Metabolite cross-feeding enables concomitant catabolism of chlorinated methanes and chlorinated ethenes in synthetic microbial assemblies.

Isolate studies have been a cornerstone for unraveling metabolic pathways and phenotypical (functional) features. Biogeochemical processes in natural and engineered ecosystems are generally performed by more than a single microbe and often rely on mutualistic interactions. We demonstrate the rational bottom-up design of synthetic, interdependent co-cultures to achieve concomitant utilization of chlorinated methanes as electron donors and organohalogens as electron acceptors. Specialized anaerobes conserve energy from the catabolic conversion of chloromethane or dichloromethane to formate, H2, and acetate, compounds that the organohalide-respiring bacterium Dehalogenimonas etheniformans strain GP requires to utilize cis-1,2-dichloroethenene and vinyl chloride as electron acceptors. Organism-specific qPCR enumeration matched the growth of individual dechlorinators to the respective functional (i.e. dechlorination) traits. The metabolite cross-feeding in the synthetic (co-)cultures enables concomitant utilization of chlorinated methanes (i.e. chloromethane and dichloromethane) and chlorinated ethenes (i.e. cis-1,2-dichloroethenene and vinyl chloride) without the addition of an external electron donor (i.e. formate and H2). The findings illustrate that naturally occurring chlorinated C1 compounds can sustain anaerobic food webs, an observation with implications for the development of interdependent, mutualistic communities, the sustenance of microbial life in oligotrophic and energy-deprived environments, and the fate of chloromethane/dichloromethane and chlorinated electron acceptors (e.g. chlorinated ethenes) in pristine environments and commingled contaminant plumes.

[Characterization of Reductive Dechlorination of Chlorinated Ethylenes by Anaerobic Consortium].

Tetrachloroethylene （PCE） and trichloroethylene （TCE） are typical volatile halogenated organic compounds in groundwater that pose serious threats to the ecological environment and human health. To obtain an anaerobic microbial consortium capable of efficiently dechlorinating PCE and TCE to a non-toxic end product and to explore its potential in treating contaminated groundwater， an anaerobic microbial consortium W-1 that completely dechlorinated PCE and TCE to ethylene was obtained by repeatedly feeding PCE or TCE into the contaminated groundwater collected from an industrial site. The dechlorination rates of PCE and TCE were （120.1 ±4.9） µmol·ï¼ˆL·d）-1 and （172.4 ±21.8） µmol·ï¼ˆL·d）-1 in W-1， respectively. 16S rRNA gene amplicon sequencing and quantitative PCR （qPCR） showed that the relative abundance of Dehalobacter increased from 1.9% to 57.1%， with the gene copy number increasing by 1.7×107 copies per 1 µmol Cl- released when 98.3 µmol of PCE was dechlorinated to cis-1，2-dichloroethylene （cis-1，2-DCE）. The relative abundance of Dehalococcoides increased from 1.1% to 53.8% when cis-1，2-DCE was reductively dechlorinated to ethylene. The growth yield of Dehalococcoides gene copy number increased by 1.7×108 copies per 1 µmol Cl- released for the complete reductive dechlorination of PCE to ethylene. The results indicated that Dehalobacter and Dehalococcoides cooperated to completely detoxify PCE. When TCE was used as the only electron acceptor， the relative abundance of Dehalococcoides increased from （29.1 ±2.4）% to （7.7 ±0.2）%， and gene copy number increased by （1.9 ±0.4）×108 copies per 1 µmol Cl- released， after dechlorinating 222.8 µmol of TCE to ethylene. The 16S rRNA gene sequence of Dehalococcoides LWT1， the main functional dehalogenating bacterium in enrichment culture W-1， was obtained using PCR and Sanger sequencing， and it showed 100% similarity with the 16S rRNA gene sequence of D. mccartyi strain 195. The anaerobic microbial consortium W-1 was also bioaugmented into the groundwater contaminated by TCE at a concentration of 418.7 µmol·L-1. The results showed that （69.2 ±9.8）% of TCE could be completely detoxified to ethylene within 28 days with a dechlorination rate of （10.3 ±1.5） µmol·ï¼ˆL·d）-1. This study can provide the microbial resource and theoretical guidance for the anaerobic microbial remediation in PCE or TCE-contaminated groundwater.

Age at menarche and chemical exposure: per- and polyfluoroalkyl substances (PFAS), dichloro-diphenyl-trichloroethane (DDT), dichloro-diphenyl-dichloroethylene (DDE), and polychlorinated biphenyls (PCBs).

CONTEXT: Humans are now exposed to a multitude of chemicals throughout the life course, some of which may affect growth and development owing to their endocrine-like activity. OBJECTIVE: To assess the relationship of suspect toxicants to maturation, specifically to age at menarche. METHODS: We conducted two systematic reviews of age at menarche and PFOA, PFOS, PCBs and DDE/DDT based on publications indexed by pubmed. RESULTS: 16 unique reports were identified. Most studies of PFOA and PFOS reported either no association or delays in the age at menarche; only one reported an earlier age. Studies of DDT and DDE were more mixed. Reports on PCBs varied by PCB congener group with an equal number of them reporting delays and no association but one an acceleration. Sources of variation in results include the timing of exposure assessment (prenatal vs. postnatal), level of the toxicant, and sample size. No obvious pattern to the variation in results could be tied to those sources of variation. CONCLUSION: The absence of consistent evidence from multiple reports of earlier age at menarche suggests that these toxicants may not be responsible for accelerated sexual maturation in girls. However, human populations naturally vary in the variety and levels of exposure, making the comparison of studies difficult. Further, studies vary in methodology, complicating aggregation of results and generalisations.

Sensitive room-temperature phosphorescence for luminometric and visual monitoring of the dynamic evolution of acrylate-vinylidene chloride copolymers.

Unlike fluorescence, room-temperature phosphorescence (RTP) has never been utilized to monitor the dynamic variation of polymer. In the present study, acrylate-vinylidene chloride (VDC) copolymers were doped with a good RTP molecule, N-hydroxyethyl 4-bromo-1,8-naphthalimide (HBN). During the maturation process, marked RTP-intensity enhancement of HBN was observed due to the crystallinity increase of copolymers, verified by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). For ensuring the more efficient RTP emission of HBN, copolymers with a higher content of crystallizable VDC segments and a more polar acrylate comonomer, i.e. methyl acrylate (MA) were preferred. According to the RTP characterizations, the following deductions could be obtained: (1) Maturation for 8-9 days at room temperature was needed for the copolymers with a high VDC content to ensure the complete crystallization; (2) Raising the maturation temperature to 50 and 70 °C not only accelerated the crystallization rate, but also increased the crystallinity of copolymers; (3) RTP method was more sensitive to the slight crystallinity variation than XRD and FTIR. Moreover, the dynamic maturation processes of acrylate-VDC copolymers could be also visually monitored through contacting with certain organic solvents that led to the emission color transition from orange to blue.

The importance of proper pH adjustment and control to achieve complete in situ enhanced reductive dechlorination.

In situ bioremediation of chlorinated compounds such as perchloroethylene (PCE) and trichloroethylene (TCE) through enhanced reductive dechlorination (ERD) requires appropriate growth conditions for organohalide-respiring bacteria (OHRB). One of the most important factors controlling OHRB metabolism is groundwater pH. Dehalococcoides spp. (DHC) growth may be inhibited when pH is lower than 6.0, which can lead to the accumulation of toxic daughter compounds including cis-dichloroethylene (cDCE) and vinyl chloride (VC). Aquifer pH may decline as HCl is released during reductive dechlorination and from substrate fermentation to fatty acids and carbonic acid. In this article, we demonstrate that using proper pH adjustment and control in situ is an appropriate strategy to achieve complete ERD (i.e., complete conversion of PCE and TCE to nontoxic ethylene) in remediation sites with inherently low pH values and/or low buffering capacity. To analyze the effectiveness of this approach, field monitoring results are presented for a challenging site containing high concentrations of PCE and TCE (>10 000 µg/L and >1000 µg/L, respectively) and low aquifer pH (~4.9). Addition of a bioaugmentation culture, emulsified vegetable oil (EVO), and a colloidal buffer (CoBupHTM ) to increase pH, stimulated rapid conversion of PCE and TCE to cDCE and VC. However, further conversion of cDCE and VC was very limited. To stimulate complete conversion to ethylene, additional CoBupHTM and nutrients were injected, resulting in a rapid increase in metabolic rates, and maintained the aquifer pH at ~6.5 for more than five years, thus demonstrating that complete ERD can be achieved in sites with similar characteristics. Proper pH adjustment and control is needed to limit the accumulation of toxic intermediates, maintaining in situ bioremediation as an efficient, affordable, and environmentally friendly option to treat chlorinated compounds. Integr Environ Assess Manag 2023;19:943-948. © 2022 SETAC.

Phyto-Fenton remediation of a dichloro-diphenyl-trichloroethane contaminated site in Ha Tinh Province, Vietnam.

A field trial was conducted at a site in Cam Binh commune, Ha Tinh province, Vietnam, highly contaminated with organo-pesticides. The phyto-Fenton process was applied to remove pesticide residues in soils. In addition to magnetite (Fe3O4) materials added to the soils, fertilizers and elicitors for oxidative burst were also added in the different experimental treatments. Dichloro-diphenyl-trichloroethane (DDT) and isomers were removed in all experimental lots. The removal efficiency was highest in lot B1, a site where only iron materials were added. The removal efficiency and the final content of DDTs in B1 were 98.4% and 0.009 mg kg-1, respectively. In the presence of elicitors, the conversion of DDT to dichloro-diphenyl-dichloroethylene was more favorable. Analysis of soil properties indicated that the phyto-Fenton process can occur at neutral soil pH, and when there are only small changes in soil organic carbon content and cation exchange capacities. Shifts in the composition of the microbial communities were observed. Further studies on the interactions between materials added to soil, plants, and the soil microbiome are needed to understand the mechanism of action of the phyto-Fenton process during soil remediation.

Highly selective molecular sieving of cis- over trans-1,2-dichloroethene isomers.

An intrinsically porous trianglimine macrocycle 1 is reported to display energy-efficient and cost-effective adsorptive properties by selectively separating cis-1,2-dichloroethene (cis-DCE) from an equimolar cis- and trans-DCE mixture with a purity of over 96%. The selectivity is enhanced by host/guest C-H⋯π intermolecular interactions. Moreover, the macrocycle can be reused many times without any decrease in performance, which further supports the sustainability of using molecular sieves in chemical separation.

Genomic analysis of Acinetobacter pittii CEP14 reveals its extensive biodegradation capabilities, including cometabolic degradation of cis-1,2-dichloroethene.

Halogenated organic compounds are naturally occurring in subsurface environments; however, accumulation of the degradative intermediate cis-1,2-dichloroethene (cDCE) at soil and groundwater sites contaminated with xenobiotic chlorinated ethenes is a global environmental and public health issue. Identifying microorganisms capable of cDCE degradation in these environments is of interest because of their potential application to bioremediation techniques. In this study, we sequenced, assembled, and analyzed the complete genome of Acinetobacter pittii CEP14, a strain isolated from chloroethene-contaminated groundwater, that has demonstrated the ability for aerobic cometabolic degradation of cDCE in the presence of n-hexane, phenol, and toluene. The A. pittii CEP14 genome consists of a 3.93 Mbp-long chromosome (GenBank accession no. CP084921) with a GC content of 38.9% and three plasmids (GenBank accession no. CP084922, CP084923, and CP084924). Gene function was assigned to 83.4% of the 3,930 coding DNA sequences. Functional annotation of the genome revealed that the CEP14 strain possessed all genetic elements to mediate the degradation of a range of aliphatic and aromatic compounds, including n-hexane and phenol. In addition, it harbors gene clusters involved in cytosol detoxification and oxidative stress resistance, which could play a role in the mitigation of toxic chemical intermediates that can arise during the degradation of cDCE. Gene clusters for heavy metal and antibiotic resistance were also identified in the genome of CEP14. These results suggest that CEP14 may be a versatile degrader of xenobiotic compounds and well-adapted to polluted environments, where a combination of heavy metal and organic compound pollution is often found.

Degrading chlorinated aliphatics by reductive dechlorination of groundwater samples from the Santa Susana Field Laboratory.

Microbial reductive dechlorination is one of the chosen methods for remediation of chlorinated compounds in anaerobic environments. In this study we examined the degradation of chlorinated aliphatics in groundwater samples from the Santa Susana Field Laboratory (SSFL) containing a concentration of 0.228 mM trichloroethylene (TCE) and 0.279 mM 1,2 dichloroethylene (DCE). We tested the influence of adding different carbon sources on the dechlorinating activity in batch cultures with and without dechlorinating bacteria. In-situ microcosms were established using SSFL groundwater supplemented with EVO (5%) (vol/vol) SRS emulsion and with or without species of Dehalocococcoides (DCB-1, DCB-2 or DCB-3). Emulsified vegetable oil (EVO) gave the highest dechlorinating activity with DCB-1 added compared to any other substrate addition tested. All three bacterial cultures tested had significant dechlorinating activities while the native populations in the SSFL groundwater samples only showed limited degradation of trichloroethylene into intermediates in the form of DCE, vinyl chloride and ethane. The conversion of chlorinated ethylenes (CEs) was optimal in the bioreactors amended with DCB-1 followed by DCB-2, and DCB-3 all supplemented with EVO. We further analyzed the TCE degradation first order kinetics in batch cultures and found that the culture with DCB-1 supplemented with EVO showed 43.59% and 51.38% increased degradation rate compared to the same condition with cultures of DCB-2 or DCB-3 added. The microcosm studies further showed that with DCB-1 and EVO, reductive dechlorination of TCE in the SSFL converted 90% of the input TCE to ethane with a degradation rate of 0.0039 mM/day.

Sequential anaerobic and aerobic bioaugmentation for commingled groundwater contamination of trichloroethene and 1,4-dioxane.

Chlorinated solvents, notably trichloroethene (TCE), and the cyclic ether stabilizer, 1,4-dioxane (dioxane), have been frequently detected commingling in contaminated aquifers. Here we developed a sequential anaerobic and aerobic treatment strategy effective to mitigate the co-contamination of TCE and dioxane, particularly when dioxane is present at ppb levels relevant to many impacted sites. After the primary anaerobic treatment by a halorespiring consortium SDC-9, TCE was effectively removed, though lingering less-chlorinated metabolites, vinyl chloride (VC) and cis-dichloroethene (cDCE). Subsequent aerobic bioaugmentation with Azoarcus sp. DD4, a cometabolic dioxane degrader, demonstrated the ability of DD4 to degrade dioxane at an initial concentration of 20 µg/L to below 0.4 µg/L and its dominance (~7%) in microcosms fed with propane. Even better, DD4 can also transform VC and cDCE in tandem, though cDCE and VC at relatively high concentrations (e.g., 1 mg/L) posed inhibition to propane assimilation and cell growth of DD4. Mutagenesis of DD4 revealed group-2 toluene monooxygenase and group-5 propane monooxygenase are responsible for cDCE and VC co-oxidation, respectively. Overall, we demonstrated the feasibility of a treatment train combining reductive dehalogenation and aerobic co-oxidation processes in tandem to not only effectively clean up prevalent co-contamination of TCE and dioxane at trace levels but also mitigate persistent products (e.g., cDCE and VC) when complete reductive dehalogenation of less-chlorinated ethenes occurs slowly in the field.

Sex differences in the association of measures of sexual maturation to common toxicants: Lead, dichloro-diphenyl-trichloroethane (DDT), dichloro-diphenyl-dichloroethylene (DDE), and polychlorinated biphenyls (PCBs).

Many studies of human toxicant exposure examine the hypothesis that human sexual maturation can be affected through endocrine disruption. Within this body of literature there is significant variation in the findings. Variation may be related to the differential effects by toxicants between males and females as well as variation in sample size, toxicant levels, and the timing of exposure. We review sexual maturation outcomes between males and females when exposed to lead, dichlorodiphenyldichloroethylene (DDE), dichloro-diphenyl-trichloroethane (DDT), and polychlorinated biphenyls (PCBs) using a systematic process to gather peer-reviewed studies published from January 1994 through December 2019 on the NCBI website's PubMed search engine. The review includes 34 studies, some comprised of multiple analyses, to compare effects on sexual maturation by sex. The analysis shows that both boys and girls have delayed sexual maturation in relation to lead exposure. There are differences in the direction of effects associated with DDE/DDT and PCB exposure in boys and girls. PCBs exist as congeners of many structural forms, and that variation is considered in this review. Dioxin-like and non-dioxin-like PCBs exposure directionality differed between boys and girls as well. Future investigations into the basis of sex variation in DDE/DDT and PCB relationships to sexual maturation are warranted.

Examining aerobic degradation of chloroethenes mixture in consortium composed of Comamonas testosteroni RF2 and Mycobacterium aurum L1.

An environmental isolate Comamonas testosteroni RF2 has been previously described to cometabolize trichloroethene (TCE), 1,2-cis-dichloroethene (cDCE), 1,2-trans-dichloroethene (tDCE), and 1,1-dichloroethene (1,1DCE) when grown on phenol and lactate sodium. In this study, three vinyl chloride (VC) degrading strains, Mycobacterium aurum L1, Pseudomonas putida PS, and Rhodococcus ruber Sm-1 were used to form consortia with the strain RF2 in terms to achieve the removal of VC along with above-mentioned chloroethenes. Degradation assays were performed for a binary mixture of cDCE and VC as well as for a mixture of TCE, all DCEs and VC. The consortium composed of C. testosteroni RF2 and M. aurum L1 showed to be the most efficient towards the removal of cDCE (6.01 mg L-1) in the binary mixture with VC (10 mg L-1) and was capable of efficiently removing chloroethenes in the mixture sample at the initial concentrations of 116 µg L-1 for TCE, 662 µg L-1 for cDCE, 42 µg L-1 for tDCE, 16 µg L-1 for 1,1DCE, and 7 mg L-1 for VC with a removal efficiency of nearly 100% for all of the compounds. Although complete removal of VC took a significantly longer time than the removal of other chloroethenes, the consortium composed of C. testosteroni RF2 and M. aurum L1 displayed strong bioremediation potential for aquifers with downstream contamination characterized by the presence of less chlorinated ethenes.

Groundwater geochemical constituents controlling the reductive dechlorination of TCE by nZVI: Evidence from diverse anaerobic corrosion mechanisms of nZVI.

The corrosion mechanisms of nanoscale zero-valent iron (nZVI) vary with different geochemical constituents, which affect the reductive dechlorination process of trichloroethylene (TCE). In this study, the effect of nZVI anaerobic corrosion on the reductive dechlorination of TCE with different groundwater geochemical constituents (Ca2+-SO42-, Ca2+-HCO3-, Na+-NO3-) was investigated. Microscopic characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM) combined with pH, oxidation-reduction potential (ORP) and dissolved Fe2+ in solutions to illustrate the corrosion mechanism of nZVI. In the four systems including ultrapure water (UPW), the reduction of TCE conformed to pseudo-first-order kinetics, the generation of Cl- accorded with zero-order kinetics, and multi-step reaction kinetics was used to fit the generation and degradation of chlorinated byproducts (Dichloroethylene, DCEs). Compared with UPW system, the dissolution corrosion of Ca2+-HCO3- and Ca2+-SO42- promoted the reductive dechlorination of TCE (kobs, TCE = 0.658 ± 0.010 & 0.245 ± 0.028 d-1 and kobs, Cl- = 41.682 ± 1.016 & 20.623 ± 1.923 µM⋅d-1 for Ca2+-HCO3- & Ca2+-SO42-, respectively) and the degradation of DCEs (0.444 ± 0.036 & 0.244 ± 0.040 µM⋅d-1 for Ca2+-HCO3- & Ca2+-SO42-, respectively); redox-active NO3- competed for electrons and passivated the surface of nZVI, which limited the reductive dechlorination of TCE (kobs, TCE = 0.111 ± 0.025 d-1 & kobs, Cl- = 14.943 ± 0.664 µM⋅d-1) and the degradation of DCEs (0.078 ± 0.018 µM⋅d-1), and the passivation layer promoted the adsorption of TCE. This study from the perspective of nZVI corrosion provides a theoretical basis for the long-term application of nZVI technology in the remediation of TCE-contaminated sites with different groundwater geochemical types.

Discovery of an Inducible Toluene Monooxygenase That Cooxidizes 1,4-Dioxane and 1,1-Dichloroethylene in Propanotrophic Azoarcus sp. Strain DD4.

Cometabolic degradation plays a prominent role in bioremediation of commingled groundwater contamination (e.g., chlorinated solvents and the solvent stabilizer 1,4-dioxane [dioxane]). In this study, we untangled the diversity and catalytic functions of multicomponent monooxygenases in Azoarcus sp. strain DD4, a Gram-negative propanotroph that is effective in degrading dioxane and 1,1-dichloroethylene (1,1-DCE). Using a combination of knockout mutagenesis and heterologous expression, a toluene monooxygenase (MO) encoded by the tmoABCDEF gene cluster was unequivocally proved to be the key enzyme responsible for the cometabolism of both dioxane and 1,1-DCE. Interestingly, in addition to utilizing toluene as a primary substrate, this toluene MO can also oxidize propane into 1-propanol. Expression of this toluene MO in DD4 appears inducible by both substrates (toluene and propane) and their primary hydroxylation products (m-cresol, p-cresol, and 1-propanol). These findings coherently explain why DD4 can grow on propane and express toluene MO for active cooxidation of dioxane and 1,1-DCE. Furthermore, upregulation of tmo transcription by 1-propanol underlines the implication potential of using 1-propanol as an alternative auxiliary substrate for DD4 bioaugmentation. The discovery of this toluene MO in DD4 and its degradation and induction versatility can lead to broad applications, spanning from environmental remediation and water treatment to biocatalysis in green chemistry.IMPORTANCE Toluene MOs have been well recognized given their robust abilities to degrade a variety of environmental pollutants. Built upon previous research efforts, this study ascertained the untapped capability of a toluene MO in DD4 for effective cooxidation of dioxane and 1,1-DCE, two of the most prevailing yet challenging groundwater contaminants. This report also aligns the induction of a toluene MO with nontoxic and commercially accessible chemicals (e.g., propane and 1-propanol), extending its implications in the field of environmental microbiology and beyond.

Aerobic degradation of cis-dichloroethene by the marine bacterium Marinobacter salsuginis strain 5N-3.

An aerobic bacterium, designated strain 5N-3 (NBRC 113055), that degrades cis-dichloroethene (cDCE) was isolated from a sea sediment in Japan. Strain 5N-3 was able to degrade a certain amount of cDCE in the presence of pyruvate without the action of inducers. In the presence of inducers, such as phenol and benzene, the strain completely removed cDCE. By the application of 16S ribosomal RNA (16S rRNA) gene sequencing and average nucleotide identity analyses, the strain 5N-3 was identified as Marinobacter salsuginis. On the other hand, identified species of Marinobacter are not known to degrade cDCE at all. A draft genome sequence analysis of the strain 5N-3 suggested that the dmp-homologous operon (operon for phenol degradation) may be contributing to the aerobic degradation of cDCE. This is the first report on an aerobic marine bacterium that has been found to degrade cDCE.

Effect of nickel, cobalt, and iron on methanogenesis from methanol and cometabolic conversion of 1,2-dichloroethene by Methanosarcina barkeri.

Methanogens are responsible for the last step in anaerobic digestion (AD), in which methane (a biofuel) is produced. Some methanogens can cometabolize chlorinated pollutants, contributing for their removal during AD. Methanogenic cofactors involved in cometabolic reductive dechlorination, such as F430 and cobalamin, contain metal ions (nickel, cobalt, iron) in their structure. We hypothesized that the supplementation of trace metals could improve methane production and the cometabolic dechlorination of 1,2-dichloroethene (DCE) by pure cultures of Methanosarcina barkeri. Nickel, cobalt, and iron were added to cultures of M. barkeri growing on methanol and methanol plus DCE. Metal amendment improved DCE dechlorination to vinyl chloride (VC): assays with 20 µM of Fe3+ showed the highest final concentration of VC (5× higher than in controls without Fe3+ ), but also in assays with 5.5 µM of Co2+ and 5 µM of Ni2+ VC formation was improved (3.5-4× higher than in controls without the respective metals). Dosing of metals could be useful to improve anaerobic removal of chlorinated compounds, and more importantly decrease the detrimental effect of DCE on methane production in anaerobic digesters.

Co-encapsulation of slow release compounds and Rhodococcus rhodochrous ATCC 21198 in gellan gum beads to promote the long-term aerobic cometabolic transformation of 1,1,1-trichloroethane, cis-1,2-dichloroethene and 1,4-dioxane.

Rhodococcus rhodochrous ATCC 21198 (strain ATCC 21198) was successfully co-encapsulated in gellan gum beads with orthosilicates as slow release compounds (SRCs) to support aerobic cometabolism of a mixture of 1,1,1-trichloroethane (1,1,1-TCA), cis-1,2-dichloroethene (cis-DCE), and 1,4-dioxane (1,4-D) at aqueous concentrations ranging from 250 to 1000 µg L-1. Oxygen (O2) consumption and carbon dioxide (CO2) production showed the co-encapsulated cells utilized the alcohols that were released from the co-encapsulated SRCs. Two model SRCs, tetrabutylorthosilicate (TBOS) and tetra-s-butylorthosilicate (T2BOS), which hydrolyze to produce 1- and 2-butanol, respectively, were encapsulated in gellan gum (GG) at mass loadings as high as 10% (w/w), along with strain ATCC 21198. In the GG encapsulated beads, TBOS hydrolyzed 26 times faster than T2BOS and rates were ∼4 times higher in suspension than when encapsulated. In biologically active reactors, the co-encapsulated strain ATCC 21198 effectively utilized the SRC hydrolysis products (1- and 2-butanol) and cometabolized repeated additions of a mixture of 1,1,1-TCA, cis-DCE, and 1,4-D for over 300 days. The transformation followed pseudo-first-order kinetics. Vinyl chloride (VC) and 1,1-dichloroethene (1,1-DCE) were also transformed in the reactors after 250 days. In the long-term treatment, the batch reactors with co-encapsulated T2BOS GG beads achieved similar transformation rates, but at much lower O2 consumption rates than those with TBOS. The results demonstrate that the co-encapsulation technology can be a passive method for the cometabolic treatment of dilute groundwater plumes.

Impact of iron- and/or sulfate-reduction on a cis-1,2-dichloroethene and vinyl chloride respiring bacterial consortium: experiments and model-based interpretation.

Process understanding of microbial communities containing organohalide-respiring bacteria (OHRB) is important for effective bioremediation of chlorinated ethenes. The impact of iron and sulfate reduction on cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) dechlorination by a consortium containing the OHRB Dehalococcoides spp. was investigated using multiphase batch experiments. The OHRB consortium was found to contain endogenous iron- and sulfate-reducing bacteria (FeRB and SRB). A biogeochemical model was developed and used to quantify the mass transfer, aquatic geochemical, and microbial processes that occurred in the multiphase batch system. It was determined that the added SRB had the most significant impact on contaminant degradation. Addition of the SRB increased maximum specific substrate utilization rates, kmax, of cDCE and VC by 129% and 294%, respectively. The added FeRB had a slight stimulating effect on VC dechlorination when exogenous SRB were absent, but when cultured with the added SRB, FeRB moderated the SRB's stimulating effect. This study demonstrates that subsurface microbial community interactions are more complex than categorical, guild-based competition for resources such as electron donor.

Electrochemical transformation of an aged tetrachloroethylene contamination in realistic aquifer settings.

Electrochemical removal of chlorinated ethenes in groundwater plumes may potentially overcome some of the challenges faced by current remediation technologies. So far, studies have been conducted in simplified settings of synthetic groundwater and inert porous matrices. This study is a stepwise investigation of the influence of field-extracted groundwater, sandy sediment and groundwater aquifer temperatures on the removal of an aged partially degraded contamination of tetrachloroethylene (PCE) at a typical groundwater flow rate. The aim is to assess the potential for applying electrochemistry at contaminated sites. At a constant current of 120 mA, pH and conductivity were unaffected downgradient the electrochemical zone. Major groundwater species were reduced and oxidized. Some minerals deposited, others dissolved. Hydrogen peroxide, a strong oxidant, was formed in levels up to 5 mg L-1 with a limited distribution into the sandy sediment. Trichloromethane was formed, supposedly by oxidation of organic matter in the sandy sediment in the presence of chloride. The more realistic the settings, the higher the PCE removal, bringing concentrations down to 7.8 ±â€¯2.3 µg L-1. A complete removal of trichloroethylene and cis-1,2-dichloroethylene was obtained. The results suggest that competing reactions related to the natural complex hydrogeochemistry are insignificant in terms of affecting the electrochemical degradation of PCE and chlorinated intermediates.

Preparation of 4'-Spirocyclobutyl Nucleoside Analogues as Novel and Versatile Adenosine Scaffolds.

Despite the large variety of modified nucleosides that have been reported, the preparation of constrained 4'-spirocyclic adenosine analogues has received very little attention. We discovered that the [2+2]-cycloaddition of dichloroketene on readily available 4'-exo-methylene furanose sugars efficiently results in the diastereoselective formation of novel 4'-spirocyclobutanones. The reaction mechanism was investigated via density functional theory (DFT) and found to proceed either via a non-synchronous or stepwise reaction sequence, controlled by the stereochemistry at the 3'-position of the sugar substrate. The obtained dichlorocyclobutanones were converted into nucleoside analogues, providing access to a novel class of chiral 4'-spirocyclobutyl adenosine mimetics in eight steps from commercially available sugars. Assessment of the biological activity of designed 4'-spirocyclic adenosine analogues identified potent inhibitors for protein methyltransferase target PRMT5.