Identification of microorganisms involved in reductive dehalogenation of chlorinated ethenes in an anaerobic microbial community

In this study, we report on phylogenetic and physiological characterization of an anaerobic culture capable of reductive dehalogenation of tetrachloroethene (PCE) obtained from a PCE-contaminated site. The culture was enriched using different combinations of electron donors (hydrogen and acetate) and electron acceptors (PCE, cis-1,2-dichloroethene (cDCE) and controls without chlorinated ethenes). The resulting subcultures were analyzed using three different approaches: chemical analysis to document conversion of chlorinated ethenes; polymerase chain reaction (PCR) of 16S rRNA gene fragments and denaturing gradient gel electrophoresis (DGGE) to compare community compositions; fluorescence in situ hybridization (FISH) to quantify specific groups of microorganisms using oligonucleotide probes previously designed or newly designed based on the sequences retrieved from sequence analysis of specific DGGE bands. Members of two genera which contain bacteria capable of reductive dehalogenation were detected in the culture: Dehalococcoides and Desulfitobacterium. The combined analyses suggested that Dehalococcoides-like bacteria are associated with complete dehalogenation of chlorinated ethenes to ethene with hydrogen as electron donor; and Desulfitobacterium-like bacteria, in contrast, are associated with incomplete PCE dehalogenation to cDCE and appear to be able to use acetate as electron donor. In addition, Sporomusa-like bacteria were identified, which most likely act as homoacetogens. The results demonstrated that combination of culture enrichment with different substrates, DGGE, and FISH allowed a detailed qualitative and quantitative characterization of the dominant microorganisms associated with reductive dehalogenation.