Characterization of Dehalogenimonas Strains from a Louisiana Superfund Site that Reductively Dehalogenate Polychlorinated Alkanes

The research described in this dissertation was aimed at expanding understanding of the diversity and functional roles of microorganisms able to anaerobically transform chlorinated compounds. During the course of the research, a novel strictly anaerobic bacterial isolate originating from chlorinated solvent contaminated groundwater at a Superfund Site in south Louisiana (USA) was characterized. Phylogenetic analysis based on 16S rRNA gene sequencing placed the newly isolated strain, designated as NSZ-14 T, within the genus Dehalogenimonas but within a separate lineage from previously described species. Like previously described species within the genus Dehalogenimonas (i.e., D. lykanthroporepellens and D. alkenigignens), strain NSZ-14T was found to couple growth with reductive dehalogenation of environmentally important polychlorinated alkanes. The strain was found to dehalogenate 1,2-dichloroethane to ethene, 1,2-dichloropropane to propene, 1,1,2,2-tetrachloroethane to dichloroethenes, 1,1,2-trichloroethane to vinyl chloride, and 1,2,3-trichloropropane to allyl chloride. Testing revealed that strain NSZ-14T is able to use either formate or H2 as an electron donor for dechlorination. Testing of the type strains of the species D. lykanthroporepellens and D. alkenigignens revealed that these species are also able to use formate, a feature that further differentiates members of the genus Dehalogenimonas from the related genus Dehalococcoides. Genome sequences for strain NSZ-14T and its closest previously cultured relative, Dehalogenimonas alkenigignens IP3-3T, were determined using a combination of 454, Illumina and PacBio sequencing platforms. Analysis of the genome sequences revealed the presence of several reductive dehalogenase homologous genes (rdhA), some of which shared high identity with rdhA genes from other species and others that appear to be novel. Consistent with the experimental observation that Dehalogenimonas strains were able to utilize formate, analysis of the NSZ-14T and D. alkenigignens IP3-3T genome sequences revealed the presence of genes putatively encoding selenocysteine–containing formate dehydrogenases. The isolation and characterization of the strain NSZ-14T expands the diversity of strains from the genus Dehalogenimonas known to reductively dehalogenate environmentally important chlorinated solvents. Based on the collective results reported in this dissertation, strain NSZ-14T is proposed as the type strain of a novel genus with the name Dehalogenimonas formicexedens sp. nov