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Qiao W, Liu G, Li M, Su X, Lu L, Ye S, Wu J, Edwards EA, Jiang J. Complete Reductive Dechlorination of 4-Hydroxy-chlorothalonil by Dehalogenimonas Populations. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:12237-12246. [PMID: 35951369 DOI: 10.1021/acs.est.2c02574] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile, TePN) is one of the most widely used fungicides all over the world. Its major environmental transformation product 4-hydroxy-chlorothalonil (4-hydroxy-2,5,6-trichloroisophthalonitrile, 4-OH-TPN) is more persistent, mobile, and toxic and is frequently detected at a higher concentration in various habitats compared to its parent compound TePN. Further microbial transformation of 4-OH-TPN has never been reported. In this study, we demonstrated that 4-OH-TPN underwent complete microbial reductive dehalogenation to 4-hydroxy-isophthalonitrile via 4-hydroxy-dichloroisophthalonitrile and 4-hydroxy-monochloroisophthalonitrile. 16S rRNA gene amplicon sequencing demonstrated that Dehalogenimonas species was enriched from 6% to 17-22% after reductive dechlorination of 77.24 μmol of 4-OH-TPN. Meanwhile, Dehalogenimonas copies increased by one order of magnitude and obtained a yield of 1.78 ± 1.47 × 108 cells per μmol Cl- released (N = 6), indicating that 4-OH-TPN served as the terminal electron acceptor for organohalide respiration of Dehalogenimonas species. A draft genome of Dehalogenimonas species was assembled through metagenomic sequencing, which harbors 30 putative reductive dehalogenase genes. Syntrophobacter, Acetobacterium, and Methanosarcina spp. were found to be the major non-dechlorinating populations in the microbial community, who might play important roles in the reductive dechlorination of 4-OH-TPN by the Dehalogenimonas species. This study first reports that Dehalogenimonas sp. can also respire on the seemingly dead-end product of TePN, paving the way to complete biotransformation of the widely present TePN and broadening the substrate spectrum of Dehalogenimonas sp. to polychlorinated hydroxy-benzonitrile.
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Affiliation(s)
- Wenjing Qiao
- Department of Microbiology, Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Guiping Liu
- Department of Microbiology, Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Mengya Li
- Department of Microbiology, Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Xiaojing Su
- Department of Microbiology, Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
| | - Lianghua Lu
- Jiangsu Provincial Academy of Environmental Science, Jiangsu Provincial Key Laboratory of Environmental Engineering, Nanjing 210036, China
| | - Shujun Ye
- Key Laboratory of Surficial Geochemistry, Ministry of Education, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
| | - Jichun Wu
- Key Laboratory of Surficial Geochemistry, Ministry of Education, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
| | - Elizabeth A Edwards
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto M5S 3E5, Canada
| | - Jiandong Jiang
- Department of Microbiology, Key Laboratory of Agricultural and Environmental Microbiology, Ministry of Agriculture and Rural Affairs, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
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2
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Pourrajab F, Zare-Khormizi MR. Extrachromosomal circular DNAs (eccDNAs), Amplified Oncogenes, and CRISPR-Cas9 System. Mol Pharmacol 2022; 102:209-215. [PMID: 35940609 DOI: 10.1124/molpharm.122.000553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 07/19/2022] [Indexed: 11/22/2022] Open
Abstract
Structurally rearranged extrachromosomal circular DNAs (eccDNAs) have been identified in tumor cells, many of which carrying regions related to cancer-driver recurrent oncogenes (e.g. CCND1, EGFR and MYC) In a tumor cell, eccDNAs are carrying regions associated with oncogene amplification (>10-fold amplified-copy numbers in human tumors) and poor outcome across multiple cancers. Even though dual-delivery of pairs of CRISPR/Cas9 guide RNAs into human normal cells was reported to induce circularization of genes and chromosomes, but in bacteria, CRISPR-Cas9 system primarily targets extrachromosomal rearranged elements. Likewise, in cancer cells, it is expected that a designed CRISPR-Cas9 system is able to target extrachromosomal copy-number amplifications and produces double strand breaks to be detrimental to cellular fitness through dictating gene-independent copy-number loss-of-fitness (LOF) effects and anti-proliferative responses. A designed system against amplified amplicons may provide a novel approach for cancer therapy and propose a practical implication for CRISPR-Cas9 as a path in therapeutic strategies of cancer. Significance Statement Structurally rearranged extrachromosomal circular DNAs (eccDNAs) have been identified in tumor cells. Many of eccDNAs are carrying regions related to cancer-driver recurrent oncogenes (e.g. CCND1, EGFR and MYC) It is expected that a designed CRISPR-Cas9 system is able to target extrachromosomal recurrent oncogenes.
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Affiliation(s)
- Fatemeh Pourrajab
- Yazd Cardiovascular Research Center, Shahid S, Yazd Cardiovascular Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran, Iran, Islamic Republic of
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Morson N, Molenda O, Picott KJ, Richardson RE, Edwards EA. Long-term survival of Dehalococcoides mccartyi strains in mixed cultures under electron acceptor and ammonium limitation. FEMS MICROBES 2022; 3:xtac021. [PMID: 37332513 PMCID: PMC10117805 DOI: 10.1093/femsmc/xtac021] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Revised: 06/11/2022] [Accepted: 07/06/2022] [Indexed: 11/06/2023] Open
Abstract
Few strains of Dehalococcoides mccartyi harbour and express the vinyl chloride reductase (VcrA) that catalyzes the dechlorination of vinyl chloride (VC), a carcinogenic soil and groundwater contaminant. The vcrA operon is found on a Genomic Island (GI) and, therefore, believed to participate in horizontal gene transfer (HGT). To try to induce HGT of the vcrA-GI, we blended two enrichment cultures in medium without ammonium while providing VC. We hypothesized that these conditions would select for a mutant strain of D. mccartyi that could both fix nitrogen and respire VC. However, after more than 4 years of incubation, we found no evidence for HGT of the vcrA-GI. Rather, we observed VC-dechlorinating activity attributed to the trichloroethene reductase TceA. Sequencing and protein modelling revealed a mutation in the predicted active site of TceA, which may have influenced substrate specificity. We also identified two nitrogen-fixing D. mccartyi strains in the KB-1 culture. The presence of multiple strains of D. mccartyi with distinct phenotypes is a feature of natural environments and certain enrichment cultures (such as KB-1), and may enhance bioaugmentation success. The fact that multiple distinct strains persist in the culture for decades and that we could not induce HGT of the vcrA-GI suggests that it is not as mobile as predicted, or that mobility is restricted in ways yet to be discovered to specific subclades of Dehalococcoides.
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Affiliation(s)
- Nadia Morson
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord St, Toronto, ON M5S 3G5, Canada
| | - Olivia Molenda
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada
| | - Katherine J Picott
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada
| | - Ruth E Richardson
- School of Civil and Environmental Engineering, Cornell University, 220 Hollister Dr, Ithaca, NY, Ithaca, NY, United States
| | - Elizabeth A Edwards
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord St, Toronto, ON M5S 3G5, Canada
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada
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Ewald JM, Schnoor JL, Mattes TE. Combined read- and assembly-based metagenomics to reconstruct a Dehalococcoides mccartyi genome from PCB-contaminated sediments and evaluate functional differences among organohalide-respiring consortia in the presence of different halogenated contaminants. FEMS Microbiol Ecol 2022; 98:6602352. [PMID: 35665806 DOI: 10.1093/femsec/fiac067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 04/27/2022] [Accepted: 05/31/2022] [Indexed: 11/12/2022] Open
Abstract
Microbial communities that support respiration of halogenated organic contaminants by Dehalococcoides sp. facilitate full-scale bioremediation of chlorinated ethenes and demonstrate the potential to aid in bioremediation of halogenated aromatics like polychlorinated biphenyls (PCBs). However, it remains unclear if Dehalococcoides-containing microbial community dynamics observed in sediment-free systems quantitatively resemble that of sediment environments. To evaluate that possibility we assembled, annotated, and analyzed a Dehalococcoides sp. metagenome-assembled genome (MAG) from PCB-contaminated sediments. Phylogenetic analysis of reductive dehalogenase gene (rdhA) sequences within the MAG revealed that pcbA1 and pcbA4/5-like rdhA were absent, while several candidate PCB dehalogenase genes and potentially novel rdhA sequences were identified. Using a compositional comparative metagenomics approach, we quantified Dehalococcoides-containing microbial community structure shifts in response to halogenated organics and the presence of sediments. Functional level analysis revealed significantly greater abundances of genes associated with cobamide remodeling and horizontal gene transfer in tetrachloroethene-fed cultures as compared to halogenated aromatic-exposed consortia with or without sediments, despite little evidence of statistically significant differences in microbial community taxonomic structure. Our findings support the use of a generalizable comparative metagenomics workflow to evaluate Dehalococcoides-containing consortia in sediments and sediment-free environments to eludicate functions and microbial interactions that facilitate bioremediation of halogenated organic contaminants.
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Affiliation(s)
- Jessica M Ewald
- Department of Civil and Environmental Engineering, 4105 Seamans Center, University of Iowa, Iowa City, IA, 52242, USA
| | - Jerald L Schnoor
- Department of Civil and Environmental Engineering, 4105 Seamans Center, University of Iowa, Iowa City, IA, 52242, USA
| | - Timothy E Mattes
- Department of Civil and Environmental Engineering, 4105 Seamans Center, University of Iowa, Iowa City, IA, 52242, USA
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Differentiating closely affiliated Dehalococcoides lineages by a novel genetic marker identified via computational pangenome analysis. Appl Environ Microbiol 2021; 88:e0218121. [PMID: 34910572 DOI: 10.1128/aem.02181-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
As a group, Dehalococcoides dehalogenate a wide range of organohalide pollutants but the range of organohalide compounds that can be utilized for reductive dehalogenation differs among the Dehalococcoides strains. Dehalococcoides lineages cannot be reliably disambiguated in mixed communities using typical phylogenetic markers, which often confounds bioremediation efforts. Here, we describe a computational approach to identify Dehalococcoides genetic markers with improved discriminatory resolution. Screening core genes from the Dehalococcoides pangenome for degree of similarity and frequency of 100% identity found a candidate genetic marker encoding a bacterial neuraminidase repeat (BNR)-containing protein of unknown function. This gene exhibits the fewest completely identical amino acid sequences and among the lowest average amino acid sequence identity in the core pangenome. Primers targeting BNR could effectively discriminate between 40 available BNR sequences (in silico) and 10 different Dehalococcoides isolates (in vitro). Amplicon sequencing of BNR fragments generated from 22 subsurface soil samples revealed a total of 109 amplicon sequence variants, suggesting a high diversity of Dehalococcoides distributed in environment. Therefore, the BNR gene can serve as an alternative genetic marker to differentiate strains of Dehalococcoides in complicated microbial communities. Importance The challenge of discriminating between phylogenetically similar but functionally distinct bacterial lineages is particularly relevant to the development of technologies seeking to exploit the metabolic or physiological characteristics of specific members of bacterial genera. A computational approach was developed to expedite screening of potential genetic markers among phylogenetically affiliated bacteria. Using this approach, a gene encoding a bacterial neuraminidase repeat (BNR)-containing protein of unknown function was selected and evaluated as a genetic marker to differentiate strains of Dehalococcoides, an environmentally relevant genus of bacteria whose members can transform and detoxify a range of halogenated organic solvents and persistent organic pollutants, in complex microbial communities to demonstrate the validity of the approach. Moreover, many apparently phylogenetically distinct, currently uncharacterized Dehalococcoides were detected in environmental samples derived from contaminated sites.
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6
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Matturro B, Zeppilli M, Lai A, Majone M, Rossetti S. Metagenomic Analysis Reveals Microbial Interactions at the Biocathode of a Bioelectrochemical System Capable of Simultaneous Trichloroethylene and Cr(VI) Reduction. Front Microbiol 2021; 12:747670. [PMID: 34659183 PMCID: PMC8516407 DOI: 10.3389/fmicb.2021.747670] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 09/09/2021] [Indexed: 01/04/2023] Open
Abstract
Bioelectrochemical systems (BES) are attractive and versatile options for the bioremediation of organic or inorganic pollutants, including trichloroethylene (TCE) and Cr(VI), often found as co-contaminants in the environment. The elucidation of the microbial players' role in the bioelectroremediation processes for treating multicontaminated groundwater is still a research need that attracts scientific interest. In this study, 16S rRNA gene amplicon sequencing and whole shotgun metagenomics revealed the leading microbial players and the primary metabolic interactions occurring in the biofilm growing at the biocathode where TCE reductive dechlorination (RD), hydrogenotrophic methanogenesis, and Cr(VI) reduction occurred. The presence of Cr(VI) did not negatively affect the TCE degradation, as evidenced by the RD rates estimated during the reactor operation with TCE (111±2 μeq/Ld) and TCE/Cr(VI) (146±2 μeq/Ld). Accordingly, Dehalococcoides mccartyi, the primary biomarker of the RD process, was found on the biocathode treating both TCE (7.82E+04±2.9E+04 16S rRNA gene copies g-1 graphite) and TCE/Cr(VI) (3.2E+07±2.37E+0716S rRNA gene copies g-1 graphite) contamination. The metagenomic analysis revealed a selected microbial consortium on the TCE/Cr(VI) biocathode. D. mccartyi was the sole dechlorinating microbe with H2 uptake as the only electron supply mechanism, suggesting that electroactivity is not a property of this microorganism. Methanobrevibacter arboriphilus and Methanobacterium formicicum also colonized the biocathode as H2 consumers for the CH4 production and cofactor suppliers for D. mccartyi cobalamin biosynthesis. Interestingly, M. formicicum also harbors gene complexes involved in the Cr(VI) reduction through extracellular and intracellular mechanisms.
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Affiliation(s)
| | - Marco Zeppilli
- Department of Chemistry, Sapienza University of Rome, Rome, Italy
| | - Agnese Lai
- Department of Chemistry, Sapienza University of Rome, Rome, Italy
| | - Mauro Majone
- Department of Chemistry, Sapienza University of Rome, Rome, Italy
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Maucourt B, Vuilleumier S, Bringel F. Transcriptional regulation of organohalide pollutant utilisation in bacteria. FEMS Microbiol Rev 2020; 44:189-207. [PMID: 32011697 DOI: 10.1093/femsre/fuaa002] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 01/31/2020] [Indexed: 12/13/2022] Open
Abstract
Organohalides are organic molecules formed biotically and abiotically, both naturally and through industrial production. They are usually toxic and represent a health risk for living organisms, including humans. Bacteria capable of degrading organohalides for growth express dehalogenase genes encoding enzymes that cleave carbon-halogen bonds. Such bacteria are of potential high interest for bioremediation of contaminated sites. Dehalogenase genes are often part of gene clusters that may include regulators, accessory genes and genes for transporters and other enzymes of organohalide degradation pathways. Organohalides and their degradation products affect the activity of regulatory factors, and extensive genome-wide modulation of gene expression helps dehalogenating bacteria to cope with stresses associated with dehalogenation, such as intracellular increase of halides, dehalogenase-dependent acid production, organohalide toxicity and misrouting and bottlenecks in metabolic fluxes. This review focuses on transcriptional regulation of gene clusters for dehalogenation in bacteria, as studied in laboratory experiments and in situ. The diversity in gene content, organization and regulation of such gene clusters is highlighted for representative organohalide-degrading bacteria. Selected examples illustrate a key, overlooked role of regulatory processes, often strain-specific, for efficient dehalogenation and productive growth in presence of organohalides.
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Affiliation(s)
- Bruno Maucourt
- Université de Strasbourg, UMR 7156 CNRS, Génétique Moléculaire, Génomique, Microbiologie, Strasbourg, France
| | - Stéphane Vuilleumier
- Université de Strasbourg, UMR 7156 CNRS, Génétique Moléculaire, Génomique, Microbiologie, Strasbourg, France
| | - Françoise Bringel
- Université de Strasbourg, UMR 7156 CNRS, Génétique Moléculaire, Génomique, Microbiologie, Strasbourg, France
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Esken J, Goris T, Gadkari J, Bischler T, Förstner KU, Sharma CM, Diekert G, Schubert T. Tetrachloroethene respiration in Sulfurospirillum species is regulated by a two-component system as unraveled by comparative genomics, transcriptomics, and regulator binding studies. Microbiologyopen 2020; 9:e1138. [PMID: 33242236 PMCID: PMC7755780 DOI: 10.1002/mbo3.1138] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Revised: 10/20/2020] [Accepted: 10/21/2020] [Indexed: 12/23/2022] Open
Abstract
Energy conservation via organohalide respiration (OHR) in dehalogenating Sulfurospirillum species is an inducible process. However, the gene products involved in tetrachloroethene (PCE) sensing and signal transduction have not been unambiguously identified. Here, genome sequencing of Sulfurospirillum strains defective in PCE respiration and comparative genomics, which included the PCE-respiring representatives of the genus, uncovered the genetic inactivation of a two-component system (TCS) in the OHR gene region of the natural mutants. The assumption that the TCS gene products serve as a PCE sensor that initiates gene transcription was supported by the constitutive low-level expression of the TCS operon in fumarate-adapted cells of Sulfurospirillum multivorans. Via RNA sequencing, eight transcriptional units were identified in the OHR gene region, which includes the TCS operon, the PCE reductive dehalogenase operon, the gene cluster for norcobamide biosynthesis, and putative accessory genes with unknown functions. The OmpR-family response regulator (RR) encoded in the TCS operon was functionally characterized by promoter-binding assays. The RR bound a cis-regulatory element that contained a consensus sequence of a direct repeat (CTATW) separated by 17 bp. Its location either overlapping the -35 box or 50 bp further upstream indicated different regulatory mechanisms. Sequence variations in the regulator binding sites identified in the OHR gene region were in accordance with differences in the transcript levels of the respective gene clusters forming the PCE regulon. The results indicate the presence of a fine-tuned regulatory network controlling PCE metabolism in dehalogenating Sulfurospirillum species, a group of metabolically versatile organohalide-respiring bacteria.
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Affiliation(s)
- Jens Esken
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Jena, Germany.,Leibniz Institute for Natural Product Research and Infection Biology - Hans Knöll Institute, Jena, Germany
| | - Tobias Goris
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Jena, Germany
| | - Jennifer Gadkari
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Jena, Germany
| | - Thorsten Bischler
- Core Unit Systems Medicine, University of Würzburg, Würzburg, Germany
| | - Konrad U Förstner
- ZB MED - Information Center for Life Sciences, Cologne, Germany.,TH Köln - University of Applied Sciences, Institute of Information Science, Cologne, Germany
| | - Cynthia M Sharma
- Core Unit Systems Medicine, University of Würzburg, Würzburg, Germany
| | - Gabriele Diekert
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Jena, Germany
| | - Torsten Schubert
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Jena, Germany.,Research Group Anaerobic Microbiology, Institute of Microbiology, Friedrich Schiller University, Jena, Germany
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Lin WH, Chen CC, Sheu YT, Tsang DCW, Lo KH, Kao CM. Growth inhibition of sulfate-reducing bacteria for trichloroethylene dechlorination enhancement. ENVIRONMENTAL RESEARCH 2020; 187:109629. [PMID: 32460090 DOI: 10.1016/j.envres.2020.109629] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 04/26/2020] [Accepted: 05/03/2020] [Indexed: 06/11/2023]
Abstract
Trichloroethylene (TCE) is a frequently found organic contaminant in polluted-groundwater. In this microcosm study, effects of hydrogen-producing bacteria [Clostridium butyricum (Clostridium sp.)] and inhibitor of sulfate-reducing bacteria (SRB) addition on the enhancement of TCE dechlorination were evaluated. Results indicate that Clostridium sp. supplement could effectively enhance TCE reductive dechlorination (97.4% of TCE removal) due to increased hydrogen concentration and Dehalococcoides (DHC) populations (increased to 1 × 104 gene copies/L). However, addition of Clostridium sp. also caused the increase in dsrA (dissimilatory sulfide reductase subunit A) (increased to 2 × 108 gene copies/L), and thus, part of the hydrogen was consumed by SRB, which would limit the effective application of hydrogen by DHC. Control of Clostridium sp. addition is a necessity to minimize the adverse impact of Clostridium sp. on DHC growth. Ferric citrate caused the slight raise of the oxidation-reduction state, which resulted in growth inhibition of SRB. Molybdate addition inhibited the growth of SRB, and thus, the dsrA concentrations (dropped from 4 × 107 to 9 × 105 gene copies/L) and sulfate reduction efficiency were decreased. Increased DHC populations (increased from 8 × 103 to 1 × 105 gene copies/L) were due to increased available hydrogen (increased from 0 to 2 mg/L), which enhanced TCE dechlorination (99.3% TCE removal). Metagenomic analyses show that a significant microbial diversity was detected in microcosms with different treatments. Clostridium sp., ferric citrate, and molybdate addition caused a decreased SRB communities and increased fatty acid production microbial communities (increased from 4.9% to 20.2%), which would be beneficial to the hydrogen production and TCE dechlorination processes.
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Affiliation(s)
- Wei-Han Lin
- Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan
| | - Chien-Cheng Chen
- Department of Biotechnology, National Kaohsiung Normal University, Kaohsiung, Taiwan
| | - Yih-Terng Sheu
- Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan
| | - Daniel C W Tsang
- Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
| | - Kai-Hung Lo
- Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan
| | - Chih-Ming Kao
- Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan.
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Abstract
The class Dehalococcoidia within the Chloroflexi phylum comprises the obligate organohalide-respiring genera Dehalococcoides, Dehalogenimonas, and “Candidatus Dehalobium.” Knowledge of the unique ecophysiology and biochemistry of Dehalococcoidia has been largely derived from studies with enrichment cultures and isolates from sites impacted with chlorinated pollutants; however, culture-independent surveys found Dehalococcoidia sequences in marine, freshwater, and terrestrial biomes considered to be pristine (i. The class Dehalococcoidia within the Chloroflexi phylum comprises the obligate organohalide-respiring genera Dehalococcoides, Dehalogenimonas, and “Candidatus Dehalobium.” Knowledge of the unique ecophysiology and biochemistry of Dehalococcoidia has been largely derived from studies with enrichment cultures and isolates from sites impacted with chlorinated pollutants; however, culture-independent surveys found Dehalococcoidia sequences in marine, freshwater, and terrestrial biomes considered to be pristine (i.e., not impacted with organohalogens of anthropogenic origin). The broad environmental distribution of Dehalococcoidia, as well as other organohalide-respiring bacteria, supports the concept of active halogen cycling and the natural formation of organohalogens in various ecosystems. Dechlorination reduces recalcitrance and renders organics susceptible to metabolic oxidation by diverse microbial taxa. During reductive dechlorination, hydrogenotrophic organohalide-respiring bacteria, in particular Dehalococcoidia, can consume hydrogen to low consumption threshold concentrations (<0.3 nM) and enable syntrophic oxidation processes. These functional attributes and the broad distribution imply that Dehalococcoidia play relevant roles in carbon cycling in anoxic ecosystems.
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11
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Ewald JM, Humes SV, Martinez A, Schnoor JL, Mattes TE. Growth of Dehalococcoides spp. and increased abundance of reductive dehalogenase genes in anaerobic PCB-contaminated sediment microcosms. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2020; 27:8846-8858. [PMID: 31209752 PMCID: PMC6918016 DOI: 10.1007/s11356-019-05571-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 05/24/2019] [Indexed: 06/09/2023]
Abstract
Polychlorinated biphenyls (PCBs) contaminate 19% of US Superfund sites and represent a serious risk to human and environmental health. One promising strategy to remediate PCB-contaminated sediments utilizes organohalide-respiring bacteria (OHRB) that dechlorinate PCBs.However, functional genes that act as biomarkers for PCB dechlorination processes (i.e., reductive dehalogenase genes) are poorly understood. Here, we developed anaerobic sediment microcosms that harbor an OHRB community dominated by the genus Dehalococcoides. During the 430-day microcosm incubation, Dehalococcoides 16S rRNA sequences increased two orders of magnitude to 107 copies/g of sediment, and at the same time, PCB118 decreased by as much as 70%. In addition, the OHRB community dechlorinated a range of penta- and tetra-chlorinated PCB congeners including PCBs 66, 70 + 74 + 76, 95, 90 + 101, and PCB110 without exogenous electron donor. We quantified candidate reductive dehalogenase (RDase) genes over a 430-day incubation period and found rd14, a reductive dehalogenase that belongs to Dehalococcoides mccartyi strain CG5, was enriched to 107 copies/g of sediment. At the same time, pcbA5 was enriched to only 105 copies/g of sediment. A survey for additional RDase genes revealed sequences similar to strain CG5's rd4 and rd8. In addition to demonstrating the PCB dechlorination potential of native microbial communities in contaminated freshwater sediments, our results suggest candidate functional genes with previously unexplored potential could serve as biomarkers of PCB dechlorination processes.
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Affiliation(s)
- Jessica M Ewald
- Department of Civil and Environmental Engineering, IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA, 52242, USA
| | - Shelby V Humes
- Department of Civil and Environmental Engineering, IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA, 52242, USA
| | - Andres Martinez
- Department of Civil and Environmental Engineering, IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA, 52242, USA
| | - Jerald L Schnoor
- Department of Civil and Environmental Engineering, IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA, 52242, USA
| | - Timothy E Mattes
- Department of Civil and Environmental Engineering, IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA, 52242, USA.
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Molenda O, Puentes Jácome LA, Cao X, Nesbø CL, Tang S, Morson N, Patron J, Lomheim L, Wishart DS, Edwards EA. Insights into origins and function of the unexplored majority of the reductive dehalogenase gene family as a result of genome assembly and ortholog group classification. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2020; 22:663-678. [PMID: 32159535 DOI: 10.1039/c9em00605b] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Organohalide respiring bacteria (OHRB) express reductive dehalogenases for energy conservation and growth. Some of these enzymes catalyze the reductive dehalogenation of chlorinated and brominated pollutants in anaerobic subsurface environments, providing a valuable ecosystem service. Dehalococcoides mccartyi strains have been most extensively studied owing to their ability to dechlorinate all chlorinated ethenes - most notably carcinogenic vinyl chloride - to ethene. The genomes of OHRB, particularly obligate OHRB, often harbour multiple putative reductive dehalogenase genes (rdhA), most of which have yet to be characterized. We recently sequenced and closed the genomes of eight new strains, increasing the number of available D. mccartyi genomes in NCBI from 16 to 24. From all available OHRB genomes, we classified predicted translations of reductive dehalogenase genes using a previously established 90% amino acid pairwise identity cut-off to identify Ortholog Groups (OGs). Interestingly, the majority of D. mccartyi dehalogenase gene sequences, once classified into OGs, exhibited a remarkable degree of synteny (gene order) in all genomes sequenced to date. This organization was not apparent without the classification. A high degree of synteny indicates that differences arose from rdhA gene loss rather than recombination. Phylogenetic analysis suggests that most rdhA genes have a long evolutionary history in the Dehalococcoidia with origin prior to speciation of Dehalococcoides and Dehalogenimonas. We also looked for evidence of synteny in the genomes of other species of OHRB. Unfortunately, there are too few closed Dehalogenimonas genomes to compare at this time. There is some partial evidence for synteny in the Dehalobacter restrictus genomes, but here too more closed genomes are needed for confirmation. Interestingly, we found that the rdhA genes that encode enzymes that catalyze dehalogenation of industrial pollutants are the only rdhA genes with strong evidence of recent lateral transfer - at least in the genomes examined herein. Given the utility of the RdhA sequence classification to comparative analyses, we are building a public web server () for the community to use, which allows users to add and classify new sequences, and download the entire curated database of reductive dehalogenases.
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Affiliation(s)
- Olivia Molenda
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Ontario, Canada.
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Puentes Jácome LA, Wang PH, Molenda O, Li YXJJ, Islam MA, Edwards EA. Sustained Dechlorination of Vinyl Chloride to Ethene in Dehalococcoides-Enriched Cultures Grown without Addition of Exogenous Vitamins and at Low pH. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:11364-11374. [PMID: 31441646 DOI: 10.1021/acs.est.9b02339] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Trichloroethene (TCE) bioremediation has been demonstrated at field sites using microbial cultures harboring TCE-respiring Dehalococcoides whose growth is cobalamin (vitamin B12)-dependent. Bioaugmentation cultures grown ex situ with ample exogenous vitamins and at neutral pH may become vitamin-limited or inhibited by acidic pH once injected into field sites, resulting in incomplete TCE dechlorination and accumulation of vinyl chloride (VC). Here, we report growth of the Dehalococcoides-containing bioaugmentation culture KB-1 in a TCE-amended mineral medium devoid of vitamins and in a VC-amended mineral medium at low pH (6.0 and 5.5). In these cultures, Acetobacterium, which can synthesize 5,6-dimethylbenzimidazole (DMB), the lower ligand of cobalamin, and Sporomusa are dominant acetogens. At neutral pH, Acetobacterium supports complete TCE dechlorination by Dehalococcoides at millimolar levels with a substantial increase in cobalamin (∼20-fold). Sustained dechlorination of VC to ethene was achieved at pH as low as 5.5. Below pH 5.0, dechlorination was not stimulated by DMB supplementation but was restored by raising pH to neutral. Cell-extract assays revealed that vinyl chloride reductase activity declines significantly below pH 6.0 and is undetectable below pH 5.0. This study highlights the importance of cobamide-producing populations and pH in microbial dechlorinating communities for successful bioremediation at field sites.
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Affiliation(s)
- Luz A Puentes Jácome
- Department of Chemical Engineering and Applied Chemistry , University of Toronto , Toronto , Ontario M5S 3E5 , Canada
| | - Po-Hsiang Wang
- Department of Chemical Engineering and Applied Chemistry , University of Toronto , Toronto , Ontario M5S 3E5 , Canada
| | - Olivia Molenda
- Department of Chemical Engineering and Applied Chemistry , University of Toronto , Toronto , Ontario M5S 3E5 , Canada
| | - Yi Xuan Jine-Jine Li
- Department of Chemical Engineering and Applied Chemistry , University of Toronto , Toronto , Ontario M5S 3E5 , Canada
| | - M Ahsanul Islam
- Department of Chemical Engineering and Applied Chemistry , University of Toronto , Toronto , Ontario M5S 3E5 , Canada
| | - Elizabeth A Edwards
- Department of Chemical Engineering and Applied Chemistry , University of Toronto , Toronto , Ontario M5S 3E5 , Canada
- Department of Cell and Systems Biology , University of Toronto , Toronto , Ontario M5S 3G5 , Canada
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