Microbial communities are defined by a complex interrelationship between microbial geno- and phenotypes and by the interaction of each community member with the physical-chemical environment. A profound knowledge of the physiology and ecology of microbial communities is essential to manage their application in contaminant removal to protect and sustain human and environmental health.
Tetrachloroethene (PCE) and trichloroethene (TCE) are the most abundant groundwater contaminants in the United States. Dehalococcoides species are able to couple the complete reductive dehalogenation of PCE to ethane to growth. In a four-step series of reductive dechlorination reactions PCE is reduced via the intermediates TCE, cis-dichloroethene (DCE), and vinyl chloride (VC) to ethene. While PCE-dehalogenating bacteria of genera other than Dehalococcoides dechlorinate PCE to DCE, dechlorination past DCE has been linked exclusively to members of the genus Dehalococcoides.
Anaerobic reductive dehalogenation of tetrachloroethene (PCE) was studied in a laboratory scale continuous flow column with soil from a contaminated field site and a Dehalococcoides enrichment culture. The abundance and activity of Dehalococcoides spp. and key enzymes involved in halorespiration (the reductive dehalogenases pceA, tceA, bvcA, and vcrA) were quantified by real-time PCR. 16S rRNA gene clone libraries revealed insights into the diversity and composition of the bioaugmented aquifer microbial community.
The published genome sequences of Dehalococcoides strains revealed information about the metabolic capabilities and physiological constrains limiting growth and dechlorination activity of this group of microorganisms. Recently, two additional Dehalococcoides sp. genomes became available what enabled a comparative analysis of genotypic strain-level congruence and diversity. The study provided novel insights into adaptive processes that shaped the genomes of these highly specialized pollutant degrading microorganisms. Furthermore, our study showed that the main genotypic diversity among the sequenced Dehalococcoides strains is directly associated with their metabolic dechlorination capabilities. These findings have direct implications for future studies on the ecology and population dynamics of Dehalococcoides spp. under bioremediating conditions. They also suggest a whole microbial community sequencing approach as a next step to further our knowledge on how essential (eco)physiological functions of in situ chloroethene dehalogenation are partitioned in and among the microbial populations that build an active and stable dechlorinating microbial community.