Different organic-rich soils and a series of organic substances regarded as monomeric constituents of humus were investigated for their release of trichloromethene. The influence of iron(III), hydrogen peroxide, halide, and pH on its formation was assayed. The optimal reaction turn over for the representative compound catechol was 58.4 ng of CHCl3 from 1.8 mg of carbon applying chloride and 1.55 microg of CHBr3 from 1.8 mg of carbon applying bromide; resorcin and hydroquinone displayed similar numbers. Results presented in this paper pinpoint 1,2,4,5-tetrahydroxybenzene as playing a key role as intermediate in the formation pathway of the trihalomethanes. The highest THM yields were obtained when applying the oxidized form of 1,2,4,5-tetrahydroxybenzene as THM precursor. These findings are consistent with the well-known degradation pathway starting from resorcin-like dihydroxylated compounds proceeding via further hydroxylation and after halogenation finally ending up in trihalomethanes. In conclusion, Fenton-like reaction conditions (iron(III) and hydrogen peroxide), elevated halide content and an extended reaction time can be seen as the most important parameters required for an optimal THM formation.

Possible role of reactive chlorine in microbial antagonism and organic matter chlorination in terrestrial environments

Several studies have demonstrated that extensive formation of organically bound chlorine occurs both in soil and in decaying plant material. Previous studies suggest that enzymatic formation of reactive chlorine outside cells is a major source. However, the ecological role of microbial-induced extracellular chlorination processes remains unclear. In the present paper, we assess whether or not the literature supports the hypothesis that extracellular chlorination is involved in direct antagonism against competitors for the same resources. Our review shows that it is by no means rare that biotic processes create conditions that render biocidal concentrations of reactive chlorine compounds, which suggest that extracellular production of reactive chlorine may have an important role in antagonistic microbial interactions. To test the validity, we searched the UniprotPK database for microorganisms that are known to produce haloperoxidases. It appeared that many of the identified haloperoxidases from terrestrial environments are originating from organisms that are associated with living plants or decomposing plant material. The results of the in silico screening were supported by various field and laboratory studies on natural chlorination. Hence, the ability to produce reactive chlorine seems to be especially common in environments that are known for antibiotic-mediated competition for resources (interference competition). Yet, the ability to produce haloperoxidases is also recorded, for example, for plant endosymbionts and parasites, and there is little or no empirical evidence that suggests that these organisms are antagonistic.

Tracking functional guilds: "Dehalococcoides" spp. in European river basins contaminated with hexachlorobenzene

Hexachlorobenzene (HCB) has been widely used in chemical manufacturing processes and as a pesticide. Due to its resistance to biological degradation, HCB has mainly accumulated in freshwater bodies and agricultural soils. "Dehalococcoides" spp., anaerobic dechlorinating bacteria that are capable of degrading HCB, were previously isolated from river sediments. Yet there is limited knowledge about the abundance, diversity, and activity of this genus in the environment. This study focused on the molecular analysis of the composition and abundance of active Dehalococcoides spp. in HCB-contaminated European river basins. 16S rRNA-based real-time quantitative PCR and denaturing gradient gel electrophoresis in combination with multivariate statistics were applied. Moreover, a functional gene array was used to determine reductive dehalogenase (rdh) gene diversity. Spatial and temporal fluctuations were observed not only in the abundance of Dehalococcoides spp. but also in the composition of the populations and rdh gene diversity. Multivariate statistics revealed that Dehalococcoides sp. abundance is primarily affected by spatial differences, whereas species composition is under the influence of several environmental parameters, such as seasonal changes, total organic carbon and/or nitrogen content, and HCB contamination. This study provides new insight into the natural occurrence and dynamics of active Dehalococcoides spp. in HCB-contaminated river basins.

Biohalogenation: nature's way to synthesize halogenated metabolites

Halogenated natural products are widely distributed in nature, some of them showing potent biological activities. Incorporation of halogen atoms in drug leads is a common strategy to modify molecules in order to vary their bioactivities and specificities. Chemical halogenation, however, often requires harsh reaction conditions and results in unwanted byproduct formation. It is thus of great interest to investigate the biosynthesis of halogenated natural products and the biotechnological potential of halogenating enzymes. This review aims to give a comprehensive overview on the current knowledge concerning biological halogenations.