Pangenomic insights into evolution and acquisition of functional genes for bioremediation.

is a genus of organohalide-respiring bacteria that is recognized for its fastidious growth using reductive dehalogenases (RDases). In the SC05 culture, however, a population also mineralizes dichloromethane (DCM) produced by chloroform dechlorination using the cassette, just downstream of its active RDase. A closed genome of this DCM-mineralizing lineage has previously evaded assembly. Here, we present the genomes of two novel strains, each of which was assembled from the metagenome of a distinct subculture from SC05. A pangenomic analysis of the genus, including RDase synteny and phylogenomics, reveals at least five species of based on average nucleotide identity, RDase and core gene synteny, as well as differential functional genes. An integration hotspot is also pinpointed in the genome, in which many recombinase islands have accumulated. This nested recombinase island encodes the active RDase and cassette in both SC05 genomes, indicating the transfer of key functional genes between species of . Horizontal gene transfer between these two novel strains has implications for the evolutionary history within the SC05 subcultures and of the genus as a whole, especially regarding adaptation to anthropogenic chemicals.