Collaborative Research: Microbial chain-elongation mediated dehalogenation and carbon transformation

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Chlorinated solvents consist of a large family of chlorinated hydrocarbons that have been used worldwide in large quantities to support various industrial applications. Chlorinated solvents such as perchloroethylene (PCE) and trichloroethylene (TCE) are among the most ubiquitous groundwater contaminants in the United States and worldwide. Bioremediation using Dehalococcoides mccartyi has emerged as a promising technology to treat groundwater contaminated by PCE and TCE. Dehalococcoides mccartyi are anaerobic microorganisms that can reduce and convert PCE and TCE to ethene which can subsequently be mineralized to carbon dioxide by other anerobic and/or aerobic microorganisms present in groundwater. However, Dehalococcoides mccartyi require the use of hydrogen (H2) as a sole electron donor to convert PCE and TCE to ethene. The overarching goal of this project is to investigate the use of microbial chain elongation-mediated dehalogenation as a novel groundwater bioremediation process that leverages the ability of a consortium of anaerobic microorganisms to produce the amount of H2 required to carry out the reduction and conversion of PCE/TCE to ethene using organic substrates such as lactic acids, molasses, and vegetable oil. The successful completion of this project will benefit society through the generation of new fundamental knowledge to advance the development and implementation of more efficient and cost-effective bioremediation technologies for the treatment of groundwater contaminated by chlorinated solvents. Additional benefits to society will be achieved through education and outreach activities including the mentoring of two graduate students and two undergraduate students at Arizona State University and the University of Vermont.Dehalococcoides mccartyi are organohalide-respiring bacteria that utilize halogenated compounds as terminal electron acceptors in an anaerobic respiration process to generate the energy required for their growth using electron donors such as hydrogen (H2). During the last two decades, Dehalococcoides mccartyi have emerged as the most promising microorganisms with capability to carry out the reductive dehalogenation of chlorinated hydrocarbons such as perchloroethylene (PCE) and trichloroethylene (TCE) in contaminated groundwater. However, competing microorganisms (e.g., iron or sulfate reducing bacteria) in groundwater that utilize H2 as electron donor can adversely impact the rate and extent of PCE/TCE dehalogenation and conversion to ethene by Dehalococcoides mccartyi. This competition has been consistently linked to slow rates of PCE/TCE dehalogenation and/or the accumulation of toxic intermediates such as vinyl chloride. Building upon the results of promising preliminary studies, the Principal Investigators (PIs) of this project propose to explore the coupling of microbial chain elongation with reductive dehalogenation with the goal of identifying a consortium of anaerobic microorganisms that can reduce and convert PCE/TCE to ethene while using chain elongation to generate the amount of H2 required to carry out this conversion. To advance this goal, the PIs propose to carry out an integrated experimental and modeling research program to 1) uncover critical metabolic pathways and ecological interactions that govern microbial chain elongation-mediated dehalogenation, and 2) develop and validate computational metabolic models of microbial chain elongation coupled with dehalogenation. The specific objectives of the research are to: 1) Characterize the growth and inhibition kinetics and metabolic networks of a consortium of organo-halide respiring and chain-elongating bacteria that has shown promising potential to convert PCE/TEC to ethene and 2) Unravel the interactions of microbial chain elongation with the competing metabolic pathways of methanogenesis and homoacetogenesis in organo-halide respiring microbial communities. The successful completion of this research has the potential for transformative impact through the generation of new fundamental knowledge and computational metabolic models to advance the development and deployment of groundwater bioremediation by microbial chain elongation-mediated dehalogenation. To implement the educational and training goals of this project, the PIs propose to leverage existing programs at their respective institutions to integrate the findings from this research into an RET (Research Experience for Teachers) program at Arizona State University and an extension program (4-H) at the University of Vermont (UVM) to teach and inspire high school teachers and students to explore the use of microorganisms in environmental remediation. In addition, the PIs plan to leverage existing REU (Research Experiences for Undergraduates) programs at ASU and UVM to recruit undergraduate students from underrepresented groups to work on the project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.