Groundwater contamination is a serious threat to global health and prosperity.  Chlorinated solvents are widely used as industrial degreasers, dry-cleaning agents and precursors in chemical synthesis, and therefore are common groundwater contaminants.  Owing to their toxicity, even small spills render groundwater unsuitable for use, and cleanup is typically a costly and long-term undertaking.  Recently, a fascinating group of subsurface microorganisms, called Dehalococcoides, has been discovered that can dechlorinate the common solvents tetrachloroethene and trichloroethene to the benign product ethene.  Remarkably, these organisms obtain energy for growth from dechlorination and several successful demonstrations of bioaugmentation, where an aquifer is inoculated with culture, have lead to the development of commercially available cultures.  Community genome sequencing and DNA microarray expression analysis are being used to identify the important functional and regulatory elements in one such commercial culture called KB-1.  KB-1 is a strictly anaerobic, mixed microbial culture harbouring several Dehalococcoides that is very effective at detoxifying chloro-organic pollutants.  An understanding of the genetic and physiological diversity in the culture, as well as interspecies interactions is sought to identify key biomarkers to improve the success of bioremediation. Specifically, differential gene expression experiments using microarrays and quantitative polymerase chain reaction (PCR) are providing valuable insights into the mechanisms of and controls on dechlorination and into the interactions between the non-dechlorinating and dechlorinating populations in the mixed culture.