Showing papers on "Dehalococcoides published in 2002"

Field demonstration of successful bioaugmentation to achieve dechlorination of tetrachloroethene to ethene.

Abstract: A laboratory microcosm study and a pilot scale field test were conducted to evaluate biostimulation and bioaugmentation to dechlorinate tetrachloroethene (PCE) to ethene at Kelly Air Force Base. The site groundwater contained about 1 mg/L of PCE and lower amounts of trichloroethene (TCE) and cis-1,2-dichloroethene (cDCE). Laboratory microcosms inoculated with soil and groundwater from the site exhibited partial dechlorination of TCE to cDCE when amended with lactate or methanol. Following the addition of a dechlorinating enrichment culture, KB-1, the chlorinated ethenes in the microcosms were completely converted to ethene. The KB-1 culture is a natural dechlorinating microbial consortium that contains phylogenetic relatives of Dehalococcoides ethenogenes. The ability of KB-1 to stimulate biodegradation of chlorinated ethenes in situ was explored using a closed loop recirculation cell with a pore volume of approximately 64 000 L. The pilot test area (PTA) groundwater was first amended with methanol and ac...

Molecular Analysis of Dehalococcoides 16S Ribosomal DNA from Chloroethene-Contaminated Sites throughout North America and Europe

Abstract: The environmental distribution of Dehalococcoides group organisms and their association with chloroethene-contaminated sites were examined. Samples from 24 chloroethene-dechlorinating sites scattered throughout North America and Europe were tested for the presence of members of the Dehalococcoides group by using a PCR assay developed to detect Dehalococcoides 16S rRNA gene (rDNA) sequences. Sequences identified by sequence analysis as sequences of members of the Dehalococcoides group were detected at 21 sites. Full dechlorination of chloroethenes to ethene occurred at these sites. Dehalococcoides sequences were not detected in samples from three sites at which partial dechlorination of chloroethenes occurred, where dechlorination appeared to stop at 1,2-cis-dichloroethene. Phylogenetic analysis of the 16S rDNA amplicons confirmed that Dehalococcoides sequences formed a unique 16S rDNA group. These 16S rDNA sequences were divided into three subgroups based on specific base substitution patterns in variable regions 2 and 6 of the Dehalococcoides 16S rDNA sequence. Analyses also demonstrated that specific base substitution patterns were signature patterns. The specific base substitutions distinguished the three sequence subgroups phylogenetically. These results demonstrated that members of the Dehalococcoides group are widely distributed in nature and can be found in a variety of geological formations and in different climatic zones. Furthermore, the association of these organisms with full dechlorination of chloroethenes suggests that they are promising candidates for engineered bioremediation and may be important contributors to natural attenuation of chloroethenes.

Chlorinated Hydrocarbon Metabolism

Abstract: The widespread global distribution of chlorinated hydrocarbons, their high lipophilicity and their recalcitrance have contributed to their importance as environmental toxicants. Their metabolism under oxic and anoxic conditions mediated by prokaryotic and eukaryotic cells is discussed. Various aerobic bacteria are able to use chlorinated hydrocarbons as the sole source of carbon and energy and some anaerobic bacteria can use some of these as an artificial electron acceptor in reductive dechlorination. Liver enzymes are responsible for the formation of hydrophilic metabolites ready for excretion which often lead to highly reactive and potentially toxic intermediates. Whereas fungi, especially ligninolytic ones, usually only exhibit ‘side activities’ for chlorinated hydrocarbons. The capabilities of bacteria had led to the development of various bioremediation processes. Both, successes and failures within these processes are known. Therefore, current research aims at a better understanding of global community interactions. Key Concepts: Chlorinated hydrocarbons have been produced by the chemical industry since nearly a decade in large amounts, but they can also be observed as natural compounds, sometimes exceeding the industrially produced amounts. Even though toxicological properties have pushed the chlorochemistry into the focus of considerable debate and governmental regulatory action, chlorinated hydrocarbons remain essential for certain applications. The aerobic metabolism of chlorinated hydrocarbons by bacteria has been studied in detail and an immense amount of information is available on pathways, enzymes and genes involved in the mineralisation of chloroaromatics. The anaerobic degradation of chlorinated hydrocarbons is due to the capablity of anaerobic bacteria to use them in anaerobic respiration, which results in dechlorination. Dehalococcoides organisms are the most versatile reductive dehalogenators as being capable to dehalogenate chlorinated dioxins, biphenyls, benzenes and vinyl chloride, among others. Microbial activities have been widespread used for bioremediation purposes through natural attenuation, biostimulation and bioaugmentation. The poor understanding of the functioning of the complex microbial activities in situ made bioremediation efforts quite unreliable. The rapid development of molecular techniques in recent years allows immense insights into the processes in situ, but also on the overall physiology of biocatalysts. Keywords: biodegradation; bioremediation; chlorochemistry; dechlorination; toxicology