A highly purified enrichment culture couples the reductive dechlorination of tetrachloroethene to growth

Abstract

A microscopically pure enrichment culture of a gram-negative anaerobic bacterium, in the present article referred to as PER-K23, was isolated from an anaerobic packed-bed column in which tetrachloroethene (PCE) was reductively transformed to ethane via trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), chloroethene, and ethene. PER-K23 catalyzes the dechlorination of PCE via TCE to cis-1,2-DCE and couples this reductive dechlorination to growth. H2 and formate were the only electron donors that supported growth with PCE or TCE as an electron acceptor. The culture did not grow in the absence of PCE or TCE. Neither 02, N03 N02-, so42-, s032-, S2032-, S, nor CO2 could replace PCE or TCE as an electron acceptor with H2 as an electron donor. Also, organic electron acceptors such as acetoin, acetol, dimethyl sulfoxide, fumarate, and trimethylamine N-oxide and chlorinated ethanes, DCEs, and chloroethene were not utilized. PER-K23 was not able to grow fermentatively on any of the organic compounds tested. Transferring the culture to a rich medium revealed that a contaminant was still present. Dechlorination was optimal between pH 6.8 and 7.6 and a temperature of 25 to 35°C. H2 consumption was paralleled by chloride production, PCE degradation, cis-1,2-DCE formation, and growth of PER-K23. Electron balances showed that all electrons derived from H2 or formate consumption were recovered in dechlorination products and biomass. Exponential growth could be achieved only in gently shaken cultures. A maximal specific growth rate of 0.024 h-1 was estimated, and a growth yield of 2.1 g of protein per mol of Clwas measured. Experiments with '4C02 revealed that CO2 was incorporated only via heterotrophic CO2 fixation under the growth conditions tested. The rest of the carbon was apparently assimilated from organic compounds present in the fermented yeast extract added. On the basis of physiological characteristics, the gram-negative rod could not be assigned to a known group of anaerobic bacteria.

A strictly anaerobic betaproteobacteriumGeorgfuchsia toluolicagen. nov., sp. nov. degrades aromatic compounds with Fe(III), Mn(IV) or nitrate as an electron acceptor

“…Soil cores were taken anaerobically using a core pushing device (Delft Geotechnics, Delft, the Netherlands) at approximately 20 m downstream of the landfill body in the plume of the leachate in November 2002 (Botton & Parsons, 2006). Microcosms were obtained by inoculating about 5 g soil of core Poll-02 in 120-mL serum bottles filled with 40 mL sterile, anaerobic and phosphate-bicarbonate-buffered medium (pH 7.3) as described previously, but with the modification that cysteine (1 mM) was used as a reducing agent instead of 1 mM Na 2 S (Holliger et al, 1993). The bottles were closed with viton or butyl rubber stoppers, depending on the substrate used, and sealed with aluminum crimp caps.…”

Reductive dechlorination of β-hexachlorocyclohexane (β-HCH) by a Dehalobacter species in coculture with a Sedimentibacter sp.

“…Sandy soil samples were taken from an HCH-polluted location in Hengelo, The Netherlands [13], and stored under nitrogen at 4°C until use. About 4 g (wet weight) of soil were added in a anaerobic glove box to 120-ml serum bottles containing 20 ml of methanogenic mineral medium as described by Holliger et al [21], but without the addition of fermented yeast extract (FYE). The bottles were closed with viton stoppers (Maag Technik, Dübendorf, Switzerland) and aluminium crimp caps and the headspace was replaced with N 2 /CO 2 (80:20 (v/v); 140 kPa).…”

“…Apparently, the Dehalobacter in the coculture differs from D. restrictus [16]. This Dehalobacter was initially enriched in our laboratory [21] and it is able to reductively dechlorinate tetrachloroethene and trichloroethene with H 2 as electron donor. Recently, a bacterium related to Dehalobacter was found that is capable to reductively dechlorinate trichloroethane to chloroethane [20].…”

Hydrogen threshold concentrations in pure cultures of halorespiring bacteria and at a site polluted with chlorinated ethenes

“…The threshold concentrations for H 2 were determined in batch experiments at 30∞C using an anaerobic phosphate-bicarbonate buffered medium with a low chloride concentration (Holliger et al, 1993). Initially, the bacteria were pregrown with an excess of H 2 present in the headspace.…”