Publications by authors named "Siavash Atashgahi"

29 Publications

  • Page 1 of 1

High biodiversity in a benzene-degrading nitrate-reducing culture is sustained by a few primary consumers.

Commun Biol 2021 May 5;4(1):530. Epub 2021 May 5.

Department of Molecular Cell Biology, AIMMS, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

A key question in microbial ecology is what the driving forces behind the persistence of large biodiversity in natural environments are. We studied a microbial community with more than 100 different types of species which evolved in a 15-years old bioreactor with benzene as the main carbon and energy source and nitrate as the electron acceptor. Using genome-centric metagenomics plus metatranscriptomics, we demonstrate that most of the community members likely feed on metabolic left-overs or on necromass while only a few of them, from families Rhodocyclaceae and Peptococcaceae, are candidates to degrade benzene. We verify with an additional succession experiment using metabolomics and metabarcoding that these few community members are the actual drivers of benzene degradation. As such, we hypothesize that high species richness is maintained and the complexity of a natural community is stabilized in a controlled environment by the interdependencies between the few benzene degraders and the rest of the community members, ultimately resulting in a food web with different trophic levels.
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http://dx.doi.org/10.1038/s42003-021-01948-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8099898PMC
May 2021

2,4-Dichlorophenoxyacetic acid degradation in methanogenic mixed cultures obtained from Brazilian Amazonian soil samples.

Biodegradation 2021 Apr 20. Epub 2021 Apr 20.

Environmental Technology, Wageningen University & Research, PO BOX 17, 6700 EV, Wageningen, The Netherlands.

2,4-Dichlorophenoxyacetic acid (2,4-D) is the third most applied pesticide in Brazil to control broadleaf weeds in crop cultivation and pastures. Due to 2,4-D's high mobility and long half-life under anoxic conditions, this herbicide has high probability for groundwater contamination. Bioremediation is an attractive solution for 2,4-D contaminated anoxic environments, but there is limited understanding of anaerobic 2,4-D biodegradation. In this study, methanogenic enrichment cultures were obtained from Amazonian top soil (0-40 cm) and deep soil (50 -80 cm below ground) that biotransform 2,4-D (5 µM) to 4-chlorophenol and phenol. When these cultures were transferred (10% v/v) to fresh medium containing 40 µM or 160 µM 2,4-D, the rate of 2,4-D degradation decreased, and biotransformation did not proceed beyond 4-chlorophenol and 2,4-dichlorophenol in the top and deep soil cultures, respectively. 16S rRNA gene sequencing and qPCR of a selection of microbes revealed no significant enrichment of known organohalide-respiring bacteria. Furthermore, a member of the genus Cryptanaerobacter was identified as possibly responsible for phenol conversion to benzoate in the top soil inoculated culture. Overall, these results demonstrate the effect of 2,4-D concentration on biodegradation and microbial community composition, which are both important factors when developing pesticide bioremediation technologies.
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http://dx.doi.org/10.1007/s10532-021-09940-3DOI Listing
April 2021

Long-Chain Fatty Acids Degradation by Species and Proposal of " Desulfomonile Palmitatoxidans".

Front Microbiol 2020 17;11:539604. Epub 2020 Dec 17.

Centre of Biological Engineering, University of Minho, Braga, Portugal.

Microbial communities with the ability to convert long-chain fatty acids (LCFA) coupled to sulfate reduction can be important in the removal of these compounds from wastewater. In this work, an enrichment culture, able to oxidize the long-chain fatty acid palmitate (C) coupled to sulfate reduction, was obtained from anaerobic granular sludge. Microscopic analysis of this culture, designated HP culture, revealed that it was mainly composed of one morphotype with a typical collar-like cell wall invagination, a distinct morphological feature of the genus. 16S rRNA gene amplicon and metagenome-assembled genome (MAG) indeed confirmed that the abundant phylotype in HP culture belong to genus [ 92% 16S rRNA gene sequences closely related to spp.; and . 82% whole genome shotgun (WGS)]. Based on similar cell morphology and average nucleotide identity (ANI) (77%) between the sp. in HP culture and the type strain strain DCB-1, we propose a novel species designated as " Desulfomonile palmitatoxidans." This bacterium shares 94.3 and 93.6% 16S rRNA gene identity with strain DCB-M and strain DCB-1, respectively. Based on sequence abundance of -morphotype in HP culture, its predominance in the microscopic observations, and presence of several genes coding for enzymes involved in LCFA degradation, the proposed species " Desulfomonile palmitatoxidans" most probably plays an important role in palmitate degradation in HP culture. Analysis of the growth of HP culture and strain DCB-1 with short- (butyrate), medium- (caprylate) and long-chain fatty acids (palmitate, stearate, and oleate) showed that both cultures degraded all fatty acids coupled to sulfate reduction, except oleate that was only utilized by HP culture. In the absence of sulfate, neither HP culture, nor strain DCB-1 degraded palmitate when incubated with as a possible methanogenic syntrophic partner. Unlike strain DCB-1, " Desulfomonile palmitatoxidans" lacks reductive dehalogenase genes in its genome, and HP culture was not able to grow by organohalide respiration. An emended description of the genus is proposed. Our study reveals an unrecognized LCFA degradation feature of the genus.
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http://dx.doi.org/10.3389/fmicb.2020.539604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7773648PMC
December 2020

Metagenomic- and Cultivation-Based Exploration of Anaerobic Chloroform Biotransformation in Hypersaline Sediments as Natural Source of Chloromethanes.

Microorganisms 2020 May 2;8(5). Epub 2020 May 2.

Laboratory of Microbiology, Wageningen University & Research, 6708 WE Wageningen, The Netherlands.

Chloroform (CF) is an environmental contaminant that can be naturally formed in various environments ranging from forest soils to salt lakes. Here we investigated CF removal potential in sediments obtained from hypersaline lakes in Western Australia. Reductive dechlorination of CF to dichloromethane (DCM) was observed in enrichment cultures derived from sediments of Lake Strawbridge, which has been reported as a natural source of CF. No CF removal was observed in abiotic control cultures without artificial electron donors, indicating biotic CF dechlorination in the enrichment cultures. Increasing vitamin B concentration from 0.04 to 4 µM in enrichment cultures enhanced CF removal and reduced DCM formation. In cultures amended with 4 µM vitamin B and C labelled CF, formation of CO was detected. Known organohalide-respiring bacteria and reductive dehalogenase genes were neither detected using quantitative PCR nor metagenomic analysis of the enrichment cultures. Rather, members of the order , known to co-metabolically transform CF to DCM and CO, were detected. Accordingly, metagenome-assembled genomes of encoded enzymatic repertoires for the Wood-Ljungdahl pathway and cobalamin biosynthesis, which are known to be involved in fortuitous and nonspecific CF transformation. This study indicates that hypersaline lake microbiomes may act as a filter to reduce CF emission to the atmosphere.
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http://dx.doi.org/10.3390/microorganisms8050665DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7284496PMC
May 2020

Organohalide-respiring Desulfoluna species isolated from marine environments.

ISME J 2020 03 2;14(3):815-827. Epub 2020 Jan 2.

Laboratory of Microbiology, Wageningen University & Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands.

The genus Desulfoluna comprises two anaerobic sulfate-reducing strains, D. spongiiphila AA1 and D. butyratoxydans MSL71, of which only the former was shown to perform organohalide respiration (OHR). Here we isolated a third strain, designated D. spongiiphila strain DBB, from marine intertidal sediment using 1,4-dibromobenzene and sulfate as the electron acceptors and lactate as the electron donor. Each strain harbors three reductive dehalogenase gene clusters (rdhABC) and corrinoid biosynthesis genes in their genomes, and dehalogenated brominated but not chlorinated organohalogens. The Desulfoluna strains maintained OHR in the presence of 20 mM sulfate or 20 mM sulfide, which often negatively affect other organohalide-respiring bacteria. Strain DBB sustained OHR with 2% oxygen in the gas phase, in line with its genetic potential for reactive oxygen species detoxification. Reverse transcription-quantitative PCR revealed differential induction of rdhA genes in strain DBB in response to 1,4-dibromobenzene or 2,6-dibromophenol. Proteomic analysis confirmed expression of rdhA1 with 1,4-dibromobenzene, and revealed a partially shared electron transport chain from lactate to 1,4-dibromobenzene and sulfate, which may explain accelerated OHR during concurrent sulfate reduction. Versatility in using electron donors, de novo corrinoid biosynthesis, resistance to sulfate, sulfide and oxygen, and concurrent sulfate reduction and OHR may confer an advantage to marine Desulfoluna strains.
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http://dx.doi.org/10.1038/s41396-019-0573-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7031245PMC
March 2020

Reductive dechlorination of 1,2-dichloroethane in the presence of chloroethenes and 1,2-dichloropropane as co-contaminants.

Appl Microbiol Biotechnol 2019 Aug 28;103(16):6837-6849. Epub 2019 Jun 28.

Laboratory of Microbiology, Wageningen University & Research, Wageningen, The Netherlands.

1,2-Dichloroethane (1,2-DCA) is one of the most abundant manmade chlorinated organic contaminants in the world. Reductive dechlorination of 1,2-DCA by organohalide-respiring bacteria (OHRB) can be impacted by other chlorinated contaminants such as chloroethenes and chloropropanes that can co-exist with 1,2-DCA at contaminated sites. The aim of this study was to evaluate the effect of chloroethenes and 1,2-dichloropropane (1,2-DCP) on 1,2-DCA dechlorination using sediment cultures enriched with 1,2-DCA as the sole chlorinated compound (EA culture) or with 1,2-DCA and tetrachloroethene (PCE) (EB culture), and to model dechlorination kinetics. Both cultures contained Dehalococcoides as most predominated OHRB, and Dehalogenimonas and Geobacter as other known OHRB. In sediment-free enrichments obtained from the EA and EB cultures, dechlorination of 1,2-DCA was inhibited in the presence of the same concentrations of either PCE, vinyl chloride (VC), or 1,2-DCP; however, concurrent dechlorination of dual chlorinated compounds was achieved. In contrast, 1,2-DCA dechlorination completely ceased in the presence of cis-dichloroethene (cDCE) and only occurred after cDCE was fully dechlorinated. In turn, 1,2-DCA did not affect dechlorination of PCE, cDCE, VC, and 1,2-DCP. In sediment-free enrichments obtained from the EA culture, Dehalogenimonas 16S rRNA gene copy numbers decreased 1-3 orders of magnitude likely due to an inhibitory effect of chloroethenes. Dechlorination with and without competitive inhibition fit Michaelis-Menten kinetics and confirmed the inhibitory effect of chloroethenes and 1,2-DCP on 1,2-DCA dechlorination. This study reinforces that the type of chlorinated substrate drives the selection of specific OHRB, and indicates that removal of chloroethenes and in particular cDCE might be necessary before effective removal of 1,2-DCA at sites contaminated with mixed chlorinated solvents.
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http://dx.doi.org/10.1007/s00253-019-09985-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6667407PMC
August 2019

Influence of different redox conditions and dissolved organic matter on pesticide biodegradation in simulated groundwater systems.

Sci Total Environ 2019 Aug 10;677:692-699. Epub 2019 Apr 10.

Sub-department of Environmental Technology, Wageningen University & Research, P.O. Box 47, 6700 AA Wageningen, the Netherlands. Electronic address:

Insights into the influence of redox conditions, that is the availability of electron acceptors, and dissolved organic matter (DOM) on pesticide biodegradation in groundwater are key to understanding the environmental fate of pesticides in natural groundwater systems. Here, the influence of redox conditions and supplemental DOM addition on biodegradation of pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D), 2,6-dichlorobenzamide (BAM), mecoprop-p (MCPP) and bentazone, was tested in microcosm and subsequent column experiments. Pesticide degradation, functional genes and changes in specific fractions and quantity of DOM were systematically quantified. In aerobic microcosm experiments, the highest 2,4-D degradation rate was obtained with the presence of more assimilable DOM. In column experiments, minimal pesticide degradation (≤33.77%) in any anaerobic redox conditions was observed in the absence of DOM. However, in the presence of DOM, 2,4-D biodegradation was considerably enhanced under nitrate-reducing conditions (from 23.5 ± 10.2% to 82.3 ± 11.6%) and in a column without external electron acceptor amendment (from -6.3 ± 12.6% to 31.1 ± 36.3%). Observed preferential depletion of the fulvic acid fraction of DOM provides indications for specific functional DOM properties. The qPCR results show an increase in microbial biomass and functional genes (tfdA) in liquid phase after DOM addition. The results of this work provide insights into the interplays among DOM, redox geochemistry, and pesticide biodegradation, and show the potential of a novel approach - DOM addition to groundwater systems - for in situ biostimulation technology to remove pesticides from groundwater systems.
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http://dx.doi.org/10.1016/j.scitotenv.2019.04.128DOI Listing
August 2019

Discovered by genomics: putative reductive dehalogenases with N-terminus transmembrane helixes.

FEMS Microbiol Ecol 2019 05;95(5)

Laboratory of Microbiology, Wageningen University & Research, Stippeneng 4, 6708 WE Wageningen, The Netherlands.

Attempts for bioremediation of toxic organohalogens resulted in the identification of organohalide-respiring bacteria harbouring reductive dehalogenases (RDases) enzymes. RDases consist of the catalytic subunit (RdhA, encoded by rdhA) that does not have membrane-integral domains, and a small putative membrane anchor (RdhB, encoded by rdhB) that (presumably) locates the A subunit to the outside of the cytoplasmic membrane. Recent genomic studies identified a putative rdh gene in an uncultured deltaproteobacterial genome that was not accompanied by an rdhB gene, but contained transmembrane helixes in N-terminus. Therefore, rather than having a separate membrane anchor protein, this putative RDase is likely a hybrid of RdhA and RdhB, and directly connected to the membrane with transmembrane helixes. However, functionality of the hybrid putative RDase remains unknown. Further analysis showed that the hybrid putative rdh genes are present in the genomes of pure cultures and uncultured members of Bacteriodetes and Deltaproteobacteria, but also in the genomes of the candidate divisions. The encoded hybrid putative RDases have cytoplasmic or exoplasmic C-terminus localization, and cluster phylogenetically separately from the existing RDase groups. With increasing availability of (meta)genomes, more diverse and likely novel rdh genes are expected, but questions regarding their functionality and ecological roles remain open.
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http://dx.doi.org/10.1093/femsec/fiz048DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6797604PMC
May 2019

Microbial Synthesis and Transformation of Inorganic and Organic Chlorine Compounds.

Front Microbiol 2018 12;9:3079. Epub 2018 Dec 12.

Laboratory of Microbiology, Wageningen University & Research, Wageningen, Netherlands.

Organic and inorganic chlorine compounds are formed by a broad range of natural geochemical, photochemical and biological processes. In addition, chlorine compounds are produced in large quantities for industrial, agricultural and pharmaceutical purposes, which has led to widespread environmental pollution. Abiotic transformations and microbial metabolism of inorganic and organic chlorine compounds combined with human activities constitute the chlorine cycle on Earth. Naturally occurring organochlorines compounds are synthesized and transformed by diverse groups of (micro)organisms in the presence or absence of oxygen. In turn, anthropogenic chlorine contaminants may be degraded under natural or stimulated conditions. Here, we review phylogeny, biochemistry and ecology of microorganisms mediating chlorination and dechlorination processes. In addition, the co-occurrence and potential interdependency of catabolic and anabolic transformations of natural and synthetic chlorine compounds are discussed for selected microorganisms and particular ecosystems.
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http://dx.doi.org/10.3389/fmicb.2018.03079DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6299022PMC
December 2018

Flux, Impact, and Fate of Halogenated Xenobiotic Compounds in the Gut.

Front Physiol 2018 10;9:888. Epub 2018 Jul 10.

Laboratory of Microbiology, Wageningen University and Research, Wageningen, Netherlands.

Humans and their associated microbiomes are exposed to numerous xenobiotics through drugs, dietary components, personal care products as well as environmental chemicals. Most of the reciprocal interactions between the microbiota and xenobiotics, such as halogenated compounds, occur within the human gut harboring diverse and dense microbial communities. Here, we provide an overview of the flux of halogenated compounds in the environment, and diverse exposure routes of human microbiota to these compounds. Subsequently, we review the impact of halogenated compounds in perturbing the structure and function of gut microbiota and host cells. In turn, cultivation-dependent and metagenomic surveys of dehalogenating genes revealed the potential of the gut microbiota to chemically alter halogenated xenobiotics and impact their fate. Finally, we provide an outlook for future research to draw attention and attract interest to study the bidirectional impact of halogenated and other xenobiotic compounds and the gut microbiota.
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http://dx.doi.org/10.3389/fphys.2018.00888DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6048469PMC
July 2018

Prospects for harnessing biocide resistance for bioremediation and detoxification.

Science 2018 05;360(6390):743-746

Wageningen University & Research, Laboratory of Microbiology, Stippeneng 4, 6708 WE Wageningen, Netherlands.

Prokaryotes in natural environments respond rapidly to high concentrations of chemicals and physical stresses. Exposure to anthropogenic toxic substances-such as oil, chlorinated solvents, or antibiotics-favors the evolution of resistant phenotypes, some of which can use contaminants as an exclusive carbon source or as electron donors and acceptors. Microorganisms similarly adapt to extreme pH, metal, or osmotic stress. The metabolic plasticity of prokaryotes can thus be harnessed for bioremediation and can be exploited in a variety of ways, ranging from stimulated natural attenuation to bioaugmentation and from wastewater treatment to habitat restoration.
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http://dx.doi.org/10.1126/science.aar3778DOI Listing
May 2018

A benzene-degrading nitrate-reducing microbial consortium displays aerobic and anaerobic benzene degradation pathways.

Sci Rep 2018 03 14;8(1):4490. Epub 2018 Mar 14.

Wageningen University & Research, Laboratory of Microbiology, Stippeneng 4, 6708 WE, Wageningen, The Netherlands.

In this study, we report transcription of genes involved in aerobic and anaerobic benzene degradation pathways in a benzene-degrading denitrifying continuous culture. Transcripts associated with the family Peptococcaceae dominated all samples (21-36% relative abundance) indicating their key role in the community. We found a highly transcribed gene cluster encoding a presumed anaerobic benzene carboxylase (AbcA and AbcD) and a benzoate-coenzyme A ligase (BzlA). Predicted gene products showed >96% amino acid identity and similar gene order to the corresponding benzene degradation gene cluster described previously, providing further evidence for anaerobic benzene activation via carboxylation. For subsequent benzoyl-CoA dearomatization, bam-like genes analogous to the ones found in other strict anaerobes were transcribed, whereas gene transcripts involved in downstream benzoyl-CoA degradation were mostly analogous to the ones described in facultative anaerobes. The concurrent transcription of genes encoding enzymes involved in oxygenase-mediated aerobic benzene degradation suggested oxygen presence in the culture, possibly formed via a recently identified nitric oxide dismutase (Nod). Although we were unable to detect transcription of Nod-encoding genes, addition of nitrite and formate to the continuous culture showed indication for oxygen production. Such an oxygen production would enable aerobic microbes to thrive in oxygen-depleted and nitrate-containing subsurface environments contaminated with hydrocarbons.
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http://dx.doi.org/10.1038/s41598-018-22617-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5852087PMC
March 2018

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

Environ Microbiol 2018 03 15;20(3):934-948. Epub 2017 Dec 15.

Laboratory of Microbiology, Wageningen University & Research, Stippeneng 4, Wageningen 6708 WE, The Netherlands.

Halogenated organic compounds, also termed organohalogens, were initially considered to be of almost exclusively anthropogenic origin. However, over 5000 naturally synthesized organohalogens are known today. This has also fuelled the hypothesis that the natural and ancient origin of organohalogens could have primed development of metabolic machineries for their degradation, especially in microorganisms. Among these, a special group of anaerobic microorganisms was discovered that could conserve energy by reducing organohalogens as terminal electron acceptor in a process termed organohalide respiration. Originally discovered in a quest for biodegradation of anthropogenic organohalogens, these organohalide-respiring bacteria (OHRB) were soon found to reside in pristine environments, such as the deep subseafloor and Arctic tundra soil with limited/no connections to anthropogenic activities. As such, accumulating evidence suggests an important role of OHRB in local natural halogen cycles, presumably taking advantage of natural organohalogens. In this minireview, we integrate current knowledge regarding the natural origin and occurrence of industrially important organohalogens and the evolution and spread of OHRB, and describe potential implications for natural halogen and carbon cycles.
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http://dx.doi.org/10.1111/1462-2920.14016DOI Listing
March 2018

Natural attenuation of chlorinated ethenes in hyporheic zones: A review of key biogeochemical processes and in-situ transformation potential.

Water Res 2018 01 30;128:362-382. Epub 2017 Oct 30.

Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow, UK; GroundH(2)O Plus Ltd., Quinton, Birmingham, UK.

Chlorinated ethenes (CEs) are legacy contaminants whose chemical footprint is expected to persist in aquifers around the world for many decades to come. These organohalides have been reported in river systems with concerning prevalence and are thought to be significant chemical stressors in urban water ecosystems. The aquifer-river interface (known as the hyporheic zone) is a critical pathway for CE discharge to surface water bodies in groundwater baseflow. This pore water system may represent a natural bioreactor where anoxic and oxic biotransformation process act in synergy to reduce or even eliminate contaminant fluxes to surface water. Here, we critically review current process understanding of anaerobic CE respiration in the competitive framework of hyporheic zone biogeochemical cycling fuelled by in-situ fermentation of natural organic matter. We conceptualise anoxic-oxic interface development for metabolic and co-metabolic mineralisation by a range of aerobic bacteria with a focus on vinyl chloride degradation pathways. The superimposition of microbial metabolic processes occurring in sediment biofilms and bulk solute transport delivering reactants produces a scale dependence in contaminant transformation rates. Process interpretation is often confounded by the natural geological heterogeneity typical of most riverbed environments. We discuss insights from recent field experience of CE plumes discharging to surface water and present a range of practical monitoring technologies which address this inherent complexity at different spatial scales. Future research must address key dynamics which link supply of limiting reactants, residence times and microbial ecophysiology to better understand the natural attenuation capacity of hyporheic systems.
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http://dx.doi.org/10.1016/j.watres.2017.10.059DOI Listing
January 2018

Systematics of haloarchaea and biotechnological potential of their hydrolytic enzymes.

Microbiology (Reading) 2017 05 26;163(5):623-645. Epub 2017 May 26.

Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Sevilla, Sevilla, Spain.

Halophilic archaea, also referred to as haloarchaea, dominate hypersaline environments. To survive under such extreme conditions, haloarchaea and their enzymes have evolved to function optimally in environments with high salt concentrations and, sometimes, with extreme pH and temperatures. These features make haloarchaea attractive sources of a wide variety of biotechnological products, such as hydrolytic enzymes, with numerous potential applications in biotechnology. The unique trait of haloarchaeal enzymes, haloenzymes, to sustain activity under hypersaline conditions has extended the range of already-available biocatalysts and industrial processes in which high salt concentrations inhibit the activity of regular enzymes. In addition to their halostable properties, haloenzymes can also withstand other conditions such as extreme pH and temperature. In spite of these benefits, the industrial potential of these natural catalysts remains largely unexplored, with only a few characterized extracellular hydrolases. Because of the applied impact of haloarchaea and their specific ability to live in the presence of high salt concentrations, studies on their systematics have intensified in recent years, identifying many new genera and species. This review summarizes the current status of the haloarchaeal genera and species, and discusses the properties of haloenzymes and their potential industrial applications.
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http://dx.doi.org/10.1099/mic.0.000463DOI Listing
May 2017

Contrasting dual (C, Cl) isotope fractionation offers potential to distinguish reductive chloroethene transformation from breakdown by permanganate.

Sci Total Environ 2017 Oct 18;596-597:169-177. Epub 2017 Apr 18.

Flemish Institute for Technological Research (VITO), Separation and Conversion Technology, Boeretang 200, 2400 Mol, Belgium. Electronic address:

cis-1,2-Dichloroethene (cis-DCE) and trichloroethene (TCE) are persistent, toxic and mobile pollutants in groundwater systems. They are both conducive to reductive dehalogenation and to oxidation by permanganate. In this study, the potential of dual element (C, Cl) compound specific isotope analyses (CSIA) for distinguishing between chemical oxidation and anaerobic reductive dechlorination of cis-DCE and TCE was investigated. Well-controlled cis-DCE degradation batch tests gave similar carbon isotope enrichment factors ε (‰), but starkly contrasting dual element isotope slopes ΔδC/ΔδCl for permanganate oxidation (ε=-26‰±6‰, ΔδC/ΔδCl≈-125±47) compared to reductive dechlorination (ε=-18‰±4‰, ΔδC/ΔδCl≈4.5±3.4). The difference can be tracked down to distinctly different chlorine isotope fractionation: an inverse isotope effect during chemical oxidation (ε=+0.2‰±0.1‰) compared to a large normal isotope effect in reductive dechlorination (ε=-3.3‰±0.9‰) (p≪0.05). A similar trend was observed for TCE. The dual isotope approach was evaluated in the field before and up to 443days after a pilot scale permanganate injection in the subsurface. Our study indicates, for the first time, the potential of the dual element isotope approach for distinguishing cis-DCE (and TCE) concentration drops caused by dilution, oxidation by permanganate and reductive dechlorination both at laboratory and field scale.
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http://dx.doi.org/10.1016/j.scitotenv.2017.03.292DOI Listing
October 2017

Concurrent Haloalkanoate Degradation and Chlorate Reduction by Pseudomonas chloritidismutans AW-1.

Appl Environ Microbiol 2017 06 31;83(12). Epub 2017 May 31.

Laboratory of Microbiology, Wageningen University & Research, Wageningen, The Netherlands

Haloalkanoates are environmental pollutants that can be degraded aerobically by microorganisms producing hydrolytic dehalogenases. However, there is a lack of information about the anaerobic degradation of haloalkanoates. Genome analysis of AW-1, a facultative anaerobic chlorate-reducing bacterium, showed the presence of two putative haloacid dehalogenase genes, the l-DEX gene and , encoding an l-2-haloacid dehalogenase (l-DEX) and a halocarboxylic acid dehydrogenase (DehI), respectively. Hence, we studied the concurrent degradation of haloalkanoates and chlorate as a yet-unexplored trait of strain AW-1 The deduced amino acid sequences of l-DEX and DehI revealed 33 to 37% and 26 to 86% identities with biochemically/structurally characterized l-DEX and the d- and dl-2-haloacid dehalogenase enzymes, respectively. Physiological experiments confirmed that strain AW-1 can grow on chloroacetate, bromoacetate, and both l- and d-α-halogenated propionates with chlorate as an electron acceptor. Interestingly, growth and haloalkanoate degradation were generally faster with chlorate as an electron acceptor than with oxygen as an electron acceptor. In line with this, analyses of l-DEX and DehI dehalogenase activities using cell-free extract (CFE) of strain AW-1 grown on dl-2-chloropropionate under chlorate-reducing conditions showed up to 3.5-fold higher dehalogenase activity than the CFE obtained from AW-1 cells grown on dl-2-chloropropionate under aerobic conditions. Reverse transcription-quantitative PCR showed that the l-DEX gene was expressed constitutively independently of the electron donor (haloalkanoates or acetate) or acceptor (chlorate or oxygen), whereas the expression of dehI was induced by haloalkanoates. Concurrent degradation of organic and inorganic halogenated compounds by strain AW-1 represents a unique metabolic capacity in a single bacterium, providing a new piece of the puzzle of the microbial halogen cycle. Halogenated organic and inorganic compounds are important environmental pollutants that have carcinogenic and genotoxic effects on both animals and humans. Previous research studied the degradation of organic and inorganic halogenated compounds separately but not concurrently. This study shows concurrent degradation of halogenated alkanoates and chlorate as an electron donor and acceptor, respectively, coupled to growth in a single bacterium, AW-1 Hence, besides biogenesis of molecular oxygen from chlorate reduction enabling a distinctive placement of strain AW-1 between aerobic and anaerobic microorganisms, we can now add another unique metabolic potential of this bacterium to the roster. The degradation of different halogenated compounds under anoxic conditions by a single bacterium is also of interest for the natural halogen cycle in different aquatic and terrestrial ecosystems where ample natural production of halogenated compounds has been documented.
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http://dx.doi.org/10.1128/AEM.00325-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5452809PMC
June 2017

Benzene degradation in a denitrifying biofilm reactor: activity and microbial community composition.

Appl Microbiol Biotechnol 2017 Jun 20;101(12):5175-5188. Epub 2017 Mar 20.

Deltares, Subsurface and Groundwater Systems, Princetonlaan 6, 3584 CB, Utrecht, The Netherlands.

Benzene is an aromatic compound and harmful for the environment. Biodegradation of benzene can reduce the toxicological risk after accidental or controlled release of this chemical in the environment. In this study, we further characterized an anaerobic continuous biofilm culture grown for more than 14 years on benzene with nitrate as electron acceptor. We determined steady state degradation rates, microbial community composition dynamics in the biofilm, and the initial anaerobic benzene degradation reactions. Benzene was degraded at a rate of 0.15 μmol/mg protein/day and a first-order rate constant of 3.04/day which was fourfold higher than rates reported previously. Bacteria belonging to the Peptococcaceae were found to play an important role in this anaerobic benzene-degrading biofilm culture, but also members of the Anaerolineaceae were predicted to be involved in benzene degradation or benzene metabolite degradation based on Illumina MiSeq analysis of 16S ribosomal RNA genes. Biomass retention in the reactor using a filtration finger resulted in reduction of benzene degradation capacity. Detection of the benzene carboxylase encoding gene, abcA, and benzoic acid in the culture vessel indicated that benzene degradation proceeds through an initial carboxylation step.
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http://dx.doi.org/10.1007/s00253-017-8214-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5486827PMC
June 2017

Geochemical Parameters and Reductive Dechlorination Determine Aerobic Cometabolic vs Aerobic Metabolic Vinyl Chloride Biodegradation at Oxic/Anoxic Interface of Hyporheic Zones.

Environ Sci Technol 2017 02 11;51(3):1626-1634. Epub 2017 Jan 11.

KU Leuven , Division of Soil and Water Management, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium.

Hyporheic zones mediate vinyl chloride (VC) biodegradation in groundwater discharging into surface waters. At the oxic/anoxic interface (OAI) of hyporheic zones subjected to redox oscillations, VC is degraded via coexisting aerobic ethenotrophic and anaerobic reductive dechlorination pathways. However, the identity of aerobic VC degradation pathways (cometabolic vs metabolic) and their interactions with reductive dechlorination in relation to riverbed sediment geochemistry remain ill-defined. We addressed this using microcosms containing OAI sediments incubated under fluctuating oxic/anoxic atmosphere. Under oxic atmosphere, aerobic metabolic VC oxidation was absent in sediments with high total organic carbon (TOC) and VC was reductively dechlorinated to ethene. Ethene was oxidized by ethenotrophs that can degrade VC cometabolically. Contrastingly, VC was metabolically oxidized by ethenotrophs in low-TOC sediments with low reductive dechlorination potential. Accordingly, enrichment and isolation of metabolic VC-oxidizing ethenotrophs was successful only from the low-TOC sediment. Sequence analysis of etnE genes from the microcosms as well phylogenetic typing of the isolates showed that ethenotrophs in the sediments were facultative anaerobic Proteobacteria capable of coping with OAI-associated redox fluctuations. Our results suggest that local sediment heterogeneity supports/selects divergent VC degradation processes at the OAI and that high reductive dechlorination potential suppresses development of aerobic metabolic VC oxidation potential.
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http://dx.doi.org/10.1021/acs.est.6b05041DOI Listing
February 2017

Dechlorination of three tetrachlorobenzene isomers by contaminated harbor sludge-derived enrichment cultures follows thermodynamically favorable reactions.

Appl Microbiol Biotechnol 2017 Mar 1;101(6):2589-2601. Epub 2016 Dec 1.

Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands.

Dechlorination patterns of three tetrachlorobenzene isomers, 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-TeCB, were studied in anoxic microcosms derived from contaminated harbor sludge. The removal of doubly, singly, and un-flanked chlorine atoms was noted in 1,2,3,4- and 1,2,3,5-TeCB fed microcosms, whereas only singly flanked chlorine was removed in 1,2,4,5-TeCB microcosms. The thermodynamically more favorable reactions were selectively followed by the enriched cultures with di- and/or mono-chlorobenzene as the main end products of the reductive dechlorination of all three isomers. Based on quantitative PCR analysis targeting 16S rRNA genes of known organohalide-respiring bacteria, the growth of Dehalococcoides was found to be associated with the reductive dechlorination of all three isomers, while growth of Dehalobacter, another known TeCB dechlorinator, was only observed in one 1,2,3,5-TeCB enriched microcosm among biological triplicates. Numbers of Desulfitobacterium and Geobacter as facultative dechlorinators were rather stable suggesting that they were not (directly) involved in the observed TeCB dechlorination. Bacterial community profiling suggested bacteria belonging to the phylum Bacteroidetes and the order Clostridiales as well as sulfate-reducing members of the class Deltaproteobacteria as putative stimulating guilds that provide electron donor and/or organic cofactors to fastidious dechlorinators. Our results provide a better understanding of thermodynamically preferred TeCB dechlorinating pathways in harbor environments and microbial guilds enriched and active in anoxic TeCB dechlorinating microcosms.
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http://dx.doi.org/10.1007/s00253-016-8004-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5320011PMC
March 2017

Geochemical and microbial community determinants of reductive dechlorination at a site biostimulated with glycerol.

Environ Microbiol 2017 03 6;19(3):968-981. Epub 2016 Oct 6.

Laboratory of Microbiology, Wageningen University & Research, Wageningen, The Netherlands.

Biostimulation is widely used to enhance reductive dechlorination of chlorinated ethenes in contaminated aquifers. However, the knowledge on corresponding biogeochemical responses is limited. In this study, glycerol was injected in an aquifer contaminated with cis-dichloroethene (cDCE), and geochemical and microbial shifts were followed for 265 days. Consistent with anoxic conditions and sulfate reduction after biostimulation, MiSeq 16S rRNA gene sequencing revealed temporarily increased relative abundance of Firmicutes, Bacteriodetes and sulfate reducing Deltaproteobacteria. In line with C cDCE enrichment and increased Dehalococcoides mccartyi (Dcm) numbers, dechlorination was observed toward the end of the field experiment, albeit being incomplete with accumulation of vinyl chloride. This was concurrent with (i) decreased concentrations of dissolved organic carbon (DOC), reduced relative abundances of fermenting and sulfate reducing bacteria that have been suggested to promote Dcm growth by providing electron donor (H ) and essential corrinoid cofactors, (ii) increased sulfate concentration and increased relative abundance of Epsilonproteobacteria and Deferribacteres as putative oxidizers of reduced sulfur compounds. Strong correlations of DOC, relative abundance of fermenters and sulfate reducers, and dechlorination imply the importance of syntrophic interactions to sustain robust dechlorination. Tracking microbial and environmental parameters that promote/preclude enhanced reductive dechlorination should aid development of sustainable bioremediation strategies.
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http://dx.doi.org/10.1111/1462-2920.13531DOI Listing
March 2017

Impact of a wastewater treatment plant on microbial community composition and function in a hyporheic zone of a eutrophic river.

Sci Rep 2015 Nov 26;5:17284. Epub 2015 Nov 26.

Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, The Netherlands.

The impact of the installation of a technologically advanced wastewater treatment plant (WWTP) on the benthic microbial community of a vinyl chloride (VC) impacted eutrophic river was examined two years before, and three and four years after installation of the WWTP. Reduced dissolved organic carbon and increased dissolved oxygen concentrations in surface water and reduced total organic carbon and total nitrogen content in the sediment were recorded in the post-WWTP samples. Pyrosequencing of bacterial 16S rRNA gene fragments in sediment cores showed reduced relative abundance of heterotrophs and fermenters such as Chloroflexi and Firmicutes in more oxic and nutrient poor post-WWTP sediments. Similarly, quantitative PCR analysis showed 1-3 orders of magnitude reduction in phylogenetic and functional genes of sulphate reducers, denitrifiers, ammonium oxidizers, methanogens and VC-respiring Dehalococcoides mccartyi. In contrast, members of Proteobacteria adapted to nutrient-poor conditions were enriched in post-WWTP samples. This transition in the trophic state of the hyporheic sediments reduced but did not abolish the VC respiration potential in the post-WWTP sediments as an important hyporheic sediment function. Our results highlight effective nutrient load reduction and parallel microbial ecological state restoration of a human-stressed urban river as a result of installation of a WWTP.
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http://dx.doi.org/10.1038/srep17284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4660315PMC
November 2015

Microbial Community Response of an Organohalide Respiring Enrichment Culture to Permanganate Oxidation.

PLoS One 2015 5;10(8):e0134615. Epub 2015 Aug 5.

Environmental Technology, Wageningen University, Wageningen, The Netherlands.

While in situ chemical oxidation is often used to remediate tetrachloroethene (PCE) contaminated locations, very little is known about its influence on microbial composition and organohalide respiration (OHR) activity. Here, we investigate the impact of oxidation with permanganate on OHR rates, the abundance of organohalide respiring bacteria (OHRB) and reductive dehalogenase (rdh) genes using quantitative PCR, and microbial community composition through sequencing of 16S rRNA genes. A PCE degrading enrichment was repeatedly treated with low (25 μmol), medium (50 μmol), or high (100 μmol) permanganate doses, or no oxidant treatment (biotic control). Low and medium treatments led to higher OHR rates and enrichment of several OHRB and rdh genes, as compared to the biotic control. Improved degradation rates can be attributed to enrichment of (1) OHRB able to also utilize Mn oxides as a terminal electron acceptor and (2) non-dechlorinating community members of the Clostridiales and Deltaproteobacteria possibly supporting OHRB by providing essential co-factors. In contrast, high permanganate treatment disrupted dechlorination beyond cis-dichloroethene and caused at least a 2-4 orders of magnitude reduction in the abundance of all measured OHRB and rdh genes, as compared to the biotic control. High permanganate treatments resulted in a notably divergent microbial community, with increased abundances of organisms affiliated with Campylobacterales and Oceanospirillales capable of dissimilatory Mn reduction, and decreased abundance of presumed supporters of OHRB. Although OTUs classified within the OHR-supportive order Clostridiales and OHRB increased in abundance over the course of 213 days following the final 100 μmol permanganate treatment, only limited regeneration of PCE dechlorination was observed in one of three microcosms, suggesting strong chemical oxidation treatments can irreversibly disrupt OHR. Overall, this detailed investigation into dose-dependent changes of microbial composition and activity due to permanganate treatment provides insight into the mechanisms of OHR stimulation or disruption upon chemical oxidation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0134615PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4526698PMC
May 2016

Proteomic analysis of nitrate-dependent acetone degradation by Alicycliphilus denitrificans strain BC.

FEMS Microbiol Lett 2015 Jun 14;362(11). Epub 2015 May 14.

Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, the Netherlands Centre of Biological Engineering, Campus de Gualtar, University of Minho, 4710-057, Braga, Portugal

Alicycliphilus denitrificans strain BC grows anaerobically on acetone with nitrate as electron acceptor. Comparative proteomics of cultures of A. denitrificans strain BC grown on either acetone or acetate with nitrate was performed to study the enzymes involved in the acetone degradation pathway. In the proposed acetone degradation pathway, an acetone carboxylase converts acetone to acetoacetate, an AMP-dependent synthetase/ligase converts acetoacetate to acetoacetyl-CoA, and an acetyl-CoA acetyltransferase cleaves acetoacetyl-CoA to two acetyl-CoA. We also found a putative aldehyde dehydrogenase associated with acetone degradation. This enzyme functioned as a β-hydroxybutyrate dehydrogenase catalyzing the conversion of surplus acetoacetate to β-hydroxybutyrate that may be converted to the energy and carbon storage compound, poly-β-hydroxybutyrate. Accordingly, we confirmed the formation of poly-β-hydroxybutyrate in acetone-grown cells of strain BC. Our findings provide insight in nitrate-dependent acetone degradation that is activated by carboxylation of acetone. This will aid studies of similar pathways found in other microorganisms degrading acetone with nitrate or sulfate as electron acceptor.
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http://dx.doi.org/10.1093/femsle/fnv080DOI Listing
June 2015

Microbial dynamics during and after in situ chemical oxidation of chlorinated solvents.

Ground Water 2015 Mar-Apr;53(2):261-70. Epub 2014 Jun 4.

Laboratory of Microbiology, Wageningen University, Dreijenplein 10, 6703 HB, Wageningen, The Netherlands.

In situ chemical oxidation (ISCO) followed by a bioremediation step is increasingly being considered as an effective biphasic technology. Information on the impact of chemical oxidants on organohalide respiring bacteria (OHRB), however, is largely lacking. Therefore, we used quantitative PCR (qPCR) to monitor the abundance of OHRB (Dehalococcoides mccartyi, Dehalobacter, Geobacter, and Desulfitobacterium) and reductive dehalogenase genes (rdh; tceA, vcrA, and bvcA) at a field location contaminated with chlorinated solvents prior to and following treatment with sodium persulfate. Natural attenuation of the contaminants tetrachloroethene (PCE) and trichloroethene (TCE) observed prior to ISCO was confirmed by the distribution of OHRB and rdh genes. In wells impacted by persulfate treatment, a 1 to 3 order of magnitude reduction in the abundances of OHRB and complete absence of rdh genes was observed 21 days after ISCO. Groundwater acidification (pH<3) and increase in the oxidation reduction potential (>500 mV) due to persulfate treatment were significant and contributed to disruption of the microbial community. In wells only mildly impacted by persulfate, a slight stimulation of the microbial community was observed, with more than 1 order of magnitude increase in the abundance of Geobacter and Desulfitobacterium 36 days after ISCO. After six months, regeneration of the OHRB community occurred, however, neither D. mccartyi nor any rdh genes were observed, indicating extended disruption of biological natural attenuation (NA) capacity following persulfate treatment. For full restoration of biological NA activity, additional time may prove sufficient; otherwise addition electron donor amendment or bioaugmentation may be required.
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http://dx.doi.org/10.1111/gwat.12209DOI Listing
January 2016

Kinetics of dechlorination by Dehalococcoides mccartyi using different carbon sources.

J Contam Hydrol 2014 Feb 8;157:25-36. Epub 2013 Nov 8.

Flemish Institute for Technological Research (VITO), Separation and Conversion Technology, Boeretang 200, 2400 Mol, Belgium. Electronic address:

Stimulated anaerobic dechlorination is generally considered a valuable step for the remediation of aquifers polluted with chlorinated ethenes (CEs). Correct simulation and prediction of this process in situ, however, require good knowledge of the associated biological reactions. The aim of this study was to evaluate the dechlorination reaction in an aquifer contaminated with trichloroethene (TCE) and its daughter products, discharging into the Zenne River. Different carbon sources were used in batch cultures and these were related to the dechlorination reaction, together with the monitored biomarkers. Appropriate kinetic formulations were assessed. Reductive dechlorination of TCE took place only when external carbon sources were added to microcosms, and occurred concomitant with a pronounced increase in the Dehalococcoides mccartyi cell count as determined by 16S rRNA gene-targeted qPCR. This indicates that native dechlorinating bacteria are present in the aquifer of the Zenne site and that the oligotrophic nature of the aquifer prevents a complete degradation to ethene. The type of carbon source, the cell number of D. mccartyi or the reductive dehalogenase genes, however, did not unequivocally explain the observed differences in degradation rates or the extent of dechlorination. Neither first-order, Michaelis-Menten nor Monod kinetics could perfectly simulate the dechlorination reactions in TCE spiked microcosms. A sensitivity analysis indicated that the inclusion of donor limitation would not significantly enhance the simulations without a clear process understanding. Results point to the role of the supporting microbial community but it remains to be verified how the complexity of the microbial (inter)actions should be represented in a model framework.
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http://dx.doi.org/10.1016/j.jconhyd.2013.10.006DOI Listing
February 2014

Evaluation of solid polymeric organic materials for use in bioreactive sediment capping to stimulate the degradation of chlorinated aliphatic hydrocarbons.

Appl Microbiol Biotechnol 2014 Mar 17;98(5):2255-66. Epub 2013 Aug 17.

Flemish Institute for Technological Research (VITO), Separation and Conversion Technology, Boeretang 200, 2400, Mol, Belgium.

In situ bioreactive capping is a promising technology for mitigation of surface water contamination by discharging polluted groundwater. Organohalide respiration (OHR) of chlorinated ethenes in bioreactive caps can be stimulated through incorporation of solid polymeric organic materials (SPOMs) that provide a sustainable electron source for organohalide respiring bacteria. In this study, wood chips, hay, straw, tree bark and shrimp waste, were assessed for their long term applicability as an electron donor for OHR of cis-dichloroethene (cDCE) and vinyl chloride (VC) in sediment microcosms. The initial release of fermentation products, such as acetate, propionate and butyrate led to the onset of extensive methane production especially in microcosms amended with shrimp waste, straw and hay, while no considerable stimulation of VC dechlorination was obtained in any of the SPOM amended microcosms. However, in the longer term, short chain fatty acids accumulation decreased as well as methanogenesis, whereas high dechlorination rates of VC and cDCE were established with concomitant increase of Dehalococcoides mccartyi and vcrA and bvcA gene numbers both in the sediment and on the SPOMs. A numeric simulation indicated that a capping layer of 40 cm with hay, straw, tree bark or shrimp waste is suffice to reduce the groundwater VC concentration below the threshold level of 5 μg/l before discharging into the Zenne River, Belgium. Of all SPOMs, the persistent colonization of tree bark by D. mccartyi combined with the lowest stimulation of methanogenesis singled out tree bark as a long-term electron donor for OHR of cDCE/VC in bioreactive caps.
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http://dx.doi.org/10.1007/s00253-013-5138-9DOI Listing
March 2014

Small-scale oxygen distribution determines the vinyl chloride biodegradation pathway in surficial sediments of riverbed hyporheic zones.

FEMS Microbiol Ecol 2013 Apr 13;84(1):133-42. Epub 2012 Dec 13.

Separation and Conversion Technology, Flemish Institute for Technological Research (VITO), Mol, Belgium.

Surficial riverbed sediments are often characterized by sharp redox gradients between the aerobic benthic sediment and underlying anoxic sediment, potentially representing an ideal niche for aerobic and anaerobic vinyl chloride (VC) degraders. To test this, the fate of VC in aerobic and anaerobic microcosms containing surficial sediment of a riverbed hyporheic zone receiving VC-contaminated groundwater was explored. Quantitative PCR showed that Dehalococcoides 16S rRNA gene and VC reductive dehalogenase-encoding genes (vcrA, bvcA) were highly enriched in anaerobic microcosms, with stoichiometric conversion of VC to ethene. In aerobic microcosms, etnC and etnE involved in aerobic ethene/VC oxidation were enriched with concomitant low or no accumulation of ethene. However, Dehalococcoides 16S rRNA gene, vcrA and bvcA copy numbers were also enriched in oxygen-exposed microcosms containing sediment with high organic carbon and small grain size, whereas they were reduced in oxygen-exposed sediment with low organic carbon and larger grain size in line with extensive oxygen penetration into the sediment. These results suggest the coexistence and coactivity of anaerobic and aerobic VC degraders in the same small volume of surficial sediment and that oxygen distribution, as determined by sediment grain size and organic matter content, affects the local VC-degrading bacterial community and VC biodegradation pathway.
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http://dx.doi.org/10.1111/1574-6941.12044DOI Listing
April 2013

Enhanced phenol degradation by Pseudomonas sp. SA01: gaining insight into the novel single and hybrid immobilizations.

J Hazard Mater 2010 Mar 9;175(1-3):284-92. Epub 2009 Oct 9.

National Institute of Genetic Engineering and Biotechnology (NIGEB), P.O. Box 14155-6343, Tehran, Iran.

In this work, Pseudomonas sp. SA01 cells were immobilized in a series of singular and hybrid immobilization techniques to achieve enhanced phenol removal. The singular immobilization strategies consisted of various concentrations of alginate (2-4%) and pectin (3-5%), while the hybrid strategies incorporated polyvinyl alcohol (PVA)-alginate and glycerol-alginate beads and alginate-chitosan-alginate (ACA) capsules. Immobilization protected cells against phenol and resulted in remarkable reduction (65%) in degradation time by cells immobilized in either alginate (3%) beads, in a hybrid PVA-alginate beads, or in ACA capsules compared to freely suspended cells. Cells immobilized in PVA-alginate and ACA provided the best performance in experiments using elevated phenol concentrations, up to 2000 mg/L, with complete degradation of 2000 mg/L phenol after 100 and 110 h, respectively. Electron microscopy examination indicated that cell loading capacity was increased in PVA-alginate hybrid beads through reduced cell leakage, resulting in higher activity of PVA-alginate hybrid beads compared to all other immobilization methods.
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http://dx.doi.org/10.1016/j.jhazmat.2009.10.002DOI Listing
March 2010