1
|
Hu J, Zhang Y, Wu Y, Zheng J, Yu Z, Qian H, Yu J, Cheng Z, Chen J. Heterologous expression of bacterial cytochrome P450 from Microbacterium keratanolyticum ZY and its application in dichloromethane dechlorination. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2021; 287:117597. [PMID: 34167002 DOI: 10.1016/j.envpol.2021.117597] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 05/20/2021] [Accepted: 06/12/2021] [Indexed: 06/13/2023]
Abstract
Dichloromethane (DCM) is a volatile halogenated hydrocarbon with teratogenic, mutagenic and carcinogenic effects. Biodegradation is generally regarded as an effective and economical approach of pollutant disposal. In this study, a novel strain was isolated and its cytochrome P450 was heterologously expressed for DCM degradation. The isolate, Microbacterium keratanolyticum ZY, was characterized as a Gram-positive, rod-shaped and flagella-existed bacterium without spores (GenBank No. SUB8814364; CCTCC M 2019953). After successive whole-genome sequencing, assembly and annotation, eight identified functional genes (encoding cytochrome P450, monooxygenase, dehalogenase and hydrolase) were successfully cloned and expressed in Escherichia coli BL21 (DE3). The recombinant strain expressing cytochrome P450 presented the highest degradation efficiency (90.6%). Moreover, the specific activity of the recombinant cytochrome P450 was more than 1.2 times that of the recombinant dehalogenase (from Methylobacterium rhodesianum H13) under their optimum conditions. The kinetics of DCM degradation by recombinant cytochrome P450 was well fitted with the Haldane model and the value of maximum specific degradation rate was determined to be 0.7 s-1. The DCM degradation might occur through successive hydroxylation, dehydrohalogenation, dechlorination and oxidation to generate gem-halohydrin, formyl chloride, formaldehyde and formic acid. The study helps to comprehensively understand the DCM dechlorination process under the actions of bacterial functional enzymes (cytochrome P450 and dehalogenase).
Collapse
Affiliation(s)
- Jun Hu
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| | - Yan Zhang
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| | - Yuexin Wu
- Zhejiang Haihe Environmental Technology Co., Ltd., 1389 Danxi Road, Jinhua, 321000, China
| | - Jiajun Zheng
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| | - Zhiliang Yu
- College of Biotechnology and Bioengineering, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| | - Haifeng Qian
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| | - Jianming Yu
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China.
| | - Zhuowei Cheng
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| | - Jianmeng Chen
- College of Environment, Zhejiang University of Technology, 18 Chao-wang Road, Hangzhou, 310014, China
| |
Collapse
|
2
|
Liang Z, Li G, Xiong J, Mai B, An T. Purification, molecular characterization and metabolic mechanism of an aerobic tetrabromobisphenol A dehalogenase, a key enzyme of halorespiration in Ochrobactrum sp. T. CHEMOSPHERE 2019; 237:124461. [PMID: 31374395 DOI: 10.1016/j.chemosphere.2019.124461] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 07/17/2019] [Accepted: 07/25/2019] [Indexed: 06/10/2023]
Abstract
Due to the detoxification of tetrabromobisphenol A (TBBPA) varies from different bacterial strains and depends on their specific enzymatic machinery, it is necessary to understand them for potential in situ bioremediation application. The special ability of our previously isolated Ochrobactrum sp. T to simultaneously debrominate and aerobic mineralize TBBPA urgent us to continuously study its degradation molecular mechanism. Herein, the purification and characterization of the dehalogenase which can debrominate TBBPA was investigated based on its corresponding encoding gene tbbpaA. Results showed that an enzyme with molecular mass of 117 kDa, Km of 26.6 μM and Vmax of 0.133 μM min-1 mg-1 was purified and designated as bromophenol dehalogenase. It was the only detected dehalogenase which exhibited TBBPA degradation ability (78%). Moreover, its activity was significantly enhanced by adding NADPH or methyl viologen to the reaction solution. The high similarity of substrate spectrum between the dehalogenase from the recombinant strain and the wild strain further indicated that it was the main dehalogenase responsible for the debromination in wild strain. Based on three identified metabolites, a metabolic pathway of TBBPA by purified enzyme under oxic condition was proposed. This study provides an excellent dehalogenase candidate for mechanistic study of aerobic dehalogenation of brominated aromatic compound.
Collapse
Affiliation(s)
- Zhishu Liang
- Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China; State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Guiying Li
- Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China.
| | - Jukun Xiong
- Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China
| | - Bixian Mai
- State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Taicheng An
- Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China
| |
Collapse
|
3
|
Chen L, Krol ES, Sakharkar MK, Khan HA, Alhomida AS, Yang J. Residues His172 and Lys238 are Essential for the Catalytic Activity of the Maleylacetate Reductase from Sphingobium chlorophenolicum Strain L-1. Sci Rep 2017; 7:18097. [PMID: 29273747 PMCID: PMC5741723 DOI: 10.1038/s41598-017-18475-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 12/12/2017] [Indexed: 02/08/2023] Open
Abstract
Maleylacetate reductase (PcpE), the last enzyme in the pentachlorophenol biodegradation pathway in Sphingobium chlorophenolicum L-1, catalyzes two consecutive reductive reactions, reductive dehalogenation of 2-chloromaleylacetate (2-CMA) to maleylacetate (MA) and subsequent reduction of MA to 3-oxoadipate (3-OXO). In each reaction, one molecule of NADH is consumed. To better understand its catalytic function, we undertook a structural model-based site-directed mutagenesis and steady-state kinetics study of PcpE. Our results showed that the putative catalytic site of PcpE is located in a positively charged solvent channel at the interface of the two domains and the binding of 2-CMA/MA involves seven basic amino acids, His172, His236, His237, His241 and His251, Lys140 and Lys238. Mutagenesis studies showed that His172 and Lys238 are essential for the catalytic activity of PcpE. However, the mutation of His236 to an alanine can increase the catalytic efficiency (k cat /K m ) of PcpE by more than 2-fold, implying that PcpE is still in an early stage of molecular evolution. Similar to tetrachlorobenzoquinone reductase (PcpD), PcpE is also inhibited by pentachlorophenol in a concentration-dependent manner. Furthermore, our studies showed that PcpE exhibits an extremely low but detectable level of alcohol dehalogenase activity toward ethanol and supports the notion that it is evolved from an iron-containing alcohol dehydrogenase.
Collapse
Affiliation(s)
- Lifeng Chen
- College of Pharmacy and Nutrition, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada
- Agrisoma Biosciences Inc., 4410-110 Gymnasium Place, Saskatoon, SK S7N 0W9, Canada
| | - Ed S Krol
- College of Pharmacy and Nutrition, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada
| | - Meena K Sakharkar
- College of Pharmacy and Nutrition, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada
| | - Haseeb A Khan
- Department of Biochemistry, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Abdullah S Alhomida
- Department of Biochemistry, College of Science, King Saud University, Riyadh, Saudi Arabia
| | - Jian Yang
- College of Pharmacy and Nutrition, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada.
| |
Collapse
|
4
|
Role of Dehalogenases in Aerobic Bacterial Degradation of Chlorinated Aromatic Compounds. J CHEM-NY 2014. [DOI: 10.1155/2014/157974] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
This review was conducted to provide an overview of dehalogenases involved in aerobic biodegradation of chlorinated aromatic compounds. Additionally, biochemical and molecular characterization of hydrolytic, reductive, and oxygenolytic dehalogenases was reviewed. This review will increase our understanding of the process of dehalogenation of chlorinated aromatic compounds.
Collapse
|
5
|
Chen K, Huang L, Xu C, Liu X, He J, Zinder SH, Li S, Jiang J. Molecular characterization of the enzymes involved in the degradation of a brominated aromatic herbicide. Mol Microbiol 2013; 89:1121-39. [PMID: 23859214 DOI: 10.1111/mmi.12332] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/13/2013] [Indexed: 11/26/2022]
Abstract
Dehalogenation is the key step in the degradation of halogenated aromatics, while reductive dehalogenation is originally thought to rarely occur in aerobes. In this study, an aerobic strain of Comamonas sp. 7D-2 was shown to degrade the brominated aromatic herbicide bromoxynil completely and release two equivalents of bromides under aerobic conditions. The enzymes involved in the degradation of bromoxynil to 4-carboxy-2-hydroxymuconate-6-semialdehyde, including nitrilase, reductive dehalogenase (BhbA), 4-hydroxybenzoate 3-monooxygenase and protocatechuate 4,5-dioxygenase, were molecularly characterized. The novel dehalogenase BhbA was shown to be a complex of a respiration-linked reductive dehalogenase (RdhA) domain and a NAD(P)H-dependent oxidoreductase domain and to have key features of anaerobic respiratory RdhAs, including two predicted binding motifs for [4Fe-4S] clusters and a close association with a hydrophobic membrane protein (BhbB). BhbB was confirmed to anchor BhbA to the membrane. BhbA was partially purified and found to use NAD(P)H as electron donors. Full-length bhbA homologues were found almost exclusively in marine aerobic proteobacteria, suggesting that reductive dehalogenation occurs extensively in aerobes and that bhbA is horizontally transferred from marine microorganisms. The discovery of a functional reductive dehalogenase and ring-cleavage oxygenases in an aerobe opens up possibilities for basic research as well as the potential application for bioremediation.
Collapse
Affiliation(s)
- Kai Chen
- Department of Microbiology, Key Lab of Microbiological Engineering of Agricultural Environment, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, 210095, Nanjing, China
| | | | | | | | | | | | | | | |
Collapse
|
6
|
Glasner ME, Gerlt JA, Babbitt PC. Mechanisms of protein evolution and their application to protein engineering. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2010; 75:193-239, xii-xiii. [PMID: 17124868 DOI: 10.1002/9780471224464.ch3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Protein engineering holds great promise for the development of new biosensors, diagnostics, therapeutics, and agents for bioremediation. Despite some remarkable successes in experimental and computational protein design, engineered proteins rarely achieve the efficiency or specificity of natural enzymes. Current protein design methods utilize evolutionary concepts, including mutation, recombination, and selection, but the inability to fully recapitulate the success of natural evolution suggests that some evolutionary principles have not been fully exploited. One aspect of protein engineering that has received little attention is how to select the most promising proteins to serve as templates, or scaffolds, for engineering. Two evolutionary concepts that could provide a rational basis for template selection are the conservation of catalytic mechanisms and functional promiscuity. Knowledge of the catalytic motifs responsible for conserved aspects of catalysis in mechanistically diverse superfamilies could be used to identify promising templates for protein engineering. Second, protein evolution often proceeds through promiscuous intermediates, suggesting that templates which are naturally promiscuous for a target reaction could enhance protein engineering strategies. This review explores these ideas and alternative hypotheses concerning protein evolution and engineering. Future research will determine if application of these principles will lead to a protein engineering methodology governed by predictable rules for designing efficient, novel catalysts.
Collapse
Affiliation(s)
- Margaret E Glasner
- Department of Biopharmaceutical Sciences, University of California-San Francisco, San Francisco, CA 94143, USA
| | | | | |
Collapse
|
7
|
Mutational study of the role of N-terminal amino acid residues in tetrachlorohydroquinone reductive dehalogenase from Sphingomonas sp. UG30. Res Microbiol 2009; 160:553-9. [DOI: 10.1016/j.resmic.2009.07.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2009] [Revised: 07/21/2009] [Accepted: 07/24/2009] [Indexed: 11/21/2022]
|
8
|
Harbottle MJ, Lear G, Sills GC, Thompson IP. Enhanced biodegradation of pentachlorophenol in unsaturated soil using reversed field electrokinetics. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2009; 90:1893-1900. [PMID: 19188014 DOI: 10.1016/j.jenvman.2008.12.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Revised: 11/26/2008] [Accepted: 12/21/2008] [Indexed: 05/27/2023]
Abstract
This study investigated the use of electrokinetics in unsaturated soil to promote biodegradation of pentachlorophenol through increased contact between bacteria and contaminant. Soil microcosms, contaminated with approximately 100 mg kg(-1) pentachlorophenol (containing [(14)C]-PCP as a tracer), and inoculated with a specific pentachlorophenol-degrading bacterium (Sphingobium sp. UG30-1 x 10(8) cfu g(-1)) were subjected to constant and regularly reversed electric currents (10 mA). The former caused large pH and moisture content changes due to water electrolysis and electroosmotic effects, with subsequent negative impacts on biodegradation parameters including enzyme activity and contaminant mineralisation (as measured by (14)CO(2) evolution rate). The reversed field caused little change in pH and moisture content and led to more rapid contaminant mineralisation, lower soil contaminant concentration in the majority of the microcosms and increased soil enzyme activity (with the exception of soil immediately adjacent to the anode). The presence of an electric field, if suitably applied, may therefore enhance contaminant biodegradation in unsaturated soil.
Collapse
|
9
|
Abstract
Bacterial glutathione transferases (GSTs) are part of a superfamily of enzymes that play a key role in cellular detoxification. GSTs are widely distributed in prokaryotes and are grouped into several classes. Bacterial GSTs are implicated in a variety of distinct processes such as the biodegradation of xenobiotics, protection against chemical and oxidative stresses and antimicrobial drug resistance. In addition to their role in detoxification, bacterial GSTs are also involved in a variety of distinct metabolic processes such as the biotransformation of dichloromethane, the degradation of lignin and atrazine, and the reductive dechlorination of pentachlorophenol. This review article summarizes the current status of knowledge regarding the functional and structural properties of bacterial GSTs.
Collapse
Affiliation(s)
- Nerino Allocati
- Dipartimento di Scienze Biomediche, Università G. d'Annunzio, Chieti, Italy.
| | | | | | | |
Collapse
|
10
|
Crawford RL, Jung CM, Strap JL. The recent evolution of pentachlorophenol (PCP)-4-monooxygenase (PcpB) and associated pathways for bacterial degradation of PCP. Biodegradation 2006; 18:525-39. [PMID: 17123025 DOI: 10.1007/s10532-006-9090-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2006] [Accepted: 10/26/2006] [Indexed: 11/27/2022]
Abstract
Man-made polychlorinated phenols such as pentachlorophenol (PCP) have been used extensively since the 1920s as preservatives to prevent fungal attack on wood. During this time, they have become serious environmental contaminants. Despite the recent introduction of PCP in the environment on an evolutionary time scale, PCP-degrading bacteria are present in soils worldwide. The initial enzyme in the PCP catabolic pathway of numerous sphingomonads, PCP-4-monooxygenase (PcpB), catalyzes the para-hydroxylation of PCP to tetrachlorohydroquinone and is encoded by the pcpB gene. This review examines the literature concerning pcpB and supports the suggestion that pcpB/PcpB should be considered a model system for the study of recent evolution of catabolic pathways among bacteria that degrade xenobiotic molecules introduced into the environment during the recent past.
Collapse
Affiliation(s)
- Ronald L Crawford
- Environmental Biotechnology Institute, Food Research Center 202, University of Idaho, Moscow, ID 83844-1052, USA.
| | | | | |
Collapse
|
11
|
Chu BCH, Lee H. Investigation of the role of a conserved glycine motif in the Saccharomyces cerevisiae xylose reductase. Curr Microbiol 2006; 53:118-23. [PMID: 16802208 DOI: 10.1007/s00284-005-0325-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Accepted: 03/16/2006] [Indexed: 10/24/2022]
Abstract
All yeast xylose reductases, with the exception of that from Schizosaccharomyces pombe, possess the catalytic and coenzyme-binding elements from both the aldo-keto reductase and short-chain dehydrogenase-reductase (SDR) enzyme families in their primary sequences. In the Saccharomyces cerevisiae xylose reductase (XR), the SDR-like coenzyme-binding GXXXGXG motif (Gly motif) is located between residues 128 and 134, with the third Gly residue being replaced by an Asp. We used site-directed mutagenesis to study the role of this SDR-like Gly motif in the S. cerevisiae xylose reductase. Site-directed mutagenesis of the individual conserved Gly residue positions (G128A, G132A, D134G, and D134A) did not significantly affect the specific activity, kinetic constants (K(m), K(cat), and K(cat)/K(m)), or dissociation constants (K(d)) in any of the variants compared with the wild type. Deletion of the entire Gly motif produced an unstable protein that could not be purified. These results indicate that the SDR-like Gly motif likely provides support to the overall structure of the enzyme, but it does not contribute directly to coenzyme binding in this XR.
Collapse
Affiliation(s)
- Byron C H Chu
- Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
| | | |
Collapse
|
12
|
Corvini PFX, Hollender J, Ji R, Schumacher S, Prell J, Hommes G, Priefer U, Vinken R, Schäffer A. The degradation of α-quaternary nonylphenol isomers by Sphingomonas sp. strain TTNP3 involves a type II ipso-substitution mechanism. Appl Microbiol Biotechnol 2006; 70:114-22. [PMID: 16091931 DOI: 10.1007/s00253-005-0080-0] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Revised: 06/22/2005] [Accepted: 06/24/2005] [Indexed: 11/28/2022]
Abstract
The degradation of radiolabeled 4(3',5'-dimethyl-3'-heptyl)-phenol [nonylphenol (NP)] was tested with resting cells of Sphingomonas sp. strain TTNP3. Concomitantly to the degradation of NP, a metabolite identified as hydroquinone transiently accumulated and short-chain organic acids were then produced at the expense of hydroquinone. Two other radiolabeled isomers of NP, 4(2',6'-dimethyl-2'-heptyl)-phenol and 4(3',6'-dimethyl-3'-heptyl)-phenol, were synthesized. In parallel experiments, the 4(2',6'-dimethyl-2'-heptyl)-phenol was degraded more slowly than the other isomers of NP by strain TTNP3, possibly because of effects of the side-chain structure on the kinetics of degradation. Alkylbenzenediol and alkoxyphenol derivatives identified as metabolites during previous studies were synthesized and tested as substrates. The derivatives were not degraded, which indicated that the mineralization of NP does not proceed via alkoxyphenol as the principal intermediate. The results obtained led to the elucidation of the degradation pathway of NP isomers with a quaternary alpha-carbon. The proposed mechanism is a type II ipso substitution, leading to hydroquinone and nonanol as the main metabolites and to the dead-end metabolites alkylbenzenediol or alkoxyphenol, depending on the substitution at the alpha-carbon of the carbocationic intermediate formed.
Collapse
Affiliation(s)
- P F X Corvini
- Department of Environmental Research-Environmental Biology and Chemodynamics, RWTH Aachen, Worringerweg 1, 52074 Aachen, Germany.
| | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Denich TJ, Beaudette LA, Lee H, Trevors JT. Fluorescent methods to study DNA, RNA, proteins and cytoplasmic membrane polarization in the pentachlorophenol-mineralizing bacterium Sphingomonas sp. UG30 during nutrient starvation in water. J Fluoresc 2005; 15:143-51. [PMID: 15883769 DOI: 10.1007/s10895-005-2522-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2004] [Accepted: 11/01/2004] [Indexed: 11/26/2022]
Abstract
The effect of sodium pentachlorophenolate (NaPCP) exposure on the nutrient-starved pentachlorophenol (PCP)-mineralizing bacterium Sphingomonas sp. UG30 was assessed using fluorescent methods to measure DNA, RNA, total cellular protein, and cytoplasmic membrane proteins. UG30 cells were inoculated into sterilized Speed River (Guelph, ON, Canada) water samples in the presence of 50, 100, and 250 ppm NaPCP. No marked changes were observed in the total cellular DNA, RNA or protein levels over 90 d, indicating the macromolecular composition of UG30 was not affected by both nutrient limitation and NaPCP. Total cell counts as determined by DAPI staining also did not change over 90 d. Over the same period, viable counts decreased with increasing concentrations of NaPCP. At 250 ppm NaPCP, viable cell counts decreased over 6 orders of magnitude after 1 hr exposure. Cell numbers partially recovered once NaPCP was degraded. The UG30 cytoplasmic membrane polarization ratio also decreased after NaPCP was depleted. The decreased polarization value at the end of the study period suggested the UG30 membrane was more fluid and that this increase in fluidity was due to nutrient starvation effects rather than exposure to NaPCP. These results indicated that UG30 is a robust organism that is able to degrade NaPCP even under adverse conditions and fluorescent methods are useful for determining macromolecular concentrations and cytoplasmic membrane polarization values.
Collapse
Affiliation(s)
- T J Denich
- Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada, N1G 2W1
| | | | | | | |
Collapse
|
14
|
Phillips TM, Seech AG, Lee H, Trevors JT. Biodegradation of hexachlorocyclohexane (HCH) by microorganisms. Biodegradation 2005; 16:363-92. [PMID: 15865341 DOI: 10.1007/s10532-004-2413-6] [Citation(s) in RCA: 168] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The organochlorine pesticide Lindane is the gamma-isomer of hexachlorocyclohexane (HCH). Technical grade Lindane contains a mixture of HCH isomers which include not only gamma-HCH, but also large amounts of predominantly alpha-, beta- and delta-HCH. The physical properties and persistence of each isomer differ because of the different chlorine atom orientations on each molecule (axial or equatorial). However, all four isomers are considered toxic and recalcitrant worldwide pollutants. Biodegradation of HCH has been studied in soil, slurry and culture media but very little information exists on in situ bioremediation of the different isomers including Lindane itself, at full scale. Several soil microorganisms capable of degrading, and utilizing HCH as a carbon source, have been reported. In selected bacterial strains, the genes encoding the enzymes involved in the initial degradation of Lindane have been cloned, sequenced, expressed and the gene products characterized. HCH is biodegradable under both oxic and anoxic conditions, although mineralization is generally observed only in oxic systems. As is found for most organic compounds, HCH degradation in soil occurs at moderate temperatures and at near neutral pH. HCH biodegradation in soil has been reported at both low and high (saturated) moisture contents. Soil texture and organic matter appear to influence degradation presumably by sorption mechanisms and impact on moisture retention, bacterial growth and pH. Most studies report on the biodegradation of relatively low (< 500 mg/kg) concentrations of HCH in soil. Information on the effects of inorganic nutrients, organic carbon sources or other soil amendments is scattered and inconclusive. More in-depth assessments of amendment effects and evaluation of bioremediation protocols, on a large scale, using soil with high HCH concentrations, are needed.
Collapse
Affiliation(s)
- Theresa M Phillips
- Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
| | | | | | | |
Collapse
|
15
|
|