| Despite strict regulation, chlorinated organic contaminants such as tetrachloroethene (PCE) and trichloroethene (TCE) are still used as solvents and degreasing agents in many industrial applications. As a result of previous improper disposal practices, accidental spills, and continued use, PCE and TCE have become widely distributed in the environment. The discovery of bacteria that use chloroorganic compounds as electron acceptors has revolutionized bioremediation strategies at many sites contaminated with chlorinated ethenes. Generally, bioremediation is categorized by three applications: intrinsic bioremediation (natural attenuation), biostimulation, and bioaugmentation. All three approaches require sensitive methods to monitor the presence, distribution, and activity of the organisms of interest. Pure cultures are indispensable resources to develop an understanding the physiology of the dechlorinators and the biochemistry of the key enzymes.; In order to explore the distribution and function of dechlorinating populations, sediment-free, non-methanogenic, ethene-producing enrichment cultures were derived from various chlorinated ethene contaminated and non-contaminated site materials. The findings of this study demonstrate that Dehalococcoides species are intimately involved in complete reductive detoxification of chlorinated ethenes and are widely distributed in anoxic sediments and aquifers, including non-contaminated (pristine) environments. Careful examination of enrichment culture dechlorination kinetics, 16S rRNA gene based analyses, and reductive dehalogenase gene targeted PCR approaches revealed that complete reductive dechlorination is carried out by multiple dechlorinators. The findings of this study also suggest that the existence of a different Dehalococcoides population, other than strains 195, FL2 and BAV1, may be involved in the complete detoxification of chlorinated ethenes.; Two new dechlorinating species were isolated from contaminated and non-contaminated site materials. The first new isolate, designated strain SZ, was isolated from PCE-to-ethene dechlorinating microcosms established with creek sediment. 16S rRNA gene sequence of the strain SZ indicates that the new isolate is affiliated with the genus Geobacter most closely related to G. thiogenes. Strain SZ is capable of stepwise dechlorination of PCE to cis-DCE, while the closest relatives were not able to dechlorinate PCE or TCE. Dechlorination of PCE or TCE by strain SZ was supported by acetate, hydrogen or pyruvate as electron donor. Chloroethene-dechlorinating populations have been shown to have distinct electron donor requirements. However, none of previously described chlorinated ethene degrading population can use both, acetate and hydrogen, as electron donors. PCE dechlorination by strain SZ uses both acetate and hydrogen as electron donors suggesting that the ability to versatile electron donor utilization may increase the efficiency of bioremediation approaches. Importantly, strain SZ reduced two environmental priority pollutants, PCE and U(VI) concomitantly and detected from both biostimulated chloroethene and uranium contaminated sites, strongly suggesting that strain SZ play a important roles in in-situ bioremediation of chloroethene and U(VI) contaminated sites.; The second, a new Dehalococcoides species designated strain GT, was isolated from contaminated site materials. Strain GT uses trichloroethene (TCE), cis-DCE, 1,1-dichloroethene (1,1-DCE), and the human carcinogen vinyl chloride (VC) as growth supporting electron acceptors producing products ethene and inorganic chloride. The new isolate shares common traits of Dehalococcoides such as ampicillin resistance, strict hydrogen-dependent metabolism, and a low hydrogen consumption threshold concentration. Culture-dependent and independent, 16S rRNA gene and reductive dehalogenase gene targeted PCR approaches suggested culture purity.; To investigate the reductive dechlorination of chlor... |
