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Encro • ia/insi9 hts Interpretation The overall purpose of the QuantArray®-Chlor is to give site managers the ability to simultaneously yet economically evaluate the potential for biodegradation of a spectrum of common chlorinated contaminants through a multitude of anaerobic and aerobic (co)metabolic pathways in order to provide a clearer and more comprehensive view of contaminant biodegradation. The following discussion describes the interpretation of results in general terms and is meant to serve as a guide. Reductive Dechlorination-Chlorinated Ethenes:While a number of bacterial cultures including Dehalococcoides,Dehalobacter,Desul- fitobacterium,and Desulfuromonas spp. capable of utilizing PCE and TCE as growth-supporting electron acceptors have been isolated [1-5],Dehalococcoides may be the most important because they are the only bacterial group that has been isolated to date which is capable of complete reductive dechlorination of PCE to ethene [6]. In fact,the presence of Dehalococcoides has been associated with complete reductive dechlorination to ethene at sites across North America and Europe [7],and Lu et al. [8]have proposed using a Dehalococcoides concentration of 1 x 104 cells/mL as a screening criterion to identify sites where biological reductive dechlorination is predicted to proceed at"generally useful'rates. At chlorinated ethene sites,any"stall'leading to the accumulation of daughter products,especially vinyl chloride,would be a sub- stantial concern.While Dehalococcoides concentrations greater than 1 x 104 cells/mL correspond to ethene production and useful rates of dechlorination, the range of chlorinated ethenes degraded varies by strain within the Dehalococcoides genus [6,91, and the pres- ence of co-contaminants and competitors can have complex impacts on the halorespiring microbial community [10-15]. Therefore, QuantArray®-Chlor also provides quantification of a suite of reductive dehalogenase genes(PCE,TCE,BVC,VCR,CER,and TDR) to more definitively confirm the potential for reductive dechlorination of all chlorinated ethene compounds including vinyl chloride. Perhaps most importantly,QuantArray®-Chlor quantifies TCE reductase(TCE)and both known vinyl chloride reductase genes(BVC, VCR)from Dehalococcoides to conclusively evaluate the potential for complete reductive dechlorination of chlorinated ethenes to non- toxic ethene[16-18].In addition,the analysis also includes quantification of reductive dehalogenase genes from Dehalogenimonas spp. capable of reductive dechlorination of chlorinated ethenes. More specifically,these are the trans-1,2-DCE dehalogenase gene(TDR) from strain WBC-2[19]and the vinyl chloride reductase gene(CER)from GP,the only known organisms other than Dehalococcoides capable of vinyl chloride reduction [20]. Finally, PCE reductase genes responsible for sequential reductive dechlorination of PCE to cis-DCE by Sulfurospirillum and Geobacter spp. are also quantified. In mixed cultures,evidence increasingly suggests that partial dechlorinators like Sulfurospirillum and Geobacter may be responsible for the majority of reductive dechlorination of PCE to TCE and cis-DCE while Dehalococcoides functions more as cis-DCE and vinyl chloride reducing specialists[10,211. Reductive Dechlorination-Chlorinated Ethanes: Under anaerobic conditions, chlorinated ethanes are susceptible to reductive dechlorination by several groups of halorespiring bacteria including Dehalobacter, Dehalogenimonas, and Dehalococcoides. While the reported range of chlorinated ethanes utilized varies by genus,species,and sometimes at the strain level,several general observa- tions can be made regarding biodegradation pathways and daughter product formation. Dehalobacter spp. have been isolated that are capable of sequential reductive dechlorination of 1,1,1-TCA through 1,1-DCA to chloroethane[13]. Biodegradation of 1,1,2-TCA by several halorespiring bacteria including Dehalobacter and Dehalogenimonas spp. proceeds via dichloroelimination producing vinyl chloride[22-24].Similarly,l,2-DCA biodegradation by Dehalobacter,Dehalogenimonas,and Dehalococcoides occurs via dichloroelimina- tion producing ethene. While not utilized by many Desulfitobacterium isolates,at least one strain,Desulfitobacterium dichloroeliminans strain DCA1,is also capable of dichloroelimination of 1,2-DCA [25]. The 1,2-dichloroethane reductive dehalogenase gene (DCAR) from members of Desulfitobacterium and Dehalobacter is known to dechlorinate 1,2-DCA to ethene,while the 1,1-dichloroethane re- ductive dehalogenase(DCA)targets the gene responsible for 1,1-DCA dechlorination in some strains of Dehalobacter. In addition to chloroform,chloroform reductase(CFR)has also been shown to be responsible for reductivedechlorination of 1,1,1-TCA[26]. Reductive Dechlorination-Chlorinated Methanes: Chloroform is a common co-contaminant at chlorinated solvent sites and can inhibit reductive dechlorination of chlorinated ethenes. Grostern et al. demonstrated that a Dehalobacter population was capable of reductive dechlorination of chloroform to produce dichloromethane [27]. The cfrA gene encodes the reductase which catalyzes this initial step in chloroform biodegradation[26]. Justicia-Leon et al. have since shown that dichloromethane can support growth of a distinct group of Dehalobacter strains via fermentation[28].The Dehalobacter DCM assay targets the 16S rRNA gene of these strains. Reductive Dechlorination-Chlorinated Benzenes: Chlorinated benzenes are an important class of industrial solvents and chem- ical intermediates in the production of drugs, dyes, herbicides, and insecticides. The physical-chemical properties of chlorinated benzenes as well as susceptibility to biodegradation are functions of their degree of chlorination and the positions of chlorine sub- stituents.Under anaerobic conditions,reductive dechlorination of higher chlorinated benzenes including hexachlorobenzene(HCB), 12 10515 Research Drive Knoxville,TN 37932 Phone: 865.573.8188 Fax: 865.573.8133 Web: www.microbe.com