Identification of a new biomarker linked to 1,2-dichloropropane dechlorination and its ecology and distribution in subsurface environments

1,2-dichloropropane (1,2-D) is a widespread halogenated organic pollutant. Dehalococcoides populations in two highly enriched cultures (RC and KS) have been implicated in the reductive dechlorination of 1,2-D to propene. Transcription and expression analysis in these cultures identified a putative reductive dehalogenase gene (RDase) involved in 1,2-D dechlorination. Sequence analysis revealed that the new RDase is ~90% similar at the DNA level to an RDase gene found in the Dehalogenimonas lykanthroporepellens strain BL-DC-9. DNA from the RC and KS cultures failed to produce an amplicon with Dehalogenimonas specific primers further supporting that a Dhc. population is responsible for 1,2-D dechlorination.  Further analyses imply that new biomarker is harbored in a genomic island (GI) of horizontal gene transfer origin, evidence of HGT include: (1) highly sequence similarities/identities of this gene across different species (2) difference in  nucleotide statistics (GC content, di-nucleotide and tetra-nucleotide biases) from the rest of the Dehalogenimonas chromosome, (3) is surrounded by mobility genes (transposes and integrases) (4) is flanked upstream and downstream by identical inverted repeats (5) similar gene arrangements in Dehalococcoides and Dehalogenimonas. This is the first time that a functional gene has been implicated in 1,2D dechlorination and that evidence of a HGT event has occurred between Dehalogenimonas and Dehalococcoides spp. The new biomarker has been identified in samples from different geographical locations in Europe, North and South America. Further research aims to shed light on RDase gene dissemination and the adaptation of dehalospiring populations in subsurface environments.