Competition for Hydrogen within a Chlorinated Solvent Dehalogenating Anaerobic Mixed Culture

Abstract

Use of an appropriate hydrogen level is necessary to favor dehalogenation of chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE), over other hydrogen using processes. This study examined the competition between dehalogenators and other microorganisms occurring in a benzoate-acclimated dehalogenating methanogenic mixed culture. Results show that the dehalogenators competed best against methanogens and homoacetogens when the hydrogen level was maintained between 2 and 11 nM. The 2 nM hydrogen concentration represents the lower threshold value found here for cis-1,2-dichloroethene (cis-DCE) dehalogenation. The usefulness of this hydrogen range was further confirmed with both batch-fed and continuously-fed reactors. In batch studies, three times more ethene was produced from dehalogenation of cis-DCE using propionate than benzoate as electron donor, while benzoate produced three times more methane than propionate. A three times greater hydrogen utilization efficiency for dehalogenation was obtained with a CSTR than with batch reactors when benzoate was used as substrate because a constant hydrogen concentration in the appropriate range could be maintained with the CSTR. These results suggest different approaches that might be used to favor dehalogenators in competition with other microorganisms.

Sustainable syntrophic growth of Dehalococcoides ethenogenes strain 195 with Desulfovibrio vulgaris Hildenborough and Methanobacterium congolense: global transcriptomic and proteomic analyses

“…In the tri-culture, hydrogen was completely consumed by day 6 and 250 mmol of methane was generated (Figure 3b), indicating that B90% of the lactate electrons were consumed by methanogenesis whereas only 10% were used for dechlorination. Although MC consumed most of the generated hydrogen in the tri-culture, the aqueous hydrogen concentration never dropped below 5 nM, remaining above the hydrogen threshold (2 nM) for dechlorination by Dehalococcoides (Yang and McCarty, 1998). Consequently, competition for hydrogen between MC and DE195 was not observed to affect dechlorination in this study.…”

“…In addition, methanogens were found to compete for hydrogen with dehalogenators (Smatlak et al, 1996;Fennell et al, 1997;Yang and McCarty, 1998). Although there have been a number of studies evaluating the link between methanogens and Dehalococcoides (Fathepure and Boyd, 1988;Freedman and Gossett 1989;Smatlak et al, 1996;Fennell et al, 1997;Lö ffler et al, 1997;Yang and McCarty, 1998;Booker and Pavlostathis, 2000;Heimann et al, 2006), the role of methanogens in dechlorinating communities remains unclear.…”

Heterogeneous hyporheic zone dechlorination of a TCE groundwater plume discharging to an urban river reach

“…Although methanogenesis occurrence indicates conditions were sufficiently reducing for dechlorination, rates may be negatively influenced by methanogenic activity because methanogens compete with the dechlorinating bacteria for available hydrogen (Maymo-Gatell, et al, 1995;Yang and McCarty, 1998;Yang and McCarty, 2000).…”

The Hydrogenase Chip: a tiling oligonucleotide DNA microarray technique for characterizing hydrogen-producing and -consuming microbes in microbial communities

“…In many microbial ecosystems, including phototrophic microbial mats and reductively dehalogenating microbial consortia present in organohalide-contaminated groundwater aquifers, hydrogen metabolism has a critical role for the systems-level performance and stability of the respective ecosystem; yet hydrogen flux between the community members has been difficult to determine (Yang and McCarty, 1998;Hoehler et al, 2001Hoehler et al, , 2002Smidt and de Vos, 2004). Many interspecies hydrogen transfer interactions are syntrophic, and therefore only present in the complex microbial communities rather than in pure cultures (Bryant et al, 1967;Stams and Plugge, 2009).…”