Rapid enrichment of Dehalococcoides-like bacteria by partial hydrophobic separation

Organohalide-respiring bacteria can be difficult to enrich and isolate, which can limit research on these important organisms. The goal of this research was to develop a method to rapidly (minutes to days) enrich these organisms from a mixed community. The method presented is based on the hypothesis that organohalide-respiring bacteria would be more hydrophobic than other bacteria as they dehalogenate hydrophobic compounds. The method developed tests this hypothesis by separating a portion of putative organohalide-respiring bacteria, those phylogenetically related to Dehalococcoides mccartyi, at the interface between a hydrophobic organic solvent and an aqueous medium. This novel partial separation technique was tested with a polychlorinated biphenyl-enriched sediment-free culture, a tetrachloroethene-enriched digester sludge culture, and uncontaminated lake sediment. Significantly higher fractions, up to 20.4 times higher, of putative organohalide-respiring bacteria were enriched at the interface between the medium and either hexadecane or trichloroethene. The selective partial separation of these putative organohalide-respiring bacteria occurred after 20 min, strongly suggesting that the separation was a result of physical-chemical interactions between the cell surface and hydrophobic solvent. Dechlorination activity postseparation was verified by the production of cis-dichloroethene when amended with tetrachloroethene. A longer incubation time of 6 days prior to separation with trichloroethene increased the total number of putative organohalide-respiring bacteria. This method provides a way to quickly separate some of the putative organohalide-respiring bacteria from other bacteria, thereby improving our ability to study multiple and different bacteria of potential interest and improving knowledge of these bacteria.