Sequencing and Transcriptional Analysis of the Chlorite Dismutase Gene of Dechloromonas agitata and Its Use as a Metabolic Probe

Abstract

Recent concerns over the environmental contamination of water supplies with perchlorate have focused a significant amount of attention on the microbial metabolism of oxyanions of chlorine (29). Perchlorate contamination poses a significant health threat, as preliminary toxicological studies have demonstrated that it is a competitive inhibitor of iodine uptake by the thyroid gland, and at higher concentrations (6 mg per kg of body weight per day), perchlorate can result in fatal bone marrow disease. In 1998, perchlorate was added to the U.S. Environmental Protection Agency's drinking water candidate contaminant list, and a recommended regulatory concentration of 32 g liter Ϫ1 was set, which, if exceeded, would require stoppage of water usage and remediation (http://cfpub.epa .gov/ncea/cfm/recordisplay.cfm?deid-23292). More recently, as a result of the publication of the first draft of the Environmental Protection Agency review on toxicological and risk characterization data associated with perchlorate contamination, the Californian Department of Health and Human Services revised and lowered its original provisional action level to 4 g liter Ϫ1 , which is at the limits of detection using current technologies (32; http://www.dhs.ca.gov/ps/ddwem/chemicals /perchl/actionlevel.htm).Remediation efforts of perchlorate contamination have focused primarily on microbial processes because of the unique chemical stability and high solubility of perchlorate (29). These processes are based on the ability of perchlorate-reducing bacteria to utilize perchlorate as a physiological electron acceptor in the absence of oxygen and reduce it completely to innocuous chloride. Although it has been recognized for more than 70 years that oxyanions of chlorine are suitable electron acceptors for microbial metabolism (5), this reductive process was originally associated with nitrate-respiring organisms which simply used chlorate as an opportunistic substrate for nitrate reductase (12-14). Growth was not associated with this metabolic pathway, and chlorite was formed as a toxic end product (12)(13)(14)23).It is now known that specialized microorganisms have evolved that can grow by the anaerobic dissimilation of perchlorate (1,6,9,10,18,19,22,24,28,31), and many dissimilatory perchlorate-reducing bacteria (DPRB) are now in pure culture. The known DPRB isolates represent a broad physiology and phylogeny, with members in the alpha, beta, gamma, and epsilon subclasses of the Proteobacteria (9, 31). The majority of the DPRB are members of the beta subclass of the Proteobacteria and represent two novel genera, the Dechloromonas species and the Dechlorosoma species (1). These organisms are closely related to each other and to the phototrophic Rhodocyclus species. Members of these two groups have been identified and isolated from nearly all environments screened, including both field samples and ex situ bioreactors treating perchlorate-contaminated wastes (9, 18).Although relatively little is known about the biochemistry of perchlorate reduction, s...

Microbial Isotopic Fractionation of Perchlorate Chlorine

“…Phenotypic characterization studies have demonstrated that the known perchlorate-reducing bacteria exhibit a broad range of metabolic capabilities and can thrive in adverse environments (10; J. Pollock, L. A. Achenbach, and J. D. Coates, unpublished data). Significant advances have similarly been made in the biochemistry and genetic systems involved in microbial perchlorate reduction and on the environmental factors which affect their activity (5,6,8,10). As such, the applicability of this metabolism offers great potential for the bioremediation of perchlorate-contaminated environments, and recent field studies have successfully demonstrated this potential.…”

“…Although several molecular and immunological tools based on unique signature molecules are now available to monitor the microbial populations associated with perchlorate reduction in the environment (5,6,24), monitoring of the effectiveness of a bioremediative strategy in field environments is often difficult due to the complex nature of environmental samples. Results can often be tainted by many abiotic factors, including adsorption or chemical reactivity of the target contaminant.…”

“…Physiological characterization revealed that D. suillum rapidly reduced perchlorate with acetate as the electron donor and that reduction was dependent on molybdate and was negatively regulated by the presence of either oxygen or nitrate (6,8,24). The ability of D. suillum to fractionate chlorine isotopes while growing on perchlorate was determined by culturing the organism at 37°C in modified basal medium (7) from which the major chloride salts were removed and replaced with equivalent sulfate salts.…”

Use of Dissolved Organic Carbon to Biostimulate Rapid Rhizodegradation of Perchlorate in Soil

“…The dismutation of ClO 2 -into Cl -and O 2 , an important step in the reductive pathways of perchlorate, is mediated by an enzyme chlorite dismutase [15]. Degenerate primers were recently developed by Bender et al [16] for the amplification of the chlorite dismutase gene cld [17].…”

Protocol for Enhanced in situ Bioremediation Using Emulsified Edible Oil

“…Work by Coates et al (1999), Chaudhuri et al (2002), and Bender et al (2002) indicate that the Dechloromonas and Dechlorosoma groups represent the primary chlorate and perchlorate reducing bacteria in the environment, but more than 30 different strains of perchlorate-reducing microbes have been identified (USEPA, 2005). The ratelimiting step in the three-step degradation process is the conversion of perchlorate to chlorate by a perchlorate reductase enzyme.…”