Identification of Dehalococcoides Genes Encoding Reductive Dehalogenases That Dechlorinate Specific PCB Congeners

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

Intellectual Merit: This research will elucidate the function and substrate specificity of members of a large family of respiratory enzymes. These enzymes are reductive dehalogenases (RDases) and they are found in a recently discovered group of strictly anaerobic bacteria, Dehalococcoides (Dhc). The RDases remove chlorines from toxic chlorinated organic compounds such as polychlorinated biphenyls (PCBs) and this dechlorination process provides energy for Dhc growth while detoxifying the PCBs. Individual strains of Dhc each possess many different RDases which presumably allow them to dechlorinate a broad range of substrates, but these enzymes are poorly understood and the function and substrate specificity of only three are known. This laboratory has identified two strains of Dhc that can each dechlorinate and detoxify a broad suite of polychlorinated biphenyl (PCB) congeners with 4 to 9 chlorines. This project provides a unique opportunity to gain substantial insights into the function and substrate specificity of many members of this large and novel respiratory protein family. The molecular sequence and function of multiple respiratory RDases that dechlorinate PCBs will be identified and subsequently compared and studied . Because a wide variety of PCB molecules with different chlorine substitution patterns are known to be substrates for the reductive dehalogenases in these Dhc strains, insights will be gained into the regiospecificity of these enzymes. Information will also be gained on how these enzymes have adapted to PCBs which have existed for only 80 years. This project will use tools in biochemistry, microbiology, molecular biology, and genomics to address four main objectives. Broader Impacts: Microbial reductive PCB dechlorination in aquatic sediments provides a natural and highly effective means of detoxification. This research will for the first time identify the RDases responsible for dechlorinating and detoxifying the particular PCBs that are of most concern and will enable the in-depth study of the specific RDase genes that code for the key dechlorination enzymes. The research is also a major step toward the goal of developing cost-effective methods for promoting in situ PCB remediation and toward the design of molecular biological tools that will detect, quantify and monitor PCB-dechlorinating organisms in contaminated environments. This project will support a visiting scientist, a post-doctoral fellow, and will give 6 undergraduates the opportunity to acquire valuable research skills in biochemical analysis, microbiology, molecular biology, and bioinformatics and to participate in state-of-the-art original research. They will also have opportunities to present their results at scientific meetings and to co-author publications. For outreach the PI will participate in a Young Women in Science program aimed at middle school girls. This involves introducing the girls to her research through presentations and lab sessions during the academic year and summer. She will also mentor high school girls on science projects, and she will develop and give presentations on "Stranger than Fiction: Extreme Lifestyles of Microorganisms" to multiple groups at a local high school.