Delgado's work points to another explanation and a plausible means for rectifying the stalling problem. Dehalococcoides require hydrogen (H2) as an electron donor for their respiratory cycle. The current experiments proved that in some cases, Dehalococcoides are out-competed for hydrogen by a variety of other microorganisms present in the soil or sediment.
Samples of soil and sediment from three sites (Romania, Puerto Rico and South Carolina) were examined. The first two samples were uncontaminated while the third was extracted from a military base in Parris Island, South Carolina a site contaminated with PCE, a chlorinated chemical similar to TCE.
All three samples were used in microcosm studies where general environmental conditions of a given site are replicated in a sample bottle and remediation effects can be acutely analyzed. The studies demonstrated that sites bearing wide microbial diversity (such as the uncontaminated Romanian and Puerto Rican samples) contained large numbers of bacteria capable of out-competing Dehalococcoides for essential hydrogen, thereby causing the breakdown of chlorinated chemicals to stall at the cis-DCE phase.
In the case of the contaminated sample from South Carolina, Dehalococcoides was successful in the full reduction of chlorinated chemical to ethene. The authors speculate that the toxic contaminant in the sediment likely acted to limit microbial diversity, allowing Dehalococcoides better access to hydrogen.
In the Romanian and Puerto Rican soil samples, conditions for Dehalococcoides to thrive were
|Contact: Joseph Caspermeyer|
Arizona State University