Effects of Varying Growth Conditions on Stable Carbon Isotope Fractionation of Trichloroethene (TCE) by <i>tce</i>A‑containing <i>Dehalococcoides mccartyi</i> strains

To quantify in situ bioremediation using compound specific isotope analysis (CSIA), isotope fractionation data obtained from the field is interpreted according to laboratory-derived enrichment factors. Although previous studies that have quantified dynamic isotopic shifts during the reductive dechlorination of trichloroethene (TCE) indicate that fractionation factors can be highly variable from culture-to-culture and site-to-site, the effects of growth condition on the isotope fractionation during reductive dechlorination have not been previously examined. Here, carbon isotope fractionation by <i>Dehalococcoides mccartyi</i> 195 (Dhc195) maintained under a variety of growth conditions was examined. Enrichment factors quantified when Dhc195 was subjected to four suboptimal growth conditions, including decreased temperature (−13.3 ± 0.9‰), trace vitamin B₁₂ availability (−12.7 ± 1.0‰), limited fixed nitrogen (−14.4 ± 0.8‰), and elevated vinyl chloride exposure (−12.5 ± 0.4‰), indicate that the fractionation is similar across a range of tested conditions. The TCE enrichment factors for two syntrophic cocultures, Dhc195 with <i>Desulfovibrio vulgaris</i> Hildenborough (−13.0 ± 2.0‰) and Dhc195 with <i>Syntrophomonas wolfei</i> (−10.4 ± 1.2‰ and −13.3 ± 1.0‰), were also similar to a control experiment. In order to test the stability of enrichment factors in microbial communities, the isotope fractionation was quantified for Dhc-containing groundwater communities before and after two-year enrichment periods under different growth conditions. Although these enrichment factors (−8.9 ± 0.4‰, −6.8 ± 0.8‰, −8.7 ± 1.3‰, −9.4 ± 0.7‰, and −7.2 ± 0.3‰) were predominantly outside the range of values quantified for the isolate and cocultures, all tested enrichment conditions within the communities produced nearly similar fractionations. Enrichment factors were not significantly affected by changes in any of the tested growth conditions for the pure cultures, cocultures or the mixed communities, indicating that despite a variety of temperature, nutrient, and cofactor-limiting conditions, stable carbon isotope fractionations remain consistent for given <i>Dehalococcoides</i> cultures