Interaction between methanogenic and sulfate-reducing microorganisms during dechlorination of a high concentration of tetrachloroethylene.

Abstract

Tetrachloroethylene (PCE) is a chlorinated aliphatic compound essentially used as a degreasing and drycleaning solvent. It is commonly found as a groundwater contaminant and because of its carcinogenic properties is considered a pollutant. Biotransformation of PCE in ethane or ethylene has been studied by many researchers at low concentrations under strict anaerobic conditions (De Bruin et al., 1992;Freedman and Gossett, 1989).The dechlorination process was observed in methanogenic, acetogenic, or sulfate-reducing habitats (Holliger and Schraa, 1994;Mohn and Tiedje, 1992). In anaerobic PCE-enrichment culture, methanogenesis and acetogenesis disappeared with high concentrations of PCE (Maymo-Gatell et al., 1995). Ecological understanding of such communities will probably be important in using dehalogenation in bioremediation processes (Mohn and Tiedje, 1992).A methanogenic and sulfate-reducing consortium degrading PCE was obtained in our laboratory from anaerobic-digested sludge from a wastewater treatment plant (Bourg-en-Bresse, France). Initially, high concentrations of PCE were dechlorinated in trichloroethylene (TCE) by methanogenic fermentation in batch conditions. The sulfate-reducing bacteria were not involved in PCE dehalogenation (Cabirol et al., 1996). This methanogenic and sulfate-reducing consortium was then cultivated continually in the presence of high concentrations of PCE. The methanogenic bacteria always had a deciding role in the dechlorination process after this enrichment period. The pollutant was completely degraded to carbon biomass and CO 2 . PCE dehalogenation has been studied in a semicontinuous fixed-bed reactor, revealing an attractive method for removing high concentrations of PCE in bioremediation processes (Cabirol et al., 1998 A methanogenic and sulfate-reducing consortium, which was enriched on medium containing tetrachloroethylene (PCE), had the ability to dechlorinate high concentrations of PCE. Dehalogenation was due to the direct activity of methanogens. However, interactions between methanogenic and sulfate-reducing bacteria involved modification of the dechlorination process according to culture conditions. In the absence of sulfate, the relative percentage of electrons used in PCE dehalogenation increased after an addition of lactate in batch conditions. The sulfate reducers would produce further reductant from lactate catabolism. This reductant might be used by methanogenic bacteria in PCE dechlorination. A mutualistic interaction was observed in the absence of sulfate. However in the presence of sulfate, methanogenesis and dechlorination decreased because of interspecific competition, probably between the H 2 -oxydizing methanogenic and sulfate-reducing bacteria in batch conditions. In the semicontinuous fixed-bed reactor, the presence of sulfate did not affect dechlorination and methanogenesis. The sulfate-reducing bacteria may not be competitors of H 2 -consuming methanogens in the reactor because of the existence of microbial biofilm. The presence of the fixed film may ...

Microbial Characteristics of a Reactive Permeable Barrier

“…SRB are an important group of morphologically very closely related anaerobic microorganisms which have been shown capable of dehalogenation of different chlorinated solvents including TCE, PCE, DCE and also degradation of petroleum BTEX compounds by various researchers (7,9,10). Gu et al recently reported microbially mediated iron-sulfide precipitate in ZVI columns (25).…”

“…Thus, our finding that SRB are the predominant organisms in the ZVI is in accordance with the subsurface redox chemistry at the site. SRB are an important group of morphologically closely related anaerobic microorganisms which have been shown capable of dehalogenation of different chlorinated solvents including TCE, PCE, DCE and also degradation of petroleum BTEX compounds by various researchers (7,9,10). SRB reduce subsurface sulfate and other sulfur compounds to sulfide, which can be coupled to oxidation of the ZVI forming iron sulfide mineral.…”

Influence of sulfate reduction on the microbial dechlorination of pentachloroaniline in a mixed anaerobic culture

“…Inhibition of dehalogenation under sulfate-reducing conditions has been attributed to competition between sulfate and chlorinated compounds for electron donor (Alder et al 1993). Conflicting reports exist as to the effect of sulfate reduction on microbial dechlorination, from lack of inhibition (Bagley and Gossett 1990;DeWeerd et al 1991;Hoelen and Reinhard 2004;Pavlostathis and Zhuang 1991), to partial inhibition (Aulenta et al 2008;Cabirol et al 1998), or to complete inhibition (Nelson et al 2002). Considering the significant role molecular hydrogen (H 2 ) plays as a terminal electron donor in microbial reductive dechlorination reactions (Aulenta et al 2008;DiStefano et al 1992;Fennell et al 1997;Kassenga and Pardue 2006;Löffler et al 1999;Smatlak et al 1996;Yang and McCarty 1998), the outcome of competition among various microbial groups for H 2 utilization at relatively low H 2 concentrations may be explained by the fact that the H 2 threshold of dechlorinating bacteria (\0.3-2 nM) is significantly lower than that of hydrogenotrophic methanogens (5-95 nM), and similar to that of hydrogenotrophic sulfate reducers (1-4 nM) (Aulenta et al 2008).…”

“…Provided that appropriate environmental conditions exist, chlorinated aliphatic and aromatic hydrocarbons undergo reductive dechlorination in sulfatereducing environments with different electron donors (Alder et al 1993;Aulenta et al 2008;Bagley and Gossett 1990;Cabirol et al 1998;De Best et al 1997a, b;Häggblom and Young 1990;Kennedy et al 2006;Ndon et al 2000;Palekar et al 2003;Pavlostathis and Zhuang 1991;Prytula and Pavlostathis 1996;Sonier et al 1994). Degradation of chlorinated aromatic compounds coupled to sulfate reduction yields higher free energy than degradation coupled to methane production (Häggblom and Young 1995).…”

Tetrachloroethene Dehalorespiration and Growth of Desulfitobacterium frappieri TCE1 in Strict Dependence on the Activity of Desulfovibrio fructosivorans

“…Various studies in the past have shown that sulfatereducing bacteria (for example, Desulfovibrio vulgaris, Desulfovibrio gigas, and Desulfovibrio desulfuricans) are able to metabolize substrates such as lactate to acetate, CO 2 , and H 2 when grown in the absence of sulfate or in media with low sulfate concentrations, in syntrophic association with H 2 -consuming bacteria keeping the hydrogen partial pressure low (for example, Desulfovibrio vulgaris with Methanosarcina barkeri or Desulfovibrio fructosivorans with Methanospirillum hungatei [5,6,9,40]). It was also found that a few Desulfovibrio species can either utilize or produce hydrogen (mediated by reversible hydrogenases or two different hydrogenases) during the degradation of organic matter (for example, Desulfovibrio vulgaris, Desulfovibrio gigas, Desulfovibrio salexigens, and Desulfovibrio baculatus [20]).…”