Frequently Asked Questions About Gene-Trac Dehalococcoides Testing

Q. What type and volume of sample is required for Gene-Trac testing?

A. SiREM performs Gene-Trac testing on groundwater (1 Liter), soil (50 grams) or biomass collected on membrane filters, contact SiREM for relevant sampling protocols.    

Q. Is one Gene-Trac Test enough to characterize a site?  

A. No. In order to provide sufficient replication and coverage, and to assess variability within a site, Ideally, samples from locations with varying chloroethene concentrations, as well as uncontaminated background locations provide the most useful information. SiREM recommends a minimum of three samples be analyzed at each sampling event.

Q. What are the implications a positive Gene-Trac Dehalococcoides test ?

A. A positive test provides strong evidence that Dehalococcoides organisms are present at a site and may facilitate complete dechlorination of chloroethenes if the appropriate geochemical conditions are present.  

Q. Is it possible to have Dehalococcoides organisms at a site and to not observe complete dechlorination?

A. Yes. There are several scenarios where complete dechlorination may not be observed in the presence of Dehalococcoides organisms these include: (1) Sites where electron donor concentrations are low, preventing abundant growth and dechlorination; (2) Sites where inhibitory compounds are present (e.g., 1,1,1-trichloroethane/ chloroform). (3) Sites where the strain of Dehalococcoides is not capable of, or efficient at, complete degradation of chlorinated ethenes.   

Q. Can all Dehalococcoides organisms degrade vinyl chloride efficiently?

A. No. Some strains of Dehalococcoides are more efficient at conversion of VC to ethene than others. At some sites, Dehalococcoides may be detected, but dechlorination of VC to ethene could be insufficient because of the particular strain that is present. For this reason, SiREM offers the Gene-Trac-VC test for the gene that degrades vinyl chloride (vinyl chloride reductase).  

Q. What is the difference between Quantitative Gene-Trac and Gene-Trac-VC

A. The tests target different genes. The Quantitative Gene-Trac test targets Dehalococcoides specific sequences of the 16S rRNA gene which is involved in protein synthesis and is present in all bacteria. The Gene-Trac-VC tests targets a Dehalococcoides gene called vinyl chloride reductase that codes for an enzyme that dechlorinates VC to ethene.   

Q. Do I need to provide more than one groundwater or soil sample for Quantitative Gene-Trac and Gene-Trac-VC?

A. No once the DNA is extracted from one sample both tests can be performed on the same DNA preparation. Also archived DNA samples (those previously tested by SiREM) can be retroactively tested to confirm the presence of the VC reductase gene.   

Q.  What are the implications of a positive Gene-Trac- VC test?

A. A positive Gene-Trac-VC test indicates the presence of the gene that degrades vinyl chloride efficiently. This indicates that the strain of Dehalococcoides present is less likely to cause long-term accumulation of highly toxic vinyl chloride than an organism that does not have this gene (tests negative).   

Q. If Gene-Trac tests are negative are there any options to facilitate complete dechlorination?

A. Yes. Bioaugmentation can be performed at sites that lack indigenous Dehalococcoides organisms. SiREM offers a commercially available bioaugmentation culture (KB-1®) that contains two strains of Dehalococcoides microorganisms. KB-1® has been demonstrated to facilitate complete dechlorination of chloroethenes at sites where indigenous organisms are not present.

Q. Is bioaugmentation still useful where positive Dehalococcoides results are obtained?

A. Yes, in certain cases. Bioaugmentation can be useful at sites where 1) the indigenous Dehalococcoides have low cell densities or are poorly distributed or, 2) the indigenous strains are not ideally suited for complete dechlorination. For example, the indigenous Dehalococcoides strains are inefficient VC degraders (negative Gene-Trac-VC test results). Bioaugmentation in these cases can provide 1) Better distribution and higher cell densities, 2) introduce highly efficient strains of Dehalococcoides that increase the rate and extent of dechlorination.

Q. If ethene is detected at a site, (e.g., <10's of ppb) is there still a need for Dehalococcoides testing?

A. Yes. The detection of low concentrations of ethene at chloroethene contaminated sites often indicates the presence of Dehalococcoides organisms but doesn’t rule out the abiotic production of ethene or cometabolic (biotic) production of ethene. Furthermore, ethene produced at an upgradient location can be transported downgradient, where no active conversion is occurring. The acceptance of MNA remedies by the EPA requires convincing evidence that biological processes are active under site conditions. Gene-Trac Dehalococcoides testing in conjunction with chemical parameters increases the confidence that active biodegradation is actually occurring at the location of contamination.