ABSTRACT
The genus Dehalogenimonas (Dhgm) is a recently discovered taxonomic group within the class Dehalococcoidia of the phylum Chloroflexi. To date, Dhgm consists of three formally described species including Dehalogenimonas lykanthroporepellens, Dehalogenimonas alkenigignens and Dehalogenimonas formicexedens. All isolates of these three Dhgm species are obligate organohalide-respiring bacteria. They use hydrogen and formate as electron donors and chlorinated ethanes (e.g., 1,2,3-trichloropropane, 1,2-dichloropropane, 1,2-dichloroethane) as electron acceptors in energy-conserving reductive dechlorination reaction. Chlorinated ethanes are common groundwater contaminants in China. The unique metabolic capacities of Dhgm strains implicate it may play important roles in site remediation. The recently reported Dhgm sp. strain WBC-2 and 'Candidatus Dehalogenimonas etheniformans' strain GP are capable of dechlorinating certain chlorinated ethenes. More importantly, strain GP can completely detoxify the carcinogenic vinyl chloride (VC) to ethene. These findings expand the diversity of microorganisms involved in the respiratory VC reductive dechlorination and improve the understanding of Dhgm's ecological functions. Here, we summarize the advances in physiological and biochemical characteristics, ecological functions and genomic features of Dhgm, with the aim to develop effective and sustainable strategies to facilitate the bioremediation of chlorinated compounds contaminated sites.
Subject(s)
Anaerobiosis , Biodegradation, Environmental , Chloroflexi , Water Pollutants, ChemicalABSTRACT
Lacasse is one of the extracellular enzymes excreted from white and brown rot fungi, which is involved in ligninolysis. In the present study, the effects of the addition of lacasse inducers to the medium on enhancement of enzyme production under conditions of submerged fermentation were researched. At first, a culture medium was selected suitable for lacasse production. To increase the production of lacasse using different inducers and to examine the ability of dechlorination, this article focuses on screen lacasse activity of 21 basidiomycetes isolates grown in five culture media. All inducers evaluated influenced lacasse activity positively except for gallic acid, mannitol, and malt extract for studied isolates. Our findings showed that lacasse activity of Trametes versicolor ATCC (200801) when it was induced with wheat bran reached up to 29.08 U ml-1 and was examined the ability of dechlorination of 2, 4, 5-trichlorophenol (2,4,5-TCP). The parameters including pH, initial substrate concentration, amount of enzyme, period of reaction, and temperature were tested for dechlorination process. Correlation between oxygen consumption and dechlorination processes under the determined optimum conditions was analyzed. Toxicity of 2, 4, 5-TCP before and after enzymatic treatment was evaluated by Microtox test. The results demonstrated that toxicity of intermediates formed 2, 4, 5-TCP did not change.
Subject(s)
Basidiomycota/enzymology , Chlorophenols/metabolism , Laccase/metabolism , Culture Media , Oxidation-ReductionABSTRACT
A test was conducted to examine the effect of several electron donors such as glucose, sodium acetate, Fe0, Fe0+glucose and Fe0+sodium acetate on reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) through inoculating the unacclimated anaerobic mixed bacteria. The optimum condition and sus-tainability of Fe0 as electron donor was also been discussed. The results showed that, Fe0+glucose enhanced the dechlorination of contaminant effectively compared to glucose. Sodium acetate, Fe0 and Fe0+sodium acetate were all effective electron donors and Fe0 was the optimum, the optimum initial pH was 8.0 and quantity of added Fe0 was 2.0 g/L. 4-CP was the mainly intermediate product for 2,4-DCP dechlorination. Fe0 could support the electron for reductive dechlorination of 2,4-DCP continuously. In contrast, when so-dium acetate as electron donor, the effect of dechlorination was inferior to Fe0 with the consumption of sodium acetate.
ABSTRACT
The Arabidopsis thaliana glutathione S-transferases zeta class (AtGSTZ) is a multi-functional enzyme, which plays important role in cellular metabolism and environmental purification. Error-prone PCR and cycles of DNA shuffling were used to construct a mutagenesis library of AtGSTZ. The screening of the resultant libraries was carried out by a pH indicator dye-based colorimetric assay. Nine mutants which enhanced the dichloroacetic acid dechlorination activity were obtained. Among them, NN23 contained 25 amino acid substitutions with the activity improving 120%, whereas NN20 contained 24 amino acid substitutions with the activity improving 102%. EC1 contained 2 amino acid substitutions with the activity improving 47%. The rest 6 mutants contained one amino acid substitution with their activity increasing from 9% to 60%. The enzymatic characterization showed that all the evolved enzymes increased their catalytic efficiencies towards dichloroacetic acid and binding affinity towards glutathione whereas some of them increased the renaturability. However there is no obvious change in their thermostability. Based on these data, functional residues related to catalysis and refolding of AtGSTZ were discussed.
ABSTRACT
From soils contaminated with polychlorinated biphenils (PCBs) a strain of Alcaligenes sp. able to grow in a mineral medium with a commercial mixture of PCBs as carbon source was isolated. This strain consumed up to 200 ppm in seven days in laboratory conditions. After 24 h of incubation, some new congeners of PCBs could be recognized by mass spectrometry. Through the identification of these compounds it was possible to postulate examples of possible transformations by dechlorinations of penta- and tetra-chlorinated congeners into tri-chlorinated ones. The properties of the isolated strain are appropriate for bioremediation of contaminated areas and also for using in bioreactors in order to remove the xenobiotic chemical.
A partir de suelos contaminados con bifenilos policlorados (PCBs) se aisló una cepa de Alcaligenes sp. capaz de crecer en medio mineral con una mezcla comercial de PCBs como fuente de carbono. Esta cepa consumió hasta 200 ppm de PCBs en siete días de incubación en condiciones de laboratorio. En 24 horas de incubación se han podido detectar nuevos congéneres de PCBs mediante espectrometria de masa. La identificación de estos compuestos ha permitido postular transformaciones de congéneres penta- y tetra-clorados que originarían derivados triclorados. Las propiedades de la cepa aislada son apropiadas para biorremediación y para su uso en biorreactores para eliminar estos compuestos xenobióticos.
Subject(s)
Alcaligenes/metabolism , Polychlorinated Biphenyls/metabolism , Soil Microbiology , Soil Pollutants/metabolism , Biodegradation, Environmental , Bioreactors , Chlorine/metabolism , Molecular StructureABSTRACT
A batch laboratory test was conducted to examine the effect of biological reductive dechlorination of 2,4-Dichlorophenol(2,4-DCP) by the addition of zero-valent iron(Fe0) in the anaerobic system, through inoculating the anaerobic mixed microorganism acclimated for two months. Meanwhile, several factors that affected "Fe0+ microbe" system were also being discussed. The results showed that, "Fe0+ microbe" system accelerated the biological dechlorination of 2,4-DCP effectively compared to the individual use. The opti-mum quantity of added Fe0 and inoculation was 0.5 g/L and 376.2 mgVSS/L in the combined system respec-tively. It showed the most effective transformation efficiency for 2,4-DCP when initial pH=8.0, whereas it become weaker when initial pH are keeping in acid condition. There existed a proportion between quantity of added Fe0 and inoculation. It enhanced degradable effect of 2,4-dichlorophenol when increased the quan-tity of inoculation at suitable ranges, which generated more enzyme or enzymatic series degraded pollutant.