S9: Evolution of reductive dehalogenases

Vinyl chloride is a widespread groundwater pollutant and Group 1 carcinogen. A previous comparative genomic analysis revealed that the vinyl chloride reductase operon, vcrABC, of Dehalococcoides sp. strain VS is embedded in a horizontally-acquired genomic island that integrated at the single-copy gene ssrA. Dehalococcoides are members of the ‘rare biosphere’ with slow growth rate and are highly adapted to niches, revealing a biology that is distinct from the well-studied gamma proteobacteria. This talk will discuss the biology as well as implications of the finding that the vcrABC-containing genomic islands are a recently-acquired subset of a diverse collection of ssrA-specific mobile elements. These elements are a major contributor to strain-level diversity in Dehalococcoides, and may have been throughout its evolution. The high similarity between vcrABC sequences is quantitatively consistent with recent horizontal acquisition driven by ~100 years of industrial pollution with chlorinated ethenes.