Identification of triclosan-degrading bacteria using stable isotope probing, fluorescence in situ hybridization and microautoradiography

Metatranscriptomic profiles reveal the biotransformation potential of azithromycin in river periphyton

Assessment of the interaction between the biotransformation of chemical contaminants and enzyme activity from aquatic microbial communities is critical for improving the micropollutant degradation in river remediation. Here, association mining based on metatranscriptomic analysis was initially applied to determine the genes encoding enzymes involved in the azithromycin (AZI) transformation process and the corresponding microbial hosts in periphyton, followed by revealing the dynamic variation in the community structure and function. In terms of the biotransformation potential, the highly correlated 15 enzymes were suggested to be primarily involved in AZI biotransformation, energy supply, and antibiotic resistance processes, especially aryl-alcohol dehydrogenases (EC: 1.1.1.90), hydroxylamine dehydrogenase (EC: 1.7.2.6), and monooxygenases (EC: 1.14.11.57) that were involved in the biotransformation of AZI. In the matter of community ecological function, the photosystem II (PSII) reaction center in the periphytic photosynthetic process, as indicated by Fv/Fm, was inhibited after AZI exposure, which may be attributed to the down-regulated genes enriched in the photosynthesis - antenna proteins (ko00196), photosynthesis (ko00195), and two-component system (ko02020) pathways. Furthermore, the periphytic utilization capacity for carbohydrates and phenolic acids was enhanced, which was in accordance with all the increased expression of transcripts involved in the corresponding molecular pathways, including aminobenzoate degradation (ko00627), starch and sucrose metabolism (ko00500), ABC transporters (ko02010), phosphotransferase system (ko02060), galactose metabolism (ko00052), amino sugar and nucleotide sugar metabolism (ko00520). Taken together, this study highlighted the critical role of river periphyton in the micropollutant degradation and unraveled the molecular mechanism of antibiotic biotransformation as well as the structural and functional damage in the periphyton.

Complete pentachlorophenol biodegradation in a dual-working electrode bioelectrochemical system: Performance and functional microorganism identification

Bioelectrochemical system (BES) can effectively promote the reductive dechlorination of chlorophenols (CPs). However, the complete degradation of CPs with sequential dechlorination and mineralization processes has rarely achieved from the BES. Here, a dual-working electrode BES was constructed and applied for the complete degradation of pentachlorophenol (PCP). Combined with DNA-stable isotope probing (DNA-SIP), the biofilms attached on the anodic and cathodic electrode in the BES were analyzed to explore the dechlorinating and mineralizing microorganisms. Results showed that PCP removal efficiency in the dual-working BES (84% for 21 days) was 4.1 and 4.7 times higher than those of conventional BESs with a single anodic or cathodic working electrode, respectively. Based on DNA-SIP and high-throughput sequencing analysis, the cathodic working electrode harbored the potential dechlorinators (Comamonas, Pseudomonas, Methylobacillus, and Dechlorosoma), and the anodic working enriched the potential intermediate mineralizing bacteria (Comamonas, Stenotrophomonas, and Geobacter), indicating that PCP could be completely degraded under the synergetic effect of these functional microorganisms. Besides, the potential autotrophic functional bacteria that might be involved in the PCP dechlorination were also identified by SIP labeled with ¹³C-NaHCO₃. Our results proved that the dual-working BES could accelerate the complete degradation of PCP and enrich separately the functional microbial consortium for the PCP dechlorination and mineralization, which has broad potential for bioelectrochemical techniques in the treatment of wastewater contaminated with CPs or other halogenated organic compounds.

DNA-based stable isotope probing deciphered the active denitrifying bacteria and triclosan-degrading bacteria participating in granule-based partial denitrification process under triclosan pressure

Granule-based partial denitrification (PD) is a technology that can supply stable nitrite for applying anaerobic ammonia oxidation in wastewater treatment, and triclosan (TCS) is a frequently detected antibacterial agent in wastewater treatment plants, therefore it is possible that TCS could enter into wastewater that is treated using PD technology. However, the active microorganisms responsible for PD and TCS removing in granule-based PD system have not been clearly identified and it is currently not clear how TCS affects the PD process. In this study, the impacts of TCS on PD performance, PD microbial community, antibiotic resistance genes (ARGs), active PD bacteria and TCS-degrading bacteria in a granule-based PD system were investigated. 3 mg/L TCS had adverse influence on PD process, but PD system could recover gradually after inhibiting of 10 days. After a period of domestication, PD granular sludge could achieve 10.66% of TCS degradation efficiency and 43.62% of TCS adsorption efficiency. Microbes might increase their resistance to TCS by increasing the secretion of extracellular polymeric substances, and the secretion of protein might play a more pivotal role than the secretion of polysaccharides in resisting TCS. The short-term shock of TCS might cause the propagation of acrA-03, while the long-term operation of TCS could propagate fabK and intI1. DNA stable isotope probing assay indicated that Thauera was active PD bacteria and TCS-degrading bacteria in the granule-based PD system, and it could contribute to nitrite accumulation and TCS degradation, simultaneously.

Metagenomics combined with DNA-based stable isotope probing provide comprehensive insights of active triclosan-degrading bacteria in wastewater treatment

The biotransformation of triclosan (TCS) during wastewater treatment occurred frequently, while little researches are known the identity of microorganisms involved in the biodegradation process. In this work, DNA-based stable isotope probing (DNA-SIP) was occupied to investigate the TCS assimilation microbes originated from a full-scale cyclic activated sludge system in Beijing. Results of TCS removal pathway showed that the TCS removal in nitrification process was mainly contributed by the metabolism of heterotrophic bacteria, accounting for about 18.54%. DNA-SIP assay indicated that Sphingobium dominated the degradation of TCS. Oligotyping analysis further indicated that oligotype GCTAAT and ATGTTA of Sphingobium played important roles in degrading TCS. Furthermore, the Kyoto Encyclopedia of Genes and Genomes functional abundance statistics based on PICRUSt2 showed that glutathione transferase was the most prevalent enzyme involved in TCS metabolism, and TCS might be removed through microbial carbon metabolism. Metagenomics made clear that Sphingobium might play irrelevant role on the propagation of antibiotics resistance genes (ARGs), even though, it could degrade TCS. Thauera and Dechloromonas were identified as the key hosts of most ARGs. This study revealed the potential metabolic pathway and microbial ecology of TCS biodegradation in nitrification process of wastewater treatment system.

The key active degrader, metabolic pathway and microbial ecology of triclosan biodegradation in an anoxic/oxic system

A lab-scale anoxic/oxic (A/O) system was used to reveal the key active triclosan-degrading bacteria (TCS-DB) in this study. The results showed that TCS was mainly removed by metabolism of heterotrophic bacteria (accounting for about 62%), and the potential metabolic pathway was the break of ether bond in TCS formed 2,4-dichlorophenol, and further dechlorination formed phenol or other metabolic end products. DNA-based stable isotope probing (DNA-SIP) assay further revealed that Methylobacillus accounting for 20.75% in ¹³C sample was the key active TCS-DB. Furthermore, methylotrophy and methanol oxidation were found to be the potential metabolic routes of TCS degradation by functional annotation of prokaryotic taxa analysis. Interestingly, TCS accelerated the propagation of antibiotic resistance genes (fabI) and intI1 which positively correlated with several functional microorganisms (p < 0.05). This study contributes to comprehend the potential mechanism, metabolic pathway and microbial ecology of TCS biodegradation in A/O system.

Responses of nitrification performance, triclosan resistome and diversity of microbes to continuous triclosan stress in activated sludge system

Triclosan (TCS) is commonly found in wastewater treatment plants, which often affects biological treatment processes. The responses of nitrification, antibiotic resistome and microbial community under different TCS concentrations in activated sludge system were evaluated in this study. The experiment was conducted in a sequencing batch reactor (SBR) for 240 days. Quantitative PCR results demonstrated that the abundance of ammonium oxidizing bacteria could be temporarily inhibited by 1 mg/L TCS and then gradually recovered. And the abundances of nitrite oxidizing bacteria (NOB) under 2.5 and 4 mg/L TCS were three orders of magnitude lower than that of seed sludge, which accounted for partial nitrification. When the addition of TCS was stopped, the abundance of NOB increased. The mass balance experiments of TCS demonstrated that the primary removal pathway of TCS changed from adsorption to biodegradation as TCS was continuously added into the SBR system. Moreover, TCS increased the abundance of mexB, indicating the efflux pump might be the main TCS-resistance mechanism. As a response to TCS, bacteria could secrete more protein (PN) than polysaccharide. Three-dimensional excitation-emission matrix revealed that tryptophan PN-like substances might be the main component in PN to resist TCS. High-throughput sequencing found that the relative abundances of Paracoccus, Pseudoxanthomonas and Thauera increased, which could secrete extracellular polymeric substances (EPS). And Sphingopyxis might be the main TCS-degrading bacteria. Overall, TCS could cause partial nitrification and increase the relative abundances of EPS-secreting bacteria and TCS-degrading bacteria.

Relating Metatranscriptomic Profiles to the Micropollutant Biotransformation Potential of Complex Microbial Communities

Biotransformation of chemical contaminants is of importance in various natural and engineered systems. However, in complex microbial communities and with chemical contaminants at low concentrations, our current understanding of biotransformation at the level of enzyme-chemical interactions is limited. Here, we explored an approach to identify associations between micropollutant biotransformation and specific gene products in complex microbial communities, using association mining between chemical and metatranscriptomic data obtained from experiments with activated sludge grown at different solid retention times. We successfully demonstrate proportional relationships between the measured rate constants and associated gene transcripts for nitrification as a major community function, but also for the biotransformation of two nitrile-containing micropollutants (bromoxynil and acetamiprid) and transcripts of nitrile hydratases, a class of enzymes that we experimentally confirmed to produce the detected amide transformation products. As these results suggest that metatranscriptomic information can indeed be quantitatively correlated with low abundant community functions such as micropollutant biotransformation in complex microbial communities, we proceeded to explore the potential of association mining to highlight enzymes likely involved in catalyzing less well-understood micropollutant biotransformation reactions. Specifically, we use the cases of nitrile hydration and oxidative biotransformation reactions to show that the consideration of additional experimental evidence (such as information on biotransformation pathways) increases the likelihood of detecting plausible novel enzyme-chemical relationships. Finally, we identify a cluster of mono- and dioxygenase fourth-level enzyme classes that most strongly correlate with oxidative micropollutant biotransformation reactions in activated sludge.

Aerobic biodegradation of tramadol by pre-adapted activated sludge culture: Cometabolic transformations and bacterial community changes during enrichment

The biodegradation of biorecalcitrant opioid drug tramadol (TRAM) was studied in a model biodegradation experiment performed with an enriched activated sludge culture pre-adapted to high concentration of TRAM (20 mg/L). TRAM and its transformation products (TPs) were determined by applying ultrahigh-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF-MS), the sludge culture was characterized using a 16S rRNA gene amplicon sequencing, whereas ecotoxicological evaluation was performed based on determination of toxicity to freshwater algae. Tramadol removal was much faster (t_1/2 = 1.3 days) and more efficient in glucose-containing mineral medium (cometabolic conditions) than in a medium without glucose. The elimination of the parent compound resulted in the formation of five TPs, two of which (TP 249 and TP 235) were identified as N-desmethyltramadol (N-DM TRAM) and N,N-didesmethyltramadol (N,N-diDM TRAM). The remaining 3 TPs (TP 277a-c) were isomeric compounds with an elemental composition of protonated molecules C₁₆H₂₄NO₃ and a putative structure which involved oxidative modification of the dimethylamino group. Pronounced changes in the taxonomic composition of the activated sludge were observed during the enrichment, especially regarding an enhanced percentage of 8 genera (Bacillus, Mycobacterium, Enterobacter, Methylobacillus, Pedobacter, Xanthobacter, Leadbetterella and Kaistia), which might be related to the observed transformations. The removal of TRAM resulted in proportional reduction of algal toxicity, implying a positive result of the accomplished transformation processes.

Carbamazepine, triclocarban and triclosan biodegradation and the phylotypes and functional genes associated with xenobiotic degradation in four agricultural soils

Pharmaceuticals and personal care products (PPCPs) are released into the environment due to their poor removal during wastewater treatment. Agricultural soils subject to irrigation with wastewater effluent and biosolids application are possible reservoirs for these chemicals. This study examined the impact of the pharmaceutical carbamazepine (CBZ), and the antimicrobial agents triclocarban (TCC) and triclosan (TCS) on four soil microbial communities using shotgun sequencing (HiSeq Illumina) with the overall aim of determining possible degraders as well as the functional genes related to general xenobiotic degradation. The biodegradation of CBZ and TCC was slow, with ≤50% decrease during the 80-day incubation period. In contrast, TCS biodegradation was rapid, with ~80% removal in 25 days. For each chemical, when all four soils were considered together, between three and ten phylotypes (from multiple phyla) were more abundant in the soil samples compared to the live controls. The genera of a number of previously reported CBZ, TCC or TCS degrading isolates were present; Rhodococcus (CBZ), Streptomyces (CBZ), Pseudomonas (CBZ, TCC, TCS), Sphingomonas (TCC, TCS), Methylobacillus (TCS) and Stenotrophomonas (TCS) were among the most abundant (chemical previously reported to be degraded is shown in parenthesis). From the analysis of xenobiotic degrading pathways, genes from five KEGG (Kyoto Encyclopedia of Genes and Genomes) Orthology pathways were the most dominant, including those associated with aminobenzoate, benzoate (most common), chlorocyclohexane/chlorobenzene, dioxin and nitrotoluene biodegradation. Several phylotypes including Bradyrhizobium, Mycobacterium, Rhodopseudomonas, Pseudomonas, Cupriavidus, and Streptomyces were common genera associated with these pathways. Overall, the data suggest several phylotypes are likely involved in the biodegradation of these PPCPs with Pseudomonas being an important genus.

Biochar does not attenuate triclosan's impact on soil bacterial communities

Triclosan, a broad-spectrum antimicrobial, has been widely used in pharmaceutical and personal care products. It undergoes limited degradation during wastewater treatment and is present in biosolids, most of which are land applied in the United States. This study assessed the impact of triclosan (0-100 mg kg^-1) with and without biochar on soil bacterial communities. Very little ¹⁴C-triclosan was mineralized to ¹⁴CO₂ (<7%) over the course of the study (42 days). While biochar (1%) significantly lowered mineralization of triclosan, analysis of 16S rRNA gene sequences revealed that biochar impacted very few OTUs and did not alter the overall structure of the community. Triclosan, on the other hand, significantly affected bacterial diversity and community structure (alpha diversity, ANOVA, p < 0.001; beta diversity, AMOVA, p < 0.01). Dirichlet multinomial mixtures (DMM) modeling and complete linkage clustering (CLC) revealed a dose-dependent impact of triclosan. Non-Parametric Metastats (NPM) analysis showed that 150 of 734 OTUs from seven main phyla were significantly impacted by triclosan (adjusted p < 0.05). Genera harboring opportunistic pathogens such as Flavobacterium were enriched in the presence of triclosan, as was Stenotrophomonas. The latter has previously been implicated in triclosan degradation via stable isotope probing. Surprisingly, Sphingomonads, which include well-characterized triclosan degraders were negatively impacted by even low doses of triclosan. Analyses of published genomes showed that triclosan resistance determinants were rare in Sphingomonads which may explain why they were negatively impacted by triclosan in our soil.

Why are organic micropollutants not fully biotransformed? A mechanistic modelling approach to anaerobic systems

Biotransformation of most organic micropollutants (OMPs) during wastewater treatment is not complete and an unexplained steady decrease of the biotransformation rate with time is reported for many OMPs in different biological processes. To minimize and accurately predict the emission of OMPs into the environment, the mechanisms and limitations behind their biotransformations should be clarified. Aiming to achieve this objective, the present study follows a mechanistic modelling approach, based on the formulation of four models according to different biotransformation hypotheses: Michaelis-Menten kinetics, chemical equilibrium between the parent compound and the transformation product (TP), enzymatic inhibition by the TP, and a limited compound bioavailability due to its sequestration in the solid phase. These models were calibrated and validated with kinetic experiments performed in two different anaerobic systems: continuous reactors enriched with methanogenic biomass and batch assays with anaerobic sludge. Model selection was conducted according to model suitability criteria (goodness of fitting the experimental data, confidence of the estimated parameters, and model parsimony) but also considering mechanistic evidences. The findings suggest that reversibility of the biological reactions and/or sequestration of compounds are likely the causes preventing the complete biotransformation of OMPs, and biotransformation is probably limited by thermodynamics rather than by kinetics. Taking into account its simplicity and broader applicability spectrum, the reversible biotransformation is the proposed model to explain the incomplete biotransformation of OMPs.

Transformation, CO2 formation and uptake of four organic micropollutants by carrier-attached microorganisms

A tiered process was developed to assess the transformation, CO₂ formation and uptake of four organic micropollutants by carrier-attached microorganisms from two municipal wastewater treatment plants. At the first tier, primary transformation of ibuprofen, naproxen, diclofenac, and mecoprop by carrier-attached microorganisms was shown by the dissipation of the target compounds and the formation of five transformation products using LC-tandem MS. At the second tier, the microbial cleavage of the four organic micropollutants was confirmed with ¹⁴C-labeled micropollutants through liquid scintillation counting of the ¹⁴CO₂ formed. At the third tier, microautoradiography coupled with fluorescence in situ hybridization (MAR-FISH) was used to screen carrier-attached microorganisms for uptake of the four radiolabeled micropollutants. Results from the MAR-FISH screening indicated that only a small fraction of the microbial community (≤1‰) was involved in the uptake of the radiolabeled micropollutants and that the responsible microorganisms differed between the compounds. At the fourth tier, the microbial community structure of the carrier-attached biofilms was analyzed by 16S rRNA gene amplicon sequencing. The sequencing results showed that the MAR-FISH screening targeted ∼80% of the microbial community and that several taxonomic families within the FISH-probed populations with MAR-positive signals (i.e. Firmicutes, Gammaproteobacteria, and Deltaproteobacteria) were present in both biofilms. From the broader perspective of organic micropollutant removal in biological wastewater treatment, the MAR-FISH results of this study indicate a high degree of microbial substrate specialization that could explain differences in transformation rates and patterns between micropollutants and microbial communities.

Identification of Bisphenol A-Assimilating Microorganisms in Mixed Microbial Communities Using 13C-DNA Stable Isotope Probing

A wide range of trace organic contaminants (TOrCs), including the endocrine-disrupting compound bisphenol A (BPA), are subject to microbial transformations during biological wastewater treatment. However, relatively little is known about the identity of organisms capable of assimilating emerging contaminants. Here, ¹³C-DNA stable isotope probing (DNA-SIP) was used to investigate biodegradation and assimilation of BPA by mixed microbial communities collected from two full-scale wastewater treatment plant bioreactors in New York City and subsequently enriched under two BPA exposure conditions. The four enrichment modes (two reactors with two initial BPA concentrations) resulted in four distinct communities with different BPA degradation rates. On the basis of DNA-SIP, bacteria related to Sphingobium spp. were dominant in the assimilation of BPA or its metabolites. Variovorax spp. and Pusillimonas spp. also assimilated BPA or its metabolites. Our results highlight that microbial communities originating from wastewater treatment facilities harbor the potential for addressing not only human-derived carbon but also BPA, a complex anthropogenic TOrC. While previous studies focus on microbial biodegradation of BPA, this study uniquely determines the "active" fraction of microorganisms engaged in assimilation of BPA-derived carbon. Ultimately, information on both biodegradation and assimilation can facilitate better design and operation of engineered treatment processes to achieve BPA removal.

Enzymes in removal of pharmaceuticals from wastewater: A critical review of challenges, applications and screening methods for their selection

At present, the removal of trace organic chemicals such as pharmaceuticals in wastewater treatment plants is often incomplete resulting in a continuous discharge into the aqueous environment. To overcome this issue, bioremediation approaches gained significant importance in recent times, since they might have a lower carbon footprint than chemical or physical treatment methods. In this context, enzyme-based technologies represent a promising alternative since they are able to specifically target certain chemicals. For this purpose, versatile monitoring of enzymatic reactions is of great importance in order to understand underlying transformation mechanisms and estimate the suitability of various enzymes exhibiting different specificities for bioremediation purposes. This study provides a comprehensive review, summarizing research on enzymatic transformation of pharmaceuticals in water treatment applications using traditional and state-of-the-art enzyme screening approaches with a special focus on mass spectrometry (MS)-based and high-throughput tools. MS-based enzyme screening represents an approach that allows a comprehensive mechanistic understanding of enzymatic reactions and, in particular, the identification of transformation products. A critical discussion of these approaches for implementation in wastewater treatment processes is also presented. So far, there are still major gaps between laboratory- and field-scale research that need to be overcome in order to assess the viability for real applications.

Degradation of triclosan by environmental microbial consortia and by axenic cultures of microorganisms with concerns to wastewater treatment

Triclosan is an antimicrobial agent, which is widely used in personal care products including toothpaste, soaps, deodorants, plastics, and cosmetics. Widespread use of triclosan has resulted in its release into wastewater, surface water, and soils and has received considerable attention in the recent years. It has been reported that triclosan is detected in various environmental compartments. Toxicity studies have suggested its potential environmental impacts, especially to aquatic ecosystems. To date, removal of triclosan has attracted rising attention and biodegradation of triclosan in different systems, such as axenic cultures of microorganisms, full-scale WWTPs, activated sludge, sludge treatment systems, sludge-amended soils, and sediments has been described. In this study, an extensive literature survey was undertaken, to present the current knowledge of the biodegradation behavior of triclosan and highlights the removal and transformation processes to help understand and predict the environmental fate of triclosan. Experiments at from lab-scale to full-scale field studies are shown and discussed.

Micropollutant degradation via extracted native enzymes from activated sludge

A procedure was developed to assess the biodegradation of micropollutants in cell-free lysates produced from activated sludge of a municipal wastewater treatment plant (WWTP). This proof-of-principle provides the basis for further investigations of micropollutant biodegradation via native enzymes in a solution of reduced complexity, facilitating downstream protein analysis. Differently produced lysates, containing a variety of native enzymes, showed significant enzymatic activities of acid phosphatase, β-galactosidase and β-glucuronidase in conventional colorimetric enzyme assays, whereas heat-deactivated controls did not. To determine the enzymatic activity towards micropollutants, 20 compounds were spiked to the cell-free lysates under aerobic conditions and were monitored via LC-ESI-MS/MS. The micropollutants were selected to span a wide range of different biodegradabilities in conventional activated sludge treatment via distinct primary degradation reactions. Of the 20 spiked micropollutants, 18 could be degraded by intact sludge under assay conditions, while six showed reproducible degradation in the lysates compared to the heat-deactivated negative controls: acetaminophen, N-acetyl-sulfamethoxazole (acetyl-SMX), atenolol, bezafibrate, erythromycin and 10,11-dihydro-10-hydroxycarbamazepine (10-OH-CBZ). The primary biotransformation of the first four compounds can be attributed to amide hydrolysis. However, the observed biotransformations in the lysates were differently influenced by experimental parameters such as sludge pre-treatment and the addition of ammonium sulfate or peptidase inhibitors, suggesting that different hydrolase enzymes were involved in the primary degradation, among them possibly peptidases. Furthermore, the transformation of 10-OH-CBZ to 9-CA-ADIN was caused by a biologically-mediated oxidation, which indicates that in addition to hydrolases further enzyme classes (probably oxidoreductases) are present in the native lysates. Although the full variety of indigenous enzymatic activity of the activated sludge source material could not be restored, experimental modifications, e.g. different lysate filtration, significantly enhanced specific enzyme activities (e.g. >96% removal of the antibiotic erythromycin). Therefore, the approach presented in this study provides the experimental basis for a further elucidation of the enzymatic processes underlying wastewater treatment on the level of native proteins.

Characterization of triclosan metabolism in Sphingomonas sp. strain YL-JM2C

Triclosan (TCS) is one of the most widespread emerging contaminants and has adverse impact on aquatic ecosystem, yet little is known about its complete biodegradation mechanism in bacteria. Sphingomonas sp, strain YL-JM2C, isolated from activated sludge of a wastewater treatment plant, was very effective on degrading TCS. Response surface methodology (RSM) was applied to optimize the conditions like temperature and pH. From RSM, the optimal TCS degradation conditions were found to be 30 °C and pH 7.0. Under optimal conditions, strain YL-JM2C completely mineralized TCS (5 mg L⁻¹) within 72 h. Gas chromatography-mass spectrometry analysis revealed that 2,4-dichlorophenol, 2-chlorohydroquinone and hydroquinone are three main by-products of TCS. Furthermore, stable isotope experimental results revealed that the ¹³C₁₂-TCS was completely mineralized into CO₂ and part of heavier carbon (¹³C) of labeled TCS was utilized by strain YL-JM2C to synthesize fatty acids (PLFAs). Cell surface hydrophobicity (CSH) and degradation test results suggested that the strain could enhance degradation capacity of TCS through increasing CSH. In addition, the bacterium also completely degraded spiked TCS (5 mg L⁻¹) in wastewater collected from the wastewater treatment plant. Hence, these results suggest that the strain has potential to remediate TCS in the environment.

Identification of Triclosan-O-Sulfate and other transformation products of Triclosan formed by activated sludge

Aerobic degradation experiments of Triclosan were performed in activated sludge to identify possible transformation products for this compound. During 7 days, the formation of biotransformation products such as 2,4-Dichlorophenol, 4-Chlorocatechol, 5-Hydroxy-Triclosan and other Monohydroxy-Triclosan derivatives as well as Dihydroxy-Triclosan-derivatives were observed. The structure of 5-Hydroxy-Triclosan was elucidated by NMR data for the first time in sludge degradation experiments. Additionally the production of a hitherto unknown transformation product in sludge, i.e., Triclosan-O-Sulfate was detected. During the incubations, the concentrations of this transformation product changed from zero to 330 μg L(-1). Based on the analysis of the biodegradation products, three types of reactions were identified: 1) chemical scission of ether bond to form phenols and catechols, 2) addition of OH moieties to the aromatic ring, and 3) adding of methyl or sulfate groups to the original hydroxyl group.

Perturbation and restoration of the fathead minnow gut microbiome after low-level triclosan exposure

BACKGROUND

Triclosan is a widely used antimicrobial compound and emerging environmental contaminant. Although the role of the gut microbiome in health and disease is increasingly well established, the interaction between environmental contaminants and host microbiome is largely unexplored, with unknown consequences for host health. This study examined the effects of low, environmentally relevant levels of triclosan exposure on the fish gut microbiome. Developing fathead minnows (Pimephales promelas) were exposed to two low levels of triclosan over a 7-day exposure. Fish gastrointestinal tracts from exposed and control fish were harvested at four time points: immediately preceding and following the 7-day exposure and after 1 and 2 weeks of depuration.

RESULTS

A total of 103 fish gut bacterial communities were characterized by high-throughput sequencing and analysis of the V3-V4 region of the 16S rRNA gene. By measures of both alpha and beta diversity, gut microbial communities were significantly differentiated by exposure history immediately following triclosan exposure. After 2 weeks of depuration, these differences disappear. Independent of exposure history, communities were also significantly structured by time. This first detailed census of the fathead minnow gut microbiome shows a bacterial community that is similar in composition to those of zebrafish and other freshwater fish. Among the triclosan-resilient members of this host-associated community are taxa associated with denitrification in wastewater treatment, taxa potentially able to degrade triclosan, and taxa from an unstudied host-associated candidate division.

CONCLUSIONS

The fathead minnow gut microbiome is rapidly and significantly altered by exposure to low, environmentally relevant levels of triclosan, yet largely recovers from this short-term perturbation over an equivalently brief time span. These results suggest that even low-level environmental exposure to a common antimicrobial compound can induce significant short-term changes to the gut microbiome, followed by restoration, demonstrating both the sensitivity and resilience of the gut flora to challenges by environmental toxicants. This short-term disruption in a developing organism may have important long-term consequences for host health. The identification of multiple taxa not often reported in the fish gut suggests that microbial nitrogen metabolism in the fish gut may be more complex than previously appreciated.

The MetaCyc database of metabolic pathways and enzymes and the BioCyc collection of Pathway/Genome Databases

The MetaCyc database (MetaCyc.org) is a comprehensive and freely accessible database describing metabolic pathways and enzymes from all domains of life. MetaCyc pathways are experimentally determined, mostly small-molecule metabolic pathways and are curated from the primary scientific literature. MetaCyc contains >2100 pathways derived from >37 000 publications, and is the largest curated collection of metabolic pathways currently available. BioCyc (BioCyc.org) is a collection of >3000 organism-specific Pathway/Genome Databases (PGDBs), each containing the full genome and predicted metabolic network of one organism, including metabolites, enzymes, reactions, metabolic pathways, predicted operons, transport systems and pathway-hole fillers. Additions to BioCyc over the past 2 years include YeastCyc, a PGDB for Saccharomyces cerevisiae, and 891 new genomes from the Human Microbiome Project. The BioCyc Web site offers a variety of tools for querying and analysis of PGDBs, including Omics Viewers and tools for comparative analysis. New developments include atom mappings in reactions, a new representation of glycan degradation pathways, improved compound structure display, better coverage of enzyme kinetic data, enhancements of the Web Groups functionality, improvements to the Omics viewers, a new representation of the Enzyme Commission system and, for the desktop version of the software, the ability to save display states.

Applications of biofilms in bioremediation and biotransformation of persistent organic pollutants, pharmaceuticals/personal care products, and heavy metals

In this review, the strategies being employed to exploit the inherent durability of biofilms and the diverse nutrient cycling of the microbiome for bioremediation are explored. Focus will be given to halogenated compounds, hydrocarbons, pharmaceuticals, and personal care products as well as some heavy metals and toxic minerals, as these groups represent the majority of priority pollutants. For decades, industrial processes have been creating waste all around the world, resulting in contaminated sediments and subsequent, far-reaching dispersal into aquatic environments. As persistent pollutants have accumulated and are still being created and disposed, the incentive to find suitable and more efficient solutions to effectively detoxify the environment is even greater. Indigenous bacterial communities are capable of metabolizing persistent organic pollutants and oxidizing heavy metal contaminants. However, their low abundance and activity in the environment, difficulties accessing the contaminant or nutrient limitations in the environment all prevent the processes from occurring as quickly as desired and thus reaching the proposed clean-up goals. Biofilm communities provide among other things a beneficial structure, possibility for nutrient, and genetic exchange to participating microorganisms as well as protection from the surrounding environment concerning for instance predation and chemical and shear stresses. Biofilms can also be utilized in other ways as biomarkers for monitoring of stream water quality from for instance mine drainage. The durability and structure of biofilms together with the diverse array of structural and metabolic characteristics make these communities attractive actors in biofilm-mediated remediation solutions and ecosystem monitoring.

Triclosan exposure increases triclosan resistance and influences taxonomic composition of benthic bacterial communities

Triclosan (TCS) is a broad-spectrum antimicrobial compound that is incorporated into numerous consumer products. TCS has been detected in aquatic ecosystems across the U.S., raising concern about its potential ecological effects. We conducted a field survey and an artificial stream experiment to assess effects of TCS on benthic bacterial communities. Field sampling indicated that TCS concentrations in stream sediments increased with degree of urbanization. There was significant correlation between sediment TCS concentration and the proportion of cultivable benthic bacteria that were resistant to TCS, demonstrating that the levels of TCS present in these streams was affecting the native communities. An artificial stream experiment confirmed that TCS exposure could trigger increases in TCS resistance within cultivable benthic bacteria, and pyrosequencing analysis indicated that TCS resulted in decreased benthic bacterial diversity and shifts in bacterial community composition. One notable change was a 6-fold increase in the relative abundance of cyanobacterial sequences and a dramatic die-off of algae within the artificial streams. Selection of cyanobacteria over algae could have significant implications for higher trophic levels within streams. Finally, there were no observed effects of TCS on bacterial abundance or respiration rates, suggesting that bacterial density and function were highly resilient to TCS exposure.